i April 9th 2010 To: Dr. Julio Militzer Dr. Marek Kujath From: Team 12
Contents
1. 4 Table 4 Biological Specimen Testing Results eene 12 Table 5 Displacement data for 500RPM trial with 8mm sample 32 Table 2 Displacement data for 1000RPM trial with 8mm sample 33 Table 5 Comparative Chart of Estimated to Actual Machining Hours 36 Table 6 Comparative Graph of Estimated to Actual Budget 36 1 Introduction 1 1 Background The standard uniaxial tensile tension test reveals many fundamental properties of materials Properties of the material such as the ultimate tensile stress toughness failure modes and failure location are often sought The results of uniaxial tensile tests can be applied through the application of Mohr s circle of stress and material failure theories such as Tresca s theory of stress to alternative scenarios where the material is in bending torsion under axial load or in combinations thereof It is known that the properties obtained from uniaxial tension tests are a function of the strain rate used during a test This phenomena is both true of metallurgical materials and for biological substances For biological substances especially this change in property is indicative of strain rate dependant molecular mechanisms that determine mechanical behavior As2. 10 5 Problem Exploration 10 5 1 ham 10 toic d Denia EE t denda 10 5 L2 Fimite Element Analysis eiecit ede i eg toe Deere i eet ges 11 5 3 Rapid Prototyping odere eee etate eddie 11 5 2 TIPP RUD 12 5 2 1 Biological Specimen na usuyasa nennen 12 5 2 2 Solenoid Testing un au ago dip poe 12 Calculations iuc oe eei deer haee nio 13 Final cr e t P 16 7 1 Drive Shaft ASSCMDIY 0 sesscscsonsssssesessssssonsssvsncesesesenscssesssstetesensessesvesbotessesesesnsesseseses 16 Jal Flywheel Designs vss aui oe e te dente Ce ed det ere PORTE rte 17 7 1527 dope awpa trei eae 19 7 1 3 Gripping Mechanism teret et s ed teli repe etin 20 Josh Damper atun dail ERU Leste atenta deu int te 20 12157 Safety Shield sucio ch Balle OD Guten 21 7 2 Electrical Component sissscesscnvcsacssivecesnsavssenscovscssvsavesavasevacceenessenesescacetanssvdsevecasseonese 21 7 2 1 Motor and Frequency E i 21 1 2 2 Systems u L a eet tet n et eret e e He tre desire ode 22 732 3 Sol
3. 37 16 1 Control of Initial Sample Length 37 162 Prevent deformation of critical components 38 16 3 Other Considerations 39 17 COMCIUSIOMS Rr M 39 18 References s ponerte MEE aa qasasqa 40 19 unie ce 40 Appendix A Previously Signed Documetnt s 40 Appendix B Decision Making Tables and Charts 44 Appendix C Gantt 46 Appendix Budo 47 Appendix E User s Manual 4 eee eese esee SS u 49 Appendix Engineering Drawinss 55 List of Figures Figure 1 Crosslinking of Collagen Fibers Lee 2010 2 Figure 2 Strength and Stiffness Relationships for Materials Lee 2010 2 Figure 3 Structural Mechanical Relations in Soft Tissues Lee 2010 3 Figure 4 Hopkinson Split Bar Apparatus esee nennen eene 7 Figure 5 Gra
4. 1300 0 05 0 10 0 15 0 20 0 25 0 30 0 35 0 40 time s Figure 28 Processed Signals 29 When our signals were analyzed on the basis of velocity vs time we noticed the trends seen in Figure 29 This figure shows that our transient period where acceleration is occurring is about 8mm for the case of 1000 RPM This transient period is much greater than the period we required of approximately 1mm A region of near constant velocity was achieved It would be preferable to engage and break the specimen in this region as the region is of sufficient length to break the sample Velocity Displacement Profiles 300 500 750 1000 RPM 300 RPM 500 RPM 500 RPM 750 RPM 1000 RPM Velocity mm s 10 15 Displacement mm Figure 29 Velocity vs Time Analysis When analyzing both force and displacement simultaneously we expected to see the results of Figure 30 Our bovine pericardium samples are hybrid tissues with light strain characteristics dominated by elastin and high strain characteristics dominated by collagen COLLAGEN Tension g cm ELASTIN 150 Initial radius Figure 30 Documented Force vs Displacement Characteristic for Sample 30 We were able to replicate this force displacement curve using our device The trends we witnessed are presented in Figure 31 We also were able to see a strain dependence of the resisting force This data would not be of large significance to
5. e and that a solid relationship between and e exists through an experimental determined quantity e Calculations were performed regarding the torque that the shaft was subjected to With these results the team designed the method of connecting the flywheel to the shaft The team plans to improve on the gripping mechanism performance by researching methods of decreasing the mass of grip that undergoes linear motion upon impact 7 Final Design The second term of this design project allowed for refinement of the original design and the implementation of the measurement systems The final design is presented in Figure 11 This section will detail the system in terms of both mechanical components and measurement control systems Figure 11 Final Design 7 1 Drive Shaft Assembly The drive shaft Figure 12 assembly of this system consists of a flywheel which is driven by a 3 phase motor more specs under frequency control The drive shaft is coupled to the flywheel shaft by means of a flexible spider coupling 16 Figure 12 Drive shaft Assembly 7 11 Flywheel Design When designing the flywheel the mass size and the cost of the flywheel were the main considerations Increasing the mass increases the moment of inertia that increases the available energy that is available for transfer to the specimen during impact The design utilizes this energy and the subsequent force to accelerate the gripping mechanism that fractures
6. LPTI Piezo based Oscilloscope Laser measurements 3 Force Laser Load cell measurement Table 2 Options Selected Design Propulsion Velocity measurements Force measurement 1 Pendulum Laser Laser 2 Pendulum LVDT Load cell 3 Hopkinson bar Laser Load cell 4 Flywheel Laser Load cell 5 Flywheel LVDT Load cell 6 Hopkinson bar Laser Laser 7 Flywheel Laser Laser 8 DC Actuator Laser Laser 9 Electromagnetic Laser Load cell Table 3 Evaluation Criteria Speed Accuracy Controllability Accuracy in Cost Cn YA in Sheed in Speed d MCA Estimate Toral 1 9 7 9 6 7 7 45 2 10 7 9 6 8 9 49 3 2 6 9 8 10 7 42 4 9 10 10 9 9 10 57 5 6 9 9 9 7 7 47 6 5 10 9 9 10 5 48 7 8 10 10 9 9 1 47 8 8 4 4 4 6 7 33 9 4 6 7 7 8 3 35 Table 4 Tabulation of Votes Design Ruth Rachael Geoff Ben Total 6 3 1 2 3 2 2 3 3 2 10 4 1 2 1 1 44 House of Quality pe yy xy Yur gdc nm TOR DANES HURON SON E jej EN E jji epope jej ee EE j 29 WT TP HEIL j j TT HEIL j j lI l TT i n SMALA Qs _ 5 2 795 oe LL Z Q 45 Appendix C Gantt Chart see attached 46 Appendix D B
7. ey H G tput OWOH key 3 Display hint Donte kot 4 operabrg stale key 1B Fessl On selection keys 8 Sls operat 4 siale Local key 11 e 1 oat sect or key 6 Ema Calbrate key Figure 3 Front panel of the E3631A power supply University of Pennsylvania Department of Electrical Engineering Basics of Power Supplies Use of the HP E3631A Programmable Power Supply Web Mar 27 2010 http www ese upenn edu rca instruments HPpower PS36314A 52 4 4 Flywheel Operation Turn the power to the frequency controller on Gradually increase the speed of the motor by pressing the upward arrow key until desired test speed is reached When the test is complete gradually slow the flywheel by pressing the downward arrow key Turn off the power to the frequency controller 5 Maintenance Preventative maintenance should be performed on the LAHVTR to reduce risk of failure Before performing testing on the LAHVTR inspect the contact pin for chipping or deformation Replace the pin if needed Dismantle and clean all parts of the LAHVTR exposed to biological tissue Use warm water and a disinfecting soap Agilent Technologies 2000 User s Guide Agilent E3631A Triple Output DC Power Supply 53 Appendix A Start up Checklist Issued by Effective date Report No Full Speed Motor Test Action Taken Replacement 1 Sound form bearings 1 Adjustment 1 Complete 2 Balance vibr
8. 6 19 7 1 3 Gripping Mechanism The gripping mechanism consists of two grips that hold the sample at each end a linear sliding track and support housing for bearings and the contact tooth The grips are machined out of stainless steel One side will be attached to the force transducer while the second end is attached to housing allowing it to move down the sliding track The housing is machined from a stainless steel The contact tooth will be designed using the same carbon steel as the flywheel pin Figure 17depicts an exploded view of the grip assembly Figure 17 Exploded Grip Assembly Grip 1 Grip top 2 Specimen 3 Engagement pin 4 Tooth holder 5 Tooth housing 6 Guide rod 7 Bath 8 7 1 4 Damper The team estimated the forces involved in the operation of the engagement mechanism A pre made damper was sized using these calculations and purchased This damper was fastened on the end of the track to deter the tooth housing from rebounding and distorting the sample 20 Figure 18 Damper set up Engagement mechanism support 1 Force transducer 2 Grip 3 Specimen 4 Tooth holder 5 Tooth housing 6 Grip top 7 Bath 8 Engagement pin 9 Guide rod 10 Damping system 11 Damper 12 Mounting nut 13 7 1 5 Safety Shield Due to high rotational speeds and large impact forces the device is enclosed in a safety shield The safety shield is to be constructed out polycarbonate panel
