Optimisation and validation of the ARAMIS DIC system for use in
Contents
1. et al 2009 Damage Progression Using Speckle Correlation and High Speed Imaging for Survivability of Leadfree Packaging Under Shock Strain 45 3 pp 267 282 Tiwari V et al 2008 Application of 3D image correlation for full field transient plate deformation measurements during blast loading International Journal of Impact Engineering 36 pp 862 874 Yu J H and Dehmer P G 2010 Dynamic impact deformation analysis using high speed cameras and ARAMIS photogrammetry software Army Research Laboratory UNCLASSIFIED 25 UNCLASSIFIED DSTO TN 1203 19 20 2 22 23 24 25 26 26 Reu P L and Miller T J 2008 The application of high speed digital image correlation The Journal of Strain Analysis for Engineering 43 8 1 August pp 673 388 mbH G 2009 ARAMIS User Manual Software v6 1 and higher Braunshweig Germany mbH G 2010 ARAMIS User Information Hardware Brauncshweig Germany Warden R 1993 Ship Vulnerability MK 1 High Speed Cine Footage Defence Science and Technology Organisation McHugh S Cambridge in Colour 2012 Accessed 27 11 2012 Available from http www cambridgeincolour com Fulton W A few Scanning Tips 2012 Accessed 28 11 2012 Available from http www scantips com lights histograms html Tong W 2005 An Evaluation of Digital Image Correlation Criteria for Strain Mapping Applications Strain 41 4 pp 167 175 Galanulis K and Winter D Industria2. Alastair Douglas Daniel Birt Jim Nicholls QinetiQ and Brian Crowley QinetiQ for their work in commissioning the ARAMIS DIC system for use in the synergistic blast and fragmentation event series UNCLASSIFIED 24 10 11 12 13 14 15 16 17 18 UNCLASSIFIED DSTO TN 1203 6 References Ackermann F 1984 Digital Image Correlation Performance and Potential Application in Photogrammetry The Photogrammetric Record 11 64 pp 429 439 Moser R and Lightner J G 2007 Using Three Dimensional Digital Imaging Correlation Techniques to Validate Tire Finite Element Model Experimental Techniques 31 4 pp 29 36 Bolduc M et al 2008 Improving hydrocode models using high strain rate testing Defence R amp D Canada Valcartier Sciammarella C A and Sciammarella F M 2012 Digital Image Correlation DIC In Experimental Mechanics of Solids John Wiley amp Sons Ltd pp 607 629 Hild F and Roux S 2006 Digital image correlation from displacement measurement to identification of elastic properties a review Strain 42 2 7 April 2006 pp 69 80 Verhulp E Rietbergen B v and Huiskes R 2003 A three dimensional digital image correlation technique for strain measurements in microstructures Journal of Biomechanics 31 28 December 2003 pp 1313 1220 Nicoletto G et al 2011 Application of High Magnification Digital Image Correlation Technique to Micromechanical Strain Analysis St
3. protection of the cameras was essential One of the methods for protecting the cameras was to have as much distance between the cameras and the event as possible The largest lenses available for use in the blast and fragmentation events were 180 mm lenses The maximum distance that could be achieved with these lenses and still produce quality images for data analysis was 12 m see section 3 3 The cameras were housed in open splinter proof containers The splinter proof plexiglass was not used due to image distortion Instead mirrors were used to reflect the image from the event to the protected cameras Protecting cameras from a dynamic event has been achieved using mirrors at small stand off distances and with the mirrors being protected from projectiles 11 To ensure that good images could be obtained from using mirrors at a large stand off distance in an exposed outdoor environment exploratory tests were performed These tests were to address problems occurring from mirror movement distance image distortion and angles of reflection The images captured through the mirrors also need to be inverted to make the image appear as it would without a mirror The mirrors were secured using backing frames on tripods and positioned equidistant from the cameras Care was taken to ensure the mirrors were level and square to the cameras i e not tilted The ARAMIS system requires a camera separation of 25 Figure 19 shows the setup of the high speed
4. GOM mbH Germany was acquired by the Defence Science and Technology Organisation for the evaluation of full field surface strain in large scale high strain rate synergistic blast and fragmentation events The ARAMIS system uses digital images recorded at set time intervals during a deformation event to determine the surface deformation and strain of a target over time Due to the complexity of large scale high strain rate events with high dynamic loading optimisation of the ARAMIS system was required Experiments were performed to determine the optimal set up configuration for large scale high strain rate events and confirm that the required experimental modifications did not affect the results This included assessing the use of high speed cameras mirrors large stand off distances and lighting The outcomes of these experiments are detailed in this report along with recommendations and the final set up configuration for the large scale high strain rate events Validation of the ARAMIS system was performed by comparing the accuracy of the ARAMIS strain evaluation against a tri axial strain gauge An aluminium tensile sample loaded to failure in a tensile test machine was used to perform this validation The results showed good correlation between the ARAMIS strain values and the strain gauge values in both the x and y directions UNCLASSIFIED UNCLASSIFIED This page is intentionally blank UNCLASSIFIED UNCLASSIFIED Author Vane
5. Latimape Stajge O Fight image Stage 2 through 13 left image Stage 2 through 13 night image Sape id Let irage Stays id Righimage Stage 15 through 20 left image Stage 15 through 20 right image S m Siapa 21 Lat kaga Stage 21 gh imapa Figure 1 A set of three left and right target object images in series for use in 3D ARAMIS analysis showing the facet identification in both the left and right images and subsequent images 20 UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Prior to analysis system calibration is required Calibration produces an operational area for 2D events or volume for 3D events in which the event can be accurately measured Calibration is performed by moving a calibration object through a set range of motions within the area or volume where the event is to occur Figure 2 shows the two variants of calibration objects used with the ARAMIS system the calibration plate and the calibration cross The calibration object chosen depends on the target area being analysed The calibration objects and the range of motions for calibration are defined in the ARAMIS hardware manual Section 9 21 Figure 2 Calibration objects used in ARAMIS calibration the calibration plate left which comes in various sizes and calibration cross right 21 Each calibration object is marked with unique points which the ARAMIS system identifies at each orientation to map the event volume Information on calibration and use
6. TN 1203 so the speckle pattern was applied using white spray paint Ideally a white base paint would be used with a black speckle pattern as black paint has a greater hiding power than white paint however the white speckle pattern proved acceptable in this case The tri axial strain gauge was applied to the back surface and the location of the strain gauge is indicated by the white rectangle in Figure 3 Strain gauge eee LEME epee ame SRP MARE T located location Foss 9 ae Ye AS Sev RS holes ee KT Figure 3 Image of aluminium specimen showing three holes the strain gauge location and speckle pattern This image was processed in ARAMIS for determining full field strain The ARAMIS camera system was setup following the guidelines in the ARAMIS hardware manual 21 The 50 mm GOM mbH lenses were used and the angle between the two cameras was 25 5 Calibration of the ARAMIS system for the setup described required use of the 140 mm x 170 mm calibration plate The calibration deviation or calibration error determined by the ARAMIS system was 0 071 pixels This calibration deviation was within an acceptable range and resulted in a successful calibration The determined measuring volume was 55 45 30 mm Height Width Depth The laboratory where the tensile experiment was conducted did not provide adequate light for the ARAMIS system Additional halogen lighting was used to illuminate the sample Halogen lighting produces a high heat
