常圧焼結窒素ケイ素の静的および繰返し疲労強度(<小特集>信頼性工学小特集)

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Static and cyclic fatigue tests were conducted on sintered silicon nitride at room temperature in air. The results were analysed through the fracture mechanics concept. Static tests were performed in a cantilever type bending state and the mean strength obtained was less than a half of that in the three-point bending tests on the same material. The decrease in strength was not explained satisfactorily only from the view point of size effect based on the weakest link model. Then, the fracture surface of the tested specimens was observed microscopically. The stress intensity factors evaluated for the observed flaws were smaller than the fracture toughness. The concept of equivalent crack length was introduced to represent the severity of flaw. The relation between fracture strength and this equivalent crack length obtained in the present experiment did not coincide with the expectation from the linear elastic fracture mechanics. This suggested that not all of the observed flaws were the fracture origin. Cyclic fatigue tests were conducted under fully reversed plane bending. Although a large scatter was observed in the relation between fatigue-life and stress-amplitude above 220 MPa, the endurance limit at 10^7 stress-cycles was expected to be with in the range of stress-amplitude from 170 to 200 MPa. An attempt to explain these tendencies was made based on the distribution of inherent flaws and the relation of crack growth rate versus stress intensity factor.
社団法人日本材料学会の論文
1984-01-15

常圧焼結窒素ケイ素の静的および繰返し疲労強度(<小特集>信頼性工学小特集)

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