小冲孔试样弹塑性蠕变损伤的有限元分析

AN ANALYSIS OF ELASTIC-PLASTIC-CREEP DAMAG FOR SMALL PUNCH CREEP TEST

  • 摘要: 综合考虑了小冲孔试样实验过程中的弹性、塑性及蠕变等因素,采用了Mises型流动法则和改进的K-R蠕变损伤本构方程,建立了ABAQUS有限元模型,模拟计算了550℃三种载荷条件下,Cr5Mo试样的弹塑性蠕变过程,分析试样的中心蠕变挠度、蠕变应变随时间的变化规律,当量应力的分布情况,以及试样的蠕变损伤与位置的关系,同时分析了挠度与应力对网格的敏感性。结果表明:模拟结果与实验结果很接近,且与单轴实验的应变曲线十分相似;整个试样在中心损伤比较严重,呈现明显局部化特征;讨论了试样网格的敏感性,试样半径方向0mm~1mm之内应力变化幅度比较大(除约束点),并且应力的最大值也出现在这个区域,在这个区域进行网格细化提高计算的精确性,而其他区域采用粗网格减少计算成本,达到精确性和经济性的平衡。径向上网格大小对挠度影响比较大,应力对网格大小不敏感。

     

    Abstract: An elastic-plastic-creep finite element model, incorporating the Von Mises plastic flow rule and a creep damage equation, was established based on the small punch creep test on Cr5Mo steel specimens at 550℃ under three different loads. Finite element analysis were performed to examine the variation of the central creep deflection and the creep strain with time and the evolution of creep damage. The sensitivity of the creep deflection and equivalent stress at the centre on the disc to mesh size is discussed. Numerical results presented in this paper confirm that the creep damage at the central part is high. The stress gradients are highest near the central area of the specimen (from 0 to 1 mm). Therefore, accurate stress and strain can be obtained using refined meshes near the specimen center and coarse meshes in other places. The test results are in agreement with those of the numerical simulation and three different stages appearing in the curve of creep deflection, which are quite similar to those observed in conventional creep tests.

     

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