Effect of various parameters on the effective properties of a cracked ply

Damage in composite materials accumulates in a diffuse manner. Accounting f or this damage in a progressive failure analysis requires an accurate measu re of the degraded stiffness coefficients. This paper describes micromechan ics models for predicting the effect of distributed cracks on the engineeri ng properties (extensional moduli, shear moduli, and Poisson's ratios). Qua si-3D and 3D finite element methods were employed to determine the effectiv e material properties of the cracked ply. Analyses were performed for vario us material systems, damage states, and adjacent (to the cracked ply) ply p roperties. The results show that the effective properties of cracked ply ar e very sensitive to the initial properties of a cracked ply. These properti es are also found to be sensitive to the adjacent ply properties and orient ation. However, they are not much affected by cracks in the adjacent plies. Relationships describing the sensitivity of the effective properties to th e adjacent ply properties and the initial properties of a cracked ply were obtained. These relationships are useful for explaining the degradation beh avior of laminates. Quantitative measures are presented for the errors intr oduced when shear-extension-coupling terms are ignored when calculating eff ective properties. Also, it was proven that transverse matrix cracks only a ffect the diagonal terms in the effective compliance matrix for certain con figurations.