title: The energy-absorbing behaviour of novel aerospace composite structures
Creators: name: Zhou, Jin
Publisher: name: University of Liverpool Repository
Year: 2015

description: The aim of this research is to investigate the structural response of PVC foam based sandwich structures, composite reinforced foam cores and fibre metal laminates (FMLs) subjected to quasi-static and dynamic loading conditions. It also includes the investigation of the mechanical properties and energy-absorbing characteristics of the novel hybrid materials and structures for their potential use in aerospace and a wide range of engineering applications. Firstly，a series of experimental tests have been undertaken to obtain the mechanical properties of all constituent materials and structural behavior of the composite structures, which are used to develop and validate numerical models. The material tests carried out include (1) tension properties of composite laminates and aluminium alloys, (2) compression of PVC foams, carbon and glass fibre rods and tubes, and fibre metal laminates in the edge wise and flat wise, (3) shear and bending of PVC foams, (4) Hopkinson Bar, (5) quasi-static and dynamic crushing of composite reinforced foams, and (6) projectile impact on fibre reinforced laminates, aluminium alloy panels, PVC foam based sandwich panels and fibre metal laminates. The corresponding failure modes are obtained to validate the numerical predictions. In addition, perforation energy and specific energy absorptions of various composite structures investigated are evaluated. Moreover, the rate-sensitivity of FMLs based on glass fibre reinforced epoxy and three aluminium alloys has been investigated though a series of quasi-static and impact perforation tests on multilayer configurations ranging from a simple 2/1 lay-up to a 5/4 stacking sequence. FMLs based on a combination of the composite and metal constituents exhibit a low degree of rate-sensitivity, with the impact perforation energy increasing slightly in passing from quasi-static to dynamic rates of loading. Then, finite element (FE) models are developed using the commercial code Abaqus/Explicit to simulate the impact response of PVC foam sandwich structures. The agreement between the numerical predictions and the experimental results is very good across the range of the structures and configurations investigated. The FE models have produced accurate predictions of the impact load-displacement responses, the perforation energies and the failure characteristics recorded. The analyses are used to estimate the energy absorbed by the skins and the core during the perforation process. The validated FE models are also used to investigate the effect of oblique loading and to study the impact response of sandwich panels on an aqueous environment and subjected to a pressure differential (equivalent to flying at an altitude of 10000 m). The modelling has been further undertaken on the low velocity impact response of the sandwich structures based on graded or composite reinforced PVC foam cores, with reasonably good correlation to the corresponding experimental results. Consequently, a series of finite element analyses have been conducted to investigate the influence of varying foam density, rod diameter, rod length and fibre type on the energy-absorbing characteristics of the reinforced foams. Perforation energies, impact resistance performance and unit cost of the structures have been evaluated. Furthermore, the low velocity impact response of fibre metal laminates has been studied numerically. Here, the composite layer in FMLs is modelled using the modified 3D Hashin’s failure criteria, which are implemented into the main programme through a user-defined subroutine, whilst aluminium alloys are modelled using Johnson-Cook plasticity and the corresponding damage criterion. A large number of simulations have been undertaken to cover FMLs with all stacking sequences and alloy types studied, which are compared with the experimental results in terms of the load-displacement trace and failure modes, with very good correlation. Similar modelling work has been carried out on the aluminium layer and composite layer individually. The energy to perforate the various FMLs is plotted and fitted on a single curve that can be used to predict the perforation energies of other configurations. The dynamic characteristics of the composite structures through a series experimental tests and numerical predictions investigated in this project can be used in the design of lightweight composite structures for energy-absorbing applications.