Fiber-reinforced laminates have a specific fracture mode such as ply cracking(cracking in a direction parallel to the fiber), delamination, and breakage of the fiber.Of these fracture modes, ply cracking occurs in the earliest stage, and it can result insignificant degradation in material stiffness. Furthermore, the initiation of ply crackingcauses stress redistribution, resulting in more severe forms of damage such asdelamination and breakage of the fiber due to the stress concentration at the crack tip.Therefore, it is important to clarify the mechanical behavior of laminates including plycracking. This study focuses on the stiffness reduction of laminate due to ply crackingand the ply cracking progression in a ply. First, the continuum damage mechanics(CDM) based model for predicting the stiffness reduction of composite laminates isestablished. The effective compliance of laminate based on CDM and the classicallaminate plate theory (CLPT) was used to formulate the thermo-elastic properties oflaminate of arbitrary lay-up configurations as a function of ply crack density. Thedamage variable d2 is formulated analytically by three-dimensional local stress field(3-D LSF) model in a ply including ply cracking subjected to tensile loading. Next,ply cracking progression in laminates including 90° plies was investigated. The energyrelease rate associated with ply cracking is calculated using the 3-D LSF model, andthen ply cracking progression in 90° plies of CFRP cross-ply laminates based on bothstrength and energy criteria is predicted using the Monte Carlo method. The modelsproposed in this study can predict the experiment results and finite element analysisresults.
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