Physically based finite element strength prediction in notched woven laminates under quasi-static loading

Abstract

The present paper is concerned with modelling damage and fracture in notched woven fabric composites. Previous experimental work has shown that, under tensile loading, damage at a notch in a variety of glass fibre reinforced plastic (GFRP) and carbon fibre reinforced plastic (CFRP) composites based on woven fabric reinforcement comprises matrix damage and fibre tow fracture along the plane of maximum stress. It is these experimental observations that inform the failure modelling developed here, in which a cohesive zone approach is used within a twodimensional extended finite element method framework. The traction-separation parameters used in the extended finite element method implementation are based on previously reported experimental measurements for the strength and toughness of the woven fabric materials under investigation. The approach is shown to provide predictions of notched strength that are in very good agreement with experimental results from the literature for a range of glass fibre reinforced plastic and carbon fibre reinforced plastic woven fabric systems and also agree well with results obtained from closed form analytical models, which require calibration.

Strength prediction in CFRP woven laminate bolted single-lap joints under quasi-static loading using XFEM

“…Overall agreement with experimental data is very reasonable given the complexity of the problem and it is noteworthy that this modelling approach for tensile failure at stress concentrations has now been shown to work for three rather different test problems (the open-hole [15], the double lap-joint [14] and the single-lap joint, in the present work) using the same material input parameters.…”

“…A damage stabilisation coefficient has been used to facilitate convergence. The same crack initiation and propagation model (and failure parameters) used in open-hole problems [15] and double-lap bolted joints [14] was used to model the net-tension failures found in single-lap bolted joint. This consistency provides a unified model for damage and fracture at tensile stress concentrations within a finite element analysis.…”

“…In a previous paper [14] we showed that the strength of doublelap bolted joints could be modelled reasonably well using a three-dimensional finite element model and a failure criterion based on the formation of a damage zone for which the input parameters (unnotched strength, r 0 and toughness, G c ) were taken from independent experiments. The methodology is based on experimental observations of damage in the vicinity of holes in woven fabric composites, summarised in [14], and was previously demonstrated for coupons containing open holes, using the same material parameters [15]. The current paper is concerned with single-lap joints in which we would expect the net-tension failure mode to be similar to that seen in an open hole and in double-lap bolted joints, with similar local failure mechanisms being active, but obviously the stress field is not only different, but also more complex.…”

Strength prediction in CFRP woven laminate bolted double-lap joints under quasi-static loading using XFEM

“…Overall Fig. 12 exhibits a similar response to that found for the open-hole problem [19]. The maximum failure load from FEA modelling of all lay-up systems is compared with experimentally measured strengths in the next paragraph.…”

“…In GFRP and CFRP woven fabric composites it has been shown that failure of notched samples tested in tension proceeds in a self-similar manner involving matrix cracking, delamination and fibre tow fracture [17,18]. In previous work [19] we showed that the notched strength of these woven fabric composites could be modelled accurately using a finite element model and a failure criterion based on the formation of a damage zone for which the input parameters (unnotched strength and toughness) could be taken from independent experiments. The net-tension failure mode in a bolted joint would be expected to be similar to that seen at an open hole and indeed we have seen that for GFRP woven fabric joints [18] the same local failure mechanisms operate.…”