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Title: The low velocity impact response of sandwich structures
Author: Hassan, Mohamad
ISNI:       0000 0004 2745 247X
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2012
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In this study, the mechanical properties and fracture behaviour of a range of core materials have been investigated in order to elucidate the impact properties of sandwich structures. Initially, the compression properties of the core have been evaluated at quasi-static and impact rates of strain. It has been shown that the plastic collapse strength of the cores is highly rate-sensitive, increasing by up to one hundred percent in passing from quasi-static to dynamic rates of loading. Subsequently, the SENB (Mode I) and shear (Mode II) fracture properties of the polymer foams were evaluated. Mode I tests have shown that the crosslinked PVC foams and the PET foams fail in a brittle manner, however, the linear PVC foams fail in a ductile mode. Here, it has been shown that the Mode II shear toughnesses of the crosslinked PVC foams were up to thirty-five times greater than their corresponding Mode I values. Following this, a series of indentation tests were conducted on polymer-foam sandwich structures and their response was characterised using a Meyer indentation law of the form P = Can. It has been shown that the value of the exponent parameter, n, does not vary significantly with the properties of the core or the skin, typically being close to unity for all tests. The contact stiffness, C, was found to depend on the plastic collapse strength of the foam, the indentor radius and the properties of the skin. It has been shown that a plot of contact stiffness against plastic collapse strength, containing all of the quasi-static and dynamic data, appears to yield a unique curve. Subsequently, the perforation resistances of a range of foam-based sandwich structures were investigated. The influence of the plastic collapse stress of the foam in determining the failure thresholds of the front and rear composite skins has been established. Here, a simple model has been used to successfully predict failure of the top surface composite skin in the sandwich structures. In addition, the force associated with perforating the lightweight core has been shown to be strongly dependent on the shear strength of the polymer foam. The perforation response of sandwich structures based on fully-recyclable materials has also been investigated. The design of the SRPP skin has a significant effect on the energy-absorbing characteristics of the sandwich structure, with the performance of systems based on multiple layer skins greatly exceeding that associated with a monolithic skin. It has been shown that when normalised by the areal density of the panels, those sandwich structures with multiple layer skins out-perform systems with monolithic skins as well as conventional GFRP/aluminium honeycomb sandwich structures.
Supervisor: Cantwell, Wesley Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)