9. BME researchers because the data was collected during the acceleration phase of our device and we did not achieve the targeted 300s rate when breaking the sample Force Displacement Bovine Pericardial Tissue Attempt 300s u ju c o u 2 0 Displacement mm Figure 31 Force Displacement Characteristic Obtained 10 4 High Speed Video Testing Results In order to calculate the strain rate achieved during testing the approach was taken to use a high speed video camera and analyze the video using Photron Motion Tools software Several videos were taken and analyzed however the one below was taken at 500 frames per second and a flywheel speed of 500RPM The selected software allowed the user to input a distance frame of reference which then converted the distance to pixels per unit Shown in Figure 32 is the user putting the distance of a bolt head of five millimeters then software then converted the scale to 6 4 pixels per millimeter 31 Calibration Coordinate System Scale units degrees Scale faa Pies Move Origin _ X Direction SetPoint 1 _ SetPoint 2 Flip Y Reset Dimension f Milimeters 7 m3 ME good one1_C001S0001 2 Move Coordinate System Quick Set El Set As Default Load Default E Save Load Figure 32 Creating a reference system for high speed video analysis In the next step the user picks a location on
10. The device will be designed so the operator has control of the extension rate The device will be designed for safe operation performed by trained individuals A shielding component will be incorporated if required Accompanying the device will be a comprehensive instruction manual e All set deadlines and time requirements set out in the MECH 4010 4020 Design Project Handbook will be met e The device will attempt to provide data describing the force and displacement against time for each trial The design memorandum design agreement and memorandum are located in Appendix A of this report Table 3 Design Requirements Check list Design Requirements Accomplished Size 30 x 30 inches Yes Strain rate On the order of 1000s No Loading Minimum 1 100s Life 5 years Yes Conditions of the test sample Physiological conditions No 100 humidity at 37 C Safety Instruction manual Yes Shielding component Data Force Yes Displacement The team produced a memorandum document in which the agreed design requirements were outlined The client and Team 12 before the design process begun signed the document The following subsections profile the design requirements and discuss the level of our accomplishments Size The device should be able to fit on a tabletop with one face approximately 30X30 cm The client presented this design requirement because he wanted to install th
11. University and the Design Team shall not be liable for any direct indirect consequential or other damages suffered by the Client or any others resulting from the project or the use of the research results and data from the project or any such invention or product Entire Agreement This agreement constitutes the entire agreement between the parties with respect to the subject matter hereof and supersedes all prior agreement whether written or oral 42 Memorandum To Dr Julio Militzer CC Dr Michael Lee Dr Kujath From Group 12 Ben Breen Ruth Domaratzki Geoff Beck and Rachael Schwartz Date 03 10 09 Re Design Requirements for Loading Apparatus for High Velocity Tissue Rupture LAHVTR Summary of the Project Our group will be designing a loading apparatus with the capability to conduct fractures of a controlled and rapid nature in collagen rich tissues bovine tendon for Dr Lee of the school of Biomedical Engineering After meetings with Dr Lee the design requirements have been set and are outlined below Design Requirements The requirements have been set under the following categories Size The device should be able to fit on a table top with one face approximately 30 30 Strain Rate The strain rate achievable should be on the order of 1000 Loading Achieve a minimum of 1 100 loading Lifetime Should last approximately 5 yrs Conditions The conditions of the test sample will be as close as possible
12. an example of these molecular mechanisms it was noted by Willett et al 2007 that in a case involving high strain rate rupture of collagenous tissue a large amount of visible recoil of fibers were seen These fibers were theorized to suggest a build up of elastic energy in a case where one would expect that sliding would dissipate this energy There are many facets of equipment that enable standard uniaxial tensile tension tests The equipment must be highly rigid it must be fitted with delicate instrumentation to measure force deformation time and provide visualization of the sample In the present case the equipment must enable a relatively high strain rate be achieving large velocities in short periods of distance and thus time The design presented in this report overcomes strain rate limitations inherent with the currently employed hydraulically actuated model The design overcomes this limitation at the sacrifice of other features on the present device that are not required in the research being conducted by the client Such features include the ability to conduct biaxial tests Specifically the Loading Apparatus for High Velocity Tissue Rupture LAHVTR was designed to fracture a specimen of bovine tendon up to 2 5cm at a strain rate of 1000s recording force position and velocity vs time as design criteria dictated This report outlines the progress of the team on the design construction and testing of the device The br
13. and after the pin is in the precise location Inability to locate the pin could result in partial contact of the impacting surfaces and failed experiment and destroyed specimen A rotary encoder is mounted on the shaft and acts as a signal to engage the solenoid The encoder is an infrared sensor that senses light passing between two sensors on either side of the encoder Only one hole is necessary on the rotary encoder The computer driver for the tissue rupture device was developed to allow for the pin to fire after activation of the fire button and completion of the revolution of the flywheel This allows for a failsafe method ensuring the pin will never miss fire 7 2 2 2 Stroboscope and Frequency Controller The angular velocity of the flywheel determines the strain rate experienced by the specimen The strain rate is a controlled quantity thus measurement of angular velocity is required The Strobotac is used to determine the angular velocity of the flywheel in operation by adjusting the frequency controller until the white stripe painted on the flywheel appears to be in a constant position The frequency controller displays the speed of the flywheel in RPMs while the shaft is rotating 22 7 2 2 3 Force Transducer A standard strain gauge will be mounted to a titanium component on the device This configuration will permit measurement of force loading on the specimen This is illustrated in Figure 21 Calibration of the force transd
14. output terminals Turn the power supply on The power supply s outputs will be disabled the OFF annunciator is on Enable the outputs by pressing the Output On OFF key see Point 8 Figure 3 The CV and 6V annunciators will be on to indicate that the power supply operates in the constant voltage mode and that the 6V display is selected The display is in the meter mode i e the display shows the actual output voltage and current To set up the 25 V power supply press the 25V key to select the display and adjust the 25V supply voltage Do the same for the 25V supply Set the display for imit mode by pressing the Display Limit key see Point 3 Figure 3 You will notice the LMT annunciator blinking to indicate that the display is in the limit mode The display shows the actual voltage and current limit values of the selected supply You will notice that the second digit of the voltmeter is blinking Turn the large knob to set the desired voltage limit make sure the LMT annunciator is still blinking Press the Vol Cur key see Point 11 Figure 3 The second digit of the ammeter will be blinking Adjust the desired output current that the current source will supply To return to the meter mode press the Display Limit see Point 3 Figure 3 or let the display time out to return automatically to the meter mode The LMT annunciator will be off 1 Meler and adjust selechan keys kG Gorfigurat n Secus hey 2 Track 5 enables sable
15. required revision The mock up additionally enabled the group to foresee the initial placement of the components around the flywheel The model was constructed from Foam core and wooden dowels 10 Figure 7 Mock up of Device 5 1 2 Finite Element Analysis Preliminary finite element analysis was applied to the flywheel to find the range of stress concentrations in the contact area of the flywheel This initial analysis is represented as a point load and depicted in Appendix C The team discussed the utilization of modeling a more precise finite element analysis model for the completion of the final design but the concept was passed over due to lack of usefulness 5 1 3 Rapid Prototyping Representations of the engagement mechanism and flywheel were created using rapid prototyping These components were then precisely mounted on a wooden frame to determine the validity of the design concept and finalize the dimensions of the apparatus Figure 8 Rapid Prototype of Device 11 5 2 Testing Some rudimentary tissue testing was conducted prior to construction of any device to aide in problem exploration 5 2 1 Biological Specimen Testing Initial testing was performed on the Loading Apparatus for High Velocity Tissue Rupture to verify the successful operation of the engagement mechanism Biological tissue was loaded into the LAHVTR clamps and the pin was manually engaged through the circuit board Testing was performed with the flywh
