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Title: Structural response of novel PU structures under quasi-static, impact and blast loading : experimental and numerical analyses
Author: Jamil, A.
ISNI:       0000 0004 7428 478X
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Due to the continuing risks of impacts and explosions and repercussions usually resulting in the loss of life or serious injury, the aim of this research was to develop novel structures that can be applied to scenarios of dynamic loading conditions that would assist in mitigating these risks. Two types of polyurethanes were used in this research, i.e. thermoset polyurethane (TSPU) and thermoplastic polyurethane (TPU). The TSPU allows for easy modification of the microstructure and in this study, hollow glass microspheres (HGMs) were added at different volume percentages to develop a syntactic TSPU material. This led to the development of graded foams, in order to reduce inertial effects in dynamic loading. The work was extended to investigate reinforcing the TSPU and the TPU matrix with carbon fibre reinforced polymer (CFRP) tubes, providing a higher load-bearing capacity under quasi-static loading. Reinforcing the syntactic TSPU resulted in a 47.7 % increase in specific energy absorption (SEA), with the average value reaching 56.28 kJ/kg under quasi-static loading. In addition to this, the specific compressive strength (sc/?) increased by 65 % reaching 55 kPa/(kg/m3 ). Further study was carried out on the TPU, taking advantage of the materials versatility. Although, the SEA values of TPU were lower than the TSPU under quasi-static loading conditions, presenting a low modulus and lower plateau stresses, the CFRP reinforced TPU provided greater energy absorbing characteristics. The benefits of TPU were apparent under low-velocity impact (LVI) and split-Hopkinsons pressure bar (SHPB) tests, where the TPU produced much higher plateau stress responses, which increased with higher impact energies. The competitiveness of TPU was further studied under low-velocity perforation tests, with a comparison against a widely used aluminium alloy 2024-T3 (AA 2034- T3). The results of which showed that TPU is capable of providing not only a progressive response, but also a higher energy absorption capability. With the results obtained from the dynamic tests, TPU was the chosen material to act as the core for a sandwich panel, to be tested under blast loading conditions. AA 2024-T3 skins were used as facings to enhance the blast resistance of the sandwich structures. The experimental results highlighted an improvement in blast resistance following the addition of skins to the TPU core. An increase in the impulse loading resistance was observed, relative to the monolithic 5 mm TPU, with increasing core thicknesses of 5, 10 and 20 mm, where increases of 6.3, 15.4 and 59.5 % were achieved, respectively. Finally, finite element (FE) models were developed using a commercially available software, i.e. ABAQUS and validated with the relevant experimental data. A crushable foam model was developed for the purposes of simulating the response of the TSPU specimens, with good correlation. An elasto-plastic constitutive model was used for the TPU, and strain-rate effects were introduced using the Cowper-Symonds power law. The AA 2024-T3 was modelled using the JohnsonCook constitutive model. These were then used for the dynamic loading conditions, with validations under low-velocity perforation. Numerical simulations of the blast response of the TPU panels were conducted by converting the explosive loading regime applied to the panels, to a simplified pressure pulse loading. Good agreement was obtained between the numerical and experimental results for the mid-point back face deflections. A further study was carried out on the CFRP tube which was modelled using an in-built ABAQUS 2D Hashin criteria and a user defined modified 3D Hashin criteria, with more favourable results being apparent with the use of the user defined model.
Supervisor: Guan, Zhongwei ; Cantwell, Wesley Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral