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ABAQUS/CAE User`s Manual

1. in Contour integral eval uation Secti on 7 10 2 of the Analysis l5er s Mmnual Fi gure 20 3 ABAQS conputes the contour integral at each node along the crack line The entities fromwhi ch you can sel ect depend on whether the part instance is an ABAS nati ve part or an orphan nesh part and on the nodeling space of the part 15 The interaction module 3 ABAQUS Version 6 5 Documentation ABAS native part instance ABAQUS CAE User s Manual Wien you are defining the crack front on an ABAIN CAE native part the entities that you can select depend on the nodeling space of the part Two di nensi onal part instance A single vertex Connect ed edges Conect ed faces If you are defini ng the crack front on a tvo di nensi onal ABK Uy CAE nati ve part you can select the follow ng Figure 20 4 shows the entities from which you can select when defining a crack front on a two dimensional native part Figure 20 4 Selecting the crack front froma tvo di nensional native part vertex adge lace Three di nensi onal part instance Connect ed edges Connect ed f aces Connect ed cells If you are defini ng the crack front on a three di nensi onal ABAQS CAE nati ve part you can sel ect the fol l ow ng Figure 20 5 shows the entities from which you can select when defining a crack front on a three dimensional native part Figure 20 5 Selecting the crack front froma three di nensi onal native part adge laca cell Qrph
2. to keep the nidside nodes at the mdside poi nts b Fromthe Degenerate el enent control at Crack Ti p Ii ne fiel d choose Ql apsed el enent si de dupl icate nodes To create a conbi ned 1 v and l strain singul arity for a pover law hardeni ng nateri al a Fromthe Second order Msh Qxions field enter a value of 0 25 for the Mdside node paraneter b Fromthe Degenerate el enent control at Crack Ti p Ii ne fiel d choose Ql apsed el enent si de dupl icate nodes 9 Qick CKto include the singularity in the contour integral estination and to close the editor Note In nost cases you nust assi gn second order triangle or wedge el enents to the crack front regi on to incl ude the singul arity in your contour integral estinates If you assi gn first order el enents ABAQS ignores the val ue of the mdside node setting in the Singularity tabbed page Fbvever if you assign first order elenents and choose Collapsed elenent side duplicate nodes fromthe Degenerate F enent Control at Crack Tip Line field you wll create a l rstrain si ngul ari ty SS ABAQUS CAE User s Manual E 20 1 11 Defining data for contour integrals You can use the Special nenu in the Interacti on nodul e to define the data for contour integrals For nore infornation see Fracture nechani cs Section 7 10 of the ABXI5 Analysis User s Minual The entities that you sel ect to define the cont our integral depend on whet her t he part is two or three di ne
3. BOTTOMCRACKTIP 1 Contour 1 Hintecr al estimated from Ks JKs at STRESSINTBOTTOM BOTTOMCRACK BOTTOMCRACKTIP 1 Contour 2 Hintecr al estimated from Ks Ks at STRESSINTTOP TOPCRACK TOPCRACKTIP 1 Contour 1 I integral estimated from Ks JKs at STRESSINTTOP TOPCRACK TOPCRACKTIP 1 Contour 2 integral J at HNTBOTTOM BOTTOMCRACK BOTTOMCRACKTIP 1 Contnur 1 Hintegral J at JNTBOTTOM_BOTTOMCRACK_BOTTOMCRACKTIP 1_ Contnur 2 Hintegral J at INTTOP TOPCRACK TOPCRACKTIP 1 Contour 1 Fintegral J at JNTTOP_TOPCRACK_TOPCRACKTIP 1_ Contour 2 Stress intensity factor KL K1 at STRESSINTBOTTOM_BOTTOMCRACK BOTTOMCRACKTIP 1_ Contour 1T Stress intensity factor K1 K1 at BTRESSINTBOTTOM BOTTOMCRACK BOTTOMKCRACKTIP 1 Contnur 2 Stress intensity factor KL KI at STRESSINTTOP_TOPCRACK_TOPCRACKTIP 1_ Contour 1 Stress intensity factor KL K1 at STRESSINTTOP_TOPCRACK_TOPCRACKTIP 1_ Contour 2 Stress intensity factor K2 K2 at STRESSINTBOTTOM_BOTTOMCRACK _BOTTOMCRACKTIP 1_ Contour 1 Stress intensity factor K2 K2 at STRESSINTBOTTOM_BOTTOMCRACK _BOTTOMCRACKTIP 1_ Contour _2 Strass intensity factor 420 Zat STRESSINTTOF TO Py RACK TOPCRACKTIP T Contour 1 ES e BEER Dismiss output variable history contour Internal crack contour integral ype GUtpul integral lip node set number Pierre name generated from usar given crack lip node set nama For detailedinstructions see Request
