Fatigue Test Result of Large Scaled Test Piece : 1st Report, Induction Hardened Cracked Specimen

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  • 大形試験片による疲れ試験結果 : 第1報, き裂試片を高周波焼入れした場合
  • オオガタ シケンヘン ニ ヨル ツカレ シケン ケッカ 1

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Abstract

The 0.35% carbon steel specimens with crack, whose diameter is 50 mm, were made, and some of them were induction-hardened. The results of comparative tests on them show that the fatigue limit, which is only about 6 kg/mm2 in case of no heat treatment, rises nearly to 40kg/mm2 through induction-hardening. These induction-hardened specimens were rather overheated, so that the rapid heating effect could not be expected, nevertheless their fatigue limit did not remarkably fall. This is presumably due to the residual compressive stress on the surface of specimens. Strain gages were set across the crack and strain variations were measured under both compression and tension loads, respectively. When it is suspected that residual compressive stress is present, the strain is approximately equal under either load, but, when it is not, the strain becomes much larger under tension load. Such phenomenon must originate from the fact that strain at the tip of crack becomes smaller, due to the existence of residual compressive stress and seems to explain one of the main reasons for the increased fatigue limit in the above mentiones results.

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