抄録
One of the causes of unexpected structural failure is material damage induced by fatigue and impact. So far, the effects of fatigue and impact on material behavior have been investigated independently. In fact, however, sequential impact loading after fatigue loading is seen frequently in practical use of structural materials. In this paper, such a phenomenon is simulated by dynamic tensile test after low-cycle pre-fatigue for a Rolled Steel for Building Structure (JIS G 3136-1994), SN490B and a Rolled Steel for Welded Structure (JIS G 3106-1999), SM490A. The pre-fatigue is given as sinusoidal pulsating tension (stress ratio: 0, frequency: 20Hz). Maximum stresses are 425MPa and 460MPa. Basing upon the property of SN490B steel, fatigue cycle ratios are 25% and 50%. After the pre-fatigue, dynamic tensile test is conducted at room temperature (19°C) and 0°C. Even in the case of triple severe conditions, that is, low-cycle pre-fatigue, high velocity tension and low temperature, both steels are not so degraded. Only yield ratios are increased up to 90%.
