<p><span style=”font-size: 12pt;”>I am performing fatigue crack growth of a 2D specimen with an internal crack. The geometry is a square plate under tension and the internal crack is located at the center of the specimen. I am relying on XFEM for the crack growth study as SMART method is not available in 2D. I am using APDL for the entire simulation including the geometry creation, meshing, solving and post-processing. Before beginning the crack growth study, I performed validation of the SIF at the crack tips. Ansys solver computed the SIF correctly for both crack fronts\/tips (Since my crack is fully embedded, there will be two crack fronts\/tips). But when I try to perform the crack growth using either Life-cycle method or Cycle-by-cycle method, the solver is failing by showing an error and it reads “Both life-cycle and cycle-by-cycle methods for fatigue crack growth are found in the same model. Only one method is allowed in one simulation model. Please check input data”. My code for crack growth is written exactly based on the instructions provided in APDL Fracture Analysis Guide. Key information from the code is as follows.<\/span><\/p><\/p>\n
<li style=”font-size: 12pt;”><span style=”font-size: 12pt;”>Singularity based approach adopted for XFEM crack growth as mentioned in Fracture analysis guide <\/span><\/li>\n
<li style=”font-size: 12pt;”><span style=”font-size: 12pt;”>Solver successfully computed Level sets during solution phase making sure that crack is properly modelled. <\/span><\/li>\n
<li style=”font-size: 12pt;”><span style=”font-size: 12pt;”>Paris law parameters are specified as suggested in Fracture analysis guide using TB command.<\/span><\/li>\n
<li style=”font-size: 12pt;”><span style=”font-size: 12pt;”>Then the error appeared as solver started to perform crack growth. <\/span><\/li>\n<\/ol>\n
<p><span style=”font-size: 12pt;”>The code snippet for fracture parameter calculation and crack growth <\/span><\/p><p><span style=”font-size: 12pt;”>! Paris Law Constants <\/span><\/p><p><span style=”font-size: 12pt;”>C = 2.29E-13 <\/span><\/p><p><span style=”font-size: 12pt;”>M = 3 <\/span><\/p><p><span style=”font-size: 12pt;”>! Fatigue crack growth Law Specification <\/span><\/p><p><span style=”font-size: 12pt;”>TB, CGCR, 2, , , PARIS TBDATA, 1, C, M <\/span><\/p><p><span style=”font-size: 12pt;”>!Fracture Parameter calculations <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NEW, 1 ! Crack ID for first crack front <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, CXFE, _XFCRKFREL1 ! Element component name assigned by APDL for first crack front elements <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, TYPE, SIFS ! Stress intensity factor needs to be computed <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NCON, 8 ! Number of total contours required <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NORM, 11, 2 ! Define the crack plane normal <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NEW, 2 ! Crack ID for second crack front <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, CXFE, _XFCRKFREL2 ! Element component name assigned by APDL for second crack front elements <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, TYPE, SIFS <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NCON, 8 <\/span><\/p><p><span style=”font-size: 12pt;”>CINT, NORM, 11, 2 ! Define the crack plane normal<\/span><\/p><p><span style=”font-size: 12pt;”> !Crack growth calculations <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, NEW, 1 ! Crack growth set number for first crack front<\/span><\/p><p><span style=”font-size: 12pt;”> CGROW, CID, 1 ! Crack calculation ID, should be same as above [CINT, NEW, 1] <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, METHOD, XFEM ! XFEM as crack growth method <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, FCOPTION, mtab, 2 ! Fatigue crack growth law, material parameters specified as [tb, cgcr, 2, , , PARIS], if this command is not issued, the crack does not propagate <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, NEW, 2 ! Crack growth set number for second crack front<\/span><\/p><p><span style=”font-size: 12pt;”> CGROW, CID, 2 ! Crack calculation ID, should be same as above [CINT, NEW, 2] <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, METHOD, XFEM <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, FCOPTION, mtab, 2<\/span><\/p><p><span style=”font-size: 12pt;”> !Fatigue related data <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, FCG, METH, LC ! Life cycle method <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, FCG, DAMX, 1.0 ! maximum crack growth increment <\/span><\/p><p><span style=”font-size: 12pt;”>CGROW, FCG, SRAT, 0 ! stress-ratio <\/span><\/p><p><span style=”font-size: 12pt;”>KBC, 1 ! loads are stepped for fatigue analysis<\/span><\/p><p><span style=”font-size: 12pt;”>I have the follwoing questions.<\/span><\/p><\/p>\n
<li style=”font-size: 12pt;”>Is XFEM in ANSYS APDL limited to only one crack front\/ tip during crack growth? Remember, I can compute SIF for more than one crack fronts\/tips using XFEM in ANSYS APDL.<\/li>\n
<li style=”font-size: 12pt;”>Assume that in reality if only one crack tip\/front of the internal crack will propagate, then I don’t need second set of CGROW commands in my code, and the problem reduced to only one crack. But, how do we know only one crack tip\/front will propagate especially for an internal crack located at the centre of the 2D plate? Which crack front will propagate? <\/li>\n
<li style=”font-size: 12pt;”>Before suggesting a symmetric model, I started with a simplified model. My real model will not be symmetrical. The interal crack can locate anywhere in the plate. Then, how can I solve the issue of multiple crack fronts\/tips? <\/li>\n<\/ol>\n
<p style=”font-size: 12pt;”>I already saw that some open source FEM codes are capable to simulate the problem. I want to keep APDL if possible as I am more comfortable in writing APDL codes. Can someone suggest some solutions or their ideas to work out the problem? <\/p><p> <\/p><\/p>\n","protected":false},"template":"","class_list":["post-395517","topic","type-topic","status-answered","hentry","topic-tag-2d","topic-tag-apdl","topic-tag-fatigue-crack-growth","topic-tag-paris-law-1","topic-tag-structures","topic-tag-xfem"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27791"],"_bbp_topic_id":["395517"],"_bbp_subscription":["201888","436953"],"_bbp_author_ip":["139.165.123.160"],"_bbp_reply_count":["5"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["201888","436953"],"_btv_view_count":["1211"],"_bbp_topic_status":["answered"],"_bbp_last_reply_id":["397393"],"_bbp_last_active_id":["397393"],"_bbp_last_active_time":["2024-12-13 10:46:36"]},"test":"jmjosephuliege-be"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/395517","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":1,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/395517\/revisions"}],"predecessor-version":[{"id":397394,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/395517\/revisions\/397394"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=395517"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}