4. crack properties usi ng a contour integral analysis Because a seamnodi fies the nesh you cannot create a seamon a dependent part instance A seamis not a surface and you cannot specify which side of the seamis positive or negative As a result you cannot apply a load or a boundary condition to a seam Fi gure 20 12 shove a seamon t he face of a planar part and the effect of applying a tensile load to the nodel The duplicate nodes along the seamare independent of each other and are free to nove Fi gure 20 12 A seamenitedded i n a face seam crack sketched o partition Figure 20 13 shows a similar analysis of a seam embedded in a solid part The seam was created by partitioning the solid with a sketch drawn on a datum plane Figure 20 13 A seamentedded in a cell 15 The interaction module 12 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual EL sketched E partition i 1 7 seam crack 11 li l f Ly Him Pri TT I 4l Jl For detailed instructions see Creating a seam Section 20 1 9 SS ABAQUS CAE User s Manual D gt 20 1 9 Creating a seam You can use the Special nenu in the Interaction nodule to define a seamin your nodel A seamdefines a region in your nodel that can open duri ng an anal ysis ABAQS CAE pl aces overl appi ng dupl i cate nodes al ong a seamwhen the nesh is generated A seamcannot extend al ong the boundaries o
5. line by neshi ng the regi on that defines the crack front wth a ring of triangles or wedges For nore infornation see Controlling the si arity at the crack ti p for a snall strai n anal ysis section 20 1 5 15 The interaction module 11 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual You nust use the svept neshi ng techni que to create wedge el enents hovever there are linitati ons on t he regi ons that ABAQLS CAE can nesh usi ng the svept neshi ng techni que as descri bed in Svept neshi ng of three di nensi onal solids Section 17 10 3 As a result if you cannot use the swept neshi ng techni que you cannot create wedge elenents and you cannot allowfor the singul arity at the crackline In nost cases you can i gnore t he si ngul arity if your neshis sufficiently refined to nodel the def ornati on around the crack ti p or crack line and the resul ti ng hi gh strain gradi ents You can al so ignore the singularity if you are interested in onl y the contour integral out put ABAQUS CAE User s Manual D gt 20 1 8 Wiat is a sean Aseamdefi nes an edge or a face i nyour nodel that is ori gi nal l y cl osed but can open duri ng an anal ysis ABAQLS CAE places overlapping duplicate nodes along a seamwhen the nesh is generated A seamcannot extend al ong t he boundaries of a part and nust be entpedded wthi n a face of a tvo di nensi onal part or wthin a cell of a solid part After you create a seam you can determine its
6. onal nodel is a region containing edges that are free to nove apart A crack in a three di nensi onal nodel is a region containing faces that are free to nove apart The sinplest approach to performing a contour integral analysis uses a regi on that al ready contains edges or faces that are free to nove apart as the crack separates Alternatively you can nodel the crack as a line enbedded in a face in a two di nensi onal nodel or as a face entpedded in a cell in a three di nensi onal nodel The entpedded li ne or face is called a seam and you can performa cont our integral anal ysis usi ng a seam Wien you nesh t he nodel ABALY CAE creates duplicate overlapping nodes on the seam these coincident nodes are free to nove apart as the seam separates Seans are descri bed in nore detail in Wiat is a sean Section 20 1 8 Figure 20 1 show a two di nensi onal nodel wth existing edges that are free to nove apart and a simlar nodel wth an entpedded seam that is free to nove apart H gure 20 1 You can define a crack using an existing regi on or using a seam PIE edges are free to move i apart alg a a ae ET L1 E sham Crack craales edges inal are irea l move apart You can specify that the crack front is defined on a synmetry pl ane in whi ch case you need to nodel only half of the structure ABAQS doubl es the val ues cal cul ated by the contour integral to arrive at the correct val ues In nost cases you need a refined nesh surrou
7. such as a vertex datumpoint or mdpoint or you can select nodes froman orphan nesh part Alternatively you can enter the coordi nates of the points in the pronpt area If you sel ect a point froman ABAE nati ve part and subsequent y 15 The interaction module 6 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual nodi fy the part ABAIN CAE regenerates the poi nts and updates the nornal accordingly If you are vorki ng wth an orphan nesh part you nust select nodes that represent the start and the end of the normal ABACUS cal cul ates a crack extension direction 4 that is orthogonal to the crack front tangent t and the nornal n q vectors If you select q vectors you can define the crack extension direction 4 directly by selecting points from the nodel that represent the start and end of the vector If you are working wth an orphan nesh part you nust select nodes that represent the start and the end of the vector Alternatively you can enter the coordi nates of the points in the pronpt area Fi gure 20 8 show an exanpl e of a crack front forned by a circular arc al ong which t he di recti on of the vector is constantly varying In contrast the nornal to the crack pl ane is constant As a result for this case you shoul d define the crack extensi on di recti on by specifyi ng the nornal to the crack pl ane Fi gure 20 8 The direction of the Hvector varies but the direction of the nornal is constant peleri fils edge
