The performance of thermoplastic and thermoset composites subjected to impact loading
Creators: name: Liu, Jun
Publisher: name: Imperial College London
Year: 2020

description: Carbon Fibre Reinforced Polymer (CFRP) composites play an increasingly important role in the aerospace industry where CFRPs are extensively employed in the primary structures of aircrafts. These composite materials have demonstrated relatively high stiffness-to-weight and strength-to-weight ratios, as well as good fatigue and corrosion resistance, compared with the conventional metallic materials. However, these composite primary structures of aircrafts face great challenges when encounter with an impact with foreign bodies. Due to the anisotropic property and interaction between fibres and matrix, the failure of composite structure is generally a complex process, which requires a further investigation and better understanding. Bearing the above in mind, the aim of this project is to investigate the modes and extent of damage inflicted on the unidirectional carbon fibre and woven carbon fibre reinforced thermoplastic and thermoset composites, under various impact loadings. A series of low-velocity (drop-weight) and high-velocity (gas-gun) experiments were firstly performed, using rigid impactors at different energy levels, on the unidirectional Carbon Fibre Reinforced Poly (ether-ether-ketone) (CF/PEEK) and toughened Epoxy (CF/Epoxy) cross-ply composites. Particularly, for the high-velocity experiments, the three-dimensional (3D) Digital Image Correlation (DIC), coupling with high-speed cameras, is employed to measure the out-of-plane displacement from the rear face of the composite specimens during the impact events. The ultrasonic C-scan results are utilised for assessing damage in the composites and reflecting the strain rate effects on the impact response of the composites. A finite element model, based on the continuum shell elements, is developed to simulate both the low- and high-velocity impact test results. The modelling results are quantitatively validated against the experimentally obtained impact behaviour of the composites, such as the loading response, interlaminar and intralaminar damage etc. The experimental validation enables the model to be used with confidence in the future industrial applications. To better understand the failure mechanisms of woven-fabric composites, woven-fabric CF/PEEK and CF/Epoxy specimens are employed to study the behaviour of woven composite laminates subjected to impact loading by soft gelatine and hard metallic projectiles to represent the impact of foreign object, such as a small bird, hail-stone or runway debris. For this investigation, both the 3D DIC measurements and C-scan assessments are employed in the experiments performed on the CF/PEEK and CF/Epoxy specimens. A FE model is developed, based on Smoothed Particle Hydrodynamics (SPH) method, Abaqus built-in Hashin’s criteria and bilinear cohesive law, to predict the viscoelastic-plastic fluid behaviour of the gelatine project and the behaviour of composite specimens during the impact events. Good agreement is shown between the predictions from using the FE model and the experimental results. The FE model has produced accurate predictions of the deformation of the gelatine projectiles, the major strain and out-of-plane displacement of the composites, contact pressure and the damage degrees resulting in the rear-face of the composite specimens. The dynamic characteristics of the thermoplastic and thermoset composite laminates, investigated in the project through a series of experimental tests and numerical predictions, can assist the design of lightweight composite structures for energy-absorbing applications.