7. The images taken from the left and right camera for calibration and for the event need to be kept in separate folders ideally left images and right images These directories are pointed to in this panel as Camera 1 and Camera 2 as shown in Figure 15 a The calibration object used for calibration is selected from the second panel description Calibration from Image Series as shown in Figure 15 b There is an option to use instructions for calibration but when operating using an external image series this should be turned off 3 The ARAMIS sensor controller box is used to control GOM standard cameras through the ARAMIS software UNCLASSIFIED 13 UNCLASSIFIED DSTO TN 1203 Calibration from Image Series F a Calibration from Image Series Mode CC20 1000 D09834 ID 381 Camera 1 al_C001HO01S0006 tif J Camera 2 al_C002HO01S0001 tif J g CP20 250 D09857 215 366 ID 385 215 292 g CP20 175 D09849 140 855 ID 386 140 858 g CP20 55 D09626 47 526 ID 389 47 527 Edit amp HS Photon SA5 Vv LD a Filename 1S Aquisition Data example J a b Figure 15 The Calibration from Image Series panels in the ARAMIS software a the panel for identifying the external image series images and camera and b the panel for selecting the calibration object and turning off the instructions a m
8. camera contained in a splinter proof container facing the mirror The two cameras do not need to be on the same horizontal plane but they must have the same target area in view The stability of the mirrors in an outdoor environment is important Wind can cause the mirrors to vibrate which produces distortion in the image set when processed by ARAMIS This will cause calibration failure or large errors in the data To ensure the image set is free from distortion a stable mirror support base was used When the blast wave from an explosive event reaches the mirrors the mirrors vibrate under the loading When this occurs the data from that point on is no longer valid UNCLASSIFIED 17 UNCLASSIFIED DSTO TN 1203 Figure 19 Camera in splinter proof facing mirror aimed at the target 3 5 1 Noise floor The noise floor of the deflection strain results for the ARAMIS system used in the blast and fragmentation events was determined through static testing with the desired configuration Other experimental studies have performed this verification with different system configurations 11 The noise floor of the blast and fragmentation event system configuration cameras located at a 12 m stand off distance from the target viewed through front facing mirrors was tested using static images i e images recorded with no impact event on the target To determine the noise floor 10 consecutive images were taken during the static event The DIC a
9. camera separation on bar from look up tables Connect the controller box to the cameras and the acquisition laptop Place the specimen in its testing location and ensure that the lighting of the specimen is adequate Focus the cameras so that images of the specimen are clear Remove the specimen and follow the calibration instructions using the appropriate calibration object Once calibrated replace the specimen and be sure not to touch or change the camera configuration Use the desired method for image acquisition auto or manual manual will involve connecting the trigger button to the sensor controller 10 Run the test 11 Prepare the images for evaluation by Using the masking tool to remove unwanted detail Set an automatic start point see Section A 4 12 Click Compute Project 28 UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Once the images have been processed evaluation of the images can be managed on any computer using the evaluation software dongle Use the ARAMIS software in Evaluation Mode to work out displacement strain etc The use of ARAMIS as a 2D or 3D system is dependent on the user requirements the set up and calibration will vary slightly between the two options Use of the 2D system is beneficial when no out of plane motion is expected A 3 Calibration Setup Before recording data the non contact optical measuring system needs to be calibrated The DSTO ARAMIS system comes with three calibration object
10. high speed cameras are not controlled by the ARAMIS controller box the cameras must be synchronised by an external Photron system To synchronise the cameras one camera is assigned master the other slave The slave camera responds from inputs to the master camera It is important to have the two cameras synchronised for a high speed blast event to ensure that no deformation takes place between the left image and the right image being recorded If a difference occurs the ARAMIS system will have difficulty aligning the facets from the left and right camera images for each image set When loading the calibration images as an external image series the software requires the camera specifications The camera specifications are entered in the Edit Camera panel shown in Figure 14 The details required are the image width image height offset etc z Edit camera Name HS Photon SA5 Camera parameter Frame grabber para Image width 1024 Pixel ka Image height 1024 Pixel ka Principle point offset in X 512 Pixel ka Principle point offset in Y 512 Pixel ka Pixel size 20 00 um ka Binarisation offset 5 ka L Figure 14 The Edit camera panel for providing the camera specifics if not a GOM mbH specific camera Editing the camera details can be performed from the first Calibration from Image Series panel shown in Figure 15 a
11. most appropriate speckle pattern application technique for the blast and fragmentation event a variety of speckle pattern application methods were trialled The ARAMIS manual 21 describes some suggested speckle pattern application techniques It was determined that a tailored method of randomly applying the speckles for the large scale experiment had to be developed After testing a number of application techniques UNCLASSIFIED 11 UNCLASSIFIED DSTO TN 1203 the best method of application of the speckle pattern was obtained by hand painting the pattern onto the boxes the result of which is shown in Figure 13 This method had a similar application time to the stamp method and also provided the sharpest speckle pattern i e no blurred edges The greatest number of unique data points could be achieved through this method The drawback of this application method is that the process is labour intensive Another option for future application is the use of a stencil pattern that can be applied to the surface Figure 13 Pattern used on boxes from hand painting chosen as the technique to apply random speckle pattern to boxes for the blast fragment synergy trial 3 1 4 Paint and surface treatment From past explosive trials with internal detonations it was noted that paint applied to the surface of steel if not treated correctly would flake and peel off under high strain 19 22 This would result in a loss of data from both the loss of sp
