Abstract
The effect of circular notch has been evaluated for three different architectures of three-dimensional (3D) carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) through open-hole quasi-static tension and double-lap bearing strength tests in the off-axis (45°) direction. Damage characterisation is monitored using Digital Image correlation (DIC) for open-hole testing and X-ray Computed Tomography (CT) for double-lap bearing strength test. The off-axis notched 3D woven composites exhibits minor reduction (less than 10 %) of the notched strength compared to the un-notched strength. DIC strain contour clearly show stress/strain localisation regions around the hole periphery and stress/strain redistribution away from the whole due to the z-binder existence, especially for ORT architecture. Up to 50 % bearing strain, no significant difference in the bearing stress/bearing strain response is observed. However when ORT architecture was loaded up to failure, it demonstrates higher strain to failure (~140 %) followed by AI (~105 %) and lastly LTL (~85 %). X-ray CT scans reveal the effect of the z-binder architecture on damage evolution and delamination resistance. The study suggests that off-axis loaded 3D woven composites, especially ORT architecture, has a great potential of overcoming the current challenges facing composite laminates when used in composite joints’ applications.
Highlights
Composite laminates are characterised by high stiffness and strength to weight ratio, in real life application where joining structures made of composites laminates is essential, the ultimate strength and stiffness of the structure is determined by the joint strength and joining efficiency [1]
All tests were performed in a controlled environment where the temperature was 21 °C and the relative humidity (RH) was 45 %
Once damage accumulates after the Bknee^ point, there is a slight reduction in the slope of the ORT notched result compared to the un-notched ones
Summary
Composite laminates are characterised by high stiffness and strength to weight ratio (high specific stiffness and high specific strength), in real life application where joining structures made of composites laminates is essential, the ultimate strength and stiffness of the structure is determined by the joint strength and joining efficiency [1]. There are two different joining techniques for composite laminates, namely bonded joints and mechanically fastened joints; which are mainly achieved by bolting. Sometimes both techniques are combined to form bonded-bolted joints [2]. – Material ductility/yielding Composite materials are significantly less ductile than the types of metals used for similar structural. The stress, usually, cannot be distributed around a stress concentration region such as a notch or a hole, which is common in joints. The ultimate strength and stiffness of the metallic materials are not significantly affected by notches or drilling holes. Composite laminates exhibit approximately 50 % reduction in strength as compared to their un-notched strength. Composite laminates exhibit approximately 50 % reduction in strength as compared to their un-notched strength. – High strain to failure and energy absorption
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