| Resumo : |
The work presented in this thesis focuses on numerical and experimental characterisation of shape distortions of hybrid laminates. It also focuses on the numerical investigation on the e_ect of thickness variation on shape distortions of angled composites. With regards to the study done on the numerical and experimental charac-terisation of shape distortions of hybrid laminates. The results shows that in the case of hybrid unsymmetric laminates, the positional arrangement of the reinforcements in the laminate play a crucial role in determining the nature of shape distortion which would occur. This is because spring-in behaviour is driven towards the weaker reinforcement. Hence depending on the arrangement of the laminates, spring-in or spring-out could occur in the part. Secondly, the weaker reinforcement undergoes compressive stresses while the stronger reinforcements undergoes tensile stresses. This stress distribution gives an indication as to the direction of the shape distortion expected. (spring-in or spring-out). Further-more, the spring-in behaviour was equally accompanied by warpage due to the unsymmetric nature of the laminate. In the case of hybrid symmetric laminates, it was concluded that the positional arrangement of the _bres was not critical. Secondly, the geometric strength of the laminate across the line of symmetry through the thickness is a driving factor of the distortion mechanism. As the inner section of the laminate is geometrically weaker than the outer section, then irrespective of the symmetric hybrid laminate arrangement, there would be spring-in. Lastly, the results shows that free edge e_ect plays a role in the spring-in distribution along a part. With regards to the second study done on the numerical investigation of the e_ect of thickness variation, the results show that varying thickness along the length of a specimen has a signi_cant e_ect on the warpage and spring-in distribution of the specimens. Firstly, the location and nature of the warpage is dependent on the length of region of extra thickness. The warpage is also located close to the point where the region of extra thickness ends. Secondly, an increase in the thickness of this region results in reduced average spring-in distribution. Lastly, the presence of extra layer of thickness caused an initial reduction in the spring-in distribution along the length of the part. After passing the point corresponding to the length of the extra layer, the spring-in distribution resumed to match the distribution of the lower reference specimen. |