16. the moving part and tracks it though several frames of video The four frames below illustrate this process In frame 1 a point on the moving part to be tracked is selected and tracked in subsequent frames shown by red and green tracking dots All of the frames are time stamped which allows for accurate data analysis Figure 33 High speed video frames and feature tracking for 8mm sample at 500RPM and 500 frames per second After the points have been selected the data is output to Excel for analysis The data acquired from this trial is shown in Table 5 Table 5 Displacement data for 500RPM trial with 8mm sample Frame Time seconds Track Point 1 mm 32 x y 2649 5 2980003 33 125 28 125 2648 5 2960005 35 15625 28 125 2647 5 2940001 46 09375 28 125 2646 5 2920003 57 1875 27 96875 From the output data the velocity was found by dividing the distance the time In this case the maximum velocity was found by analyzing frames 2646 and 2647 Ad _ 97 1875 46 09375 0 752920003 5 2940001 v 5547 mm s From the calculated velocity and know the sample gauge length 8mm in this case the strain rate can be found using the following formula v 5547 693 375 s71 lg 8 The maximum strain rate found for the device was calculated to be 814 st this was calculated using the same method as above at 1000RPM and an 8mm sa
17. 01 Drawing 2 Linear Track Block L 02 02 Specimen Bath 1 02 03 Drawing 1 Specimen Bath L 02 03 Drawing 2 Specimen Grip 2 L 02 04 Grip Top L 02 05 Tooth Guide L 02 06 Drawing 1 Tooth Guide L 02 06 Drawing 2 10 Impact Tooth L 02 07 11 Bushing L 02 08 12 Damper Plate L 02 09 13 Damper Rod L 02 10 14 Stain Block L 02 11 15 Guide Shaft L 02 12 16 Housing Stop Plate L 02 13 17 Load Cell L 02 14 18 Tooth Housing L 02 15 Drawing 1 19 Tooth Housing L 02 15 Drawing 2 20 Tooth Housing L 02 15 Drawing 3 ta gt S Flywheel Explosion L 03 00 1 Flywheel L 03 01 Drawing 1 Flywheel L 03 01 Drawing 2 Flywheel L 03 01 Drawing 3 Engagement Pin L 03 02 Main Shaft L 03 03 55
18. 40 2 30 AA 20 Ex re 10 0 T T T 3 0 0 1 0 2 0 3 0 4 Size m Figure 14 Flywheel Design The flywheel is fitted with a pin Figure 15 that contacts the actuating pin on the gripping mechanism This pin and actuating pin are constructed from carbon steel This material is hard and strong and holds low ductility These characteristics are necessary for the high impact loading presented to these items 18 Figure 15 Engagement Pin in Flywheel 7 1 2 Main Shaft The main shaft to which the flywheel will be mounted is constructed of carbon steel it is to be one inch in diameter and eight inches long The choice to construct the shaft of carbon steel was a budgetary decision The shaft was a donation from the Mechanical Engineering Department Furthermore constructing the shaft with a one inch diameter was deemed ideal because the static shaft deflection from the flywheel was calculated to be negligible at this dimension Additionally the critical shaft speed was calculated to be approximately 12 times the operating speed of 955 rpm Figure 16 illustrates an exploded view of the drive shaft assembly Lastly Team 12 is considering different methods to couple the motor to the main shaft The team chose a flexible coupling due to its vibration management capabilities and ease of alignment Figure 16 Exploded View of Drive Shaft Assembly Shaft 1 Bearing 2 Flywheel 3 Coupling 4 Spider coupling joint 5 and Motor
19. 5 iv Figure 26 Calibration Graph for 26 Figure 27 Calibration Graph for Force Transducer 27 Figure 28 Raw Signals Acquired During Testing 29 Figure 29 Processed e e re PO Em ER RM Pd bee dew 29 Figure 30 Velocity vs Time Analysis i ete pete te ete epe Sew e ee 30 Figure 31 Documented Force vs Displacement Characteristic for Sample 30 Figure 32 Force Displacement Characteristic Obtained 31 Figure 33 Creating a reference system for high speed video analysis 22 Figure 34 High speed video frames and feature tracking for 8mm sample at 500 and 200 frames p r secondi a ae ea vidas QS S m and e SQ 32 Figure 35 Mechanical Cross Coupling ld mrs 35 Figure 36 Current control of sample lengeth 38 Figure 37 Cross sectional view of spring loaded tooth 39 List of Tables Table 1 Mechanical Properties of Collagen and Elastin Lee 2010 3 Table 2 Content and Mechanical Properties of Soft Tissue Composites Lee 2010 4 Table 3 Design Requirements Check list
20. 5 Time of Impact Analysis The bending force on the pin can be used to determine the interval of contact The following calculations illustrate this phenomenon Sy 205 x 10 Pa _ WEE M Fd 4 sj 205 x 108 20006927 00 ee dy 0 016m 0 00346m m housing pin grip lvdt core 3 mass of beam and grips 1 239g 13 2069 243 49 50832N 2 m 0243kg 2088 4m s _ F 50832N _ Spann ss RO ML S _ 6m s p 2 873 x 103 3ms 20884m s Our design requirements stated an incidence time of 1ms However were not able to theoretically derive the time interval without knowing the forces that would be encountered 34 11 Issues Encountered This section outlines some of the issues that were encountered in testing and construction 11 1 Electrical and Mechanical Crosstalk Some of the unexpected results obtain from our data capture may have been a result of crosstalk Crosstalk was likely present in the propagation and coupling to the field and between wires in our electronic system The most common form of this crosstalk between electrical lines is where a transmission line shares a common path with another line Christopoulos 2007 In this case current flow on one line results in an interference signal on the other line Radiated interference is another coupling path This interference does not involve a physical connection between the circuits Another form of crosstalk we may h
21. April 9 2010 To Dr Julio Militzer Dr Marek Kujath From Team 12 Loading Apparatus for High Velocity Tissue Rupture Geoff Beck Ben Breen Rachael Schwartz Ruth Domaratzki Re Winter Term Report April 9 2010 Team 12 designed an apparatus to perform uniaxial tensile tests on biological materials The apparatus is capable of conducting tensile tests at rates of strain above those currently attainable at the Dalhousie Department of Biomedical Engineering The design overcomes strain rate limitations inherent with the currently employed servo hydraulically actuated model at the sacrifice of other features on the present device that are not required in the current research being conducted by the client Such features include the ability to conduct biaxial tests The enclosed document outlines our successes and shortfalls in the construction of this device Team 12 Loading Apparatus for High Velocity Tissue Rupture Geoff Beck Ben Breen Rachael Schwartz Ruth Domaratzki MECH 4020 Design Project II Team 12 Loading Apparatus for High Velocity Tissue Rupture Geoff Beck Ben Breen Rachael Schwartz Ruth Domaratzki Supervisor Dr M Kujath Client Dr M Lee Abstract In fulfillment of a Mechanical Engineering degree Team 12 2009 2010 completed the Design Project courses MECH 4010 and MECH 4020 in the fall and winter semesters The team has created a loading apparatus for high velocity tissu
22. Chen W Lu F Zhou B A Quartz crystal embedded Split Hopkinson Pressure Bar for Soft Materials Experimental Mechanics V40 n1 1 6 March 2000 Willett T Labow R Avery N Lee M Increased Proteolysis of Collagen in an In Vitro Tensile Overload Tendon Model Annals of Biomedical Engineering V35 n11 1961 1972 2007 Active Power Understanding Flywheel Energy Storage Does high speed really imply a better design White paper 112 lt www activepower com gt Callister W Materials Science and Engineering An Introduction Edition Seven John Wiley and Sons Inc 2007 Lee M 2010 MECH 4650 Course Notes 19 Appendices List of Appendices Appendix A Previously Signed Documents Appendix B Decision Making Tables and Charts Appendix C Gantt Chart Appendix D Budget Appendix E User s Manual Appendix F Engineering Drawings Appendix A Previously Signed Documents List of Documents Project Agreement Project Waiver Memorandum 40 Design Project Agreement This Agreement is made and entered into for a term beginning the day of September 2009 and ending the day of May 2009 between Ben Breen Ruth Domaratzki Geoff Beck Rachael Schwartz hereinafter referred to as Design Team And Dr Michael Lee hereinafter referred to as Client The Design Team and Client hereby agree as follows 1 Scope of work The scope of work agreed upon within the memorandum 2 Principal invest
23. Ebt Where P is the force x is the working gauge length E is Young s modulus and t is the cell thickness Therefore bases on the numbers described above the strain was calculated to be 1700ue which was well within the selected gauge specifications 23 In terms of actual data measurement the voltages were collected using a Wheatstone bridge and amplified using a load cell amplifier Similar to the other measurement devices the data was input into a PC via a DAQ card and processed using software The two gauges were placed into a Wheatstone bridge configuration as per Figure 22 with Rx Ra 3500 and Rm Rm 350 strain gauges Figure 22 Wheatstone Bridge Configuration 7 2 2 4 Linear Variable Displacement Transformer As the core of the Linear Variable Displacement Transformer LVDT moves the output voltage increases from zero to a maximum The magnitude of the output voltage is proportional to the distance moved by the core This output voltage is collected by the DAC card converted to distance using calibration curves and displayed in a graph of voltage vs time and distance vs time 7 2 3 Solenoid Actuation The actuation of the contact tooth was conducted using a solenoid The solenoid is controlled through The DAQ card to enable precise deployment Figure 13 depicts the contact tooth in the initial position The contact tooth will remain in this position until the flywheel reaches the appropriate a
