Enhancing damage tolerance in carbon/epoxy composites via short-fiber reinforcement

Short Fibre Reinforced Polymer Composites (SFRPCs) are gaining significant interest within industry due to their remarkable properties. Continuous Fibre Reinforced Composites (CFRCs) with high specific stiffness and strength are increasingly applied in automotive and aerospace applications. The adoption of composite materials is increasing as the desire to reduce component mass for environmental and economic reasons. On the other hand, the manufacture of complex components with CFRCs is hampered due to wrinkles or other defects due to the continuous reinforcement preventing in-plane deformation during layup [1]. Meanwhile, the discontinuous nature of SFRPCs allow greater conformability to complex curvatures and stamp forming processes, leading to potential applications in high rate of manufacture applications.

Short fibres also permit the use of recycled reinforcement. Not only does this provide a potential improvement in sustainability, it opens the door to a less expensive feedstock material during a time where carbon fibre demand outstrips supply [2]. With the EU waste directives restricting the quantity of composite waste allowed to go to landfill [3], an effective reuse path is essential.

While CFRCs excel in strength and stiffness, SFRPCs can offer a distinct advantage in notch insensitivity and resilience to stress concentration [4, 5]. The discontinuous nature allow s greater energy dissipation through interactions between fibre and matrix based damage [6], potentially leading to improvements in toughness and damage tolerance. However, the manufacture of discontinuous material demonstrates significant challenges. Discontinuous material size and distribution methods can lead to defects and variability in in-plane strength.

The overarching objective of this research to enable the use of SFRPCs within high performance structures through improvements in manufacture and subsequently explore micromechanical damage mitigation mechanisms present in SFRPCs.

The first objective is to investigate and implement potential manufacturing processes to improve the consistency and uniformity of the discontinuous material and produce parts with minimal defects. A further manufacturing aim is to create a discontinuous reinforcement that can be handled and manipulated similar to conventional dry reinforcement. To satisfy these objectives bindered discontinuous carbon fibre preforms will be manufactured.

The effect of material parameters such as fibre length and dispersion techniques have on defects and internal mesostructured will be investigated. The aspect ratio and the thickness of the chopped carbon fibre platelets will be varied with the effect on the preforming distribution and resulting mechanical performance analysed.

The potential fracture toughness and damage tolerance effects will be compared against continuous fibre composites. This will also combine high resolution image based strain detection with thermography and X-ray Computerised Tomography. This is to provide greater insight into the progressive failure seen within discontinuous reinforcement and where it could be best applied in the future.

1. M. H. Hassan, A. Othman, S. Kamaruddin, The International Journal of Advanced Manufacturing Technology 91 (2017) 4081-4094
2. J. Zhang, V. S. Chevali, H. Wang, C.-H. Wang, Composites Part B: Engineering 193 (2020) 108053.
3. Directive 2008/98/ec of the European parliament and of the council of 19 November 2008 on waste and repealing certain directives.
4. D. E. Sommer, S. G. Kravchenko, W. B. Avery, R. B. Pipes, Composites Part A: Applied Science and Manufacturing 162 (2022) 107133.
5. C. Qian, L. Harper, T. Turner, N. Warrior, Composites Part A: Applied Science and Manufacturing 42 (2011) 293-302.
6. S. G. Kravchenko, C. Volle, O. G. Kravchenko, Composites Part A: Applied Science and Manufacturing 149 (2021) 106524.