8. to represent the norma la thia crack plane Figure 20 9 shows a crack front formed by the edge of a truncated cone along which the directions of both the Hl vector and the normal to the crack plane are varying Fi gure 20 9 The directions of both the vector and the nornal vary along the crack front 15 The interaction module 7 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual conical crack crack front For this case you should do the following Define the contour integral and use a single Hvector to specify the crack extensi on di recti on Msh the part create a job and wite the nodel to an input file Inport the input file which wll create an orphan nesh representation of the part Edit the crack that vas inported wth the nodel Fach node along the crack front wll have the crack extension di recti on defined by the H vector that you specified in Step 1 5 Use the Query tool set to deternine the start and end coordinates of the vector at each node and edit the data defining the vectors at each node along the crack front PWN Pe This technique is shown in Figure 20 10 Fi gure 20 10 Entering the vector at each node along the crack front 15 The interaction module 8 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual Aa F LOF O WF MY AU REEL t Crack Extension Direction j j h d 1 Normal to crack plane 0 0 707 0 707 Edit ae Model FullConi
9. ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual ABAQUS CAE User s Manual 20 1 Mdel ing fracture nechani cs You can study the onset of cracking in a quasi static nodel by selecting regi ons fromyour nodel that wll be used to conpute contour integral estinates During the anal ysis ABX LS Standard writes t he val ues of the cont our integral s to the out put database as hi story out put For a detail ed descri pti on of contour integrals see Cont our integral eval uation Section 7 10 2 of the ABIS Anal ysis U5er s Mnual This secti on descri bes howyou defi ne a crack in ABUN CAE The follow ng topics are covered e An overview of contour integral anal ysis Section 20 1 1 e Defining the crack front Section 20 1 2 e Defining the crack ti p or crack line Section 20 1 3 e Defining the crack extension direction Section 20 1 4 e Controlling the si arity at the crack tip for a snall strain analysis Section 20 1 5 e Contour integral output Section 20 1 6 e Mshing the crack regi on and assi gni ng el enents Section 20 1 7 e Wit is a seam Section 20 1 8 e Creating a seam Section 20 1 9 e Controlling the si arity at the crack ti p Secti on 20 1 10 e Defining data for contour integrals Section 20 1 11 e Mbdifying data for contour integrals Section 20 1 12 e Requesting contour integral output Section 20 1 13 SS ABAQUS CAE User s M
10. S Version 6 5 Documentation ABAQUS CAE User s Manual and the type of contour integral analysis to perform For nore infornation see Mdi fying hi story out put requests Section 14 11 3 and Contour integral eval uation Section 7 10 2 of the ABAS Analysis User s N nual To request contour integral output g Enter the Step nodul e Fromthe nain nenu bar select Qitput H story Qtput Fequest Create ABAL F CAE di spl ays the Greate H story dialog box Fromthe Create H story dialog box enter the nane of the output request and the step in wichit wll be created dick Conti nue to close the dial og box ABAIN CAE displ ays the Hstory Qtput Requests editor Fromthe Donain field select Contour integral and select the desi red contour integral Fromthe fields that appear in the Hstory Qitput Requests editor enter the output frequency Select the type of contour integral calculation to perform You can select fromthe follow ng J integral You use the J integral in rate independent quasi static fracture analysis to characterize the energy rel ease associ ated wth crack growth The J integral can be rel ated to the stress intensity factor if the naterial response is linear For nore infornation see The J integral in Gontour integral eval uati on Section 7 10 2 of the ABRAB Analysis User s Manual C i integral You use the C integral for tine dependent creep behavior where it characterizes creep crac