24. ainstorming sequence surrounding the flywheel design the final CAD drawings for the design biological sample test results a Gantt Chart a final budget and a description of the progress of the design unto completion are outlined in the report Team 12 is comprised of 4 members Geoff Beck Ben Breen Ruth Domaratzki and Rachael Schwartz Our supervisor is Dr Marek Kujath and our client is Dr Michael Lee of the Dalhousie Biomedical Engineering Department 1 2 Tissue Mechanics Research into the mechanical behavior of tissue allows for better understanding of failure mechanisms which can influence treatment of such tissues Research into impact loading of tissue could provide valuable information on the behavior of the collagen and elastin at a molecular level Currently few institutes are performing such research Collagen is the most common protein in the human body making up 60 of its dry weight Lee 2010 Collagen fibrils are secured by means of both intra and inter molecular bonds Figure 1 aa RVI intermolecular crosslink Figure 1 Crosslinking of Collagen Fibers Lee 2010 The crosslinking presented above increased fibril elastic modulus tensile strength and toughness Lee 2010 Stiffness MPa Figure 2 Strength and Stiffness Relationships for Materials Lee 2010 The properties of collagen are somewhat surprising in that its strength is on the order of almost 10 Mpa which is similar to s
25. ation present 2 mH 3 Flywheel electric components 3 Repaired 4 other Ja Other Maintenance Action Required as a Result of i 1 Suspected Failure or Malfunction E 2 Improper Maintenance 3 Damaged Accidently Symptoms Visual Inspection Cause of Trouble 1 Inoperative Threads worn Design Deficiency Tarnish Faulty Maintenance Chipped cracked contact pin Faulty Sterilization Spring tension Foreign Object Sharp edges User Adjustment Exposed wiring Wrong Part Used Undetermined Other Disposition or Corrective Action 1 Reason for No Action HL Action TTT Followup Pull from Operation 1 Scheduled Adjusted Repaired Retest and Hold Maintainability Information Hours Min Time to Locate Trouble Time to Repair Replace Total Time Non Operative Remarks Furnish additional information concerning failure of corrective action Department Signature Date 54 Appendix F Engineering Drawings List of Drawings See Attached Frame Explosion L 00 00 Frame Explosion L 01 00 Bottom Mount L 01 01 Horizontal Mount L 01 02 Grip Support L 01 03 Removable Block L 01 04 LVDT Support L 01 05 Removable Block 2 L 01 06 Vertical Mount L 01 07 Bearing Mount L 01 08 Bearing Mounts L 01 09 SO 2008 OY GN Qo Test Bed Explosion L 02 00 1 Linear Track Block B L 02 01 Drawing 1 Linear Track Block B L 02
26. ave observed is that of mechanical cross coupling depicted in Figure 34 The moving components the housing pin and gripper shown as m are coupled by the tissue c1 to the force transducer and grip ki mi This was problematic for us as our measurement equipment was connected to the two cross coupled systems v const Figure 34 Mechanical Cross Coupling 12 Impact on Society In creating an effective and reliable device we hope to give Dr Michael Lee a research tool that will help progress the state of biomaterials research Thus with this research 35 tool valuable information will be obtained in how biomaterials fail in high impact high strain rate settings With this information Doctors could possibly learn how to better treat patients that have suffered impact injuries 13 Life Cycle Analysis The specimen s linear displacement and velocity will be fully determined when testing begins At this point the team will complete the design of the data acquisition system specifically regarding the LVDT measurement device and software 14 Work Allotment All fabrication was completed by in the Mechanical Engineering Machine Shop The design entails cutting and machining Table 7 compares the estimated time of machining to the actual amount of machining time required Table 7 Comparative Chart of Estimated to Actual Machining Hours Part Description Quantity Es
27. carbonate Safety Essential Piedmont Plastics Dartmouth 130 71 Function Generator Elect Control Essential Allied Electronics 375 00 Miscellaneous Misc Essential 50 00 TOTAL 2 446 13 47 Mechanical Department Budget Item Description Mechanical Department Funds SELF Funds RP Prototyping 106 86 RP Prototyping 55 80 McMaster Carr 131 84 Metals R Us 25 64 110 24 Metals R Us 62 15 Piedmont Plastics 130 71 RP Prototyping 11 70 Ben Breen 40 47 RP Prototyping 15 72 RP Prototyping 2 34 RP Prototyping 15 66 TOTAL 200 00 509 13 RN EIE GRAND TOTAL 709 13 Appendix E User s Manual User Manual for Loading Apparatus for High Velocity Tissue Rupture Team 12 Ben Breen Geoff Beck Rachael Schwartz Ruth Domaratzki This manual contains an overview of the safe operation of the Loading Apparatus for High Velocity Tissue Rupture LAHVTR 49 1 General Use The apparatus is designed to perform tensile tests on biological tissues at strain rates at a strain rate of 10005 The loading apparatus will fracture a specimen of bovine tendon up to 2 5cm recording force position and velocity 2 Safety Precautions The Loading Apparatus for High Speed Tissue Rupture holds several areas of safety concern This section is to inform the operator of the risks and necessary precautions taken to operate
28. d upon criteria that were deemed integral to the design From this ranking process we were able to attain the three design ideas discussed in this report Finally the three designed were assessed using the House of Quality as shown in Appendix B The House of Design determined that the flywheel design satisfied the outlined criteria the most The team supervisor and client accepted the flywheel design and the team began brainstorming more detailed design specifications The first design consisted of two flywheels and a clutch One of the wheels held one side of the sample and does not rotate The second wheel is stationary until the motor is at full velocity and the clutch is engaged to the flywheel which breaks the specimen This flaw in this design lies in the fact that having two wheels is unnecessary if the gripping mechanism is attached to the ground and the moment of inertia of the flywheel is not being utilized The next design consisted of the gripping mechanism situated on the tabletop to enable the filming of the specimen breaking with a high speed camera The flywheel was connected to the motor and when the flywheel reaches the needed velocity an electromagnetic clamp engaged the flywheel This would pull a cable that is attached to the gripping apparatus This design was not chosen because a mechanism could not be sourced that could grip the flywheel quickly enough to get up to the velocity needed to break the specimen 4 2 Design Se
29. device that could be made in the future 16 1 Control of Initial Sample Length The client has expressed that the ability to load samples into the apparatus to a predetermined length is desirable At this point the operator loads the sample tensions it and then confirms the length The current method of tensioning the sample is by moving the mounting block along the line of the arrow shown in Figure 35 37 Figure 35 Current control of sample length In the future a calibrated drive screw mechanism could be implemented to move the mounting block with precision This design would be similar to what is found on a precision microscopy stage 16 2 Prevent deformation of critical components In an effort to reduce deformation of the tooth component the mass of the moving parts could potentially be reduced This could be done by reducing mass by part redesign Furthermore material could be removed by drilling holes in non critical areas of the moving parts Other suggestions included changing material to aluminum or titanium However other issues arise with aluminum such as corrosion due to the saline solution and low yield strength As well titanium is substantially more expensive than steel and more difficult to machine One example of reducing mass by component re design would be to move the location of the spring acting on the pin The current design shown in Figure 37 incorporates the spring below the tooth Mass could be remov
30. e device on a laboratory counter in the Biological Tissue Testing Lab The final apparatus measures 23X22 cm Strain Rate The strain rate achievable should be on the order of 1000s The velocity of the moving grip is modeled as instantaneous A sample of the length 0 8cm was tested and the velocity of the moving grip was measured to be 6 5 m s Using these variables the strain rate was found to be jo d g lo 6 5m s 0 008m 2814s The maximum strain rate reached by the LAHVTR is 81 that of the design requirement Loading Achieve a minimum of Ims loading A confirmed loading was 4m seconds Lifetime Should last approximately 5 yrs The LAHVTR is created from sturdy components with overall robust design considered in every developing decision Spare critical components were machined for the client This design requirement was met Conditions of Test Sample The conditions of the test sample will be as close as possible to physiological conditions 100 humidity at 37 C Used spray bottle to keep sample at conditions while loading and unloading sample Control The device will be designed so the operator has control of the strain rate Using the frequency controller and the stroboscope the operator has control over the velocity of the device and therefore the operator has control over the strain rate This design requirement was met Safety The device will be designed to be safely operated by trained individua
