Fatigue of glass reinforced plastics under complex stresses

Griffiths, John R. (1974) Fatigue of glass reinforced plastics under complex stresses. PhD thesis, University of Nottingham.

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Many failure theories have been postulated to predict the behaviour of glass reinforced plastics (GRP) under complex stresses. However, the efficient use of these theories for design purposes is inhibited because the experimental complex stress data needed to verify and discriminate between them is not available. This thesis presents some of the experimental data required.

Uniaxial stress test results from flat laminates, and biaxial stress test results from thin-walled tubes under combined internal pressure and axial force, are presented for various damage states under both static and fatigue loading for a plane isotropic material and an orthotropic material. The data were then used to establish which failure theory provided the most acceptable prediction of the observed behaviour. For ultimate strength, the Norris Failure theory gave adequate predictions, but not for resin cracking. The most generally acceptable predictions, for both materials, were given by those theories whose equations contain a constant which is derived from complex stress data, these being the modified Marin and the strength tensor theories.

For the orthotropic material, three-dimensional representations of the plane stress ultimate strength and damage failure surfaces are presented for both static and fatigue loading. However, even though a considerable number of specimens were tested, only very few failure surface sections were experimentally established.

It was found for both materials that fatigue loading was more damaging than static loading, for both uniaxial and biaxial stress conditions, and that the behaviour of the materials was dependent upon the ratio of the biaxial stresses.

Jointed reinforcement layers severely affect the zero-tension fatigue behaviour of the plane isotropic material, but the effect on the orthotropic material decreases with increasing fatigue life.

The effect of macro-voids on crack initiation should be acknowledged if damage is used as a design criterion.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Owen, M.J.
Keywords: Glass reinforced plastics, Strength tensor theories, Fatigue loading, Static loading, Uniaxial stress, Biaxial stress
Subjects: T Technology > TP Chemical technology
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 13950
Depositing User: EP, Services
Date Deposited: 31 Jan 2014 13:25
Last Modified: 17 Dec 2017 07:22
URI: https://eprints.nottingham.ac.uk/id/eprint/13950

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