Influence of fibre misalignment and voids on composite laminate strength

Abstract

This article studies the effects of manufacturing defects of laminate composite materials on the first ply failure load and ultimate strength of the laminate, which are calculated using finite element modelling with Zinoviev’s damage model. The following types of defects are considered for cross-ply and quasi-isotropic layups: in-plane misalignement and out-of-plane waviness of fibres, misorientation of the layers and void content. The list of laminates studied in this article includes cross-ply and quasi-isotropic layups, loaded in tension and compression in 0°, 90°, 45° and 5° directions. The limits of the first ply failure load and strength degradation for a realistic range of the defect intensities are estimated.

Process Induced Defects in Liquid Molding Processes of Composites

“…Misalignment angles ranging from 1 to 68 were observed to lead to a reduction in compressive strength from 1.9 to 1.5 GPa. Similarly, Fedulov et al (2015) reported a 16 % reduction in ultimate compression load for a fiber misalignment of 58 in carbon/epoxy composites, along with a linear reduction in failure initiation load due to misalignment. Furthermore, Vallons et al (2011) reported tensile property reductions for a biaxial non-crimp fabric composite at small off-axis angles.…”

“…Depending on the manufacturing process, other types of defects can prove to be much more difficult to eliminate. LCM processes are associated with a number of specific manufacturing defects such as voids, dry spots, in-and out-of-plane fiber undulations, microcracks and part distortions (Fedulov et al, 2015;Hagstrand et al, 2005;Hamidi and Altan, 2017;Mukhopadhyay et al, 2015;Anders et al, 2016). As depicted in Fig.…”

“…These unwanted deformations of fiber preforms include preform misalignment, waviness, and wrinkling. Wrinkling and waviness are often used interchangeably and considered to be a type of fiber misalignment that indicates preform defects within the composite parts (Bloom et al, 2013;Fedulov et al, 2015). For clarity, a distinction is made in this article.…”

“…Given the distribution of misalignment angles within a graphite/epoxy composite, the model predicts effective axial shear modulus, transverse Young's modulus, as well as axial Young's modulus. Other authors (Fedulov et al, 2015;Karami and Garnich, 2005;Li et al, 2016;Mukhopadhyay et al, 2015) used finite element micromechanical models for fibrous materials to pre-Intern. Polymer Processing XXXII (2017) 5 Li et al (2016) used a continuum mechanical model based on microsphere approach to predict the mechanical properties of unidirectional composites using the distribution of fiber misalignment.…”

“…Recently, significant developments of robotized preform placement allowed LCM processes to be more competitive (Fedulov et al, 2015;Heuer et al, 2015;Lukaszewicz et al, 2012). Currently, LCM variants, such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM), are increasingly used to fabricate structural parts in a wide variety of industrial applications.…”