基于缺口应力法的焊接接头多轴疲劳分析

鉴于当前焊接接头疲劳评估曲线只适用于单轴加载情况,基于缺口应力法对焊接接头进行了多轴疲劳分析。通过联合焊接接头的多轴疲劳试验名义应力数据和有限元法所计算的缺口应力集中系数,获得了5种焊接接头的各向缺口应力;根据Von Mises、IIW和EESH 3种多轴疲劳准则计算出等效缺口应力并将其统一在同一坐标系统下;最后采用最小二乘法拟合出适用于多轴疲劳评估的缺口寿命曲线。与IIW标准推荐的单轴曲线相比,这些多轴缺口疲劳曲线具有更低的倾斜度和更高的疲劳等级,即多轴加载时明显降低了10~3~10~6次中周范围内的疲劳强度值,而对10~6~10~7次高周疲劳范围的影响则相对有限。

The multi-axle fatigue analysis of welded joints based on notch stress method

As the existing fatigue assessment curves of welded joints are only applicable to uniaxial load,we analyzed the multi-axial fatigue of welded joints on the basis of notch stress method.Firstly,through the combination of the nominal stress data in the multi-axial fatigue test of welded joints and the notch stress concentration factor calculated by finite element method,the notch stresses of 5 kinds of welded joints in different directions were obtained.Secondly,equivalent notch stresses were respectively calculated according to 3 kinds of multi-axial fatigue criteria,i.e.Von Mises,IIW (International Institute of Welding) and EESH (equivalent effective stress hypothesis),and they were unified into the same coordinate system.Finally,the fatigue life curves that were applicable to the assessment of the multi-axial notch fatigue were fitted out with the least square method.Compared with the uniaxial curve recommended by IIW,the multi-axial fatigue curves have lower inclination and higher fatigue class.The fatigue strength value within the mid-circle range from 10a to 106 circles is obviously reduced when multi-axial is loaded,while the influence on the high circle fatigue range from 106 to 107 circles is relatively limited.