Joseph Mohan

Effect of an Atmospheric Pressure Plasma Treatment on the Mode I Fracture Toughness of a Co-cured Composite Joint

In this study, the surface of a composite prepreg was treated using an atmospheric pressure plasma in an attempt to improve the fracture toughness of a co-cured joint system. Three gas mixtures were investigated; helium, helium/nitrogen, and helium/oxygen. The processing parameters of the system were varied to obtain the maximum increase in surface energy of the prepreg. A He/O2 plasma was found to be the most efficient treatment, giving the largest increase in surface energy in the shortest time. Co-cured joints were then fabricated using prepreg that had been treated with various plasmas. A modest 15–18% increase in the Mode I fracture toughness was achieved. However, the locus of failure remained interfacial. It was also observed that a He/O2 plasma treatment could be detrimental to joint toughness for long treatment times.

An Experimental and Numerical Investigation of the Mixed- mode Fracture Toughness and Lap Shear Strength of Aerospace Grade Composite Joints

In the present study, the mixed-mode fracture toughness of an adhesively bonded composite joint system was examined using a variety of linear elastic fracture mechanics (LEFM) based tests. These tests include the mode I double cantilever beam (DCB), mixed-mode asymmetrical DCB (ADCB) and mode II end load split (ELS) test. The joint system was also evaluated using the wide area lap shear (WALS) test that is often employed by the aerospace industry. While lap shear type tests are relatively simple to perform and post-process compared to their LEFM counterparts, the results can often be misleading and are greatly dependent on the overlap length, thickness of substrate and type of fillet. The experimental tests were also simulated using OpenFOAM, a finite volume based software package. Through this combined experimental-numerical approach, a greater understanding of the influence of the peel ply surface treatment and scrim cloth on the behaviour of the WALS test was achieved.