Study on the Characteristic Curve of Stiffness Degradation Caused by Transverse Matrix Cracking in Multidirectional Composite Laminates

Abstract

By introducing two concepts of the "equivalent residual lamina stiffness" and the "equivalent crack density" to eliminate the different stiffness degradation characteristics caused by transverse matrix cracks, the degradation of the three lamina stiffness components can be described by a same characteristic curve which is independent of the laminate layup. But the residual stress has some effect on the stiffness degradation, especially to the inplane Poisson's ratio of the laminate. Results show that for the same matrix crack density, the residual Poisson's ratio is always less than the residual shear modulus and Young's modulus. Due to the existence of the matrix crack saturation state, the degradation of the lamina stiffness has the low boundary value; this value seems to be independent of the laminate configuration and materials.