Some Fundamental Fracture Mechanisms Applicable to Advanced Filament Reinforced Composites

Abstract

The object of this study is to establish experimentally the critical fracture modes of an epoxy m a t r i x in the vicinity of a break in a high modulus, high strength filament. Three distinct failure modes were observed to occur and the nature of these three modes is explained through an analysis of the s t r e s s state in the matrix. A single filament embedded in an epoxy novolac was used to examine the fracture process.this type of resin a r i s e s f r o m its ability to be modified to varying degrees of crack sensitivity. The advantage of usingThe effects of varying gross strain r a t e were evaluated and the study

The role of matrix cracks and fibre/matrix debonding on the stress transfer between fibre and matrix in a single fibre fragmentation test

“…Three failure modes are encountered; a transverse matrix crack, an inclined conical matrix crack and/or fibre/matrix debond [3,4]. The failure mode depends on the quality of interface [4] as indicated below; (a) If the interface is strong in an elastic matrix, a fibre-break is accompanied by a transverse matrix crack.…”

“…Studies by various authors [3,4,6,7 ] have shown that matrix cracks propagate with applied strain, perpendicular to the fibre fracture. Matrix cracks which form at lower applied strains propagate a shorter distance into the polymer than those which form at high strains, because of a lower stored elastic energy [7].…”

“…Matrix cracks which form at lower applied strains propagate a shorter distance into the polymer than those which form at high strains, because of a lower stored elastic energy [7]. It was also shown that transverse matrix cracks propagate faster than conical matrix cracks which are usually at 45º to the fibre axis [4]. The existence of a matrix crack changes the stress field surrounding the fibrebreak and influences the stress transfer across the interface.…”

“…A matrix crack emanating from a fibre-break can cause premature failure of a high volume fraction composite because the stress concentration on adjacent fibres and matrix leads to the formation a crack of critical dimensions which propagates through the composite. Thus the fibres do not reach their full load carrying potential [4]. Recently Behzadi et al [10] have studied the role of multiple fibre-breaks on the failure of a 0 o fibre composite.…”

Acoustic Emission of 3D Angle Interlock Glass Fibre Composites

“…In addition, in a same composite material, wave attenuation is more significant in cracked than in healthy state, which will complicate the signal processing after few damage modes have developed, especially for the amplitude distribution. Qualifying damage started first in 2D composites and Mehan and Mullin in 1968 [2] managed to identify three basic failure mechanisms: (i) fiber fracture; (ii) matrix cracking; (iii) and fibre/matrix interfacial debonding. The authors reported the application of AE in composites in 1971 [3], discriminating audible types for these three basic damage modes using an AE system.…”