Fracture and fatigue study of unidirectional glass/epoxy laminate under different mode of loading

Abstract

A B S T R A C TInterlaminar fracture is the dominant failure mechanism in most advanced composite materials. The delaminating behaviour of materials is quantified in terms of the strain energy release rate G. In this paper, the experimental measurements of the fatigue delaminating growth for some combinations of energy release rate mode ratio have been carried out on unidirectional glass/epoxy laminates. On this base the constants in the Paris equation have been determined for each G II /G T considered modal ratio. The fatigue threshold strain energy release rate G Tth , below which delaminating doesn't occur, were measured. Three type specimens were tested, namely: double cantilever beam (DCB), end-loaded split (ELS) and mixed-mode bending (MMB) under mode I, mode II and mixed-mode (I + II) loading, respectively. Scanning electron microscopy techniques were used to identify the fatigue delamination growth mechanisms and to define the differences between the various modes of fracture.Keywords composite; fatigue; fatigue threshold strain energy release rate; mixed mode fracture; strain energy release rate; unidirectional glass/epoxy laminates. I N T R O D U C T I O NA considerable amount of current research is devoted to the study of failure mechanisms in laminated composite materials. The interlaminar damage is the most common one and can cause major reductions in the stiffness or strength of a structure. Delaminating grow between laminates as a consequence of the presence of unidirectional fibres above and below a ply interface. 1,2 It results generally from different loading arrangements labelled 'modes'. Mode I is tensile (opening) loading, mode II (in-plane) shear loading, and mixed-mode (I + II) conditions are also of interest. 3 Several test configurations have been proposed for studying delaminating fracture behaviour under various kinds of loading as summarized in a recent study. 4 Double cantilever beam (DCB) for mode I, endloaded split (ELS) for mode II and mixed-mode bending (MMB) for mixed mode (I + II) specimens are used in these experiments. Several studies have shown that the MMB specimen is the unique test which presents some advantages, including the possibility of working a wide range of mixed mode ratios. 4-6 Correspondence: M. Kenane.The total fracture strain energy release rate, G TC (G TC = G IC + G IIC ) describe the resistance of a material against delaminating growth under the applied static load. Both can be determined for different mode ratios considered. In previous study, 7 these experimental results have permitted us to propose a semi-empirical criterion through the plotting of the G TC versus the GII GT modal ratio. We note that this semi-empirical criterion was verified for several materials 8,9 and it was found to accurately predict the critical delamination length.In order to study the mechanics of delaminating 10-17 growth under cyclic loading, constant amplitude cyclic loading was conducted to establish the delamination growth rate da/dN as function of the total strain energy r...

Methods for the prediction of fatigue delamination growth in composites and adhesive bonds – A critical review

“…Schön proposed the use of the threshold growth value and the onset of unstable delamination growth. According to Schön the threshold SERR value is independent of mode-mix and R. Note this is not in agreement with other results published in literature [2,29,85,152]. Schön further contends that the critical delamination growth rate (but not the attendant SERR value) is independent of mode-mix and R, which would seem to be merely a question of definition.…”

Experimental study of a woven fiberglass composite delamination under impact shock

“…interlaminar rupture that occurs in the interface between two plies of a laminate. This type of failure in fact studied by (Pereira & Morais, 2004;Kenane at al., 2010) for the case of epoxy matrix composites.…”

Antiplane–inplane shear mode delamination between two second-order shear deformable composite plates

“…Utilizing (30) and taking it back into (29) results in a system of ODEs. The latter should be manipulated so that each equation contains the second derivative of only one displacement parameter.…”

“…[14,15]) and changes the dynamic properties significantly, and therefore has a major influence on the lifetime of the structure. The delamination behavior of composite materials is characterized by different specimens for mode-I [16][17][18][19][20][21][22][23], mode-II [24][25][26], mixed-mode I/II [27][28][29][30][31][32][33][34][35][36][37], mode-III [38][39][40][41][42][43][44][45][46][47][48], mixed-mode I/III [49] mixed-mode II/III [42,[50][51][52][53][54][55][56][57][58][59] and mixed-mode I/II/III [60][61]…”