A fracture mechanics approach to static and fatigue failure in glass reinforced plastics

Cann, Robert James (1977) A fracture mechanics approach to static and fatigue failure in glass reinforced plastics. PhD thesis, University of Nottingham.

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Abstract

The aim of this project was to examine the application of fracture mechanics to static and fatigue failure in GRP. The performance of two materials commonly used in-shipbuilding was compared, and the stress intensity factor approach was chosen as being most useful in the design of GRP structures.

The literature survey showed that the conditions for its valid application to fracture toughness measurement were not established. Fracture toughness tests were carried out to examine the effect on critical stress intensity factor, Kc of prolonged water immersion, specimen geometry and size. For the latter, a machine was designed and developed to apply static and pulsating loads to sheets of GRP up to one metre square. The material reinforced with woven roving fabric (WRF/PR) had a much higher fracture toughness than the material reinforced with chopped strand mat (CSM/PR), and was found to be virtually notch insensitive, implying that the Kc approach is not applicable. Large specimens of CSM/PR failed at very low stresses compared with small specimens. This material is notch sensitive and some of the conditions for the valid fracture toughness testing of notch sensitive GRP were established. The critical stress intensity factor of both materials was little affected by water immersion.

Fatigue crack propagation tests were carried out to establish crack growth laws and examine the effect on growth rate of prolonged water immersion. Growth laws were found that were applicable to dry and wet CSM/PR, but water immersion greatly increased the rate of fatigue crack growth. The resistance to fatigue cracking of WRF/PR is superior to CSM/PR, because crack growth is blocked by rovings running normal to the crack, so that a growth law could not be found. Prolonged water immersion was found to destroy this blocking mechanism greatly reducing the resistance to fatigue crack growth, and a growth law could be determined. The material is still superior to CSM/PR in the wet condition.

The finite element method was used to determine the stress intensity factors of fracture toughness specimens, and compliance-crack length relations in fatigue crack propagation specimens.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Owen, M.J.
Keywords: Glass-reinforced plastics, fatigue, testing
Subjects: T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 13084
Depositing User: EP, Services
Date Deposited: 08 Feb 2013 10:44
Last Modified: 17 Sep 2016 07:58
URI: http://eprints.nottingham.ac.uk/id/eprint/13084

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