权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Study on Fatigue Crack Growth Behavior of Small and Long Cracks at Elevated Temperatures

高温下细长裂纹疲劳裂纹扩展行为研究

基本信息

批准号：
60460081
负责人：
OGURA Keiji
金额：
$ 0.77万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1987
项目状态：
已结题

项目摘要

Fatigue crack growth (FCG) was investigated at elevated temperatures up to 500゜C. The emphasis was made on examining the role of crack closure on the near threshold FCG behAvior at elevated temperatures. FCG tests were made on the samples of low carbon steels (SM41A and SS41), a stainless steel (SUS304) and an aluminum alloy (A2218-T6) in air environment. Some additional tests were made in SM41A and SUS304 in Ar gas in order to examine the effect of oxidation ot the FCG behavior. The results are summarized as follows.(1) The FCG rate was accelerated at elevated temeratures at far threshold or higher <delta><kappa> region.(2) The FCG rate, on the other hand, was decelerated at elevated temperatures near threshold region, and the fatigue threshold, <delta><kappa>th, increased with increase in temperature in air environment.(3) The increase in <delta><kappa>th at elevated temperatures was found to be caused both by the enhanced crack closure due to the oxide products induced on the fracture surface and the increase in <delta><kappa>eff.th, the intrinsic FCG resistance of the material.(4) The contcibution of the crack closure to the increase in <delta><kappa>th was different for different materials. The crack closure was an important role on the increase in <delta><kappa>th in SM41A, but it was a less important role in SUS304.(5) Much increase in <delta><kappa>eff.th in SUS304 was observed in air environment in comparison withe the value in Ar gas at 300゜C. The intrinsic FCG resistance itself was found to be much influened by oxdation in this material, although the detail mechanisms is still unknown.(6) It was concluded that the oxide products could contribute to the increase in <delta><kappa>th only when the relative thickness of the crack tip opening displacement memained small.

在高达500 ℃的高温下研究了疲劳裂纹扩展（FCG）。重点研究了裂纹闭合对高温下近门槛FCG行为的影响。对低碳钢（SM 41 A和SS 41）、不锈钢（SUS 304）和铝合金（A2218-T6）试样在空气环境中进行了疲劳裂纹扩展试验。为了研究氧化对FCG行为的影响，在SM 41 A和SUS 304中进行了一些附加的试验。结果总结如下。(1)在远阈值或更高温度区，FCG速率随温度升高而加快<delta><kappa>。(2)另一方面，FCG速率在阈值区域附近的温度升高时减慢，并且疲劳阈值<delta><kappa>th在空气环境中随着温度的升高而增加。(3)发现<delta><kappa>在升高的温度下th的增加是由由于断裂表面上诱导的氧化物产物引起的增强的裂纹闭合<delta><kappa>eff.th和材料的固有FCG抗性的增加引起的。(4)不同材料的裂纹闭合对裂纹扩展<delta><kappa>的贡献不同。在SM 41 A中裂纹闭合是提高应力强度因子的重要因素<delta><kappa>，而在SUS 304中裂纹闭合的作用较小。(5)与<delta><kappa>eff.th300 ℃ Ar气中的值相比，在空气环境中观察到SUS 304中的www.example.com显著增加。氧化对材料的抗疲劳断裂性能有很大的影响，但具体的影响机理尚不清楚。(6)结果表明，<delta><kappa>只有当裂纹尖端张开位移相对厚度较小时，氧化产物才能对裂纹尖端的扩展起作用。