基于晶体塑性不均匀变形分析的Q235钢疲劳寿命规律预测

Q235 steel fatigue life prediction based on crystal plasticity inhomogeneous deformation analysis

结合试验和有限元多晶晶体塑性计算模拟,研究循环载荷下Q235钢非均质性和不均匀变形对疲劳的影响,探讨疲劳寿命预测方法。完成Q235钢材料试样一系列对称循环下的低周疲劳试验,采用反映细观随机生成多晶结构的VORONOI多晶“代表性单元”(RVE)模型进行材料疲劳循环模拟。材料循环塑性特性用晶体塑性模型来描述,通过数值模拟对循环加载中材料晶粒尺度不均匀局部应变(最大主应变和轴向应变)的计算和统计分析,得到以下结果:应变统计标准差随循环不断增长,并存在极限;不同应变幅循环下对应的极限值相近;用该极限值作评判材料疲劳破坏的指标参量,借助多晶RVE晶体塑性循环模拟,可预测材料应变疲劳寿命曲线(现有方法必须通过系列试验才能获得);无论按BCC或FCC晶体晶格进行计算,对材料疲劳寿命规律的预测结果基本相同。

In this paper,experiments and crystal plasticity finite element calculations are combined to research the effects to materials inhomogeneous deformation and fatigue caused by meso-mechanic non-homogeneity.A series of symmetrical cyclic loading strains are adopted on tubular specimens of Q235 structure steel.A representative volume element(RVE)is constructed for Q235 steel as a material model which features a polycrystalline Voronoi aggregation consisting of a number of crystal grains.The crystal plasticity model is adopted to reflect inhomogeneous cyclic plastic behavior of grains as a constitutive model.Key simulations are performed to model the cyclic evolution,where the grain-size inhomogeneous deformations(maximum principal strains and longitudinal strains)are calculated and statistically analyzed.The simulation results show that the statistical standard deviations(SD)of strains increase gradually with cycles and always achieve the similar limit value although under different strain loadings.In the polycrystalline crystal plasticity RVE simulations,using the limit values as fatigue indicator parameters(FIP)can help predict the strain-life line,which could only be revealed through a series of experiments before.In addition,the calculated results show basically identical predictions whether in BCC lattice or FCC one.