Independent thesis Advanced level (degree of Master (Two Years)), 40 credits / 60 HE credits
A new method to fabricate cross-ply laminates by RTM was developed. Glass-fibre roving was wound on a steel sheet using a turning machine to produce 90 degree layers and Lyvertex 21130 "woven" roving was used as 0 degree layers. By using the steel sheet as a core, two laminates could be produced for each injection and fibres were kept straight and parallel. The fibre volume fraction in the 90 degree layer was found to be 52%.
Cross-ply laminates with one vinylester and two polyester matrices were tested for transverse cracking in the 90 degree layer. A tougher matrix was found to yield a higher crack initiation mechanical strain and total strain.
In order to determine the total strain at crack initiation, residual chemical and thermal strains were measured on unbalanced [01/904]t laminates. Added residual strains in the order of 0.2% were recorde for polyester 42-10 and vinylester 80-84 matrices. Polyester 75-00 matrix laminates had added residual strains reaching 1.5% due to a Tg below room temperature.
Cross-ply laminates with 42-10 and 80-84 matrices were found to have a "knee" in the stress-strain realtionship at the crack initiation strain.
42-10 and 80-84 matrix laminates had evenly distributed transverse cracks with a closest spacing equaling the 90 degree layer thickness of 1.0 mm. Few cracks had extended through the whole width which implies that the fibres were not perfectly parallel. In these two laminates it was possible to relate visible cracks to cracks recorded by acoustic emission.