Inter-fibre failure of through-thickness reinforced laminates in combined transverse compression and shear load

Abstract

Extensive studies have been reported on the improvement of through-thickness reinforcement to inter-laminar performance of composite laminates; current understanding on the in-plane performance is relatively limited, although it is also concerned in industrial application. The influence of through-thickness reinforcement (Z-pinning) on the inter-fibre failure in compression of unidirectional laminates was investigated. Both unpinned and Zpinned laminates were tested at four different off-axis angles, representing different combinations of transverse compression and in-plane shear stress. It was found that the stiffness of Z-pinned laminates decreased significantly in all off-axis angles. The failure strain and strength were reduced in shear dominated failure modes, while improved in the compression dominated failure modes by the presence of the Z-pins. A further investigation on the angle of failure plane was carried out and a comparison with analytical failure models is presented.

Dynamic inter-fibre failure of unidirectional composite laminates with through-thickness reinforcement

“…The standard Zwick Roell 250 test machine has been used for the quasi-static tests. Detailed test setup may be referred to [17]. The split Hopkinson tension/compression bars were employed for dynamic experiments, both tension and compression bars are shown in Fig.2a&b.…”

“…The microstructures of laminates around Z-pins are then changed generating considerable fibre waviness and deflection [16]. There are resin-rich pockets formed around Z-pins, which reduce the average fibre volume fraction [17]. As a result of these microstructural changes, the in-plane stiffness and strength will inevitably be influenced.…”

“…Compared to research on the fibre dominated failure modes, there is limited work studying the matrix dominated interfibre failure response. Systematic study on the mechanical behaviour of Z-pinned laminates in combined compression and shear load has been conducted by the authors recently [17]. It was shown that the Z-pinned laminate stiffness and the strength of shear dominated failure modes is significantly reduced.…”

“…It was shown that the Z-pinned laminate stiffness and the strength of shear dominated failure modes is significantly reduced. Interestingly, improvements in the compression dominated failure modes were observed with the addition of Z-pins [17].…”

“…The resin matrix and interface between fibre and matrix has been reported to be very sensitive to strain rate [22]. Considering the presence of resin pockets and complicated interaction between laminates and Z-pins discovered recently [17], the inter-laminar failure process under dynamic loading condition may be different from that in quasi-static case.…”