11. an nesh part instance Wien you are defini ng the crack front on an orphan nesh part you can select the el enents or el enent edges or faces that define the crack front Alternatively you can select the nodes fromthe corresponding region Wien you are defini ng the crack front on an orphan nesh part the entities that you can select depend on the nodel i ng Space of the part 15 The interaction module ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual Two di nensi onal part instance If you are defining the crack front on a tve di nensi onal orphan nesh part you can select the followng e Asingle node e Connected el enent edges e Connected el enents Figure 20 6 shows the entities from which you can select when defining a crack front on a two dimensional orphan mesh part Figure 20 6 Selecting the crack front froma two di nensi onal orphan nesh part i L node element edges elements Three di nensi onal part instance If you are defining the crack front on a three dinensional orphan nesh part you can select the follow ng e Connected el enent edges e Connected el enent f aces e Connected el enents Figure 20 7 shows the entities from which you can select when defining a crack front on a three dimensional orphan mesh part Figure 20 7 Selecting the crack front froma three di nensi onal orphan nesh part alament edges element laces elements ABAQUS CAE User s Manual OT 20 1 3 Defining the crack tip or crack l
12. anual GE 20 1 1 An overview of contour integral analysis You can study t he onset of cracki ngin quasi static probl ens usi ng contour integral estinates hovever a contour integral estinate does not predict howa crack wll propagate You can conpute contour integrals for two or three di nensi onal nodels and you can choose to performone of the follow ng types of contour integral cal cul ati ons e J integral e Ci integral for creep e stress for linear naterial s e Stress intensity factors for li near honogeneous nateri al s and for interfacial cracks yi ng ont he interface bet wen tvo linear honoegeneous nateri als For more information see Contour integral evaluation Section 7 10 2 of the ABAQUS Analysis User s Manual You define cracks in the Interaction nodule To performa contour integral analysis you nust select the crack front the crack ti p or crack line and the crack extension direction as descri bed in the foll ow ng secti ons The entities that you can select depend on whether the part is two or three di nensi onal and whether you are 15 The interaction module 1 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual defining the part using geonetry froman ABAS native part or using elenents and nodes froman orphan nesh part In sone cases the crack tipor the cracklineis the sane as the crack f ront that you sel ected and ABAQUS CAE selects the crack tip or crack line for you A crack in a tvo di nensi
13. calcrackorphan Step f q vectors me FullconicalCrack Model FullConicalCrackOrphan Ste Data D 0 707 0 707 D 0693 0 704 0 707 i 138 0 8694 0 707 0 205 0 877 0 707 i 271 0 6553 0 707 i 333 0 824 0 707 i 383 0 588 0 707 0 449 0 547 0 707 D 5 0 5 0 707 Edi 0 547 0 448 0 707 1 588 0 393 0 707 0 624 0 333 0 707 0 653 0 271 0 707 0 677 0 205 0 707 0 694 0 1356 0 707 1 7 SSS C aaa Daaa Ma Figure 20 10 is taken from Conical crack in a block modeled with and without submodeling Section 1 4 2 of the ABAQUS Example Problems Manual An ABAQUS Scripting Interface script is provided with this example that illustrates how you can enter the vector at each node along the crack front SS ABAQUS CAE User s Manual D gt 20 1 5 Controlling the singularity at the crack tip for a snall strain analysis If the geonetry of the crack region defines a sharp crack the strain field becones singular at the crack tip as descri bed in Constructing a fracture nechanics nesh for snall strain analysis in Contour integral eval uation Section 7 10 2 of the ABAE Analysis U5er s Mnual Incl udi ng the singularity in your nodel for a snall strain anal ysis inproves the accuracy of the contour integral and the stress and strai n cal cul ati ons To incl ude the singul arity in your contour integral estinates click the S ngul arity tab in the Crack edit
14. contour integral data in the output database generated by the analysis For nore infornation see Contour integral output Section 20 1 6 and Mdi fying history output requests Section 14 11 3 For information on related topics click any of the following items 15 The interaction module 16 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual e Mpdeling fracture nechani cs Section 20 1 e Fracture nechani cs Section 7 10 of the Analysis User s Minual SS ABAQUS CAE User s Manual D 20 1 12 Mdi fyi ng data for contour integrals If desired you can nodi fy the entities that you selected to define the crack front the crack tip and the crack extension di recti on that wll be used to define a contour integral You can al so specify that the crack front is defi ned on a synmet ry pl ane that nodel s only hal f of the structure For noreinfornation see Synmetry in Gontour integral eval uation Section 7 10 2 of the ABXI5 Analysis U5er s Manual To define a crack to be used in a contour integral analysis 1 spay the Qrack editor using one of the follow ng net hods e To configure a new contour integral followthe instructions in Defining data for contour integrals Section 20 1 11 e To edit an existing contour integral select Speci al Grack 3 Edi t crack nane fromthe nain nenu bar in the Interaction nodul e 2 Toggle on Qn symmetry pl ane hal f crack nodel to speci
