复杂面内应力状态下平面编织高铝纤维增强氧化铝基复合材料强度及疲劳寿命预测方法

Prediction of strength and fatigue life for 2D plain-woven high-alumina fiber reinforced alumina matrix composites under a complex in-plane stress state

针对平面编织氧化铝基复合材料提出了一种复杂面内应力状态下的强度准则和疲劳寿命预测方法。通过拉伸、压缩及纯剪切试验,分别获得了材料的静强度指标。考虑材料拉、压性能的差异和面内拉-剪联合作用对材料强度的影响机制,提出了修正的Hoffman强度理论。采用该强度理论预测得到的偏轴拉伸强度与试验结果基本一致,偏差不超过10%。开展了偏轴角θ=0°、15°、30°、45°,应力比R=0.1,频率f=10 Hz的拉伸疲劳试验,试验结果表明随着偏轴角的增加,相同轴向拉伸载荷下的疲劳寿命逐渐降低。由于面内剪切应力分量的作用,疲劳失效由纤维主导逐渐过渡到纤维和基体共同主导的模式。基于单轴疲劳寿命曲线,采用Broutman-Sahu剩余强度模型表征剩余强度随疲劳循环次数的变化规律,结合剩余强度演化模型和修正的Hoffman强度理论,提出了一种面内复杂载荷条件下的疲劳寿命预测模型,并引入疲劳剪切损伤影响因子表征拉-剪应力联合作用对材料疲劳行为的影响。采用本文提出的疲劳寿命预测模型,预测不同偏轴角拉伸疲劳寿命,预测结果与试验结果基本一致,偏差在1倍寿命范围内。比较结果表明在给定应力比、温度和疲劳载荷频率条件下,该疲劳寿命预测模型可以用来预测平面编织氧化铝基复合材料拉-剪复杂面内载荷条件下疲劳寿命。

This paper presents a strength criterion and fatigue life prediction method for 2D braided alumina matrix composites under a complex in-plane stress state.The static strength of the material was obtained by in-plane tensile,compression,and pure shear tests.Considering the difference between tensile and compressive properties of materials and the influence mechanism of in-plane tensile and shear coupling on material strength,a revised Hoffman strength theory was proposed.The predicted off-axis tensile strength is consistent with the test results,and the deviation is not more than 10%.Tensile fatigue tests were carried out with the off-axis angleθ=0°,15°,30°,45°,the stress ratio R=0.1,and frequency f=10 Hz.The test results show that the fatigue life decreases with the increase of off-axis angle.Due to the in-plane shear stress component,the fatigue failure is gradually changed from fiber-dominated to fiber-matrix dominated mode.Based on a combination of the uniaxial tensile fatigue life curve,the Broutman-Sahu residual strength model,which is used to characterize the variation of the residual strength with the fatigue cycles,and the modified Hoffman strength theory,the paper proposes a fatigue life prediction model under complex in-plane loading conditions.The fatigue shear damage factor is defined to characterize the effect of the normal and shear stress interaction on fatigue life.The fatigue life prediction model is used to predict the fatigue life of specimens in the off-axis tensile fatigue tests.The predicted result agrees with the test result,and the deviation is within the 1-time life span.The results indicate that the proposed fatigue life prediction model can be used to predict the fatigue life of 2D braided alumina matrix composites under the complex in-plane stress condition with the given stress ratio,temperature,and fatigue load frequency.