12. of the ARAMIS system is provided in the GOM user manuals 20 21 2 1 DIC verification in small scale low speed application Validation experiments were undertaken to commission the ARAMIS software prior to use in the large scale blast and fragmentation trial to be conducted by DSTO A tensile test on an aluminium sample was performed and the results of the ARAMIS strain analysis were compared with strain gauge results to verify the accuracy of the ARAMIS system in measuring strain from an image series Similar validation work on DIC systems has been performed in the past by Tong 25 This validation also enabled familiarisation with the ARAMIS analysis program The aluminium specimen used for the validation test had the dimensions of 100 mm x 200 mm W L with 1 mm thickness The specimen had three drilled holes located along the central vertical axis as shown in Figure 3 The diameter of the central hole was 3 mm The diameter of the other holes was 5 mm A tri axial strain gauge was located 25 mm to the left of the central hole on the reverse side of the specimen to that shown in Figure 3 The tensile testing was performed in a 100 kN Instron machine The surface of the aluminium shown in Figure 3 was analysed by the ARAMIS system The speckle pattern seen in the image was applied with canned spray paint as described in Appendix A Section A 5 The aluminium specimen already had a painted black surface UNCLASSIFIED UNCLASSIFIED DSTO
13. optimisation of the ARAMIS v6 3 0 digital image correlation system GOM mbH Germany for use in a large scale high strain rate synergistic blast and fragmentation event The ARAMIS system uses 3D digital photogrammetry to track surface deformation of an object during an event and produces the resultant strain data This document highlights some key considerations for use of high speed photogrammerty for synergistic events not fully covered by the hardware and software manuals or literature Page classification UNCLASSIFIED
14. output which heats the sample and can also heat the cameras The halogen lights were turned off to prevent overheating when calibration and testing were not being performed Schmidt et al 11 makes recommendations on the lighting used in laboratory environments 1 Hiding power is an optical property which measures the ability to obscure a background of contrasting colour UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 The validation of the ARAMIS system experiment was performed by loading the specimen in tension until failure which occurred at 28 kN The tensile specimen was loaded in increments of 2 kN and an image was recorded with the ARAMIS system using the manual acquisition method at every 2 kN increment This resulted in a 14 stage ARAMIS file Comparison of the ARAMIS strain data to the measured strain gauge data was performed using equivalent strain gauge data points selected in the ARAMIS program Two points were selected on the strain field in the ARAMIS program in both the x and y direction These points approximated the strain gauge location on the specimen The full field ARAMIS strain results and the location of the approximated strain gauge in the y direction depicted by the red vertical line as applied in the ARAMIS program is shown in Figure 4 Figure 5 shows the full field ARAMIS strain results and the location of the approximated strain gauge in the x direction depicted by the red horizontal line The strain was determin
15. speckle area 1 46 mm x 1 46 mm 5 x 2 13 mm 2 13 mm 10 65 mm WLU T Figure 11 Average speckle size determination based on event size and image quality Due to the speckle application method chosen for the large scale blast and fragmentation event the speckle size was approximately 30 mm roughly three times the minimum acceptable size 3 1 2 Consistency of pattern It was found from DIC analysis on multiple speckle patterns that consistency of a pattern is important for obtaining full field results Each facet needs to contain at least one speckle therefore to ensure that no facets are indistinguishable and to prevent loss of data the facet size needs to be based upon the largest speckle or area of singular colour If the speckle pattern is inconsistent with a few large speckles or areas of singular colour there is a risk that there will be a loss of information Figure 12 a shows a speckle pattern with too many speckles resulting in large black areas Figure 12 b shows a speckle pattern with too few speckles producing large white areas Consistency of a pattern is important to ensure that uniform data across the surface can be obtained om 7 es aE u i L re 1 et e Bj a OH aati ae i hr ae Areas of oA ee singular A o Ap tt colour rop oe Figure 12 Examples of poor speckle pattern consistency a too much black b too much white 3 1 3 Application Techniques To determine the
16. A1 3 6 2 Overexposure Overexposure of an image is a result of the presence of bright light or light reflections which produces inconsistencies in light level across the image There are two ways overexposure can cause data loss in DIC The first is overexposure in the reference image where bright spots or reflections can appear from the image light source artificial lighting or sunshine One method for varying the perceived light level is adjusting the aperture of the camera Adjusting the aperture also affects the depth of field available for the event so this should be done with caution Calibration of the software can be affected if overexposure occurs in the calibration images DIC may interpret reflections as data points which causes an error If an overexposure occurs in an area that is not required for data processing the unwanted area can be removed from evaluation by masking UNCLASSIFIED 20 UNCLASSIFIED DSTO TN 1203 The second type of overexposure occurs from a change in light level throughout the image series The ARAMIS program displays indeterminate areas in an image series as yellow shown in Figure 22 a Any overexposure in images may cause a loss of data shown in Figure 22 b where the presence of light from explosive detonation causes data loss a b Figure 22 a Data loss displayed in ARAMIS and b high contrast lighting example from Blast Fragment Synergy trial The reason for the data loss is ex
17. FIED DSTO TN 1203 The spread of a greyscale histogram identifies the amount of black white and grey pixels in the image A greater spread e g 50 black 50 white corresponds to a better contrasting image An ideal greyscale histogram would include only black and white values for perfect contrast but this is unlikely in an outdoor environment It is instead optimal to have a greater spread of values in the reference image histogram to increase the number of reference points for the DIC software to determine the corresponding pixels in subsequent event images For event Al the greyscale histogram Figure 21 shows a spread of grey values There is a reasonable difference between the lightest values the peak and the darker values However there are no white values in the histogram the 159 grey value dominates replacing white This is acceptable as long as the darkest values and the lightest values are distinguishable Use of the greyscale histogram prior to an event to check there is a good spread of black and white in the image helps to ensure that all data can be fully processed by the system after the event Histogram Display channel tf ae o Walue s an 3 In Range 6 Below E 6 Above Mean izi Median 144 e Greyscale values 299 Figure 21 Image of Event A1 used to create greyscale histogram where only the speckle area is used and luminosity Greyscale histogram for the speckle region of Event
18. IC or Deputy OIC POTENTIAL HAZARDS E Laser Type 1 x Trip hazards m Slip hazards UNCLASSIFIED 31 Page classification UNCLASSIFIED DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION a A ON 2 TITLE 3 SECURITY CLASSIFICATION FOR UNCLASSIFIED REPORTS THAT ARE LIMITED RELEASE USE L NEXT TO DOCUMENT Optimisation and Validation of the ARAMIS Digital Image CLASSIFICATION Correlation System for use in Large scale High strain rate Events Document Title Abstract 4 AUTHOR S 5 CORPORATE AUTHOR Vanessa Pickerd DSTO Defence Science and Technology Organisation 506 Lorimer St Fishermans Bend Victoria 3207 Australia 6a DSTO NUMBER 6b AR NUMBER 6c TYPE OF REPORT 7 DOCUMENT DATE DSTO TN 1203 AR 015 700 Technical Note August 2013 8 FILE NUMBER 9 TASK NUMBER 10 TASK SPONSOR 11 NO OF PAGES 12 NO OF REFERENCES 2012 1093947 1 NAV 07 359 NAV 31 26 13 DSTO Publications Repository 14 RELEASE AUTHORITY http dspace dsto defence gov au dspace Chief Maritime Platforms Division 15 SECONDARY RELEASE STATEMENT OF THIS DOCUMENT Approved for public release OVERSEAS ENQUIRIES OUTSIDE STATED LIMITATIONS SHOULD BE REFERRED THROUGH DOCUMENT EXCHANGE PO BOX 1500 EDINBURGH SA 5111 16 DELIBERATE ANNOUNCEMENT No Limitations 17 CITATION IN OTHER DOCUMENTS Yes 18 DSTO RESEARCH LIBRARY THESAURUS ARAMIS Digital Image Correlation DIC blast high strain rate 19 ABSTRACT This document provides an overview for the