15. dupl i cate nodes al ong a seamwhen the nesh is generated A seamcannot extend al ong the boundaries of a part and nust be entpedded wthi n a face of a tvo di nensi onal part or wthin a cell of a solid part You can use the seamwhen you are selecting t he crack front and the crack ti p that wll be used in a contour integral analysis For nore infornation see What is a sean Section 20 1 8 To create a seam 1 Fromthe nain nenu bar in the Interaction nodule select Special Grack 3 Greate seam Fromt he nodel inthe viewport sel ect the entities representing the seam The entities nust be entpedded edges wthin a face of a tvo di nensi onal part or enbedded faces wthin a cell of a solid part you cannot select any entities that lie on the boundary of the part 9 ick nouse button 2 to indicate that you have finished selecting the seam APAIN CAE creates the seam 4 Toinclude the seamin a contour integral analysis followthe procedure descri bed i n Defining data for contour integrals Section 20 1 11 For information on related topics click any of the following items e Wat is a sean Section 20 1 8 e Fracture nechani cs Section 7 10 of the Anal ysis User s Minual ABAQUS CAE User s Manual ee 20 1 10 Controlling the singularity at the crack tip If the geonetry of the crack regi on defines a sharp crack the strain field becones singular at the crack ti p as descri bed in Constructi ng a fracture necha
16. f a part and nust be entpedded wthi n a face of a tvo di nensi onal part or wthin a cell of a solid part You can use the seamwhen you are selecting the crack front and the crack ti p that wll be used in a contour integral analysis For nore infornation see What is a seam Section 20 1 8 To create a seam 1 Fromthe nain nenu bar in the Interaction nodule select Special Crack Create seam Fromt he nodel in the viewport select the entities representing the seam The entities nust be entpedded edges wthin a face of a tvo di nensi onal part or enbedded faces wthin a cell of a solid part you cannot select any entities that lie on the boundary of the part 9 ick nouse button 2 to indicate that you have finished selecting the seam APAIN CAE creates the seam 4 Toinclude the seamin a contour integral analysis followthe procedure descri bed i n Defining data for contour integral s Section 20 1 11 For information on related topics click any of the following items e Wat is a seam Section 20 1 8 e Fracture nechani cs Section 7 10 of the Analysis User s Mmnual ABAQUS CAE User s Manual is en 15 The interaction module 13 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual 20 1 9 Creati ng a seam You can use the Special nenu in the Interaction nodule to define a seamin your nodel A seamdefines a regi on in your nodel that can open duri ng an anal ysis ABALY CAE pl aces overl appi ng
17. fy that the crack front is defi ned on a synmetry plane that nodels only half of the structure ABAQS doubles the change in potential energy cal cul at ed fromthe virtual crack front advance to conpute the correct contour integral values 3 If desired click Edit to nodify your selection of entities that define the crack front crack tip or crack line If ABIN CAE sel ected the crack ti p or crack li ne regi on to be the sane as the crack front you cannot edit the sel ecti on 4 If desired change t he net hod f or defi ni ng the crack ext ensi on direction You can al so cli ck Edi t to nodi fy your selection of entities that define the crack extension di recti on 5 dick CK to configure the contour integral and to close the editor ABAX5 displays green crosses on the regi on to represent the crack front You nust use the H story Qitput Request editor in the Step nodule to incl ude the contour integral data in the output database generated by the analysis For nore infornation see Contour integral output Section 20 1 6 and Mdi fying history output requests Section 14 11 3 e ABAQUS CAE User s Manual 20 1 13 Requesti ng contour integral output You use the H story Qit put Request editor inthe Step nodul e to request out put fromthe cont our integral anal ysis You nust sel ect Contour integral fromthe Donain field The edi tor then all ovs you to sel ect the out put frequency 15 The interaction module 17 ABAQU
