基于线性强化结构应变法的低周疲劳分析

Low-cycle fatigue analysis based on linear hardening structural strain method

焊接结构的低周疲劳分析对于轨道车辆尤为重要。为了有效评估焊接结构的低周疲劳,提出一种基于线性强化本构的结构应变数值计算方法。该方法基于经典板壳理论和弹塑性力学。通过考虑材料的应变硬化行为,将材料的真实应力应变关系简化为线性强化本构关系。利用有限元分析软件ABAQUS和Fe-safe计算焊接结构焊趾位置的结构应力,给出基于径向回退算法的线性强化本构塑性修正模型。利用MATLAB编写结构应变数值计算程序对结构应力进行塑性修正,并计算结构应变。基于该结构应变,给出了考虑板厚效应和载荷模式的等效结构应变范围计算公式,利用主应变-寿命曲线分析低周疲劳数据,建立了广泛用于轨道车辆的Q450高强度耐候钢材料制成的3种焊接接头的有限元模型。采用结构应力法的主应力-寿命曲线和结构应变数值计算方法的主应变-寿命曲线对试验获得的疲劳数据进行分析,并对比2种方法计算的等效结构应变范围。结果表明,各焊接接头的试验数据均分布在主应变-寿命曲线的线性窄带内,验证了结构应变数值计算法的可行性;与结构应力法相比,结构应变数值计算方法能更好地反映低周疲劳过程中材料的应变硬化现象,更适用于焊接结构的低周疲劳评估。该方法对轨道车辆焊接板结构的低周疲劳评估具有研究价值。与传统的通过提取节点力的方式计算结构应力和结构应变参数的方法相比,利用MATLAB编写结构应变数值计算程序极大地提高了结构应变参数计算的效率。

Low-cycle fatigue analysis of welded structures is particularly important for rail vehicles.To effectively evaluate the low-cycle fatigue of welded structures,a numerical calculation method for structural strain based on a linear hardening constitutive model was proposed.This method is based on classical plate-shell theory and elastoplastic mechanics.By considering the strain hardening behavior of materials,the true stressstrain relationship of materials was simplified into a linear hardening constitutive model.The structural stress at the welding toe position of the welded structure was calculated using finite element analysis software ABAQUS and Fe-safe.The linear hardening constitutive model with plasticity correction was presented based on the radial mapping algorithm.The structural stress was plastically corrected using a structural strain numerical calculation program written in MATLAB,and the structural strain was calculated.Based on this structural strain,the calculation formula of the equivalent structural strain range considering the plate thickness effects and load mode was provided,and low-cycle fatigue data were analyzed using the main strain-life curve.The finite element models of three welded joints made of Q450 high-strength weather-resistant steel material widely used in rail vehicles were established.The fatigue data obtained from tests were analyzed using both the main stress-life curve of the structural stress method and the main strain-life curve of the numerical calculation method for structural strain.The equivalent structural strain ranges calculated by the two methods were compared.The results show that the test data for each welded joint are distributed within a linear narrow band of the main strainlife curve,which verifies the feasibility of the numerical calculation method for structural strain.Compared to the structural stress method,the numerical calculation method for structural strain can better reflect the strain hardening phenomenon during low-cycle fatigue and be more suitable for evaluating the low-cycle fatigue of welded structures.This method has research value for the low-cycle fatigue evaluation of welded plate structures in rail vehicles.Compared to the traditional method of calculating structural stress and structural strain parameters by extracting node forces,the numerical calculation program for structural strain written by MATLAB greatly improves the efficiency of calculating structural strain parameters.