19. Instructions When setting up the cameras for image acquisition the two cameras need to be aligned so that the left and right cameras are pointing at the same location The cross hair in the Photron software is a useful tool for alignment 3 3 Calibration and setup distances To protect equipment from blast waves fragmentation and debris a safe operating distance was required for the dynamic blast and fragmentation events An estimate of 15 m stand off was initially used as the safe operating distance for the high speed cameras Calculations showed that this distance would provide an appropriate image area using 180 mm lenses as well as minimise the risk of damage to equipment from the event Testing was performed to check the 15 m operating distance estimate would be suitable for DIC Before an event the ARAMIS system must be calibrated for light and depth of field Calibration of the ARAMIS system for the large scale blast and fragmentation events was undertaken using the calibration cross Figure 16 The calibration process enabled verification of the appropriate operating distances for the event UNCLASSIFIED 14 UNCLASSIFIED DSTO TN 1203 Figure 16 Calibration cross on concrete slab during explosive field trial calibration The calibration at 15 m failed due to a bundle adjustment error This indicated that the 15 m stand off was too large The stand off distance was decreased to 14 m This incre
20. UNCLASSIFIED Australian Government Department of Defence Defence Science and Technology Organisation Optimisation and Validation of the ARAMIS Digital Image Correlation System for use in Large scale High otrain rate Events Vanessa Pickerd Maritime Division Defence Science and Technology Organisation DSTO TN 1203 ABSTRACT This document provides an overview for the optimisation of the ARAMIS v6 3 0 Digital Image Correlation system GOM mbH Germany for use in a large scale high strain rate synergistic blast and fragmentation event The ARAMIS system uses 3D digital photogrammetry to track surface deformation of an object during an event and produces the resultant strain data This document highlights some key considerations for use of high speed photogrammerty for synergistic events not fully covered by the hardware and software manuals or literature RELEASE LIMITATION Approved for public release UNCLASSIFIED UNCLASSIFIED Published by Maritime Division DSTO Defence Science and Technology Organisation 506 Lorimer St Fishermans Bend Victoria 3207 Australia Telephone 1300 DEFENCE Fax 03 9626 7999 Commonwealth of Australia 2013 AR 015 700 August 2013 APPROVED FOR PUBLIC RELEASE UNCLASSIFIED UNCLASSIFIED Optimisation and Validation of the ARAMIS Digital Image Correlation System for use in Large scale High Strain rate Events Executive Summary The ARAMIS Digital Image Correlation system
21. ain gage y direction Aramis in gage location Figure 6 ARAMIS strain result in y direction compared with strain gauge result in y direction ARAMIS vs strain gauge data in x direction 0 00E 00 0 5 00E 02 1 00E 03 1 50E 03 Microstrain 2 00E 03 Load KN Strain gage x direction Aramis in gage location Figure 7 ARAMIS strain result in x direction compared with strain gauge result in x direction 3 Application in large scale high strain rate events The ARAMIS system was acquired with the objective of performing full field non contact strain analysis on simple structures undergoing internal blast and fragmentation deformation Before the ARAMIS system could be used for such events it had to be tested validated and optimised for use in a high strain rate environment A series of tests were performed to validate the ARAMIS system for use in blast and fragmentation events A blast event is highly dynamic with extreme loading of the target The introduction of fragmentation to a blast event provides added complexity including localised strain The objective for the use of the ARAMIS system in the blast and fragmentation events was to observe the full field strain caused by blast the localised strain caused by fragmentation and the synergistic effect of the combination of blast and fragmentation UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 The main de
22. ased the percentage area of the image occupied by the target object This resulted in an increased number of calibration points recognised by the system However not all calibration data points were recognised For the best calibration results all calibration data points are required The stand off distance was finally reduced to 12m which was the maximum distance at which full calibration was achieved 3 4 Field of view limitations Performing DIC on the edge of the target as opposed to the flat surface provided assessment of the edge constraints of the target undergoing internal blast pressures and associated deformation Viewing the edge of the target with DIC introduced field of view restrictions due to the visualisation of each side of the edge from the opposite camera A feasibility study was performed to simulate the use of the ARAMIS system on an edge The view of the ARAMIS system in this configuration was two 1 m x 1 m panels joined at a right angle to create an edge as shown in Figure 17 from the left camera view 4 A bundle adjustment is a ray tracing process to establish unique intersection points in the images which are used to computationally align the two cameras 11 UNCLASSIFIED 15 UNCLASSIFIED DSTO TN 1203 Figure 17 Left camera view of two 1m x 1m panels used to simulate the edge of a cube in pre trial experimentation with the ARAMIS system One of the panels was impacted with a hammer to assess the ability o
23. ckles The minimum speckle size for system recognition depends on the resolution of the images pixel count and the image area 11 The image area is comprised of the area occupied by the speckle pattern and the background Figure 10 shows the speckle pattern on the 1 m x 1 m panel used in the blast and fragmentation event The area inside the square contains the area for analysis The area outside the square highlighted red is the background image which contains no data points for analysis Figure 10 The speckle patterned area for data analysis is contained within the square boundary on the image The rest of the image is the background area highlighted red which does not contribute data to the analysis For the ARAMIS system the minimum speckle size required is 5 pixels For the large scale blast and fragmentation event 1024 x 1024 pixel resolution images were used at a frame rate of 7 500 fps The total image area speckle pattern area and background was approximated at 1 5 m x 1 5 m Therefore each pixel was 1500 mm divided by 1024 and had an area of 2 13 mm Using the minimum pixel number of 5 for the ARAMIS system this gives a speckle area of 10 65 mm or approximately 11 mm as shown in Figure 11 This minimum speckle size is the smallest readable size by the software Anything larger is acceptable UNCLASSIFIED 10 UNCLASSIFIED DSTO TN 1203 5 pixels 1500 1024 1 46mm Pixel or 146mm Minimum pixel area Minimum