31. e rupture for the Department of Biomedical Engineering The device held a design criterion of fracturing a specimen of bovine tendon up to 2 5cm at a strain rate of 1000s recording force position and velocity vs time This report describes the design construction and testing of this senior design project Our device when tested was capable of reaching linear velocities of 7000 mm s in the specimen track which would correspond to a strain rate of 800s for a typical sample The period of acceleration however covered a longer distance than was reasonable for the client so some additional modifications would be necessary before publication quality tests are capable from this device All measurements were verified through the use of high speed camera imagery Table of Contents T Sai ed UNC UU aM oco bo i KATOKA LO 1 1 1 Back round AA ER 1 12 1550 ui 2 Mur ecc 4 3 Generation of Alternatives 6 3 1 Hopkinson Split Bar Apparatus 6 3 2 Gravitational Impact Pendulum 7 4 Selected DES usan 8 41 Evol ti n uy u 8 4 2 Design Selection Matrices
32. ed by placing the spring above the tooth holder 38 Figure 36 Cross sectional view of spring loaded tooth Contact Tooth 1 Tooth holder 2 Tooth housing 3 16 3 Other Considerations The pin could be hardened to withstand tests with the motor run at 1000rpm The shaft could be stepped to reduce ware when assembling disassembling In the future a stainless steel bath could replace the current plastic one This would allow the client to steam sterilize it between uses The moment acting on the tooth could be reduced by minimizing the vertical distance between the bath and the outer rim of the flywheel This could be achieved by shimming the bearings and motor mounts Also in an effort to reduce electrical crosstalk dedicated circuit boards could be created and shielded 17 Conclusions In conclusion the device constructed is able to achieve a strain rates of 800s 1 for samples of a typical length This figure is 200s 1 short of our intended goal of 1000s 1 In addition a greater than anticipated transient period of acceleration was encountered indicating that minor machine modification would be necessary before the device is capable of research quality work Despite these shortfalls many successes were encountered 39 18 References Cheng M Chen W Weerasooriya T Mechanical Behavior of Bovine Tendon with Stress Softening and Loading rate Effects Advanced Theory of Applied Mechanics V2 n2 59 74 2009
33. eel is e 0 95 but is susceptible to both changes in geometry and surface hardening V 8 1 r gt Voz V w l 8 2 f e ro 1 095 L2 T0 2 0 1 m 00 rad s Solving 1 and 2 results in the following grip velocity of 16 75 m s a final grip kinetic energy of 140 J a flywheel angular velocity of 72 5 rad s a final flywheel kinetic energy of 160 J energy losses of 11 J These answers coincide strongly with solutions obtained through the application of the Working Model software package with errors in terms of energy of less than 796 14 Friction and the load posed by the sample are thought to have no effect on the motor of the grip The following calculations highlight this reasoning For the load assuming the specimen to be spring like we were told that the breaking force was 15 N at a length of 3mm so the spring constant is about with a safety factor 10000 N m This generalization is likely weak The energy dissipated in a stretch to breaking for the specimen should be about 0 045 J These calculations follow below with an additional safety factor present for strain distance Avis said to be the maximum elongation of the specimen pee SF 10000N 0 003 m B uu a 1 Ax 10000 m SF 0 003 0 5 J The frictional losses are based upon the coulomb model for a w 0 3 which is common for steel on steel surfaces without lubrication The l
34. eel at four speeds Table 4 outlined the information gained during the testing Table 4 Biological Specimen Testing Results Test Flywheel Speed Successful Engagement Observations rpm Mechanism Employment 1 300 Yes No wear 2 500 Yes Engagement pin surface chip 3 700 Engagement pin surface chip 4 1000 Yes Engagement pin deformation 5 2 2 Solenoid Testing The solenoid was tested under several applied voltages to determine the time encountered when fully extending the solenoid core This time period was then compared against the necessary time period needed to successfully engage the pin with the flywheel Five trials were performed and the average of the data was recorded Figure 9 compares the experimental to the theoretical data of applied voltage to time encountered for full extension of the solenoid core The obtained data shows that the solenoid is well within the needed operating range for the task of engaging the pin to the flywheel 12 Solenoid Voltage Displacement Relationship 70 60 50 40 30 a 20 10 0 10 0 Time to Extension ms 13 0 14 0 Applied Voltage V Figure 9 Solenoid voltage vs Time theoretical red experimental blue 6 Calculations A valid concern about the flywheel driven impact apparatus was its ability to provide an acceptable output displacement profile An acceptable profile has constant strain rate past the transient period and a transien
35. enoid Actuation se a n Hee qa h u ree river 24 8 Implementation of Measurement Systems 26 8 1 Calibration Of 1 26 8 2 Calibration of Force Transducer 26 9 Safety 27 TO i a a qa q us ui a a 27 10 1 Test Procedures m 27 10 2 Validation Method 28 10 3 Measurement Equipment Testing Results 28 10 4 High Speed Video Testing Results 31 10 5 Time of Impact Analysis 34 11 Issues Encountered 35 111 Electrical and Mechanical Crosstalk 35 iii 12 AMpact OM SOC 35 13 Life Cycle E Worte 36 14 Work Allotment 36 DI t T 36 16 Future Considerations
36. ent Figure 5 Gravitational Impact Pendulum The gripping system will consist of corrosion resistant material A corrosion resistant material is necessary because the biological specimen will be placed in a corrosive aqueous saline solution It was suggested by the client that Polyacetel would be a preferable material due to its non hydroscopic not absorbing liquid characteristic If the material is to absorb liquid the assembly may not come apart easily after long exposures to the liquid The grips will be mounted on a track to eliminate buckling and restrict the strain to the axial direction 4 Selected Design The following section outlines our selected design and the mechanism that we used to select it from the alternatives 4 1 Design Evolution The selected design consists of several different operational sections The device is broken down into the flywheel and motor the engagement mechanism and the gripping device sections The flywheel is a reasonable design due to its significant moment on inertia resulting in a storage device for rotational energy This characteristic lends itself to be a useful device in controlling a constant velocity The flywheel design was initially thought to be constructed out of stainless steel with an estimated diameter of twenty centimeters The brushless motor will have variable speed capabilities so the operator may test under a range of speed variables and thus strain rates The e
37. ery accurate specifications Gas gun actuator Incident bar transmission Striker tube Momentum ELVS trap bar Figure 4 Hopkinson Split Bar Apparatus 3 22 Gravitational Impact Pendulum A method of biological specimen testing biological specimens based on a gravitational impact pendulum was considered Figure 6 outlines the core components of such a device A pendulum based approach has been employed in metallurgical testing to determine properties such as hardness necessary modifications would be needed to meet the specifications set by the client A pendulum based design would be capable of meeting the objectives for lifetime conditions control and data acquisition as defined in our Design Memorandum The pendulum based design however was considered likely to fail on the objectives of our chosen size and control criteria A base size of 30in x 30in was deemed optimal for the laboratory setting of the device and it was likely that the swing of such a pendulum would be capable of fitting within these dimensions while achieving the rate required A pendulum approach was considered also to be susceptible to control issues as a mechanism for reproducibly determining required drop heights from requested strain rates was needed Pendulum actuator Sample LVDT Measurment of position and velocity Load cell for force measurem
38. his reason the operator will select in the operating range of 110 690 rpm or 670 4170 rpm The outer surface of the RPM dial is the precision control The dial is adjusted to the frequency of rotation at which the testing is performed Turn on the Strobotac the frequency controller and the power supply Adjust the frequency control using the arrow keys until the white stripe painted on the flywheel seems to slow and stop At this point the frequency of the stroboscope equals the frequency of rotation of the flywheel The frequency controller displays the frequency of the rotation of the flywheel in rotations per minute while the shaft is rotating 4 2 Sample Loading Loosen the screws on the clamps and remove the tops of the clamps Figure 1 4 Place these parts on the laboratory table The sample should be precisely measured and not exceed the length of one centimeter Attach the sample to clamps by placing the sample on the clamp bottoms Figure 2 3 and tightening the screws with supplied the Allen key Loosen the setscrews Figure 2 1 and apply tension to the sample by adjusting the outcropping of the load cell Tighten the setscrews using the supplied Allen key Figure 2 Linear Track Setscrews 1 Biological sample 2 Grip bottom 3 Grip top 4 51 4 3 Power source The power supply can be used as a current source The set up of this method is described below 1 Connect the desired circuit to the power supply
