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Effects of Constraint-Induced Normal Stress on the Failure of Notched Titanium Aluminides

机译:约束诱导的正应力对缺口钛铝化物失效的影响

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Titanium aluminides are candidates for replacing nickel superalloys in some aircraft engine compoents. In uniaxial tension tests, these materials experimence plastic strains at failure that place them in-between traditional definitions fro ductile and brittle materials. This study considers the appropriate continuum mechanics failure criterion for these materials under multiaxial loading conditiosn (based on either the maximum equivalent plastic strain or the maximum normal stress). The material tested has a predominantly lamellar microstructure with approximately 25 vol. percent equiaxed gamma grains. Cylindrical notched tensile specimens are tested which experiemnce elevated normal stresses in their interiors due to circumferential constraint during plastic deformation. Results are presented which quantify reductions in failure loads due to elevated normal stress, compared to those predicted by a maximum equivalent plastic strain criterion. To properly interpret the experimental results, the effects of notch strenghening must be included in the model predictions. Model and experimental results suggest that this TiAl alloy has some sensitivity to normal stress and that a combined failure criterion is needed to accurately predict failure under multiaxial loading conditions. A fracture initiation and failure mechanism requiring a combination of normal stress and plastic straining is suggested that is consistent with observed features at fracture initiation sites.
机译:铝化钛是替代某些飞机发动机组件中的镍超合金的候选材料。在单轴拉伸试验中,这些材料在破坏时会经历塑性应变,从而使它们介于韧性和脆性材料的传统定义之间。这项研究考虑了在多轴载荷条件下(基于最大等效塑性应变或最大法向应力)这些材料的适当连续力学失效准则。测试的材料主要具有约25 vol。的层状微结构。等轴γ颗粒百分比。测试了圆柱形带缺口的拉伸试样,该试样在塑性变形过程中由于周向约束而内部的法向应力升高。与最大等效塑性应变准则所预测的结果相比,给出了量化因高法向应力而导致的失效载荷减少的结果。为了正确解释实验结果,在模型预测中必须包括缺口增强的影响。模型和实验结果表明,该TiAl合金对法向应力具有一定敏感性,因此需要一个组合的破坏准则来准确预测多轴载荷条件下的破坏。提出了需要将法向应力和塑性应变相结合的骨折萌生和破坏机制,这与在裂缝萌生部位观察到的特征是一致的。

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