24. d fragmentation events Some issues were identified with the use of the system for large scale high strain rate events using high speed photogrammetry These issues included adequate lighting conditions the use of mirrors large stand off distances speckle pattern application and use of high speed cameras In each case a solution was found to optimise the system and the final setup configuration for use in synergistic blast and fragmentation events was determined Some of the key results from this experimental series were Speckle size and application is important for high resolution results For highly dynamic events paint adhesion is critical For 180 mm lenses the furthest stand off distance achievable is 12 m Ambient lighting conditions are adequate for outdoor events When using mirrors in explosive events effort must be taken to secure mirrors and avoid mirror shake For 3D events camera synchronisation is important Greyscale histograms can be used to predict image quality The ARAMIS system was also validated against a conventional localised strain measurement technique to determine the accuracy in strain determination An aluminium tensile test was performed with a tri axial strain gauge and the ARAMIS system both recording the strain output The results showed good correlation between the two techniques UNCLASSIFIED 23 UNCLASSIFIED DSTO TN 1203 5 Acknowledgments I would like to thank Michael Buckland Pat McCarthy
25. e considered in addition to those provided in the ARAMIS manuals and online help to establish the system to be used for a large scale high strain rate event are outlined UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 2 ARAMIS DIC System Background DIC systems operating in both 2D and 3D events use a series of sequential digital images to determine the surface deformation and surface strain of objects The systems identify features of an object and track the relative movement of those features throughout the sequential images The ARAMIS DIC system uses a random speckle pattern applied to the surface of the target object to create the unique features identifiable to the system To identify these features each image is divided into an overlapping grid of facets and each facet must be unique from its neighbouring facets Further information on facets is included in Appendix A To determine surface displacement of the target object each facet is tracked from one image to the next creating a series of data points which are mapped to create the displacement field For 3D displacement two views left and right are required for each time step The corresponding facets from the left and right image are identified in each image in the series as shown in Figure 1 The same facet is shown in each image in Figure 1 shaded green and highlighted by a red arrow The specimen deformation is mapped by the changing orientation and shape of the facet Fao
26. e pair Figure 8 DIC system layout for the synergistic blast and fragmentation event 3 1 Speckle pattern The ARAMIS system requires a speckle pattern be applied to the face of the test object Displacement deformation and strain are determined based on the relative movement of the speckle pattern between images The ARAMIS program groups neighbouring pixels of the speckle pattern together to create facets shown in Figure 9 The number of pixels in a facet is defined by the user As each facet distorts the amount of distortion is measured relative to the previous image determining the displacement and strain of the material Figure 9 Facet field with overlap viewed over speckle pattern from software user manual 20 The number of pixels chosen for each facet determines the facet size Smaller facets correspond to higher data resolution as each facet corresponds to a data point during UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 analysis However if the facet size is smaller than ideal the facet will be indeterminable and measurement accuracy will be compromised The resolution of the speckle pattern applied is important as it dictates the minimum facet size that can be used The method of speckle application affects the achievable speckle size and distribution which influences the accuracy of the deformation and strain data obtained Pixel Speckle Facet Image dependent Pixel and area dependent Speckle dependent 3 1 1 Size of spe
27. eckle detail on the surface and from the resulting debris travelling between the target and the camera obstructing the images To ensure that this did not occur in the blast and fragmentation events the external surface of each box was grit blasted prior to painting to improve paint adhesion The grit blasting used was approximately 60 microns The base coating paint used was a white primer undercoat high performance epoxy polyamide primer undercoat 2 part Interprotect applied to a thickness of 45 microns2 The speckles were applied with commercially available matt black enamel paint Under extreme plastic deformation the relative deformation of the coating could cause the coating to separate resulting in loss of data 3 2 Use of Photron high speed video cameras in ARAMIS The cameras used in the large scale blast and fragmentation event for high speed imaging were Photron SA5 cameras These are not GOM mbH standard cameras therefore were Details are available from the Interprotect Primer data sheet Interprotect is made by International Paints UNCLASSIFIED 12 UNCLASSIFIED DSTO TN 1203 not compatible with the ARAMIS image sensor controller box gt The images from the Photron SA5 cameras could not be read directly from the camera into the ARAMIS software for data acquisition The images acquired using these cameras had to be loaded as an external image series into the ARAMIS software after all images were acquired As the Photron
28. ed based on the displacement of the two points that make up the line for both the x and y direction The strain values at each stage were used to create a strain curve LY direction Figure 4 Aluminium tensile specimen with ARAMIS full field strain overlayed and representative strain gauge in y direction UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Figure 5 Aluminium tensile specimen with ARAMIS full field strain overlayed and representative strain gauge in x direction The results for the y and x directions from the ARAMIS equivalent strain gauge compared with the actual strain gauge are presented in Figure 6 and Figure 7 respectively The results in the y directions show excellent correlation The results in the x direction show good correlation between the ARAMIS determined strain values and the measured strain gauge values The small differences between the ARAMIS curves and the strain gauge curves could be a result of the approximation used to create the ARAMIS equivalent strain gauge locations The resolution of the ARAMIS data restricts selection of the equivalent data points to a facet This means an exact match of strain gauge location cannot always be obtained UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 ARAMIS vs strain gauge data in y direction 4 00E 03 3 00E 03 Microstrain 5 00E 03 1 00E 03 0 00E 00 1 00E 02 a0 Load KN Str
29. ed speckle pattern is achieved UNCLASSIFIED 30 UNCLASSIFIED DSTO TN 1203 Appendix B Standard Operating Procedures Appropriate footwear with Use of safety glasses substantial uppers must be worn Q PRE OPERATIONAL SAFETY CHECKS Contact authorised user before operation of equipment Read and familiarise with Aramis operation manual Use of appropriate PPE Inspect all electrical cords are tested and current see label Check condition of electrical cords for damage Read and familiarise with facility laboratory SSO Visually inspect equipment for damage EYE PROTECTION MUST BE WORN OPERATIONAL SAFETY PROCEDURES Use correct manual handling practices and lifting equipment where required Do not point camera mount laser in the direction of any persons Ensure electrical cords are laid in a manner preventing tripping hazards Protect equipment from damaging environments impact temperature etc Post OPERATIONAL PROCEDURES Ensure all electrical items are switched off at the source before removing items from power source Secure all cords to avoid creating a tripping hazard Make sure items are clean wiped with cloth before storing in correct housing Use correct manual handling practices and lifting equipment where required HOUSEKEEPING e All items are to be kept in a neat and tidy state and stored neatly e All items are stored at the owner s risk It is an open area e If in doubt please contact the O
