Matrix microcracking of laminated composites lead to stiffness degradation. Microscopic critical stresses are defined according to the linear elastic fracture mechanics and are found to be independent of the crack density. The microscopic critical stresses are constant as long as the material and the thickness of the cracked plies are constant, and can be used to obtain the semi-analytical expression of the equivalent transverse moduli and in-plane shear moduli of the cracked plies versus the crack density. The equivalent longitudinal moduli and in-plane shear moduli of [0/±θ₄/0_1/2]_S laminates are obtained by using the semi-analytical model and the classical laminate theory, and are compared with the available experimental data and conventional finite element analysis (FEA) results.

层压复合材料的基体微裂纹导致刚度下降。微观临界应力是根据线弹性断裂力学定义的，并且被发现与裂纹密度无关。只要裂纹层的材料和厚度不变，微观临界应力就恒定，可用于获得裂纹层与裂纹的等效横向模量和面内剪切模量的半解析表达式密度。[0/±θ ₄ /0 _1/2 ] _S的等效纵向模量和面内剪切模量 通过使用半解析模型和经典层压理论获得层压板，并与可用的实验数据和常规有限元分析 (FEA) 结果进行比较。