表面小裂纹热锻模的疲劳寿命分析

基于材料自由表面特性并考虑微观结构非均匀性,根据金属疲劳裂纹萌生的微细观过程理论,建立材料表面塑性应变分布模型。由于局部塑性变形在萌生可分辨疲劳小裂纹的循环周次中占主导地位,本文将局部应力应变法应用于热锻模表面小裂纹扩展分析,选取表面最大塑性应变作为出现热机械疲劳裂纹的预测依据,计算的热锻模使用寿命与实践结果相吻合,能基本预测热锻模寿命。该模型为表面强化工艺能提高热锻模的疲劳强度提供了理论依据。

Analysis of Fatigue Life of Surface Short Cracks of Thermal Die Forging

A physical model for distribution of plastic strain on materials surface is established based on the nature of free surface,microstructures of a material and the mecro-meso-process theory of fatigue crack initiation in metals.Because the local plastic behavior is mainly in the cycles of initiating distinguishable fatigue cracks,the local stress-strain method will be applied to microanalysis for propagation of surface short cracks of the thermal die forging.The fatigue cracks of the thermal die forging are based on the maximum plastic strain on materials surface.The computation results of fatigue life are in agreement with the practice.The analysis model can predict the fatigue life of the thermal die forging.The analysis provides the theoretic basis for the surface reinforcement technology to enhance the material fatigue strength.