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Stress ratio effects in fatigue of lost foam cast aluminum alloy 356.

机译：应力比对消失模铸造铝合金356疲劳的影响。

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摘要

Lost foam casting is a highly versatile metalcasting process that offers significant benefits in terms of design flexibility, energy consumption, and environmental impact. In the present work, the fatigue behavior of lost foam cast aluminum alloy 356, in conditions T6 and T7, was investigated, under both zero and non-zero mean stress conditions, with either as-cast or machined surface finish. Scanning electron microscopy was used to identify and measure the defect from which fatigue fracture initiated. Based on the results, the applicability of nine different fatigue mean stress equations was compared. The widely-used Goodman equation was found to be highly non-conservative, while the Stulen, Topper-Sandor, and Walker equations performed reasonably well. Each of these three equations includes a material-dependent term for stress ratio sensitivity. The stress ratio sensitivity was found to be affected by heat treatment, with the T6 condition having greater sensitivity than the T7 condition. The surface condition (as-cast vs. machined) did not significantly affect the stress ratio sensitivity. The fatigue life of as-cast specimens was found to be approximately 60--70% lower than that of machined specimens at the same equivalent stress. This reduction could not be attributed to pore size alone, and is suspected to be due to the greater concentration of pyrolysis products at the as-cast surface. Directions for future work, including improved testing methods and some possible methods of improving the properties of lost foam castings, are discussed.
机译：泡沫消失模铸造是一种用途广泛的金属铸造工艺，在设计灵活性，能耗和环境影响方面具有显着优势。在目前的工作中，研究了在零和非零平均应力条件下，铸态或机加工表面光洁度消失的泡沫铸造铝合金356在T6和T7条件下的疲劳行为。扫描电子显微镜用于识别和测量疲劳断裂的缺陷。根据结果​​，比较了九种不同的疲劳平均应力方程的适用性。发现广泛使用的Goodman方程是高度非保守的，而Stulen，Topper-Sandor和Walker方程的性能相当好。这三个方程式中的每个方程式都包含一个与材料有关的应力比敏感性项。发现应力比敏感性受热处理的影响，其中T6条件比T7条件具有更高的敏感性。表面条件（铸态与机加工态）并未显着影响应力比灵敏度。发现在相同的等效应力下，铸态试样的疲劳寿命比机加工试样的疲劳寿命低约60--70％。这种减少不能仅归因于孔径，并且怀疑是由于铸态表面上热解产物的浓度更高。讨论了未来工作的方向，包括改进的测试方法和一些改善丢失泡沫铸件性能的可能方法。

著录项

  • 作者

    Palmer, David E.;

  • 作者单位

    The University of Wisconsin - Milwaukee.;

  • 授予单位 The University of Wisconsin - Milwaukee.;
  • 学科 Engineering Materials Science.
  • 学位 M.S.
  • 年度 2014
  • 页码 187 p.
  • 总页数 187
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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