- 學位論文
混合型裂縫成長方向的統計預測
Statistical Prediction for Mixed-Mode Crack Growth Direction
摘要
本研究乃是針對一不銹鋼材，在材料未破壞前推估受混合型負載下之裂縫成長的相對概率，由ANSYS模擬所得考慮裂縫前端塑性區內的應變量及塑性區發展範圍，並假設材料內缺陷分佈的機率皆相同的情形下，分析統計其結果，據此計算各角度裂縫成長的相對頻率，並比較其可能發生破壞的概率，進而推估其裂紋可能成長之方向。結果可以發現在不同外力混合比例下時，其最大裂縫成長相對概率所發生的位置皆有所不同。當考慮裂縫成長風險正比於塑性應變時，即m=1時，發現mode 1與mode 2的應力強度因子比例為一比一時，此時最大概率發生在15度角度上；mode 2應力強度因子比例遠大於mode 1應力強度因子時，最大概率發生在5度角度上。由上述可觀察到，當mode 2比例逐漸增加時，其裂縫成長會朝裂縫尖端水平方向而發展。另外一方面，當mode 1應力強度因子比例遠大於mode 2應力強度因子，隨塑性應變著重放大因子(m > 1)的增大，發現裂縫成長會從兩翼方向逐漸變為-20度角度方向，由此可知，畸變能、塑性應變較高的角度方向，其相對概率會隨 值增加而相對提高。
並列摘要
The statistical prediction of crack growth direction under mixed-mode conditions is studied. By assuming that the probability of finding flaws within the material is uniform, and that the growth risk is related to the plastic strain around the crack tip, using the results of finite element analysis(provided by ANSYS), we determine the most probable direction of crack growth. When the growth risk is proportional to plastic strain (i.e.m=1), it is found that the crack growth direction is at about 15 degree from the crack line with stress intensity factor of mode 1 and mode 2 is 1:1. When stress intensity factor of mode 2 is much larger than mode 1, it occurs at about 5 degree. It is concluded that the crack tend to propagate along the crack line when mode 2 loading is increasingly dominant. On the other hand, when stress intensity factor of mode 1 is much larger than mode 2, for higher value of m(m > 1 ), the crack growth direction is about -20 degree.