Water Jet Energy and Mechanical Properties of Test Material.

Water jet machining depends on the state of the water jet when it collides with the material. However, since the microscopic characteristics of a water jet and the mechanism of a water jet colliding with the solid material are not clear yet, they continue to be studied. Although water is sometimes said to be a flexible and weak substance metaphorically, it sometimes has a tremendous breaking force. The breaking force of a water jet is determined by the energy just before it collides with the material. There are many reports about machining principles of water jet(1)∼(13) ;1) breaking by dynamic pressure, 2) breaking by impact load, 3) cavitation processing, 4) wedge effect by pore water pressure, 5) polishing effect, .6) fatigue failure by pulsation load and 7) thermal stress. According to the principle of soft material erosion, if the pressure caused by blocking pressure (corresponding to the water jet's dynamic pressure) is larger than the hardness of the material (tensile stress), the material breaks. In the case of hard material such as metals, even if the blocking pressure is smaller than the material's tensile stress, the material breaks. This is because the impact which is caused by liquid mass and drops when they collide with the material is larger than the tensile stress of the material. In order to clarify the machining power of single, intermittent and continuous water jet and the relation between mechanical properties of the material, such as hardness and tensile stress, and machining, basic research are performed.