Damage tolerance is the ability of a structure to retain required structural strength or stiffness after it has sustained damaged.
When a composite part is damaged, there are numerous failure modes that can exist. These failure modes are constituent-level defects (i.e. fiber and matrix level defects) so it is appropriate to model damage at this level. Helius PFA is well-suited for modeling damage tolerance because it lets you specify constituent-level damage in elements at the start of the analysis. For example, consider a plate impacted by a mass resulting in diffuse matrix damage in the impacted region. You can designate a region representing the damaged region and assign matrix failure to that region prior to the start of the analysis. At the start of the analysis, this region will have an SVAR1 value of 2 (matrix failure) and as the simulation progresses, the region can undergo fiber failure which will result in an SVAR1 value of 3. The initial value of SVAR1 that is assigned to the damaged region is not fixed and can change if either the matrix or fiber failure criterion is satisfied.
The initial value of SVAR1 must be an integer value equal to 1, 2, or 3. For unidirectional materials, 1 corresponds to no failure, 2 corresponds to matrix failure, and 3 corresponds to fiber and matrix failure. For woven materials, 1 corresponds to no failure, 2 corresponds to matrix failure in all tows and the matrix pocket, and 3 corresponds to fiber failure in all tows plus matrix failure in all tows and the matrix pocket. The ANSYS commands listed below are used to activate damage tolerance:
HELIUSPFA, …
TB, STATE, < MATID >, , < NSTATV >
TBDATA, 1, < initial value of SVAR1 (2 or 3) >