Impact study of composite scarf joints with interspersed particles

In this Final Year Project (FYP), the impact properties of scarf repair were enhanced with the application of Core Shell Polymer (CSP) particles at a density of 30g/m2 to the interply interfaces of the central repair patch. The application of CSP particles is expected to improve impact properties through 2 mechanisms; 1) improving elastic energy absorption which has the greatest potential of reducing extent of damage in a laminate and 2) reduction or elimination of stiffness mismatch faced in a typical scarf repair. In the first phase of the project, the ability of CSP particles to enhance elastic energy absorption was looked at. Glass Fiber Reinforced Polymer (GFRP) samples, both reference and CSP-modified, were impact tested with energy of 17J and 12.5J. A reduction in elastic energy absorption in the modified samples at 17J coupled with an increase in elastic energy absorption at a lower energy of 12.5J, served to suggest that the CSP particles have an elastic limit beyond which the effectiveness of the particles to improve elastic energy absorption is reduced. In the second phase of the FYP, the modeling of reduction in stiffness mismatch was performed. In order to do so, 4-point bending tests were first carried out to measure the stiffness values of GFRP and Carbon Fiber Reinforced Polymer (CFRP) and quantify the drop in stiffness due to incorporation of CSP particles to the interply interfaces. It was found that CFRP has higher stiffness than GFRP. Accordingly, CFRP was used as the repair patch to a parent GFRP structure. This stiffness mismatch was reduced with the incorporation of CSP particles to the CFRP repair patch. Fabrication and impact testing were then carried out for the hybrid samples, both reference and CSP-modified. However, the use of a stiffer CFRP leads to a stronger scarf repair. This altered the impact response of the reference samples from super-critical to sub-critical. In the sub-critical range, CSP particles were observed to have limited effects on the impact properties of the scarf repair.Bachelor of Engineering (Aerospace Engineering