Improved cohesive zone model: integrating strain rate, plastic strain, variable damping, and enhanced constitutive law for fracture propagation

Cohesive zone model has been used widely in fracture propagations, but few of them have considered strain rate, plastic strain, and variable damping together. In this paper, artificial compliance and spurious oscillation in bilinear cohesive law are investigated through dynamic simulations. Several constitutive laws and damage criteria used in bilinear cohesive law are presented first, and the properties in these constitutive laws are analyzed about deficiency of plastic strain, inherent discontinuity of constitutive law, and inherent discontinuity of force. Two damage evolution methods (effective separation method and damage factor method) are compared, and the latter one that strictly follows damage criterion and has no healing effect is a better choice for damage evolution. Numerical investigations are conducted to help select proper stiffness and to make sure artificial compliance in an acceptable range. Apart from strain rate and plastic strain, variable damping is considered into bilinear cohesive law, which can remove discontinuous force caused by constant damping at the start and end of bilinear cohesive law. One fixed delamination propagation and two free fracture propagation examples are used to verify the methodology proposed in this paper. From the simulation results, the methodology used in this paper removes spurious oscillation caused by constitutive law itself and enables correct force response, and variable damping reduces spurious oscillation.