Compressive failure of laminates containing an embedded wrinkle; experimental and numerical study

Abstract

An experimental and numerical study has been carried out to understand and predict the compressive failure performance of quasi-isotropic carbon-epoxy laminates with out-of-plane wrinkle defects. Test coupons with artificially induced fibre-wrinkling of varied severity were manufactured and tested. The wrinkles were seen to significantly reduce the pristine compressive strength of the laminates. High-speed video of the gauge section was taken during the test, which showed extensive damage localisation in the wrinkle region. 3D finite element (FE) simulations were carried out in Abaqus/Explicit with continuum damage and cohesive zone models incorporated to predict failure. The FE analyses captured the locations of damage and failure stress levels very well for a range of different wrinkle configurations. At lower wrinkle severities, the analyses predicted a failure mode of compressive fibrefailure, which changed to delamination at higher wrinkle angles. This was confirmed by the tests.

Predictive model for the detection of out-of-plane defects formed during textile-composite manufacture

“…These blades can experience catastrophic failure due to fiber misalignment resulting from unintended out-of-plane features [14]. Furthermore, Hallett et al demonstrated that wrinkles in composite coupons severely reduce the compressive strength by 33%, regardless of wave angle, and observed premature delamination under tensile loading due to straightening of misaligned fibers causing increased inter-laminar shear [15][16][17]. Therefore, it is clear that measures should be taken during the forming process to inhibit this tow buckling.…”

“…By using these known values and the relationship developed in Eq. (16), the ratio of axial moduli can be calculated and Eq. (8) can be used to solve for the compressive modulus.…”

A Bayesian framework for assessing the strength distribution of composite structures with random defects

“…With more available data, which includes a broader class of wrinkle defects [4,5,7,17], this definition could be generalized. Yet, here the choice is sufficient to demonstrate the methodology, and draw some interesting preliminary engineering results.…”

“…While manufacturing large, complex composite components, small process-induced defects can form [1], for example porosity [2], in-plane fibre waviness [3], out-of-plane wrinkles [4,5]. In practice, we observe a distribution of locations, sizes and shapes of these defects, and therefore the direct effect they have on part performance is uncertain.…”

“…The formation of wrinkles not only disrupts the even distribution of fibre and resin, but can significantly increase interply shear stresses triggering failure at significantly reduced loads [5,[15][16][17]. Numerical studies have used wrinkle measurements, to perform parametric studies using finite elements to explore the deterministic effect of variations of wrinkle shape on structural integrity [5,15,18]. These studies include prediction of both, failure initiation [16,17] and mix-mode propagation [5].…”