30. ent and low strain rate calculations has become common for material testing and model validation 2 3 Other strain and displacement techniques such as single point deflection histories or post deformation analysis are inadequate for model validation The full field nature of DIC enables large data capture and accurate model validation DIC in three dimensional 3D analyses uses photogrammetric techniques to determine the full field and localised strain of an object A pattern printed onto the surface of the object undergoing deformation is used to determine the displacement under loading with time This displacement is then used to calculate the surface strain on the object The technique requires the use of images taken in sequence over a period of time 4 For 3D correlation the system requires two sets of images of the target taken from separate camera angles A system calibration is required to determine the 3D space where the event occurs This is then used to correlate the images for the determination of deflection and strain 5 DIC has been used extensively for small scale deformation events and strain measurements in microstructures 6 7 8 The majority of these events are conducted in a laboratory environment 9 10 The target area analysed through DIC is generally small millimetres or centimetres and the setup used requires a small stand off distance 11 Due to this DIC is well understood for material testing in controlled lab
31. esosesosesocesecesscesscesscssoosssosssosssosesosessse 14 34 Field of view limitations siinsamas aeiia 15 3 5 Camera protection and the use Of MIrtrorS seesseessesssessoessoessoessoosssosesosesosesoses 17 3 5 1 Noe TOO sencia a a a cares aee emai aedee E ETE 18 36 Lieh aina E A 19 3 6 1 Larminosity and CONTAS Tosia n a 19 3 6 2 OVET gale SUTE Ta a S 20 de C ONCECUSION i eR ene cer aOR eC SDI DER ONE Py eT enn 23 De ACKNOWLEDGMENT S arere see concen oiseeeseeeseiveasteacceass 24 6 REFERENCE Se PP ne ne EERE PE OEE eo OS Eee rN Per Ree eg rr er re error rer 25 APPENDIXAS SYSIEM NOIES zonne R A RE S 27 A1 Terminology seinieissenenen sien eesi sian ence eaeseaeeestenas 27 A2 nikal SOU Pen n 28 AS MAND rain SetuP sneren ea E TE 29 Ad Start Polni orren rnn aa o cicbacaustoacececauaceasshoccesecasbecaustondees 29 A 5 Speckle pattern application for small targets esses 30 APPENDIX B STANDARD OPERATING PROCEDUREG cc cetceeeceeeeeeeeee 31 UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 This page is intentionally blank UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 1 Introduction Conventional methods of determining the strain on a material under loading generally consist of localised strain measurements from devices such as strain gauges When a full field strain profile is required a technique called digital image correlation DIC provides a solution Since the development of DIC in the 1980s 1 its use for displacem
32. f ARAMIS to determine the deformation and strain on the object for this configuration The event was recorded with two high speed cameras The edge added complexity to the field of view by reducing the viewing area common to both cameras Due to the angle of the plates the ARAMIS system was unable to identify all the speckles on both sheets in each image left and right This is shown in Figure 18 a by the yellow patches highlighting the areas the ARAMIS system could not identify The missing deflection data is visible in Figure 18 b Loss of speckle recognition resulted in a reduced data field This determined that viewing the edge would not give a complete analysis of each of the flat surfaces of the box but did give good resolution for the edge itself Hence the requirement of four high speed cameras for these events one pair for the flat panel view and one pair for the edge view 0 0600 0 0400 0 0200 0 0000 0 0200 0 0400 0 0600 0 0856 b Figure 18 a Right camera view of two 1 m x 1 m panels used to simulate the edge of a cube in pre trial experimentation The yellow area indicates the speckles which are not identified by the system b the resulting ARAMIS deflection data from the test UNCLASSIFIED 16 UNCLASSIFIED DSTO TN 1203 3 5 Camera protection and the use of mirrors Due to the highly dynamic nature of blast and fragmentation from the detonation of the weapon in the blast and fragmentation events
33. formation in a blast and fragmentation event occurs in the first 10 ms after detonation Measurement of the deformation and strain in such an event requires the use of high speed video The introduction of fragmentation to a blast event requires an increase in the safe operating distances or stand off distances of equipment to that documented for a controlled blast only or ballistic impact event Synergistic events require a specific camera setup and operational techniques not covered by the literature available for blast only or ballistic impact events or by the ARAMIS operating manuals The internal synergistic blast and fragmentation event on simple structures required the detonation of both bare and fragmenting charges inside a 1 m steel container Due to the highly dynamic nature of this type of event equipment protection was required Protection of the high speed cameras from fragmentation was achieved with the use of splinter proof containers Normally the ballistic plexiglass in a splinter proof would be used for viewing an event however this was not suitable for DIC images due to the low image quality obtained Instead the cameras faced the opening of the splinter proof containers and mirrors were used to view the event The layout for the DIC system in the synergistic blast and fragmentation events is shown in Figure 8 There are four high speed cameras used in this layout two pairs of high speed cameras One camera pair is focused on t
34. he flat face of the target the other pair is focused on the edge The flat face DIC system was used to examine how the internal loading affects the full field strain and displacement on the surface of the flat plate the edge DIC system was used to examine the high strain region that occurs on the edge of a welded structure The high speed cameras for the DIC system were housed in open fronted splinter proof containers orientated towards the front facing mirrors These mirrors then reflected the target object to the cameras for image recording The safe operating distance of the equipment is the distance from the target to the centre of a camera pair The camera separation between the two cameras in a pair is the distance required to obtain a 25 angle between the recorded images The two cameras recording the edge view had a stand off distance of 12 m and were separated by 5 6 m The 12 m stand off flat face view were separated by 6 5 m UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Splinterproof HSY Aramis Mirror P aas an er AE ES paa ae eee pet Fd ee ge pair i Pr a on pE ane a eel ae Splinterproof HSY Aramis Mirror Pes m mmr _ ee mma oa oe ee ee 4 plinterproof Instrumentation lt lt pamm Gjo A anamma ag a _ _ e Tr se _ se ee Splinterproof HSY Aramis Flat fac
35. isplay channel 3 G l wt T reyscale Walue s a So in Range Oo 36 Below D 6 Abowe i Mean 59 Median BS co 255 Greyscale values b Figure 24 Event B4 image and greyscale histogram for a the reference image at time 0 ms and b time 1 07 ms UNCLASSIFIED 22 UNCLASSIFIED DSTO TN 1203 To reduce the overexposure in images it is recommended to Use materials with a low reflective surface Use matt paint on surfaces such as matt white and matt black paint Adjust the aperture on the camera lenses to control the perceived light level and When possible reduce the light intensity Images taken pre event can also be used to check the contrast of an image If the image histogram has a good spread of values then the likelihood of data loss is reduced 4 Conclusion The use of DIC for full field strain determination in ballistic impact and blast events has been well reported in literature for applications in controlled environments with single penetrators at small stand off distances However these reports lack the considerations for use of DIC in synergistic blast and fragmentation events with large stand off distances This report identifies and offers solutions to some of the issues associated with the use of DIC in such events Through a number of simulated test scenarios the ARAMIS v6 3 0 GOM mbH DIC system was optimised and validated for use in large scale high strain rate synergistic blast an
