A Study of the Abrasive Waterjet Machining Process for Carbon Fibre-Reinforced Polymers

Following a comprehensive literature review on the progress of abrasive waterjet (AWJ) machining, an experimental study of the AWJ machining of carbon fibre-reinforced polymers (CFRPs) of various thicknesses was conducted, showing that clean cuts can be achieved with good processing rates. The effect of process parameters on the machined kerf and hole characteristics is amply discussed in the thesis. It was demonstrated that AWJ machining is a good process for thick CFRPs that other processes may be unable to cut. However, material delamination in the form of edge pop-up in the jet entry and push-out at the jet exit caused by the initial pure waterjet impact of an AWJ piercing operation was observed. It was experimentally shown that using a steel mask on top of the workpiece can eliminate pop-up delamination, while push-out delamination at the jet exit can be reduced or eliminated by proper process parameters. However, the mechanisms involved require further investigation. Mathematical models for predicting the major machining performance indicators were developed using dimensional and regression analysis. Experimental verification confirms that the predictive models are reasonable and reliable for assisting in the planning of AWJ machining processes. A computational model is developed and verified experimentally to study the interaction between a pure waterjet and CFRPs. The behaviour of the waterjet is modelled using the smoothed particle hydrodynamics method while the CFRP is modelled by finite element using a continuum damage material model and cohesive zone method. A computational study using the developed model reveals that the material pop-up delamination is initiated due to the material’s elastic response to a rapid release of shock pressure to stagnation pressure and the traverse shear stresses induced by the downward bending of the laminated layers. The pure waterjet impact causes flow divergence and a hydro wedging effect between the material plies, which propagates the delamination. The delamination magnitude is found to increase initially with waterjet pressure up to a threshold after which a change in pressure does not affect the pop-up delamination significantly. The smallest pop-up delamination area occurs on the [0]12 laminate, followed by the [0/45/90/-45/0/45]s and [0/90]3s laminate. It is also found that the push-out loading towards the jet exit and the hydro wedging effect act jointly to result in push-out delamination