摘要
研究热作模具钢在应力控制下的等温疲劳和同相热机械疲劳寿命 ,发现在相同的应力幅下 ,同相 (最高温度5 5 0℃ ,最低温度 2 5 0℃ )热机械疲劳寿命低于上限温度的等温 (温度 5 5 0℃ )疲劳寿命。这表明在相同的应力幅下 ,热机械疲劳比等温疲劳产生更严重的损伤 ,用最高温度下的等温疲劳寿命代替热机械疲劳寿命并不一定得到可靠的结果。在等温疲劳条件下 ,疲劳裂纹主要为穿晶萌生与扩展 ,而在热机械疲劳条件下 ,疲劳裂纹主要沿晶萌生与扩展。文中还以Chaboche高温疲劳损伤模型为基础 ,考虑损伤系数是最高温度和温度范围的函数来评价载荷控制下材料的热机械疲劳寿命。在热机械疲劳试验中 ,考虑温度变化产生的附加内应力 ,因此每一循环的损伤不仅是最大应力和平均应力的函数 ,而且与最高温度和温度循环范围有关。根据累计损伤的等效温度法 ,取最大温度为等效温度。热作模具钢在热机械疲劳过程中 ,由热循环产生的附加损伤通过损伤指数系数表示。结果表明 。
The fatigue lives of in phase thermo mechanical fatigue (TMF) and isothermal fatigue (IF) were carried out in cast hot work die steel in stress control in this paper. It is found that the lives obtained under in phase thermomechanical fatigue condition (at a temperature interval of 250℃～550℃) are lower than those obtained under isothermal fatigue condition (at 550℃) at the same stress amplitude. It can be concluded that the TMF of Cr Ni Mo cast hot work die steel brings more damage than IF at the same stress amplitude. Therefore, if temperature varies, it is not reliable to design on the basis of dada from the isothermal fatigue at maximum temperature. Under IF conditions, the path of the crack initiation and growth are mainly transgranular. The intergranular cracks dominate in TMF tests under the lower stress amplitude and the feature of transgranular propagation occurs with the increment of the stress amplitude. A model of life prediction, based on Chaboche law, was discussed. Damage coefficients that are functions of the maximum temperature and the variation of temperature are introduced in the model so as to evaluate TMF lives in load control. Considering the additional stress caused by the varying temperature under the thermo mechanical fatigue, the damage coefficients per cycle can be described by a function with not only maximum stress and mean stress, but also maximum temperature and temperature range. According to the equivalent temperature method in accumulated damage, the maximum temperature was taken as the equivalent temperature in this paper. It is considered that the additional damage produced by the variation of temperature may be simulated by exponential coefficient. With this method, the lifetime prediction gives results corresponding well to experimental data.
出处
《机械强度》
CAS
CSCD
北大核心
2002年第4期571-574,共4页
Journal of Mechanical Strength
基金
国家自然科学基金 (59771 0 0 3)
国家计委基金 ([1 999] 31 7)资助项目
关键词
高温
热作模具钢
热机械疲劳寿命
温度循环
应力控制
Cast hot work die steel
Thermo mechanical fatigue
Isothermal fatigue
Temperature cycle
Stress control
