Fracture behavior and deformation capacity of welded joint in high-speed tensile tests

Many steel structures were damaged by recent earthquake.It can be considered that effect of strain rate is one of the substantial factors of these damages.But the effect of strain rate was elucidated only on virgin steel.Generally，steel structure is damaged in weld zone。Moreover，it is also well known that the cold forming and aging makes steels also brittle.In this study，experiments were carried out in order to elucidate the effect of strain rate on tensile properties of the weld heat-affected zone。Moreover，the effect of strain rate of aged and heat-affected area。In the experiment，the heat-affected zone and aged zone simulated on tensile specimen，and the tensile test under3tensile speeds(0.1 mm/s，100 mm/s，1200 mm/s)was carried with those specimens.The main results are summarized as follows。·In case of the small Charpy absorbed energy specimen，crystallinity became large as the tensile speed increase。·Tensile strength of ductile-fractured specimen became large as the tensile speed increase，even in the weld heat-affected steel and aged steel。And it is elucidate that the increase-ratio of tensile strength by increasing of tensile speed related well to the tensile strength under static loading。But tensile strength of brittle-fractured specimen does not increase if the tensile speed increase。·In case of the no stress concentration specimen，deformation capacity became small as the tensile speed increase。·In case of the notched specimen，deformation capacity of large Charpy absorbed energy specimen became large as the tensile speed increase，even in the weld heat-affected steel and aged steel。But deformation capacity of small Charpy absorbed energy specimen became decrease greatly as the tensile speed increase。Thus，it is elucidate that the change of deformation capacity is affected well by the Charpy absorbed energy。

Many steel structures were damaged by recent earthquake. It can be considered that effect of strain rate is one of the substantial factors of these damages. But the effect of strain rate was elucidated only on virgin steel. Generally, steel structure is damaged in weld zone. Moreover, it is also well known that the cold forming and aging makes steels also brittle.In this study, experiments were carried out in order to elucidate the effect of strain rate on tensile properties of the weld heat-affected zone. Moreover, the effect of strain rate of aged and heat-affected area. In the experiment, the heat-affected zone and aged zone simulated on tensile specimen, and the tensile test under 3 tensile speeds (0.1mm/s, 100mm/s, 1200mm/s) was carried with those specimens.The main results are summarized as follows.・ In case of the small Charpy absorbed energy specimen, crystallinity became large as the tensile speed increase.・Tensile strength of ductile-fractured specimen became large as the tensile speed increase, even in the weld heat-affected steel and aged steel. And it is elucidate that the increase-ratio of tensile strength by increasing of tensile speed related well to the tensile strength under static loading. But tensile strength of brittle-fractured specimen does not increase if the tensile speed increase.・In case of the no stress concentration specimen, deformation capacity became small as the tensile speed increase.・In case of the notched specimen, deformation capacity of large Charpy absorbed energy specimen became large as the tensile speed increase, even in the weld heat-affected steel and aged steel. But deformation capacity of small Charpy absorbed energy specimen became decrease greatly as the tensile speed increase. Thus, it is elucidate that the change of deformation capacity is affected well by the Charpy absorbed energy.