39. igators The Principal investigators of the design project shall be the Design Team as stated above Students at the Department of Mechanical Engineering Dalhousie University 3 Confidentiality and Publication The project and corresponding presentations reports and web pages will be in the public domain 4 Ownership of Intellectual Property The intellectual property will remain the shared property of the Client and Design Team The fabricated device will be the property of the Client The project presentation and reports with the exception of some possible proprietary information will be in the public domain 41 Design Project Waiver This Agreement is made and entered into for a term beginning the day of September 2009 and ending the day of May 2009 between Ben Breen Ruth Domaratzki Geoff Beck Rachael Schwartz hereinafter referred to as Design Team And Dr Michael Lee hereinafter referred to as Client The Design Team and Client hereby agree as follows Indemnity Each party shall indemnify and save harmless the other party against all costs actions suits claims losses or damages for all matters arising out of this agreement and the performance of the project The Client shall indemnify the Design Team against all costs suits or claims resulting from the use by client or licensees of and deliverables or intellectual property developed by the Design Team under this agreement Warranties Dalhousie
40. ional validation of the load cell was considered This potentially could be completed using the video processing software On the video one can track how the load cell moves linearly when the sample is stretched Using this information in addition to the properties of the cantilever load cell length height width material and can calculated the required force to move the load cell the distance calculated in the video software Given the high R value of the load cell this additional validation was deemed unnecessary 10 3 Measurement Equipment Testing Results When tested the signals of Figure 27 were acquired 28 Raw Data 3 Load Cell Voltage V Co 0 05 0 10 0 15 0 20 0 25 0 30 0 35 0 40 time s Figure 27 Raw Signals Acquired During Testing The signals were processed and are presented in processed form in Figure 28 The root mean square of the LVDT signal was taken for each half period and then multiplied by because Vpeak Label A of the figure indicates the action of the gas spring Label B indicates a region of constant velocity over a long distance of travel Label C indicates that the specimen displaced before it strained and that the sample was likely under tensioned Label D indicates resonance of the beam which was easily seen under high speed video analysis Processed Data A Load Cell 4 2 5 2 0 Voltage V D
41. lection Matrices Breaking the design into several sub components and listing the various solutions to these sub components obtained from brainstorming sessions resulted in design selection Next reasonable combinations of design sub components were listed as design solutions as shown in the morphological chart in Appendix B Following this the reasonable combinations were then ranked based upon criteria that were deemed integral to the design From this ranking process we were able to attain the three design ideas discussed in this report Finally the three designed were assessed using the House of Quality as shown in Appendix B 5 Problem Exploration In order to more clearly understand the intricacies of the design and conceptualize the requirements the team completed research and testing on several aspects of the design Initial testing was conducted to determine the validity of the engagement mechanism and solenoid operation A mock up of the device was constructed to determine the optimal placing of members and a rapid prototyped model was created to confirm the final dimensions of the device 5 1 Modeling Several methods of modeling were performed to aide in the conceptualization of the device determination of high stress areas and the dimensions of the engagement mechanism with respect to the flywheel 5 11 LAHVTR Mock Up First a mock up of the device was constructed to help the team conceptualize the aspects of the design that
42. ls A shielding component will be incorporated if required The device operated well within safe operating conditions The device is designed to be operated by an individual that is trained by reviewing the operation and safety manual Within this demographic this design criteria is met It became apparent during the design process that it was necessary to fit the LAHVTR with a polycarbonate safety shield Documentation The device will be accompanied with a comprehensive instruction manual The team achieved this requirement by completing an instruction manual for the operation of the device along with some safety recommendations This manual is located in Appendix E Timing and Deadlines All set deadlines and time requirements set out in the MECH 4010 4020 Design Project Handbook will be met Throughout the year Team 12 has met or exceeded all deadlines and requirements associated with the course work deliverables and testing Data Acquisition The device should provide data describing the force displacement and time for each trial This design requirement was met and the output from the device is discussed in detail in later sections An LVDT and Bending Load Cell are incorporated in design and the data is processed using DAQ 3 Generation of Alternatives The following section presents two alternative designs that were considered and the benefits and the drawbacks of each design The designs of this section were rejected with the acce
43. mple The data acquired is outlined below in Table 6 Furthermore it should be noted that the velocity below was in fact very similar to the LVDT velocity acquired for testing the device at 1000RPM however it was less than the predicted 10m s during the design phase Table 6 Displacement data for 1000RPM trial with 8mm sample Frame Time Track Point 1 X y 7218 7 218000412 15 3488369 22 5581398 7217 7 217000484 17 4418602 22 5581398 7216 7 21600008 21 9767437 22 5581398 7215 7 215000153 28 4883728 22 6744194 For this set of data the team looked at frames 7215 and 7216 v v Ad At 28 4883728 21 9767437 7215000153 7 21600008 v 6512 mm s g S It fell short of our design requirement of 1000s however we are quite satisfied with the result Some of the items that held the team back in achieving the design requirement included plastic yielding of the engagement pin at 1000RPM and as a result the team could only effectively test the device up 700RPM on a regular basis Furthermore the device did not show the expected behavior and higher speeds did not always yield the best results Additionally the team did not see the acceleration that was expected partially due to plastic yielding of the pin and thus strain rates were not as high as 1000 s as the sample was breaking during the acceleration and not at the maximum velocity 10
44. ngagement of the actuation method will be performed in response to an electrical signal generated by the data acquisition system Several methods for engaging the flywheel were under consideration Initially the design was thought to hold a lightweight weight engagement wheel that will not continue to rotate with the flywheel after the needed energy is removed from the flywheel with the use of a sacrificial part electromagnetic engagement and a clutch system The gripping system consists of corrosion resistant material A corrosion resistant material is necessary because the biological specimen will be placed in a corrosive aqueous Saline solution The grips will be mounted on a track to eliminate buckling and restrict the strain to the axial direction Flywheel actuator Electromagnetic clutch o Variable Lightweight Sample in watertight engagement aS Y M ES wheel KO J motor Load cell Laser system for ee velocity measurement Figure 6 Early depiction of LAHVTR Breaking the design into several sub components and listing the various solutions to these sub components obtained from brainstorming sessions obtained the selected design Next reasonable combinations of design sub components were listed as design solutions as shown in the morphological chart in Appendix B Following this the reasonable combinations were then ranked base
45. ngular velocity At that point the technician will activate The DAQ card and the solenoid will push the contact tooth into the final position In this position the contact tooth will meet the flywheel pin The flywheel pin will move the contact tooth along with the grip along the track This motion will rupture the tissue The second position is also depicted in Figure 24 and Error Reference source not found 24 Figure 23 Initial Position of Contact Tooth Solenoid 1 Contact tooth 2 Tooth holder 3 Tooth housing 4 Pin 5 Flywheel 6 Figure 24 Final Position of Contact Tooth Solenoid 1 Contact tooth 2 Tooth holder 3 Tooth housing 4 Pin 5 Flywheel 6 25 8 Implementation of Measurement Systems 8 1 Calibration of LVDT Figure 25 below shows a calibration curve for the LVDT This was generated by measuring the voltage at known distances from the starting position The data was then correlated using a linear regression to project the measured voltage to a given distance If one notes the R value of 0 9982 the data is almost a perfect fit LVDT Calibration y 6 1484x 0 9763 R 0 9982 cDisplacement mm a o Voltage V Figure 25 Calibration Graph for LVDT 8 2 Calibration of Force Transducer The calibration of the force transducer was done in a similar fashion to the LVDT Known masses were hung from the load cell and voltages were recorded The masse
