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Title: The structural performance and frequency filtering effects of perforated metal to composite joints
Author: Brambleby, Reuben
ISNI:       0000 0004 6496 0203
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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Glass fibre reinforced polymer (GFRP) composites are becoming increasingly common place in structural load bearing applications. Many of these applications require that loads from the GFRP are transmitted to steel elements. The aim of this thesis was to investigate the performance of joints between steel and vinyl-ester GFRP, comparing the tension strength at quasi-static loading rates with that at impact loading rates. The effect of loading rate on the mode II fracture toughness of the GFRP material was also investigated in order to establish a link between the increase in joint strength under dynamic loads and the increase in mode II fracture toughness under dynamic loads. The effect that typical manufacturing flaws have on the performance of the joints was also assessed. Specimens were manufactured using the vacuum assisted resin transfer moulding process, steel adherends were co-bonded during manufacture. The investigation was undertaken using both physical tests and numerical analyses, physical tests on joints were conducted at both quasi-static and impact loading rates. The effect of loading rate on the mode II fracture toughness of vinyl-ester GFRP was investigated using four point bending end notch flexure tests at a range of loading rates. Digitial image correlation techniques were used to measure crack propagation during the end notch flexure testing. The phononic crystal behaviour of perforated steel adherends was investigated in order to demonstrate that attenuation of in-plane stress waves could be achieved at frequencies relevant to the likely joint applications . Finite element analyses and plots of the in-plane wave dispersion relations were employed for the frequency filtering studies. It was shown that the tension strength of the joints was significantly higher under impact loads than quasi-static loads and that this increase in strength could be attributed to an increase in the mode II fracture toughness of the GFRP at the higher loading rate. The perforations in the steel plates enhanced both the static and impact tension strength of the joints, the joints were found to be relatively insensitive to the types of manufacturing flaw that were assessed. It was demonstrated that finite element surface based cohesive behaviour was able to effectively simulate the debond failures in the physical specimens. The investigation into frequency filtering effects has shown that finite steel plates with resin filled perforations are capable of attenuating in-plane waves at frequencies likely to be generated during a blast event.
Supervisor: Louca, Luke Sponsor: Office of Naval Research ; United States
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral