Pure (I and II) and mixed-mode (I plus II) fracture characterisation of unidirectional AS4/Low-melt-Polyaryletherketone™ polymer composites

This paper reports an experimental and numerical study on the mixed-mode I+II fracture characterisation of unidirectional AS4/low-melt-Polyaryletherketone (AS4/LMPAEK (TM)) composites. To address the fracture law characterising the material mixed-mode fracture behaviour, a suitable approach is used, simply applying two different loading conditions regarding five mechanical tests and specimen configurations. Scoping to characterise fracture under pure mode I loading and under mixed-mode I+II loading with mode I predominance, the peel test loading condition is used, respectively, for symmetric and asymmetric double-cantilever beam tests (DCB and ADCB). The three-point bending loading condition is used in order to characterise fracture under pure mode II loading by end-notch flexure test (ENF) and mixed-mode I+II with moderate and predominant mode II, respecting symmetric and asymmetric single-leg bending tests (SLB and ASLB). To diminish the influence of crack monitoring ambiguity on the crack length analysis during experiments, data reduction schemes based on the compliance-based beam method (CBBM) were used. Additionally, numerical finite element analyses were conducted in order to validate the data reduction method and the mode partition strategy based on cohesive zone modelling (CZM). Overall, a good agreement between numerical and experimental results was obtained, providing an adequate identification of the energy fracture criterion.