Deformation characteristics of microtubes in flaring test

Microtechnology is gaining widespread interest because products are becoming miniaturized in many fields. Since the microtube is one of the most important micromaterials, its material behavior is very interesting. The ductility of micromaterials is an important parameter that limits material formability. Pushing a conical tool into a tube until the onset of fracture, known as the flaring test is a suitable test for evaluating the circumferential ductility and material behavior of a tube. In this test, the degree of achievable tube expansion that expresses the circumferential ductility of the tube is limited by two instability phenomena. The first one is the loss of global stability due to the elasto-plastic buckling of the straight part of the tube, and the second one is diffuse necking followed by fracture caused by the local loss of material stability in the conical edge of the tube. In this study, the deformation modes of microtubes in the flaring test and the flaring limit of the microtubes were investigated at different conical tool angles experimentally and numerically. As a result, it is found that the flaring limit increases with increasing conical tool angle.