Abstract
The mechanism of the crack propagation in three dimensional (3D) glass-fiber warp interlock epoxy composites under fatigue loading was investigated via time-lapse micro-computed tomography (µCT) observations. Two different composite samples were manufactured by means of a resin transfer molding (RTM) process under two different constant injection pressure conditions to generate intrayarn and interyarn voids separately. Fatigue loads were applied by blocks of 105 cycles and followed by µCT measurements. Regions of interest for micro tomography scans were selected based on hot spots detected by infrared thermography. After the analysis of the obtained data, it was observed that detectable cracks were generally initiated by debonding in the zone between two adjacent warp yarns and grew along their interface. Then, these cracks propagated along one of the warp yarns aligned in the loading direction while remaining in the middle of the specimen cross-section. The coalescence of the cracks and further propagation to the weakest zones were observed around and after the middle lifetime. Finally, we demonstrated the influence of the void defects at different material scales. I was found that interyarn voids have relatively little influence on the fatigue performance whereas they can, sometimes, attract and deviate cracks in the matrix zone between adjacent yarns. It was also shown that the intrayarn voids are crucial to degenerate the fatigue performance of the yarns at the micro-scale.
Highlights
Composite materials are widely used in different industrial sectors owing to their excellent mechanical properties, such as high strength-to-weight ratios, and lightness.Among many different types of composite reinforcements, warp interlocks are attracting great attention by virtue of their improved delamination resistance [1].Due to their complex microstructure, the understanding of the mechanical behavior of this kind of 3D composite structure is a complex task
The void volume fractions were obtained by burn-off tests for nine specimens per composite plate and confirmed with an optical measurement in the tomography files
The void volume fractions were obtained by burn-off tests for nine specimens per composite plate and confirmed with an optical measurement in the tomogra6 of 14 phy files
Summary
Among many different types of composite reinforcements, warp interlocks are attracting great attention by virtue of their improved delamination resistance [1]. Due to their complex microstructure, the understanding of the mechanical behavior of this kind of 3D composite structure is a complex task. The analysis of fatigue behavior is of great importance for many researchers. The effect of the manufacturing-induced defects is an important factor to analyze the fatigue behavior of the composite materials. One of the major defects induced during the resin transfer molding (RTM) process is the porosity or voids [2,3]
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