18. i ne 15 The interaction module ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual After you have defined the crack front the next step in the procedure to configure the contour integral is to define the crack tip or crack line by sel ecti ng enti ti es fromthe assenbl y The nodel i ng space of your assenbl y governs whether you need to define a crack tip or a crack line for a contour integral analysis Two di nensi onal If your assenbl y is two di nensi onal you nust define the crack tip by selecting a vertex or a node The crack tipis the point on the crack front where you define the crack extension direction In sone cases the desi red vertex or node wll not exist and you nust create it by partitioning the crack front If you selected a vertex or a node to define the crack front the sane vertex or node defines the crack ti p Three di nensi onal If your part is three di nensi onal you nust define the crack line by sel ecti ng edges or el enent edges that form a continuous line The crack line is a series of connected edges along the crack front where you define the crack extension direction 4 In sone cases the desired edges wll not exist and you nust create them by partitioning the crack front If you selected edges or elenent edges to define the crack front the sane edges define the crack line Sel ected edges froman ABAIN CAE native part or froman orphan nesh nust be connected nust connect one si de of the c
19. i ting an orphan nesh part a neshed part and a neshed part instance in the assent y Section 41 2 You must di spl ay the original orphan nesh part and use the Edit Msh tool set to adj ust the positi on of the midsize nodes For nore infornation see Adj usting the position of mdside nodes Section 41 5 5 In addition you cannot create collapsed el enents fromtriangul ar and vedge elenents of an orphan nesh SS ABAQUS CAE User s Manual S 20 1 6 Contour integral out put After you have defined the crack you nust use the Hstory Qtput Request editor in the Step nodule to incl ude the contour integral data in the output database generated by the analysis The editor allows you to configure the foll owng e The output frequency e The type of contour integral cal cul ation to perform J integral C integral stress intensity factors or T stress e The nunber of contours to eval uate ABAQUS writes a history output variable to the output database for each contour integral that it calculates Figure 20 11 shows the format of the name of an output variable representing a contour integral Figure 20 11 The fornat of a contour integral nane in the output database 15 The interaction module 10 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual Me History Output Variables Steps Frames Output Variables Name filter Tip Fintegral estimated from Ks JKs at STRESSINTROTTOM BOTTOMCRACK
20. ing contour integral output Section 20 1 13 For noreinfornation see Mbdi fyi ng hi story out requests Section 14 11 3 and Contour integral eval uati on Section 7 10 2 of the APAQS Analysis Uer s Mmnual ABAQUS CAE User s Manual is E 20 1 7 M shi ng the crack regi on and assi gni ng el enents Large stress concentrations occur at the crack tip As a result you should create a refined nesh around the crack tip to get accurate results for stresses and strains In contrast because the integral is an energy neasure you can obtain accurate val ues wth a relatively coarse nesh Fbvever if the material becones nore nonlinear you must create a finer nesh at the crack tip to nai ntai n the accuracy of the f val ues You can control the density of the nesh at the crack ti p by partiti oni ng the regi on and by assi gni ng nesh seeds to the resul ti ng edges For nore infornation see Understanding seedi ng Section 17 4 For a large strain analysis duri ng whi ch ABKI5 wll allowfor nonlinear geonetry you shoul d nesh the cont our integral regi on wth quadrilateral or hexahedral elenents For nore infornation see Constructing a fracture nechanics nesh for finite strain analysis in Qntour integral evaluation Section 7 10 2 of the ABIS Analysis Uer s Mnual Fbvever for a snall strain anal ysis that does not all owf or nonlinear geonetry you nust all owfor the si ngul ari ty at the crack ti p or crack
21. k def ornati on under certain creep conditions including transient crack growh For nore infornation see The C integral in Gontour integral eval uation Section 7 10 2 of the ABXIS Analysis USer s Mmual I stress You use the T stress conponent to represent a stress parallel to the crack front For nore i nf ornati on see The J stress in Qntour integral eval uation Section 7 10 2 of the APAS Analysis User s N nual Stress intensity factors You use the stress intensity factors Ay Ayr and A rriin linear elastic fracture nechanics to characterize the local crack tip stress and di spl acenent fields For nore infornation see The stress intensity factors in Contour integral evaluation Section 7 10 2 of the ARAQS Analysis Uer s N nual If you request a contour integral calculation using stress intensity factors ABAQS also conputes the crack propagation direction at initiation You nust choose one of the followng to indi cate the crack initiation criteria e Mxinumtangential stress e Mxinumenergy rel ease rate 15 The interaction module 18 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual e Kl1 9 For more information see The crack propagation direction in Contour integral evaluation Section 7 10 2 of the ABAQUS Analysis User s Manual 7 Enter the nunber of contours to eval uate ABAQLS CAE conput es the next contour integral by addi ng a si ngl e layer of el enent
