三向碳碳材料在小偏轴角拉伸下的切口强度预报

PREDICTION OF NOTCHED STRENGTH OF 3D CARBON CARBON MATERIALS UNDER TENSION WITH SMALL OFF-AXIS ANGLE

  • 摘要: 在小偏轴角拉伸下,带切口的三向碳碳材料平面试件首先沿切口平面作自相似扩展。扩展到断裂的纤维束数与宽度方向的纤维束总数之比达到某一数值时,试件沿纤维束(或在另一些单层中垂直纤维束)方向剪断。断裂是灾难性的,所以这种切口强度预报与简单拉伸时的切口强度预报是相当的;区别仅在于在小偏轴角拉伸时,纤维束除受拉伸应力外,还作用有不可忽视的剪应力。本文对纤维束作了拉剪联合作用的强度测量,以得到其强度的概率分布的参数。据此预报了三向碳碳材料在小偏轴角拉伸时的切口强度,以及整个试件剪断时的断裂的纤维束数与纤维束总数之比值,理论预报与实验结果吻合良好。

     

    Abstract: Under tension with small off-axis angle, the notch in the plane specimen of 3D carbon carbon material propagates self-similarly at first.Finally the specimen shears to failure along the direction of the fiber bundles in some of the layers and perpendicular to the fiber bundles in the remaining layers,as the number of broken fiber bundles reaches a criticl value rc.The failure is catastrophic.No additional load is needed in order to break more, fiber bundles in front of the notch tip all along to the final rupture.It implies that the notchedst rangth of 3D carbon/carbon material under tension with small off-axis angle is dictated with the strength of fiber bundle at notch tip,that is just the same as in the case of simple tension.The difference lias only in that the fiber bundle in this case sustains also shear besides the tensile strass and the shear stress will substantially reduce its tensile strength.This paper performs the experimental measuroment of tensile strength and shearing strength under combined stress state.The statistical notch strength of the 3D C-C specimens were caleulated based on these strength data and the stress fields near the notch tip computed with FFM.The ratio of rc/n(n is the total number of fiber bundles in the width direction) were also pradicted.The predietions match the experimontal results vary well.

     

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