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Numerical study of micro-scale damage evolution in time dependent fracture mechanics.

机译：随时间变化的断裂力学中微观尺度损伤演化的数值研究。

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摘要

In part 1, intergranular cavity growth in regimes, where both surface diffusion and deformation enhanced grain boundary diffusion are important, is studied. In order to continuously simulate the cavity shape evolution and cavity growth rate, a fully-coupled numerical method is proposed. Based on the fully-coupled numerical method, a gradual cavity shape change is predicted and this leads to the adverse effect on the cavity growth rate. As the portion of the cavity volume growth due to jacking and viscoplastic deformation in the total cavity volume growth increases, spherical cavity evolves to V-shaped cavity. The obtained numerical results are physically more realistic compared to results in the previous works. The present numerical results suggest that the cavity shape evolution and cavity growth rate based on the assumed cavity shape, spherical or crack-like, simply cannot be used in this regime.; In part 2, intergranular creep failure of high temperature service material under a stress-controlled unbalanced cyclic loading condition is studied. The experimentally verified Murakami-Ohno strain hardening creep law and Norton's creep law are incorporated into the Tvegaard's axis-symmetric model for the constrained grain boundary rupture analysis. Based on the physically realistic Murakami-Ohno creep law, it is shown that the cavity growth becomes unconstrained upon the stress reversal from compression to tension. This leads to the prediction that the material life under a cyclic loading condition is shorter than that under a constant loading. Based on the classical Norton's law, the predicted material life under a cyclic loading condition remains the same as that under a constant loading. The obtained numerical results qualitatively match with recent experimental results by Arai, where the life under a cyclic loading can be much shorter than that under a constant loading. There are many cases where engineers use a simple Norton's creep law because of its simplicity. The present work suggests that more physically realistic creep laws should be used when cyclic loading must be considered.
机译：在第1部分中，研究了晶界空洞生长的状态，其中表面扩散和变形增强的晶界扩散都很重要。为了连续模拟腔体形状的演化和腔体的生长速率，提出了一种全耦合数值方法。基于完全耦合的数值方法，可以预测空腔的逐渐变化，从而对空腔的生长速度产生不利影响。随着由于顶升和粘塑性变形而导致的空腔体积增长在整个空腔体积增长中的增加，球形空腔演变为V形空腔。与以前的工作相比，所获得的数值结果在物理上更加真实。目前的数值结果表明，在这种情况下，根本不能使用基于假定的球形或裂纹状空腔形状的空腔形状演变和空腔生长速率。在第2部分中，研究了在应力控制的不平衡循环载荷条件下高温服务材料的晶间蠕变破坏。经过实验验证的村上大野应变硬化蠕变定律和诺顿蠕变定律被纳入Tvegaard的轴对称模型中，用于受约束的晶界破裂分析。基于物理上现实的村上大野的蠕变定律，表明了空腔的生长不受从压缩到拉伸的应力逆转的约束。这导致了以下预测：在周期性载荷条件下的材料寿命比在恒定载荷条件下的材料寿命短。根据经典的诺顿定律，在循环载荷条件下的预测材料寿命与恒定载荷下的预测材料寿命相同。所获得的数值结果与Arai的最新实验结果在质量上相匹配，后者在循环载荷下的寿命可能比在恒定载荷下的寿命短得多。在许多情况下，工程师会因为简单而使用简单的诺顿蠕变定律。目前的工作表明，当必须考虑循环载荷时，应使用更符合实际的蠕变定律。

著录项

  • 作者

    Oh, Joonyoung.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 163 p.
  • 总页数 163
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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