22. l ane to specify the nornal to the crack pl ane and sel ect points representing the start and end of the nornal q vectors Sel ect q vectors to specify the crack extension di recti on directly and select poi nts represent i ng t he start and end of the vector For more information see Defining the crack extension direction Section 20 1 4 ABAQUY CAE di spl ays a red arrowi ndi cati ng the crack extension di recti on and displays the Edit Crack di al og box Ue the Edit Crack dialog box to configure the paraneters that control a contour integral analysis e dick the General tab of the dialog box to do the follow ng Specify that the crack front is defined on a synmetry pl ane that nodel s only half of the structure Change the entities that define the crack front or crack ti p li ne hange the net hod for defining the crack extension direction You can al so change the entities that define the crack extensi on di recti on For more information see Modifying data for contour integrals Section 20 1 12 e licktheSingularity tab of the di al og box to nodel a singularity of the strain field at the crack tip For nore infornation see Controlling the si arity at the crack tip Section 20 1 10 ick CK to configure the contour integral and to close the editor APAQS5 displays green crosses on the regi on to represent the crack front You nust use the H story Qitput Request editor in the Step nodule to incl ude the
23. ndi ng the crack After you create a crack you nust use the H story Qut put Request editor to request that ABXIS wite contour integral infornation to the output database For nore infornation see Contour integral output Section 20 1 6 For detailed instructions see Defining data for contour integrals Section 20 1 11 ABAQUS CAE User s Manual ee 20 1 2 Defining the crack front The first stepinthe procedure to configure a contour integral is to define the crack front by sel ecti ng entities fromthe assenbl y The crack front is the forward part of the crack ABAQS uses the crack front to conpute the first contour integral using all of the el enents inside the crack front and one l ayer of elenents outsi de the crack front You can request output for nore than one contour integral in whi ch case ABAQS CAE adds a 15 The interaction module 2 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual single layer of el enents to the group of el enents that were used to cal cul ate the previous contour integral Fi gure 20 2 illustrates how ABAQUSN CAE conputes successi ve contour integrals for a tvo di nensi onal nodel by addi ng layers of el enents H gure 20 2 Successive contour integrals are calculated by adding a layer of el enents If your part is three di nensi onal ABAQ5 conputes contour integrals at each node al ong the crack line as shown in F gure 20 3 For noreinfornation see Defini ngthe crackfront
24. nics nesh for snall strain analysis in Contour integral eval uation Section 7 10 2 of the ARAQS Analysis U5er s Mnual Incl udi ng the singularity in your nodel for a snall strain anal ysis inproves the accuracy of the contour integral and the stress and strai n cal cul ati ons To control the singularity at the crack ti p 1 Hsplay the Crack editor using one of the follow ng net hods e To configure a new contour integral followthe instructions in Defining data for contour integrals Section 20 1 11 e To edit an existing contour integral select Speci al Grack 3 Edi t crack nane fromthe nain nenu bar in the Interacti on nodul e 15 The interaction module 14 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual 2 To include the strain singularity in your contour integral estinates click the Si ngul arity tab in the Crack editor and do one of the following To create a 1 v strain singul arity for an elastic fracture nechani cs applicati on a Fromthe Second order Msh Qxions field enter a value of 0 25 for the Mdside node paraneter to nove the nidside nodes to the 1 4gi nts b Fromthe Degenerate H enent Control at Crack Ti p Ii ne fiel d choose Col l apsed el enent si de si ngl e node To create a l strain si ngul arity for a perfect plasticity fracture nechani cs applicati on a Fromthe Second order Msh Qxti ons field enter a val ue of 0 5 for the Mdsi de node paranet er
