Mesoscale finite element analysis of cracked composite laminates under out-of-plane loads using 3D periodic boundary conditions

Abstract

The behavior of composite materials under out-of-plane loads is strongly affected by the presence of transverse ply cracks. The cracks perturb the distribution of stresses leading to large out-of-plane shear stiffness reductions. It is crucial to include these effects in the damage material models to improve their accuracy. Therefore, the stress transfer and stiffness reduction in cracked laminates have been studied with a mesoscale finite element model (FEM) under general in-plane, out-of-plane normal and shear loads. A symmetric laminate containing ply cracks in a single orientation has been considered under the hypothesis of periodicity using a novel relaxed three-dimensional formulation of Periodic Boundary Conditions (PBCs). The local stresses have been verified versus different analytical and numerical methods. In addition, the degraded effective thermo-elastic constants involving out-of-plane properties have been calculated as a function of crack density. Both uniform and non-uniform distributions of cracks have been considered for different lay-ups including angleply and unbalanced laminates. The effect of contact between the crack surfaces has been studied for specific loading conditions. It is shown that a single formulation based on three-dimensional periodic boundary conditions is sufficient to determine the interfacial stresses and the complete thermo-elastic constants under in-plane and out-of-plane loads accurately.

A computational study about the effects of ply cracking and delamination on the stiffness reduction of damaged lamina and laminate

“…Homogenization of damaged laminate. Although it is possible to implement the first homogenization approach for whole RVEs, computationally it is more realistic to use the displacement/force fields of reference nodes for calculating the effective properties of the damaged laminate based on the kinematics of PBCs (Garoz et al, 2020). Considering the macroscopic stress-strain results which are obtained based on the reference node data, the elastic constants of damaged RVEs are defined as: where the Young's moduli (EÞ, shear moduli (GÞ, Poisson's ratio (), coupling terms (k) and thermal expansion coefficients (a) have been introduced in the global coordinate system.…”

“…In this regard, Adolfsson and Gudmundson (1995) presented the influence of ply cracking on the in-plane and outof-plane mechanical properties of composite laminates. Recently, Garoz et al (2020) studied the stiffness reduction and the stress distribution of cracked composite laminates under out-of-plane loading conditions by considering the relaxed 3D periodic boundary conditions (PBCs). Moreover, implementing the second-order homogenization method, the flexural behavior of cracked composite laminates was investigated by Dinh et al (2019).…”