Fracture behaviour and damage growth in knitted carbon fibre fabric reinforced polyethylmethacrylate

Abstract

The static fracture and the damage zone growth in weft knitted carbon fibre (CF) fabric reinforced thermoplastic polyethylmethacrylate have been studied on tensile loaded, single edge notched specimens at room temperature. It was established that the fracture toughness increases with increasing number of reinforcing knit plies incorporated. This was attributed to a more homogeneous distribution of the reinforcing knit fabrics in the matrix ; this can also be considered as a reduction of the apparent mesh size of the knits. The size of the damage zone was estimated from the location of the acoustic emission (AE) events and from infrared thermography ( IT). The AE technique indicated a much bigger damage zone than IT for single layer weft knitted fabric reinforced composites. However, the damage zone size and shape derived from AE and IT agreed very well with one another for composites with multiple CF knit reinforcement, for which the diameter of the circular damage zone was found to be 15-20 mm. This indicates that the width of specimens must be greater than ∼20 mm to achieve accurate mechanical data.