Improving Mode II delamination resistance of curved CFRP laminates by a Pre-Hole Z-pinning (PHZ) process |
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Institution: | 1. State IJR Center of Aerospace Design and Additive Manufacturing, Northwestern Polytechnical University, Xi’an 710072, China;2. Shaanxi Engineering Laboratory of Aerospace Structure Design and Application, Northwestern Polytechnical University, Xi’an 710072, China;3. Shandong Institute of Non-Metallic Materials, Jinan 250031, China |
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Abstract: | This paper presents an experimental investigation of the Mode II delamination resistance of curved CFRP laminates reinforced with Z-pins. A Pre-Hole Z-pinning (PHZ) process is developed to reduce the in-plane damage of the Z-pinned laminates. The microstructural observation of the Z-pinned laminate specimens indicates that the PHZ process can effectively decrease the defects including the Z-pin offset angle and the area of eyelet zone. The influences of the volume fraction and diameter of Z-pin on the fracture toughness and the delamination crack growth rate of the specimens under End Notch Flexure (ENF) loading are then determined experimentally. The test results show that Z-pin increases the interlayer stiffness of the laminate. The delamination crack growth rate is reduced with the increase of Z-pin diameter and volume fraction, and a reduction up to 40% is achieved compared with the specimens without pins. Furthermore, the Mode II fracture toughness is significantly improved with the increase of Z-pin volume fraction. When Z-pin volume fraction increases by 1%, the achieved fracture toughness is about 200% higher compared to the unpinned laminates. |
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Keywords: | CFRP Curved laminates Delamination resistance Fracture toughness Mode II Z-pins |
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