Hello everyone,

I am working on an Abaqus model using XFEM for crack initiation and propagation in a solid structure. The crack initiates as expected and propagates through the domain; however, the global stiffness of the model does not degrade, and the global load–displacement response remains almost linear even after significant crack growth.

I´ve tried in this model:

• 3D deformable solid elements (I´ve tried Tet and Hex-dom in mesh control, C3D4 and C3D8R)
• XFEM-based damage initiation and energy-based damage evolution
• Damage evolution --> Energy method 
• Damage Stabilization Cohesive (1e-5 e 1e-6)

• Mode fracture criterion (BK and Model-independent)

   

Despite visible crack propagation, the structure does not show the expected reduction in stiffness or load-carrying capacity. I suspect this may be related to one or more of the following aspects:

• Crack not fully disconnecting the load path
• Remaining stiffness in partially damaged XFEM elements
• Stabilization or viscous regularization effects
• Boundary conditions or load redistribution masking stiffness loss

Even with low values of the damage parameters (G = 0.5 and Maxps damage = 4 N), no global stiffness degradation was observed. The fracture propagates, but the elements do not physically separate or lose their load-carrying capacity.

I would appreciate any guidance on typical causes of missing global stiffness degradation in XFEM models, and recommendations on how to correctly capture the global structural softening.

Thank you in advance for your help.