Closed-form equations for composite strengths: From constituents to structures

Closed-form equations for calculating progressive failure strengths of a laminated composite by using its constituent properties and laminate geometric parameters are available based on the micromechanics bridging model. Through a user-subroutine UGENS, the bridging model theory has been incorporated into ABAQUS to define elemental instantaneous stiffness matrix and to capture ultimate strength of a structure made of or containing composite laminates. An alternative approach to the bridging model is presented in terms of Mori-Tanaka theory and Eshelby's tensor together with necessarily appropriate simplifications. Further modifications have been achieved by introducing a modified ultimate failure criterion for a laminate, a new material degradation scheme for a failed lamina, and pure resin inter-layers in between the lamina plies. The modified bridging model has been shown much more accuracy when applied to analyze the first World-Wide Failure Exercise problems. The correlation of its predictions with the experiments is even better than that of any other theory predictions taken part in the exercise.