The development of matrix cracking in (0/8/0) glass fibre reinforced epoxy laminates, where 8 = 45°,54 0, 75° and 90°, has been investigated under quasistatic and cyclic loading. All laminates were fabricated using a wet lay-up process to impregnate the fibres before curing. Uniaxial quasi-static tension tests were carried out on samples of each laminate type. Crack initiation and crack propagation in the 8° ply were studied separately using unnotched samples (tested with both as-cut and polished edges) and notched samples, in which the notch introduced is a drilled hole parallel to the fibres in the 8° ply. The ply stresses at which cracking events occurred were calculated from laminate theory and these stresses are discussed for all four laminate types along with investigations of notch depth effects and crack growth patterns. Material non-linearity was also considered and a method presented to account for material non-linearity in shear. Ply stresses were recalculated to include the effects of non-linearity and the presence of thermal stresses. It was shown that crack propagation is controlled principally by the stress transverse to the fibres and that the stress was independent of notch length. The stress state at crack initiation did not satisfy any of the conventional failure criteria. Uniaxial tension-tension fatigue tests were carried out on samples of each laminate type. Samples were cycled to various maximum load levels and crack propagation from a single notch in each sample was monitored as it grew full width to provide crack growth rate data. Crack growth data were presented on Paris-type plots. The crack growth data were compared to experimental data obtained by other authors for 90° cracking in cross-ply samples and 90° and +45° cracking in quasi-isotropic samples. There was good agreement between the sets of data after accounting for differences in transverse ply thickness. A series of compliance experiments were carried out to obtain the change in compliance with crack length for samples of each laminate type. The experimental compliance changes in (0/90/0) samples were compared to theoretical, calculated compliance changes.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:265648 |
| Date | January 1998 |
| Creators | Crocker, Louise |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/804468/ |
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