Fatigue Strength Simulation of Natural Porous Structure

Japan, which is the poor country in natural resources, is required to use renewable energy. The rice is a staple food and the amount of its production is about 9 million tons per year in Japan [1]. Rice hull is a non-edible part and has produced 1.9 million tons per year [2]. Among them, about 1.2 million tons have been utilized as fertilizer and soil conditioner. However, about 700 thousand tons are disposed of as agricultural waste. The rice hull silica carbon material (RHSC) is developed in order to utilize the rice hull to protect the global environment and promote recycling. The various basic physical properties have already been evaluated for the RHSC by this research group [3]. The RHSC is a porous carbon material utilizing natural porous structure originated from the rice hull. The RHSC is manufactured by impregnating a phenol resin with rice hull, and carbonizing it in a nitrogen gas atmosphere [4, 5]. The raw rice hull contains about 20 mass% of inorganic constituent and 80 mass% of the organic constituent. Among them, about 95 mass% of the inorganic constituent is silica. Therefore, the RHSC is material with high water resistant [6] and seawater resistant [7, 8]. Moreover, the RHSC, which has excellent low friction and abrasion resistant under unlubricated conditions [6], is expected to be used as sliding materials such as the linear slide rail in future. Generally, structures and machine elements are subjected to cyclic loads. Since fatigue failure caused by cyclic load often brings disaster, evaluation of fatigue strength is important. However, obtaining the strength experimentally is required several weeks. Therefore, simulation method of fatigue strength is useful for machine designer. Murakami has derived [9] a fatigue strength evaluation formula for metallic materials which is based on material hardness and defect size. The fatigue strength simulation method for steel gears adopting Murakami’s formula was proposed by one of the authors [10]. The dispersion of fatigue strength is also estimated by the simulation method. There is a similarity between the RHSC and metallic materials in the viewpoint of defect including materials. In this study, fatigue strength simulation for the RHSC test piece was carried out.