Delamination Fracture of Multidirectional Carbon-Fiber/Epoxy Composites under Mode I, Mode II and Mixed-Mode I/II Loading

Abstract

The purpose of the present study was to characterize the delamination fracture of continuous carbon fiber/epoxy multidirectional-laminates under Mode I, Mode II and Mixed-Mode I/II loading conditions. The present study considers the variation of the interlaminar failure energy, G C, with the extent of crack jumping, and ensuing fiber bridging, which arises during the growth of the delamination in the multidirectional-laminates under the various modes of loading. The main type of laminate which was studied was a multidirectional fiber composite prepared from 24 ply lay-ups of (-45°/0°/+45°)2S (+45°/0°/-45°)2S. The initial delamination was located at the +45°/-45° mid-plane of the specimen. It has been found that when the values of the interlaminar fracture energy, G c, are ascertained as a function of the length of the propagating crack, a, then very complex relationships are observed. This was the case for all the different modes of loading, and these observations reflected the complex failure paths which occurred as the delamination propagated through the multidirectional fiber composites. It was, however, possible to define clearly the onset of crack initiation. These results also revealed that the values for the interlaminar fracture energy, G C-(initiation), at crack initiation for the (-45°/O°/+45°)2S (+45°/O°/-45°)2S multidirectional laminates were always significantly greater than that for the corresponding unidirectional (i.e., 0°/0°) laminates.

Interactions between propagating cracks and bioinspired self-healing vascules embedded in glass fibre reinforced composites

“…However, fracture in multiaxial laminates has been shown to be considerably more complex compared to that of unidirectional Mode I or II tests [31].…”

Mixed mode I + II interlaminar fracture of carbon/epoxy laminates

“…However, actual applications involve mixed mode loadings. Therefore, recent focus has been on mixed mode I + II fracture [2][3][4][5][6][7][8][9][10][11][12][13]. The mixed mode bending (MMB) test is considered the most appropriate for characterising interlaminar fracture resistance of unidirectional (UD) specimens over a wide range of mode combinations [2][3][4].…”

“…However, the MMB test is not suitable for experimental compliance calibration and inconsistencies in specimen compliance and toughness values have been reported when using beam models [3]. On the other hand, few studies have been conducted on multidirectional (MD) specimens [2][3][4][5][6][7][8][9][10][11][12][13], which are more representative of actual applications. Moreover, complicated problems exist in testing of MD specimens i.e intraply damage [5][6][7][8][9] and ambiguity in mode partitioning for delamination between differently oriented plies [13][14][15].…”

Experimental Methods of Determining Fracture Toughness of Fiber Reinforced Polymer Composites under Various Loading Conditions

“…Early studies were concentrated on pure Mode I and pure Mode II fracture of unidirectional laminates, but in recent years the attention has diverted on realistic Mixed Mode I + II loadings [26]. However, a few literatures are available on Mixed Mode fracture of multidirectional and woven laminates [26-29,].…”