Causes of delamination caused by waterjet cutting of carbon fiber sheet

Causes of delamination caused by waterjet cutting of carbon fiber sheet

Waterjet is an emerging special processing method. It has strong process adaptability, high cutting efficiency, and no environmental pollution. Because it is cold processing and does not produce residual stress, it has been applied in many industries. Because the structure and performance of various materials are different, the cutting mechanism is also different, and the current research on the processing mechanism of many materials is not mature, which restricts the application of waterjet processing. In this paper, combined with the experiment of cutting carbon fiber composite materials, the cutting mechanism of waterjet cutting carbon fiber composite materials and the causes of delamination failure are analyzed.

When waterjet processing hard and brittle materials, the most common processing method is the impact of abrasive flow on the material. In this processing state, the abrasive particles are accelerated and hit the processed material at a very high speed and cracks are generated on the surface. Then the high pressure water promotes the extension of the cracks and finally leads to the destruction of the material to complete the removal of the material. When waterjet processing carbon fiber composite materials, when the cracks are formed and extended, since the strength of the junctions of each layer of the composite material is lower than other areas, the cracks will stop extending in the free direction and turn when they reach the vicinity of the boundaries of each layer. The fragile part in the direction of the boundary extends. That is to say, the boundary of each layer will become the main area where the crack releases energy, and it will form an obvious destructive effect here.

When the material to be processed cracks, the water jet sprayed by the machine tool has a great pressure. When it enters the crack and has no place to release, it will complete the expansion of the formed crack and complete the auxiliary material damage. This effect is the water wedge effect. In waterjet processing of carbon fiber composite materials, since the strength of each layer of the composite material is relatively small, the effect of water wedge on the crack extension of the fragile part at the boundary of each layer is also more significant.

Waterjet impact on carbon fiber composite materials generally destroys the layered structure of the material and causes failure, which is specifically manifested as the delamination of the composite material. From the observations in the experiment, it is found that under normal cutting conditions, the cutting of carbon fiber materials does not produce delamination. This shows that under normal circumstances, the grinding effect of abrasives on processed materials is the main way of material destruction and removal. When the abrasive jet directly impinges on the carbon fiber composite material or the maximum processing depth cannot cut the material through, the energy of the jet will be released from nowhere, which will damage the boundary of each layer of material and cause delamination failure. The material destruction and removal method at this time is the synergy of the impact of the abrasive water jet and the water wedge.

Since the delamination of carbon fiber composite materials during processing is undesirable during processing, the destruction and removal of materials during processing should be led by the grinding mechanism of abrasive water jets to avoid abrasive jets on the materials. Impact and water wedge effect. In order to avoid the frontal impact of the abrasive water jet on the material, it is generally avoided by selecting a large length of the knife edge or using the grinding action of the abrasive under low pressure to drill the composite material first and start cutting from the hole. If the maximum cutting depth cannot cut through the delamination caused by the material, it is necessary to predict the cutting depth in advance and compare it with the material thickness to solve it.