46. osses due to friction and work against gravity in the vertical configuration are expected to be about 0 5 J and are presented below Ax 0 3 1 kg 9 81 N kg SF 0 003 SF 0 2 J E mg Ax 1 kg SF 9 81 N kg 0 003 SF 0 3 J lost gravity The mass of the grip 1 kg and its velocity at impact provides for more than adequate amounts of kinetic energy to overcome friction gravity and the specimen without appreciable changes to its velocity The amount of time to reach the desired velocity following impact is determined from the following expression where o is the speed in sound within the material for steel 5000 m s L At 2 oO The time was found to be 645 for a pin of 2 inches in diameter Since the pin is of less than this diameter the value for this ramp time is surely less than any maximum acceptable value Due to the variable nature of the coefficient of restitution it is only through experimentation following the build of a prototype that a solid relationship between the t http tinyurl com yea2xt4 15 3 4 5 6 7 flywheel rate of rotation and the linear velocity of the specimen grip may be determined However these calculations show e that the desired velocity and thus strain rate will be obtained in the transient region e that the resulting displacement profile should be free of large decelerations in the time leading to fracture
47. placed in specimen grips 2 The specimen is placed in pretension by adjustment of the force transducer The Allen key tightens the setscrews at the desired tension 3 The zero position of the LVDT in the centre of the throw so centre the initial position around the centre of the entire throw to obtain the most accurate results 27 4 Place the safety case over the flywheel section 5 Turn on the Stroboscope and set the RPM dials to the desired angular speed 6 Turn on the frequency controller and gradually increase the speed until the white stripe on the flywheel appears to be stationary This indicates that the angular speed of the flywheel is the same as the displayed angular speed on the stroboscope 7 Press enter to record the data 10 2 Validation Method The LVDT and the force transducer were calibrated to aide in verifying the method used While the machine is stationary the voltage output for several distances was rerecorded and these points were used to create a calibration curve The device is activated and the output data from the test is compared to the calibration curve to verify the validity of the data Furthermore the LVDT was validated using a high speed camera and video processing software Testing was recorded using video capture at 500 frames per second The acquired video was then processed and the software was able to match image points in several frames over time and output velocities and positions Addit
48. pted design presented following this section 3 1 Hopkinson Split Bar Apparatus The Hopkinson Split Bar apparatus HSBA is used extensively in materials testing because of its ability to achieve extremely high strain rates The HSBA functions by propelling a striker tube using a compressed air gas gun actuator towards an incident bar When the striker tube impacts the incident bar a pulse wave is transmitted through the incident bar and into the sample Some of the pulse wave is then reflected back through the incident bar and captured in the momentum trap bar and some is dispersed in the transmission bar Using an Enhanced Laser Velocity System ELVS the deformation and velocity of the sample can be measured dynamically This data would then be input into The DAC card to be analyzed and recorded The HSBA is shown in Figure 5 The main benefit of this design is that extremely high strain rates have been reported additionally the ELVS can attain the dynamic stress strain curve However there are several drawbacks of this design Firstly the gas gun raises several safety concerns as extremely high pressures are needed to propel the striker tube Additionally the HSBA is difficult to calibrate as pulse wave magnitude has to be finely tuned to the pressure the gas gun actuator Finally we foresee this device being expensive because the compressed air system needed for the gas gun and incident and transmission bar have to be machined to v
49. s were then multiplied by the acceleration due to gravity to get the force applied Again the data was fit using a linear regression and is shown in Figure 26 Once again note the nearly perfect linear match with an R value of 0 9991 26 Force Transducer Calibration 35 30 y 12 371x 0 6334 R 0 9991 50 8 50 gt 5 0 1 0 0 5 1 5 2 2 5 Force Figure 26 Calibration Graph for Force Transducer 9 Safety During the design process creating a safe device was of the utmost importance Therefore we considered three levels of safe design including procedural safety engineered safety and inherent safety Firstly for procedural safety Team 12 wrote an operation manual This operation manual outlines safe operation of the device as well as clearly outlining the risks and hazards associated with device operation Secondly we encased the device in a safety shield constructed of polycarbonate panels This will ensure the operator is safe should the device catastrophically fail Lastly the design we have created is inherently safe because the operator can control the device remotely from a computer away from the actual device Safety precautions are outlined in the User s Manual in Appendix D 10 Testing The following sections outline our testing procedure our methods of validation and the data that we were able to collect 10 1 Test Procedure 1 The specimen is sized and
50. s to aid in the ability to view the flywheel operation The safety shield is depicted in Figure 11 Figure 19 Diagram of Safety Shield 7 2 Electrical Components The electrical components of this project consisted of a motor and frequency drive the measurement systems DAQ system and high speed video camera equipment 7 2 4 Motor and Frequency Drive 21 The device is driven using a 1 3 horsepower 115 volt three phase AC motor controlled using an AC Drive The motor was selected on its ability to drive the flywheel at 1000rpm and operate using a standard 115 volt power supply An AC motor was selected over a DC motor based on cost and ease of power supply v comrecs C Additionally the frequency drive was selected based on its ability to easily and accurately control the motor frequency speed Furthermore the drive is compatible with a PC computer thus if the client prefers the motor can be controlled from a PC Figure 20 Frequency Controller 7 2 2 Measurement Systems The measurement systems are all controlled through the DAC card The operator initiates the rotary encoder through the PC The rotary encoder senses the position of the flywheel and the solenoid is automatically deployed and the data requisition system is initiated to collect the data 7 2 2 1 Rotary Shaft Encoder The pin is engaged and consequently the specimen is loaded both after the flywheel reaches the desired speed
51. t period of no more than one fourth the fracture strain This document seeks to provide an assurance that an acceptable profile will be attained Figure 10 attempts to illustrate both an acceptable strain rate profile and the anticipated profile which has been obtained from our calculations that follow Desired Anticipated g 0 0625 0 25 0 25 e 4 Allowable Transient Specimen Period Ends Fractures Figure 10 Desired vs Anticipated Strain Rate Meeting 30 September 2009 13 In this scenario the motor is disconnected from the inertial load flywheel through the use of an overrunning clutch To the end of obtaining the profile the principal of inelastic impulse and momentum is applied The properties of the flywheel w and specimen grip g are selected to be m 16 kg m 1 kg d 20 0 061 kg 100 rad s Conservation of angular momentum about point A the center of flywheel rotation results in the expression H IQ I0 m v r 0 061 kg m 100 rad s 0 061 kg m o 0 1 kg my 1 The result is one equation with two unknown quantities An additional bit of knowledge is needed in this case The coefficient of restitution a function of the material in impact is applied This coefficient relates the velocities of the masses along the line of impact just before and after the collision Hibbeler 2007 This coefficient for st
52. teel and aluminum alloy Its stiffness however is lower around 10 Mpa in comparison to other materials steel is on the order of 10 Mpa Strain Figure 3 Structural Mechanical Relations in Soft Tissues Lee 2010 Elastin is a protein polymer similar to collagen but with more elastic properties The mechanicals properties of both collagen and elastin are presented in Table 1 Table 1 Mechanical Properties of Collagen and Elastin Lee 2010 Collagen 1000 50 100 10 crimped wH Researchers have been fascinated by the performance of composite tissues such as tendon ligament skin and arterial tissues These tissues are composed of differing percentages of both collagen and elastin and therefore exhibit differing behaviors as shown in Figure 3 The content and mechanical properties of some soft tissue composites are presented in Table 2 Table 2 Content and Mechanical Properties of Soft Tissue Composites Lee 2010 Collagen Elastin dry weight dry weight 2 Objectives The design requirements for the apparatus were agreed upon and were presented within the design memorandum as follows The device will be mounted on a table top with one face approximately 30x30 in e Strain rates achieved will be on the order of 1000s The device should function approximately 5 years The conditions of the test sample will be as close as possible to physiological conditions 100 humidity at 37 C
