疲劳强度期中作业(译文)
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结论
本文研究了由真空处理技术得到的管状复合材料在双轴弯曲/扭转载荷作用下的静态和疲劳强度，得到的结论总结如下：
1）随着扭转力矩产生剪切应力，结构失效机制发生改变，静态和疲劳强度大幅减小。在纯弯曲情况下，疲劳断裂出现在横截面上，同时主要的失效机制是受压屈曲。然而，扭转应力会引起失效位置和失效机制发生改变。对于双轴载荷λ=τ/σ=0.25时，剪切应力会导致面内破裂呈45°，而较高的剪切应力（λ=0.5）会引起扭转屈曲失效。在纯扭转载荷作用下，主要的失效模式发生在横截面内，这是由剪切应力导致的。
2）Tsai–Hill准则可以合理地预测双轴载荷对试样静强度的影响。
3）仅在双轴载荷情况下，平均应力才导致疲劳强度的大幅减小。当疲劳寿命在105次循环时，对于弯曲、扭转/弯曲和扭转载荷作用下，应力比R从0.05增加到0.3，按应力幅值表征的疲劳强度分别减小9%，22%和8%。
4）在扭转载荷作用的情况下，平均应力对疲劳强度的影响可以近似为二次方程关系。
5）基于Tsai–Hill方法的多项式疲劳准则预测疲劳寿命与试验值吻合得很好。
致谢
作者非常感谢本研究的赞助者——FEDER基金，该基金通过项目工程CENTRO -07-0224-FEDER -002001 (MT4MOBI)中的program COMPETE – Programa Operacional Factores de Competitividade对作者提供支持。
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