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Impact damage evaluation in woven composites using acoustic and thermoelastic techniques

The aim of this work is to investigate the potential offered by a natural fibre composite for applications that require a superior resistance to impact and other forms of dynamic loading. In order to achieve this, the post-impact behaviour of a natural fibre woven composite (jute/polyester) has been compared to that offered by two glass fibre woven composites (E-glass mat/polyester and E-glass fabric/polyester). A number of different monitoring techniques (including acoustic emission and thermoelastic stress analysis) have been used to investigate damage in these materials. This information has been compared to damage patterns identified using classical techniques. The post-impact residual properties of the three composites have been evaluated through a series of tensile and fatigue tests. The tensile tests were monitored by the acoustic emission, whilst the fatigue tests were monitored by the thermoelastic stress analysis technique. In order to evaluate the in-service behaviour of the impact-damaged composites, a series of tests based on static indentation procedures were performed. Here, acoustic emission activity was monitored during discontinuous and continuous indentation tests and flexural tests. The damage introduced by impact loading and post-impact indentation was then elucidated using optical microscopy techniques.
A methodology, involving the combined use of different real-time monitoring techniques and tests for evaluating the residual properties of the composites, has been shown to be useful for characterising the global post-impact behaviour of these materials. Work is still required to develop a real-time monitoring technique for assessing the post-impact characteristics of jute reinforced composites. This procedure may involve an evaluation of the structural properties of other natural fibres (e.g., hemp), which are also likely to be employed in the manufacture of composite structures for the aforementioned applications.

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Impact damage evaluation on woven composites using acoustic and thermoelastic techniques 19 CHAPTER 1 INTRODUCTION 1.1 The use of composites for engineering applications Composite materials enable the designer to select the optimum combination of fibre reinforcement and resin, to develop a material especially designed for a particular application. In practice, many of the raw materials required to manufacture a high-tech composite are relatively expensive. Therefore, their use as a structural material to replace metals is limited to applications where it is necessary to combine high strength and low weight, for example in the aerospace and advanced transportation industries (i.e., racing cars, high speed trains, etc.: Fig.1). Here, composites offer superior specific strength and stiffness characteristics, reduced maintenance costs, due to the absence of corrosion problems, a simplified design and a lower energy consumption. Fig.1 The Italian high-speed train ETR500B with its characteristic composite front cab

Tesi di Dottorato

Dipartimento: Engineering

Autore: Carlo Santulli Contatta »

Composta da 257 pagine.

 

Questa tesi ha raggiunto 510 click dal 20/03/2004.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.