1414 Fretting fatigue life estimation based on the critical distance stress theory

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  • 1414 特定位置応力を用いたフレッティング疲労寿命評価(OS14-3 締結・接合部のプロセスと信頼性評価-溶接、フレッティング-)

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Fretting fatigue process have many features such as early stage crack initiation at contact edge, very slow crack propagation and fatigue failure after very long life operation of machinery. In previous paper we presented new fretting fatigue model which can explain fretting fatigue life especially on the ultra high cycle region. In this paper we introduce the fretting fatigue life estimation methods especially on low cycle fatigue region. Generally fretting fatigue S-N curve have two regions, one is high cycle (low stress) region and second is low cycle (high stress) region. In previous paper we introduced the fretting fatigue life estimation methods in high cycle region by considering the wear process. And in this estimation method the fretting fatigue limit can be estimated as the crack initiation limit at contact edge. In this paper we introduce the low cycle fretting fatigue life estimation method using the critical distance theory. Generally this critical distance theory was applied for the fatigue limit estimation using fatigue limit of smooth specimen σw0, and threshold stress intensity factor range ΔKth. In this paper we estimated the low cycle fretting fatigue life based on new critical distance theory, which is modified for high stress region using ultimate tensile strength aB, and fracture toughness KIC. The critical distance for estimating low cycle fretting fatigue strength was calculated by interpolation of critical distance on fretting fatigue limit (estimated from σw0 and ΔKth) with critical distance on static strength (estimated from σB and KIC). By unifying these low cycle fretting fatigue life estimation method with high cycle fretting fatigue life estimation method which was presented previous paper we can estimate the total fretting life easily. And to confirm the availability of this estimation method we perform the fretting fatigue test using Ni-Mo-V steel.

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