Controlling Failure of Carbon-fibre Reinforced Polymer (CFRP) Structures via Structural Fuses

  • Kazemi, Erfan (Imperial College London)
  • Medeau, Victor (Imperial College London)
  • Greenhalgh, Emile (Imperial College London)
  • Pimenta, Soraia (Imperial College London)
  • Finlayson, James (Rolls-Royce)
  • Pinho, Silvestre (Imperial College London)

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Carbon fibre-reinforced polymers (CFRP) are typically susceptible to brittle failure. The absence of ductile behaviour and the large energy release rate at failure for many structural components can hinder the application of CFRP for critical structural components. As a result, controlling the failure of CFRP structures without implementing overly conservative designs is of great importance in designing CFRPbased composite structures [1]. In this study, we present a methodology for implementing structural fuses implemented using suitable engineered (micro-)crack paths in CFRP parts. By implementing engineered crack paths in structural components, tailored failure mechanisms can be achieved, and the load-displacement response at which failure occurs can also be controlled. By changing various parameters of the micro-cut patterns such as height, length, position and shape, different engineered crack paths can be obtained, which can promote different failure mechanisms, such as delamination and create various complex 3D fracture surfaces. To implement the structural fuses (engineered crack paths), we used an Oxford Lasers 4 Axis micromachining system to engrave micro-cut patterns on thin-ply Skyflex CFRP prepregs, laid up on top of the existing quasi-isotropic laminate, which co-cured in an autoclave [2]. Baseline specimens without engineered crack paths were also manufactured for comparison. Afterwards, we designed and fabricated a test rig to allow for off-centred loading of cantilever-type specimens to characterise the response of the specimens under complex loading. The clamped root includes a thicker section with a ply-drop up to one-third of the panel’s height. We tested specimens on a 50 kN Instron machine at the rate of 5 mm/min. The test results show a successful control of the crack position in the specimens with a structural fuse. Not only we did not observe a reduction in the peak load (due to the presence of the structural fuse) compared to the baseline, but also we observed displacement at peak load greater than in the baseline. Moreover, a more gradual failure (similar or greater than non-engineered specimens) was obtained in some of the implementations of the structural fuse. Detailed results will be presented for different root thicknesses and structural fuse designs at the conference. Evidence of the control of failure position will also be presented, as well as a comparison of load-displacement curves.