两种评定准则下的车轮疲劳强度分析

分别采用基于单轴疲劳理论的车轮疲劳强度评定准则和Dang-Van多轴高周疲劳评定准则2种方法,对同一车轮进行疲劳强度计算,比较2种方法的安全度和适用范围。结果表明:车轮疲劳强度在2种评定准则下均满足要求,车轮的疲劳危险区域位于轮缘侧辐板孔边中间位置,其中使用单轴疲劳准则评定辐板更偏于安全,而Dang-Van多轴高周疲劳准则适用于辐板孔的评价。

超声冲击法提高焊接接头疲劳强度的机理分析

使用工具显微镜和维氏硬度计测量了超声冲击处理前后焊趾区的几何形状与硬度的变化,并应用疲劳缺口系数的概念及Dang Van准则,对超声冲击造成的焊趾区几何形状的变化及残余压缩应力对接头疲劳性能改善的影响行为进行了研究.结果表明,对于低中强钢来说,超声冲击处理焊接接头疲劳性能的改善主要是由焊趾部位形成的残余压应力及改善焊趾几何外形这两个因素引起的,硬化的作用相比次之.研究还证明,冲击处理对焊接接头应力集中程度的降低,主要是通过增加焊趾区过渡半径来实现的.

用局部法评定焊接接头的疲劳性能

采用16Mn钢非承载十字焊接接头疲劳试验结果对使用DangVan准则的疲劳评定局部方法进行了研究。结果表明,有限元分析中应力集中区单元尺寸对局部参量计算有明显影响,为获得比较合理的预测结果需对焊趾应力集中区所划分的单元尺寸限定,当接头焊趾半径在0.15～0.8mm变化时应选择最小单元尺寸0.32～0.62mm计算局部参量;在此基础上DangVan准则可以对焊态接头做出合理的评定,但DangVan建议的β值偏安全。此外,通过计算发现焊趾半径只影响局部很小区域(约0.5mm内)的应力集中分布,在某一深度(约0.5mm)后存在稳定的应力集中,因而建议采用距应力集中区最大应力处某一深度的应力参数计算DangVan局部参量可能更为合理,这将减小局部参数对焊趾半径及单元尺寸的依赖性。

A Method of Determining Realistic Stress S/N Curves by Interpolations and Extrapolations of Two Known Best-Fit S/N Curves for Fatigue Life Predictions

The design and sizing of new mechanical components which are intended to operate under cyclic loads often require an acceptable level of confidence that the components will meet pre-defined fatigue strength objectives for crack initiation. For loads with multiple amplitudes and mean values, models based on Palmgren-Miner’s linear cumulative damage hypothesis and on multiple S/N curves (stress-no. cycles) are widely used in estimations for the duration of crack initiation. In this paper a procedure for generating S/N curves for multiple stress ratios by interpolation or extrapolation from the data available for two such curves is proposed. At any number of cycles, the stress for crack initiation is calculated from the far field macroscopic stresses of the known curves using Dang Van fatigue criterion and microscopic stresses evaluated at the grain level. An algorithm is presented for uniaxial loading and results verifications against curves established from laboratory tests with elastic and plastic stresses are shown and discussed for notched and un-notched specimens.