Cailiao gongcheng (Nov 2020)
Failure mechanism of stitched three dimension woven composite/Ti alloy hybrid board joint under shear load
Abstract
In order to study the effect of stitching density, tow size of the suture and diameter of the stitching hole on the shear property of the stitched three-dimensional woven composite/titanium hybrid board stitching connection structure, seven groups of samples with different stitching densities, tow size of the suture and diameter of the stitching hole were tested. A reference group whose samples were unstitched was also tested to show the effect of stitching on the joint. Different failure modes of the lap zone with different stitching parameters were observed in in-situ meso-experiment, and the damage morphologies of the characteristic points on the load-displacement curve were given. The result shows that increasing tow size of the suture and increasing stitching density can both increase the failure load of the hybrid joint. Increasing the stitching density is proved more effective in improving the failure load. Doubling the stitching density can increase the failure load of the stitched joint about 82.0%. Doubling the tow size of the suture can only increase the failure load of the joint about 24.3%; Whether the diameter of the stitching hole is 2 mm or 4 mm do not influence the bearing capacity of the structure obviously, and when the stitching hole diameter reaches 6 mm, the bearing capacity is reduced due to the low strength of the epoxy resin in the gap between stitching hole and suture. It is dangerous to increase diameter of stitching hole above 4 mm; the shear failure of the stitched three-dimension woven composite/titanium alloy hybrid structure is observed by mesoscopic mechanical test. Composite/titanium alloy interface failure, crack initiation and extension in composite or in lap zone and failure of the lap zone are the three main stages of the structure failure observed in the test; The suture failure in the connect zone includes suture pull out and suture cut off. There are three failure modes of the lap zone observed in test. In suture cut off mode, all sutures in lap zone are cut off. The position at which the suture is cut is related to the diameter of the stitching hole. In suture cut off/pull out mixed mode, some of the interface between suture and three-dimension woven composites fail and the suture is partly or completely pull out. In the group with high stitching density, sutures near the end of the three-dimension woven composite crush the composite and extrude out of the composite. Stitching density is the major factor in the failure mode of the joint.
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