36. l 3D measurement Techniques Accessed 2012 09 07 Available from http www gom com 3d software aramis software html UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Appendix A System Notes Prior to use of the ARAMIS system it is advisable that the DSTO Standard Operating Procedure Appendix B located with the ARAMIS acquisition laptop and the ARAMIS Safety Assessment 1997 be read Other recommended reading includes the ARAMIS Software Instruction Manual 20 and the ARAMIS Hardware Instruction Manual 21 A 1 Terminology Table 1 contains a list of terms and definitions which are used throughout this report Table 1 Glossary of terms The smallest single component of a digital image Digital Image The use of triangulation algorithms on digital images to determine Correlation DIC physical motion The number of pixels the image is comprised of required by the ARAMIS software The terms pixel facet facet field and facet overlap are described visually in Figure 25 Figure 25 shows a black and white pattern representing an example speckle pattern divided into pixels Red lines indicate the facet field over the speckle pattern which is made up of a collection on pixels Each facet in the image is 5 pixels by 4 pixels and the facet field has a 1 pixel overlap between each facet 1 pixel 5 pixel x overlap 4 pixel facet VA E AR Figure 25 Pixelated speckle pattern with facet overlay in red including facet ove
37. nalysis was performed on these images Four data points were selected from the DIC results to represent the deflection of the panel These points are referenced 0 to 3 and are shown in Figure 20 representing the displacement of each point over the 10 images Each strain stage on the curve represents an image set in the image series The maximum deflection recorded from this static event over 10 stages was 0 114 mm Other laboratory tests also reflect this value where the baseline noise of the system was recorded to be approximately 0 1 mm The 0 114 mm deflection recorded for the unloaded event can be considered the baseline noise of the system for this setup configuration The expected displacement of the target in a blast and fragmentation event is upward of 100 mm A 0 144 mm deflection therefore corresponds to a 0 144 error for a 100 mm displacement This will be greater for smaller displacements UNCLASSIFIED 18 UNCLASSIFIED DSTO TN 1203 0 1145 i Stage point 0 J iii p Stage point 1 0 080 Stage point 2 Stage point 3 0 0604 0 040 Displacement Z mm O O M alae 4 T T T T T T 1 2 3 q 5 6 7 8 9 10 Figure 20 Graph of displacement for the undeformed panel at a 12 m stand off viewed through mirrors The maximum deflection is 0 114 mm for stage point 0 3 6 Lighting Consistent and constant lighting on the specimen during an event is required to achieve the appropriate image quality requi
38. oratory situations at low frame rates 12 13 DIC has also been used with success in underwater experiments 14 at elevated temperatures 15 and for shock analysis 16 Since the advancement of high speed cameras in recent years the understanding of the use of DIC in high speed events such as blast and ballistic impact has increased Examples include buried blast loading 17 ballistic impact testing 18 shock tube analysis and air blast 10 Although some of these events have been performed in an outdoor setting 11 the majority were performed in a laboratory with controlled lighting and weather conditions at relatively small stand off distances less than 2 m The purpose of this paper is to investigate the issues associated with the use of DIC to capture the deformation and strain of a blast and fragmentation event in a large scale high strain rate field trial Although the use of DIC for ballistic impacts and blast has been documented 19 these events involved only blast or only projectiles There is currently no available literature covering the use of DIC in a synergistic blast and projectile event This paper outlines the experimental setup requirement for the use of DIC in synergistic blast and fragmentation events with a large stand off distance The DIC software used for these events is the ARAMIS v6 3 0 GOM mbH Braunschweig Germany non contact optical strain measurement system The procedures and parameters that need to b
39. plained by the relative luminosity between images in a series The luminosity of the first image in the series is the reference luminosity During the event if the luminosity profile changes dramatically the DIC will have trouble tracking the current image to previous images and data will be lost In the full field blast events this occurred in Event B2 The greyscale histogram for this event is shown for the first reference image Figure 23 a and at 1 07 ms Figure 23 b The difference between the greyscale histograms at the two time steps is significant which resulted in a loss of data for this event Conversely the greyscale histograms for Event B4 Figure 24 a and b are similar for the same two time steps so this event had minimal DIC data loss UNCLASSIFIED 21 UNCLASSIFIED DSTO TN 1203 Histogram Display channel i D Greyscale Waluels ch ral 36 in Range 6 Below i T 6 Abowe r Mean Eg Median BG c 0 255 Greyscale values a Histogram Display channel E ia ai Waluels Y 3 in Range 53 Below x elow 35 Abowe a Mean liz Median 19 Cc 0 255 Greyscale values b Figure 23 Event B2 image and greyscale histogram for a reference image at time 0 ms and b time 1 07 ms Histogram Display channel i a oO Waluelsl in Range z 3 Below z 3 Above Mean JE Median 55 Cc g 259 Histogram D
40. rain 47 pp 66 73 Dridi S Morestin F and Dogui A 2011 Use of Digital Image Correlation to Analyse the Shearing Deformation in Woven Fabric Experimental Techniques Hwang S F Horn J T and Wang H J 2008 Strain Measurement of Nickel Thin Film by a Digital Image Correlation Method Strain 44 3 pp 215 222 Hargather M J and Settles G S 2008 Laboratory scale techniques for the measurement of a material response to an explosive blast International Journal of Impact Engineering 36 pp 940 947 Schmidt T et al 2004 Full field dynamic deformation and strain measurements using high speed digital cameras In 26th International Congress on High Speed Photography and Photonics Alexandria VA September 2004 The International Society for Optical Engineering Schmidt T Tyson J and Galanulis K 2003 Full field dynamic displacement and strain measurement using advanced 3D image correlation photogrametry part 1 In Experimental Techniques Wiley pp 47 50 Tong W 2004 Plastic surface strain mapping of bent sheets by image correlation Experimental Mechanics 44 5 May 11 pp 502 511 Haile M A and Ifjfu P G 2012 Application of Elastic Image Registration and Refraction Correction for Non Contact Underwater Strain Measurement Strain 48 2 pp 136 142 Turner J L and Russell S S 1990 Application of digital image analysis to strain measurement at elevated temperature Strain 26 2 pp 55 59 Lall P
