Measurement of strain distribution and material flow in bulk deformation by the screw method

A new method for the observation of material flow and measurement of plastic strain in deformed parts is proposed. First, a specimen with machined threaded holes containing threaded bolts was deformed and then sectioned along the mid-section of the bolts. The deformed screw interfaces at the section were observed and measured by a microscope. The plastic strain on the screw interfaces was calculated by the change of screw pitch. The experimental results and numerical simulation show good agreement. In contrast to other physical modeling methods, this method utilizes the actual metal for sensor and workpiece, rather than using substitute materials. Furthermore, the proposed method can be used to observe and measure material flow and plastic strain inside the specimen without splitting it before deformation. It can be used to study material flow and predict strain distribution in general bulk metal forming processes such as upsetting, extrusion, die forging, etc.