Interlaminar fracture studies in Portugal: past, present and future

Abstract

A B S T R A C T This paper reviews the state-of-the-art in interlaminar fracture testing of composite materials, with particular emphasis on the work performed in Portugal over the last 15 years. Early work, carried out within the ESIS Polymer and Composite Technical Committee, was concerned with improving test methods on unidirectional [0 • ] n specimens. The focus was on the mode I double cantilever beam (DCB) test and on mode II end-notched flexure (ENF) and end loaded split (ELS) tests. In spite of some remaining controversy on mode II testing, the main issue nowadays is fracture toughness measurement on multidirectional specimens. Remaining difficulties are discussed in the light of the most recent work. Guidelines for ongoing and future research are also presented.

Study of the Mode I and Mode II interlaminar behaviour of a carbon fabric reinforced thermoplastic

“…The 5-harness satin weave ( Figure 1) is a fabric with high strength in both directions and excellent bending properties. The carbon PPS plates were hot pressed at 10 bars and 310 °C; only one stacking sequence was used for this study, namely a [(0º,90º) 4 , (90º,0º) 4 ] s where (0º,90º) represents one layer of fabric. By using this stacking sequence, the crack can propagate between two layers oriented in the warp or 0° direction.…”

“…As such, there are already a lot of studies dedicated to the interlaminar behaviour of fibre reinforced polymers, as illustrated in various literature reviews [1,2,3,4]. In most cases, unidirectional reinforcement is considered, quite often in combination with epoxymatrices.…”

Effect of volume fiber and crack length on interlaminar fracture properties of glass fiber reinforced polyester composites (GF/PO composites)

“…Values of G Ic determined from Mode Ι interlaminar tests were summarized in Table. Values of G Ic for GF/PO composites were significantly higher than that for the pure polyster resin, which were explained by the additional force required to fracture fiber bridging in GF/PO composites, also described by Moura and Morais, et al [13,14]. In contrast, CF/EP composite was produced using individually stacked plies of unidirectional CF preimpregnated with the epoxy resin and had little interlaminar fiber bridging.…”

“…To demonstrate the occurrence of fiber bridging, comparative DCB tests were carried out using a hybrid composite, in which two plies of unidirectional continuous fiber were incorporated into the central ply to displace the corresponding plies of GF/PO composites, also employed by Morais, et al [14]. The total number of glass fiber plies for the hybrid composite was the same as that for GF/PO composites (V f is 30%).The central two unidirectional plies can significantly reduce interlaminar fiber penetration and eliminate fiber bridging during crack propagation.…”

Generation of R-Curve from 4ENF Specimens: An Experimental Study

“…The highly anisotropic nature of laminated composite structures causes a mismatch in mechanical properties between individual lamina within the laminate, which in turn can produce interlaminar crack initiation and propagation. For example, low velocity impact can generate relatively large delamination, which is highly detrimental to compressive load because of localized buckling phenomena [1]. Testing of thin skin stiffened panels designed for aircraft fuselage applications has shown that bond failure at the tip of the frame flange is a very important failure mode.…”