### 4.2.1. Failure Initiation

Hashin failure criteria have been extensively used in modelling the prediction of impact damage in composites. However, in these criteria for fiber and matrix failure only plane stresses, σ22, σ23 and σ33, are considered. As a consequence the applicability of these criteria for out of plane impacts is questionable.

Modified versions of these failure criteria along with a criterion for delamination are presented in [6] and have been implemented into Autodyn [2]. For the fiber failure and matrix cracking criteria out of plane shear stresses are included in addition to the original criteria. The failure initiation criteria are listed below.

Delamination

| (4–4)

Fiber Failure

| (4–5)

Matrix Cracking

| (4–6)

The initiation criteria Equation 4–4 to Equation 4–6 are only applied in tension.

Release 18.2 - © ANSYS, Inc. All rights reserved.