用于棘轮变形预测的棘轮演化统一模型研究

 在大量单轴棘轮实验基础上,研究了均值、幅值、峰值和谷值应力对 304不锈钢的饱和棘轮应变的影响规律,首次提出了棘轮应力σ_r和棘轮门槛值σ_rth 的概念,建立了基于单参数控制的、用于饱和棘轮应变预测的 SRM饱和棘轮本构模型和用于独立循环应力工况下棘轮应变演化预测的 REM棘轮演化模型,并由此发展了全面描述任意循环应力工况下棘轮应变演化规律的 URM棘轮演化统一模型。抛物律模型 SRM和幂律模型 REM对实验数据拟合的相关系数均超过 0.98。URM建模容易,只需 4～ 6个试样的单轴棘轮实验数据。此外还讨论了获得 SRM本构模型的单试样实验法。

MODELING OF EVOLUTION STRAIN FOR SATURATED RATCHETING MATERIALS UNDER UNIAXIAL CYCLIC STRESSING

Based on a series of uniaxial ratcheting tests of 304 stainless steel performed, this paper investigated the influence of four stresses (mean, amplitude, peak and valley) on saturated ratcheting (SR) strain. The results show that there exists a relevant stress threshold for each of the four stresses so that the ratcheting deformation happens and its SR strain increases or decreases in a line like law with the stress as it gets over or below its threshold. An important discovery is given in this paper that there exists a unique threshold for peak stress and SR strain varies monotonously with peak stress in a parabola law closed to a line without influence from the other three stresses if SR strain is positive. So, peak stress is the essential reason that leads to positive ratcheting deformation of materials. According to this principle, this paper gives concepts of ratcheting threshold and ratcheting stress, presents a saturated ratcheting model (SRM) used to describe the constitutive relationship between SR strain and ratcheting stress and develops a ratcheting evolution model (REM) used to predict evolution of ratcheting strain for SR materials under uniaxial cyclic stressing. Correlative coefficients of SRM and REM to regress a series of relevant data of tests carried out all are larger than 0.98. A universal ratcheting model (URM) is obtained from these two models and can be used to predict satisfactorily ratcheting strain under cyclic stressing with no previous load history. URM is easy to be built based on ratcheting tests of only 4~6 uniaxial specimens and be available for engineering design on ratcheting control of materials. Specially, a single specimen test method to build SRM and to gain threshold of ratcheting stress is discussed.