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Impact of microstructural properties on the crack threshold of aluminium castings
Engineering Fracture Mechanics ( IF 5.4 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.engfracmech.2020.107431
M. Oberreiter , R. Aigner , S. Pomberger , M. Leitner , M. Stoschka

Abstract This work focuses on the technological size effect of the cast aluminium alloy EN-AC 46200. Herewith, specimens inheriting specific local cooling rates and therefore varying local dendrite arm spacings are taken from crankcases with hot isostatic pressing (HIP) post-treatment. In order to evaluate the statistically distributed microstructural properties, the dendrite arm spacing λ 2 is probabilistically assessed. Thus, the λ 2 values follow the lognormal distribution, detached of local solidification times. Crack propagation tests are conducted at varying load ratios, such that the impact of the microstructure by means of λ 2 is evaluated. The statistically assessed investigations propose the intrinsic crack threshold to be independent of microstructural properties, in opposite to the long crack threshold which is significantly affected by varying λ 2 values due to enhanced crack closure effects. The evaluated cyclic R-curve results can be generalized into a microstructural independent manner. Moreover, the load ratio effect and its convolution with microstructural properties is evaluated based on the Newman approach. The linear extrapolation of the newly raised three-dimensional Newman approach, considering arbitrary λ 2 values as technological effect, is validated by literature data and the proposed stress intensity factor threshold course is revealed to be slightly conservative by about twelve percent on average.

中文翻译:

微观组织性能对铝铸件裂纹阈值的影响

摘要 这项工作的重点是铸造铝合金 EN-AC 46200 的工艺尺寸效应。因此,从经过热等静压 (HIP) 后处理的曲轴箱中获取具有特定局部冷却速率并因此改变局部枝晶臂间距的试样。为了评估统计分布的微观结构特性,对枝晶臂间距λ 2 进行概率评估。因此,λ 2 值遵循对数正态分布,与局部凝固时间分离。裂纹扩展测试在不同的载荷比下进行,从而通过 λ 2 评估微观结构的影响。统计评估的研究表明,固有裂纹阈值与微观结构特性无关,与长裂纹阈值相反,由于裂纹闭合效应增强,长裂纹阈值受到变化 λ 2 值的显着影响。评估的循环 R 曲线结果可以推广到微观结构独立的方式。此外,基于纽曼方法评估负载比效应及其与微观结构特性的卷积。新提出的三维纽曼方法的线性外推,将任意 λ 2 值视为技术效果,得到文献数据的验证,并且表明所提出的应力强度因子阈值过程平均略微保守约 12%。基于纽曼方法评估负载比效应及其与微观结构特性的卷积。新提出的三维纽曼方法的线性外推,将任意 λ 2 值视为技术效果,得到文献数据的验证,并且表明所提出的应力强度因子阈值过程平均略微保守约 12%。基于纽曼方法评估负载比效应及其与微观结构特性的卷积。新提出的三维纽曼方法的线性外推,将任意 λ 2 值视为技术效果,得到文献数据的验证,并且表明所提出的应力强度因子阈值过程平均略微保守约 12%。
更新日期:2021-01-01
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