25. nsi onal and whether you are defining the part using geonetry froman ABAQS native part or using elenents and nodes froman orphan nesh part To define the data for contour integral s 1 Fromthe nain nenu bar in the Interaction nodule select Speci al Crack Great e The Greate Crack dialog box appears 15 The interaction module 15 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual 2 3 Enter the nane of the crack and click Conti nue to close the dialog box Fromt he nodel inthe vi ewoort select the entities representing the crack f ront region For a descri pti on of the entities to select see Defining the crack front Secti on 20 1 2 lick nouse button 2 to indi cate that you have fini shed sel ecti ng the crack front regi on Fromthe nodel in the viewport select the entities representing the crack ti p region In sone cases dependi ng on t he nodel i ng space of your nodel and the entities that you sel ected to defi ne the crack f ront APAQS CAE sel ects the crack ti p for you and ski ps to Step 7 For nore infornation see Defining the crack tip or crack line Secti on 20 1 3 Fromthe pronpt line toggle on Select nesh entities to select entities froman orphan nesh part lick nouse button 2 to indicate that you have fini shed selecting the crack tip regi on Fromthe pronpt area choose the nethod for defini ng the crack extension di recti on Nornal to crack pl ane Select Nornal to crack p
26. or and choose the desi red position of the nadside node and degenerate el enent control For detailed instructi ons see Controlling the si arity at the crack tip Secti on 20 1 10 In addition you nust do the followng in the Msh nodule e If the assenbl y or part is tvo di nensi onal you nust nodel the crack front wth a ring of triangles and assign quadrilateral elenents to the renai nder of the contour integral regi on e If the assenbly or part is three di nensi onal you nust nodel the crack front wth a ring of vedges and assign hexahedral elenents to the renai nder of the contour integral region When you mesh the crack front ABAQUS does the following 15 The interaction module 9 ABAQUS Version 6 5 Documentation ABAQUS CAE User s Manual e Converts the elenents in the crack front to collapsed quadrilateral or hexahedral elenents e If you nodel ed the crack front wth a ring of second order tri angl es or wedges ABAE noves the nidsi de nodes to the speci fi ed posi ti on al ong t he el enent edges that radi ate out fromthe crack ti p or crack line If you nodel ed the crack f ront w tha ring of first order tri angl es or wedges ABAQS5 ignores the posi ti on that you specified for the midside nodes An instance of an orphan nesh part is al ways a dependent instance As a result you cannot adjust the nidsi de nodes of instances of orphan nesh parts inthe assenbl y For nore infornation see What is the difference bet wen ed
27. rack front to the other and nust be included in the crack front ABAQUS CAE User s Manual ee 20 1 4 Defining the crack extensi on di recti on After you have defined the crack front al ong wth the crack ti p or crack line ABIN CAE pronpts you to specify the crack extensi on di recti on at the crack ti p or al ong the crack line You can specify the nornal to the crack plane n or you can specify the crack extension direction 4 directly For a detailed discussi on of howABALS uses nor to cal cul ate the crack extensi on di recti on see Specifying the virtual crack extension di recti on in Gontour integral eval uation Section 7 10 2 of the ABANS Analysis l5er s Manual Nornal to crack pl ane If you sel ect Nornal to crack pl ane you can define the nornal by selecti ng poi nts fromthe nodel that represent the start and the end of the nornal to the crack pl ane The crack pl ane contains the vector that ABAQS needs to conpute the contour integral In nany cases the crack pl ane represents the pl ane of synmetry of the crack You shoul d define the nornal to the crack pl ane only if the direction is the sane at all points al ong the crack line If the direction of the nornal to the crack pl ane vari es al ong the crack line you cannot select a si ngl e nornal that defines the crack extension direction at all points along the crack li ne To define the nornal to the crack pl ane you can select points froman ABAQS native part
28. s to the regi on defi ned by the previ ous donai n as descri bed i n Fi qure 20 2 Fach cont our generates a value or a group of values for the contour integral 8 ick CKto configure the contour integral analysis and to close the editor For exanpl es of howABAQLS nanes hi story out put vari abl es in the out put database for each contour integral that it calculates see Qontour integral output Section 20 1 6 SS 15 The interaction module 19

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