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

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 r_c.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 r_c/n(n is the total number of fiber bundles in the width direction) were also pradicted.The predietions match the experimontal results vary well.