低周疲劳预损伤对TA11合金高周疲劳强度的影响

试验研究了预先经历一定次数的低周疲劳(low cycle fatigue, LCF)对TA11合金高周疲劳(high cycle fatigue,HCF)强度的影响.考虑了LCF试验中循环最大应力、应力比和寿命比例等主要参数,根据步进法,利用旋转弯曲疲劳试验,研究了LCF预损伤对标准试件HCF强度的影响规律.结果表明:当循环最大应力为900MPa时,LCF载荷中靠前的循环产生的塑性应变大,因此加载较少的LCF预损伤也会降低该合金HCF强度;不同应力比的LCF预损伤都会降低HCF强度;当LCF预损伤的最大应力远小于材料的屈服强度时,LCF预损伤对HCF强度的影响较小,而当LCF预损伤的最大应力接近或大于材料的屈服强度时,则必须考虑LCF预损伤对TA11合金HCF强度的影响. 

Effect of low cycle fatigue pre-damage on high cycle fatigue strength of TA11 alloy

The effect of pre-damage of low cycle fatigue (LCF) on high cycle fatigue (HCF) strength of TA11 alloy was experimentally investigated. Three factors were considered, including cyclic max stress, stress ratio and the life ratio in LCF experiment. The effect of LCF pre-damage on high cycle fatigue strength of standard specimen was obtained using rotation bending fatigue experiment according to a step-by-step procedure. Result shows that the previous LCF cycles with the max stress of 900MPa generate a larger cyclic plastic strain. Therefore, even applying few LCF pre-damage can still reduce the HCF strength. Different stress ratios of LCF pre-damage will reduce the HCF strength. For different max stress in LCF pre-damage, when the LCF pre-damage max stress is far lower than the yield strength, it has less effect on the HCF strength. However, the effect on TA11 alloy must be considered when the LCF pre-damage max stress is close to or greater than the yield strength.