41. red for DIC Testing the experimental setup for the blast fragment synergy trial in an outdoor environment identified that ambient outdoor lighting conditions provided adequate lighting for DIC conditional that the lighting conditions between calibration and the event did not change significantly Even overcast conditions were acceptable The main lighting effect that influenced DIC was image contrast on sequential images A way of measuring the contrast of an image is to examine its luminosity greyscale histogram The histogram can be used to identify the quality of contrast for the event by determining the spread of luminosity values on the histogram If there is a good spread then the likelihood of data loss is reduced 3 6 1 Luminosity and contrast Luminosity is a measure of the relative brightness distribution within an image 23 taking into account that the human eye is more sensitive to green light than red or blue as shown in equation 1 24 Luminosity 0 3R 0 59G 0 11B equation 1 DIC software looks at an image in greyscale to identify markers requiring good contrast within the image Greyscale histogram data points range between 0 black and 255 white The spread of a greyscale histogram gives an indication of the contrast of the image if the greyscale histogram is mostly on the black side the image is too dark if the greyscale histogram is mostly at the white side the image is too light UNCLASSIFIED 19 UNCLASSI
42. rlap shown in solid UNCLASSIFIED 27 UNCLASSIFIED DSTO TN 1203 A 2 Initial setup The DSTO ARAMIS package includes the following items Dell laptop with acquisition and evaluation software Unclassified Dongle licence key for laptop 140x170 mm Calibration Plate 55x44mm Calibration Plate 1000 x 800 mm Calibration Cross Calibration plate stand Camera tripod with attachable camera rod 2x 5M 15 Hz cameras 50mm fixed focal length Lenses includes key for changing lenses in kit 12mm fixed focal length Lenses Image sensor controller Additional items such as extension chords lights tool kit etc Before setting up the ARAMIS system the cameras best suited for the experiment need to be determined The system operates with high speed low speed and thermal imaging cameras 26 The DSTO ARAMIS image sensor controller is designed for use with low speed cameras but the ARAMIS system can be adapted to a high speed environment as described in Section 3 The basic procedure for using the ARAMIS non contact optical measuring equipment is to use the steps outlined below I 2 3 9 Prepare the specimen with a speckle pattern refer to Section 3 1 Use the acquisition software license on the supplied Laptop Set up tripod with camera system according to the instructions in the user manual Choose appropriate camera lenses Choose appropriate calibration object Determine setup distance and
43. s The use of each of these objects depends on the size of the object you are testing Note care must be taken when handling Each calibration object is specifically designed for use with the ARAMIS calibration system The calibration objects contain markings which are recognised by the software in calibration mode The surfaces of the calibration plate are ceramic to reduce thermal expansion effects and designed to reduce light reflections Any fingerprints on the object s surface cannot be removed and may affect calibration results To determine which board is appropriate for an experiment a table is provided in the ARAMIS hardware manual 21 refer to Section 3 2 3 for the 5M system This table outlines which calibration object is required to achieve a certain measured area or volume based on the lenses used It also states the distance the calibration object should be from the cameras and the distance between the two cameras to obtain a 25 angle at that distance This table provides a guide for defined conditions to ensure the calibration is successful Ideally before calibrating set up the test with the specimen in the conditions to be tested and the ARAMIS software should be used to check the quality of the specimen images by zooming in on the image This includes the focus lighting and size of the image and the clarity of the speckle pattern The calibration must be performed in the same conditions as the test Note Once the calibra
44. ssa Pickerd Maritime Division Vanessa has a Bachelor of Aerospace Engineering BAeroEng Degree with Honours recetved from Monash University in 2010 In 2010 Vanessa joined Maritime Platforms Division now Maritime Division Defence Science and Technology Organisation DSTO where her research interests have included maritime platform survivability modelling and assessment specifically pertaining to blast and fragmentation modelling and systems vulnerability assessment Vanessa s current role is as a maritime platform vulnerability analyst UNCLASSIFIED UNCLASSIFIED This page is intentionally blank UNCLASSIFIED UNCLASSIFIED DSTO TN 1203 Contents t IN TOR OI isaac costa ase a oscesen sve A S 1 2 ARAMIS DIC SYSTEM BACKGROUND iisas iraani oasa as 2 2 1 DIC verification in small scale low speed application eesoeescesssesssesssessoe 3 3 APPLICATION IN LARGE SCALE HIGH STRAIN RATE EVENTG 0 7 31 Speckle Pathe rm wei esseccetcsce vers ecsessdivesexavscetoedalcoecvsbient vevsedeacasndesbeveslColasavastesetvsverenzastocss 9 3 1 1 DIZEOl SPEckle Seaia a n E 10 3 1 2 WONSISLENCY Or Patter eeina oE e n EE 11 3 1 3 Application TechniqueSs seesesseesessesessssesssesreseessrssessessrssrsseeseessesseses 11 3 1 4 Paint and Surtace teatme n manie a A 12 3 2 Use of Photron high speed video cameras in ARAMIS s sessesssoseesoosoossssssss 12 3 3 Calibration and setup distances essosesos
45. t points are required then selecting a start point manually can be done using Add Start Point A start point can be selected from the first image and then checked for compatibility through the rest of the series of images A start point can also be selected manually for each image by selecting the desired facet to become the start point the same facet needs to be selected in both left and right images for 3D and then manually locating the selected facet in all subsequent images A 5 Speckle pattern application for small targets A method for speckle pattern application on small surface areas as suggested in the GOM mbH user manuals is canned spray paint This spray paint application technique is appropriate for small samples due to the size of the speckles created The ARAMIS user manual provides a speckle size guide for spray paint application When using canned spray paint partially pressing the trigger reduces the flow and smaller speckles can be achieved Not pressing the trigger sufficiently may cause the nozzle to leak which will produce an undesirable amount of paint The use of spray paint should be performed in a fume cupboard or well ventilated space Initial experimentation using the canned spray paint showed that the application should be started away from the sample to avoid droplets until the correct pressure is being applied and then smoothly moved across the sample surface The application can be repeated until the desir
46. tion is done the cameras and stand off distances cannot be changed without having to repeat the calibration process Calibration is performed by placing the calibration object in front of the specimen or if possible replacing the specimen with the calibration object and following the instructions as described by the hardware manual 21 Section 9 for 3D and Section 10 for 2D analysis AA _ Start points If the specimen images are of good quality a start point should be achievable by clicking Auto Start Point in the software The start point should always be in the image frame The start point is a facet which is present in each image at each stage If the Auto Start Point UNCLASSIFIED 29 UNCLASSIFIED DSTO TN 1203 cannot find a start point it may be that the images are not suitable and the software cannot determine the equivalent facets between one image and the next For less than ideal images it may be necessary to increase the tolerance Max Deviation on the automatic start point for one to be found If a discontinuity such as a crack occurs through the object separating speckle pattern then the strain data will only be calculated for the area that contains the start point An additional start point can be made on the remaining speckle pattern to ensure that data is calculated If the image quality is poor in a region resulting in data loss adding multiple start points in the region can resolve the data If extra star
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