Modelling the nonlinear behaviour and fracture process of AS4/PEKK thermoplastic composite under shear loading

Abstract

The accurate determination of non-linear shear behaviour and fracture toughness of continuous carbonfibre/polymer composites remains a considerable challenge. These measurements are often necessary to generate material parameters for advanced computational damage models. In particular, there is a dearth of detailed shear fracture toughness characterisation for thermoplastic composites which are increasingly generating renewed interest within the aerospace and automotive sectors. In this work, carbon fibre (AS4)/ thermoplastic Polyetherketoneketone (PEKK) composite V-notched cross-ply specimens were manufactured to investigate their non-linear response under pure shear loading. Both monotonic and cyclic loading were applied to study the shear modulus degradation and progressive failure. For the first time in the reported literature, we use the essential work of fracture approach to measure the shear fracture toughness of continuous fibre reinforced composite laminates.Excellent geometric similarity in the load-displacement curves was observed for ligament-scaled specimens. The laminate fracture toughness was determined by linear regression, of the specific work of fracture values, to zero ligament thickness, and verified with computational models. The matrix intralaminar fracture toughness (ply level fracture toughness), associated with shear loading was determined by the area method. This paper also details the numerical implementation of a new three-dimensional phenomenological model for carbon fibre thermoplastic composites using the measured values, which is able to accurately represent the full non-linear mechanical 2 response and fracture process. The constitutive model includes a new non-linear shear profile, shear modulus degradation and load reversal. It is combined with a smeared crack model for representing ply-level damage initiation and propagation. The model is shown to accurately predict the constitutive response in terms of permanent plastic strain, degraded modulus as well as load reversal. Predictions are also shown to compare favourably with the evolution of damage leading to final fracture.

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“…The platen was modelled as an analytical rigid surface. The friction coefficients of ply-to-ply and ply-to-metal contact were set to 0.28 and 0.2 respectively, measured in [32]. The computational loading speed was fixed at 1m/s to reduce the CPU time whilst ensuring that the quality of the results was not affected by inertial effects.…”

The role of interfacial properties on the intralaminar and interlaminar damage behaviour of unidirectional composite laminates: Experimental characterization and multiscale modelling

“…In this scenario, strain components are calculated from the symmetric part of the deformation gradient and, therefore, shear deformation parallel or perpendicular to the fibres leads to the same response, which is not the actual behaviour. Shear parallel to the fibres leads to failure by the localization of shear deformation in the matrix (and the shear strength is similar to the matrix shear strength) while shear perpendicular to the fibres induces fibre rotation and a marked strain hardening effect associated with the load taken up by the fibres [9,10].…”

Accelerated fatigue testing of dentin-composite bond with continuously increasing load

“…However, nonlinear inelastic deformation had previously been observed in the vicinity of the loading and supporting points due to the high stress concentration there [32][33][34]. This has the effect of lowering the interfacial stress compared to that predicted by the linear elastic theory.…”