Anisotropy of Composite Shearing Strength in the Mechanical Joints

Studying of the strength characteristics of polymer composite materials, which are used in the structures for various applications, is an important subject for research. Here one of the major issues is the development of fastening techniques to maximize the strength characteristics of composite fibers. Based on the modification of the available test methods, a set of specimens and devices has been developed to determine the shearing (cut) strength from the fastener hole to the edge of the composite part. For this purpose, we used the modified specimen sequentially shearing along the contour after each test cycle in order to find the required parameter depending on the distance from the fastener to the part edge. According to the result of experimental studies, possible types of shearing test and shear test failures were identified. It is demonstrated that shearing strength and shear strength in the specimen plane are different characteristics with no correlation between them. It is found that a shearing in the classic sense is observed only for high-anisotropy structures when they are loaded in the more rigid direction, whereas the complex modes of failure occur for the heavily reinforced composites used. For example, during testing a pure shearing was observed in 0° planes in the specimens with the package structure of [0 ° 0.7 ; ±45 ° 0.2 ; 90 ° 0.1 ], while it was observed both for the holes drilled in 0° and 22.5° directions in the specimen with the structure of [0 ° 0.8 ; ±45 ° 0.2 ]. We obtained the quadratic engineering dependence to predict shearing strength of the heavily reinforced basic composite. Based on processing of the experimental results, a recommendation has been made on the need for constant experimental support of the design process, which can be implemented by the proposed specimen and testing device.