Size effect on compressive strength of T300/924C carbon fibre-epoxy laminates

Abstract

The eVect of specimen gauge section ( lengthÖ width) was investigated on the compressive behaviour of a T300/924C [45/ 45/0/90] 3 s carbon bre-epoxy laminate. A modi ed Imperial College compression test xture was used together with an antibuckling device to test 3 mm thick specimens with a 30Ö 30, 50Ö 50, 70Ö 70, and 90Ö 90 mm gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post-failure examination suggests that 0° bre microbuckling is the critical damage mechanism that causes nal failure. This is a matrix dominated failure mode and its triggering depends very much on initial bre waviness. It is suggested that manufacturing plays a signi cant role in determining the compressive strength and may be more important as the section thickness of the composite increases. Additionally, compressive tests on specimens with an open hole are performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of bre microbuckling and delamination initiates at the edge of the hole at~80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3 mm (depending on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of compressive unnotched strength and in plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.PRC/1855

Measuring the notched compressive strength of composite laminates: Specimen size effects

“…The increase in notched tensile and compressive strength with decreasing notch size has been observed previously in several studies [9,10]. However, very few scaled tests have been reported, and the effects of thickness and ply blocking have received less attention.…”

“…Although there is a significant, but inconclusive, amount of evidence that there is a size effect in composites under tensile and flexural load [2][3][4][5][6][7], scaling of composite strength is not well documented or understood. Most of the research to date has looked at the size effect on the unnotched rather than notched strength under unidirectional tensile [4][5][6][7] or compressive loading [8][9][10]. The results show the importance of ply thickness and the interactions between delamination and matrix cracking with the fibre direction failure modes.…”

“…However, very few scaled tests have been reported, and the effects of thickness and ply blocking have received less attention. The results of plates with circular holes [9] have shown that the decrease in strength with hole size can be explained using a fracture mechanics analysis [11]. This approach seems to work because the compressive failure mechanism is an unstable micro-buckle ("kink-band" failure) of the 0° fibres in a fairly sharp crack-like manner, which does not happen in tension where several blunting mechanisms are present.…”

Scale Effect on Impact Performance of Unidirectional Glass Fiber Reinforced Epoxy Composite Laminates

“…In recent years, many experimental studies have been conducted on the mechanical scaling behavior of composites. Most studies have used two main approaches for scaling composites [9,10,11,12,13,14]. The first is ply-level scaling, which involves simply increasing the number of layers for each angular ply orientation.…”

Determination of the longitudinal compressive strength of a CFRP ply through a tensile test on a laminate

“…This experimental device necessitates the use of tabbed specimens and of complex and heavy xtures. Alternatively, the EN2850 AECMA standard 2 [11] recommends to transmit the compressive force into the specimen through endloading [16], thus avoiding the use of additional tabs. This method is currently the most commonly used in aeronautical industries and corresponds to the ASTM D695-15 standard [17].…”