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Title: Fatigue behaviour and damage mechanisms of PEEK/AS4 composites
Author: Ni, Z.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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A comprehensive study of fatigue behaviour and damage mechanisms of PEEK/AS4 composites has been carried out. The microstructure of PEEK/AS4 composites was studied by the means of optical microscope, scanning electron microscope and image analysis, combined with the techniques of polishing, chemical etching and digestion. Besides the basic characterisation of fibre volume fraction and diameter, a variation of fibre distribution, matrix morphology, fibre/matrix interface and laminate quality was identified. Fatigue life behaviour of PEEK/AS4 composites was established using waisted, coupon and centrally notched specimens. A range of experimental conditions, including stress level, R value, waveform and frequency, was employed. The resultant data were analysed with Normal, log-Normal and Weibull distribution functions. Damage accumulation of PEEK/AS4 composites was monitored by modulus measurement during fatigue testing. It was found that the damage progression is strongly related to the type of laminate. The damage process for (±45)4s lay-up can be divided into three distinctive stages while the damage accumulation for (0/90)4s and QI laminates is small prior to the final fracture. It was evident by sectioning cycled specimens that matrix damage both cracking and delamination is dominant for the (±45)4s lay-up while fibre damage is significant for the laminates containing 0o fibres. Based on extensive observations of fractured specimens under various loading conditions, fracture mechanisms of PEEK/AS4 composites were elucidated. For (±45)4s lay-up, the failure process consists of intralaminar, translaminar or debonding and interlaminar fractures, which are related to the damage accumulated prior to failure. The shear stress is significant for this lay-up. For QI and (0/90)4s laminates, the 0o plies tend to exhibit translaminar fracture while the 90o plies appear to display intralaminar fracture. The failure in the ±45o plies may be either intralaminar or translaminar fractures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available