MAT162
A Rate Dependent Progressive Composite Damage Model in LS-DYNA
MAT162 is a material model for use in LS-DYNA that may be used to simulate the onset and progression of damage in unidirectional and orthotropic fabric composite continua due to 3D stress fields. This failure model can be used to effectively simulate fiber dominated failures, matrix damage, and includes a stress-based delamination failure criterion. This approach to predicting interlaminar failure is advantageous in cases when locations of delamination sites (i.e., interlaminar crack initiation surfaces) cannot be anticipated.
MAT162 accounts for several different failure modes for the fiber and matrix phases of the composite material. Fiber breakage is modeled using a strain based failure criteria, which are the quadratic interaction of the strain components associated with the fiber tension/compression, fiber shear punch, and fiber crushing damage modes normalized with respect to the correspondent failure initiation strain amplitudes. Matrix failure includes delamination, which is modeled by the quadratic interaction of the through the thickness strain components normalized with respect to the through-thickness tensile and shear failure strains. Material property variations with strain rate may be included using simple logarithmic based functions included in the model.
A set of damage history variables is introduced in MAT162 to relate the onset and growth of damage to stiffness loss in the material. The failure criteria of fiber, delamination and matrix damage modes are used as damage surfaces in strain space. Damage increases when the strain path intersects the damage surfaces and the strain increment has a non-zero component in the direction normal to the damage surfaces. The damage model assumes a linear relation for the strain region inside the updated damage surfaces with the elastic moduli reduced according to the associated accumulated damage parameters. The composite damage model is further generalized to allow a residual compressive strength. Delamination is modeled within elements adjacent to ply interfaces. For a delaminated element, the in-plane load carrying capacity within the element is assumed to be elastic. The load carrying behavior in the direction normal to the crack plane is then dependent on the opening and closure of such a crack. For an opening delamination (positive through-thickness normal strain), the normal to the thickness load carrying capacity is reduced to zero. For a closing delamination (negative thickness normal strain), the through the thickness normal stress is assumed to regain the initial elastic capacity, while the through the thickness shear stresses are assumed to be limited by a constant slide shear value. Under the crack closure condition, this approach effectively models the interface friction behavior generated by the normal stress. This model allows one to effectively approximate the dynamic delamination behavior without the use of the usual time consuming contact surface elements.