ABSTRACT

As we have seen in Chapter 7, rst ply failure (FPF) is the load at which the rst crack appears in a lamina, and last ply failure (LPF) is an approximation to the load for which the laminate is no longer able to sustain any load. In Chapter 7, predictions of FPF and LPF are done with strength failure criteria (Sections 7.1, 7.2, and 7.3). Strength failure criteria have at least three limitations, as follows:

First, some of the strength values used in strength failure criteria need to be adjusted for ply thickness and laminate stacking sequence (LSS). While the thickness dependency can be accounted for by using in-situ values (Section 7.2.1), the dependency on LSS is not easily accounted for. Even then, the criteria predict the appearance of the rst matrix crack, not the saturation of matrix cracks that corresponds to total degradation of a lamina.