53. the equipment The flywheel is rotating at high speeds The following precautions should be taken when operation the device Place the safety shield over the flywheel whenever before operating the motor Refer to Figure 1 for the correct orientation of the safety shield Safety glasses and hearing protection must be worn Remove loose clothing and jewelry prior to operating the equipment Before each test inspect the apparatus to make sure that no tools or wires are in the vicinity of the flywheel Avoid contact with the shaft coupling The coupling experiences high temperatures during and after operation m Figure 1 Correct Safety Shield Orientation 50 3 Initial Operation and start up checklist Before operating the LAHVTR apparatus read Section 2 of this manual carefully and adhere to all safety precautions Before each test session complete a visual inspection of the apparatus and complete the Start up Checklist located in Appendix A 4 Operating Instructions 4 1 The Strobotac The Strobotac is used to determine the frequency of the rotation of the flywheel in operation The Strobotac is placed on the tabletop at a distance of one foot from the face of the flywheel Dimming the laboratory lights may aid in the ease of reading the frequency of the rotation of the flywheel The RPM dial is used to select the RPM range in which the operator will test The LAHVTR operates at a maximum of 1000 rotations per minute For t
54. the specimen The flywheel is machined out of 0 2 m diameter carbon steel This material was chosen for it s low cost and high weight It is also a common material that can be ordered locally which will reduce the cost further The flywheel was modeled after a disc of uniform thickness The failure calculations show the flywheel will not fail at the intended angular velocity of the shaft These calculations are located in Appendix C The flywheel was designed with flanges to decrease stress concentrations of the flywheel at the critical areas for shear stress Tresca s theory of failure was used to find the maximum shear stress The flanges are not included in the failure calculations of the flywheel though they add a factor of safety to the design The diameter of the flywheel is sufficient such that the arc of motion needed to fracture the tissue can be modeled as approximately linear 17 Figure 13 Flywheel Figure 14 is a plot of the flywheel diameter series2 constant thickness of 5cm and thickness series1 constant diameter of 20cm versus the flywheel mass The plot used density of carbon steel for calculations This graph was created to give Team 12 an understating how the flywheel mass changed with changing dimensions This was a valuable tool that helped select the flywheel dimensions as the team could quickly see the effect of changing parameters T Mass vs Size of Flywheel 60 50
55. timated Quantity Actual Hours Hours Flywheel 1 20 1 18 Flywheel pin 3 8 1 3 Grip top 2 6 2 5 Grip bottom 2 6 2 5 Tooth housing 1 10 1 11 Contact tooth 2 5 10 10 Frame 1 10 1 10 Plexiglas 1 5 1 4 Tooth holder 0 0 1 7 support 0 0 1 3 Force Transducer 0 0 1 4 Total Hours of Machining 70 hrs 80 hrs The estimation of hours was low because some of the material for the parts was changed The parts that were changed from carbon steel to stainless steel were more difficult to machine The Mechanical Engineering Technicians completed the machining and the team completed the assembly painting and electronics 15 Budget The estimated and final budget is illustrated in Table 4 and a detailed budget is located in Appendix D Table 8 Comparative Graph of Estimated to Actual Budget Mechanical Estimated Actual 36 Frame 150 105 Flywheel 40 40 Specimen grip 315 172 Shock Absorber 0 67 Bearings 0 30 Main shaft 65 0 Electrical Motor 335 335 Measurement 1000 660 Tooth Engagement 16 16 Control 330 335 Power 30 0 Function Generator 0 375 Safety Polycarbonate 0 130 Modeling Rapid Prototyping 0 234 Misc 1220 50 Total 3500 2549 The project was funded both by the Department of Mechanical Engineering and the Department of Biomedical Engineering 16 Future Considerations This section outlines some refinements to the
56. to physiological conditions 100 humidity at 37 C Control The device will be designed so the operator has control of the strain rate Safety Features The device will be designed to be safely operated by trained individuals A shielding component will be incorporated if required Documentation The device will be accompanied with a comprehensive instruction manual Timing and Deadlines All set deadlines and time requirements set out in the MECH 4010 4020 Design Project Handbook will be met Data Acquisition The device should provide data describing the force displacement and time for each trial Intellectual Property The intellectual property will remain the shared property of the Client and Design Team The fabricated device will be the property of the Client The project presentation and reports with the exception of some possible proprietary information will be in the public domain Provisions by Client The client will provide Time weekly meetings Funding Fabrication costs supplies 43 Appendix B Decision Making Tables and Charts Group 12 Brainstorming Session Morphological Chart for High Velocity Loading Apparatus Table 1 Components of the Design Compared Component Solutions 1 Propulsion Pendulum HSBA DC Actuator Electromagnetic Flywheel 2 Velocity LVDT ADC
57. ucer is required The team measured the voltage change as a result of the application of several calibration weights These output points were then used to determine a linear relation between the deflection and voltage change This relation is used to determine the force applied to the specimen The results of the calibration are discussed in the calibrations section of this report Gauge Sensing Bending specimen Figure 21 Specimen Force Measurement The force cell was selected based on several criterions Firstly the strain gauges were selected based on the theorized forces and other characteristics that would ease mounting the gauges The size and material of the load cell was determined Titanium was selected for its relatively low Young s modulus approximately half that of steel because the project forces were thought to be approximately several hundred Newton s based on information obtained from the client Furthermore the nominal length and width were fixed as a result of geometry Therefore working gauge length and cell width was used to create a scenario that would result in strains that were compatible with the selected gauges The working gauge length was selected to be five centimeters this was mainly chosen for practicality reasons Lastly the thickness was based on available titanium sizes several thicknesses were considered however 2 millimeters yielded the best results based on the equation below Px
58. udget Total No Item Description Location in Design Hierarchy Status Distributer Quantity 0 06 Sheet Metal Mech Frame Essential Metals R Us Dartmouth 74 88 Rapid Prototyping Misc Essential Dalhousie 233 72 Stainless Steel Mech Shaft Essential Metals R Us Dartmouth 172 39 Shock Absorber Mech Frame Essential McMaster Carr 67 16 Flywheel Mech Shaft Essential Metals R Us Dartmouth 40 00 1 25 Square Tube Mech Specimen Grip Essential Metals R Us Dartmouth 35 56 External retaining rings Mech Specimen Grip Essential Mechanical Dept 0 00 Shaft Mech Shaft Essential Mechanical Dept 0 00 Plummer Block Bearings Mech Shaft Essential Fastenal 30 00 LVDT Elect Measurement Displacement Essential A Tech 401 00 Motor Elect Motor Essential Motion Industries Dartmouth 226 78 Frequency controller Elect Motor Essential Motion Industries Dartmouth 334 96 12VDC Pin Driving Solenoid Elect PinEngagement Essential McMaster Carr 15 27 Strain Gages Elect Measurement Displacement Essential Intertechnology 135 00 Precision Resistors Elect Measurement Displacement Essential Intertechnology 80 00 Titanium Elect Measurement Displacement Essential Alfa Aesar 43 70 Poly
59. vitational Impact Pendulum retient poenae id eded 8 Figure 6 Early depiction of LAEIVTR ens acid 9 Figure 7 Mock up of Device iiie eH ier te etl be eer es 11 Figure 8 Rapid Prototype of Device a 11 Figure 9 Solenoid voltage vs Time theoretical red experimental blue 13 Figure 10 Desired vs Anticipated Strain Rate eee 13 Ligure 11 Pinal adt aen enu eue 16 Figure 12 Drive shaft Assembly i de eee pit te pipa qi E Ede asp pudeat 17 Figure eei u eni E e i esce aad 18 Figure Ply wheel Design ioo oreet eo ener ds 18 Figure 15 Engagement Pm in Flywheel eei cedrus 19 Figure 16 Exploded View of Drive Shaft Assembly 19 Figure 17 Exploded Grip Assembly e eite teer ace 20 Pipure 18 Damper set tp acce c dem ack Ee IGI Ema da a aes 2 Figure 19 Diagram of Safety Shield Hep et te t 21 Figure 20 Frequency Controller ree Edel shored eee 22 Figure 21 Specimen Force Measurement ettet tie e ente ted 23 Figure 22 Wheatstone Bridge Configuration ierit 24 Figure 23 Initial Position of Contact Tooth 25 Figure 24 Final Position of Contact Tooth 2
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