I have carried out fracture toughness of Zr-2.5Nb pressure tube using CT specimens in transverse and longitudinal direction. The transverse CT specimens got buckled during fracture testing. I want to model buckling of transverse specimen. I want to know the boundary conditions for this and any other requirement like element types, meshing etc.
with regards
AKBIND
Hi.
In modeling of cracked specimens it’s very important to mesh crack tip very well. You can use very small size element in whole specimen. But it’s takes a long run time. Instead you can employ medium size element in specimen while using very small element in crack tip. Thus I recommend simulating CT in 3D Shell. Use S8R5 element to meshing. This element can handle buckling problem very well. For crack tip you can partition crack tip area in size of other elements or twice size of other elements. Then in this square partition, partition concentric circles centered in crack tip with different radius. This radius size is optional, but I recommend each circle be in half radius of previous one. Sweep type of element must be used in these circles. For boundary condition bottom grip could be encastre.
Good luck
Dear Salimi,
I have one doubts about your reply. How asymmetric loading will be introduced in FEM model?
The buckling of CT specimen means lateral movement in thickness direction. When modelling the buckling we have to introduce non symmetric loading in FEM model. I want to know how to introduce non symmetric loading in FEM model.
In buckling analysis, we need non symmetric loading, as you said, or inhomogeneous geometry. Crack makes geometry inhomogeneous. In cracked plate, specimen buckled even though tensile loading was applied. Abaqus in linear buckling analysis module, calculates buckling loads and modes. For this purpose Abaqus founds stiffness matrix and finds Eigen values and Eigen vectors. For nonlinear analysis or study of post-buckling behavior, Riks method should be used.
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