Experiment and analysis of unidirectional CFRP with a hole and crack as sandwich-form inhomogeneous composite

In modern mechanical industry, many designs are incorporating lightweight materials. Known as the future’s lightweight material; Carbon Fiber Reinforced Plastic (CFRP) contains a fiber structure and therefore is vulnerable to cracks and holes that may be generated during machining. However, in a mechanical structure, it requires bonding the multiple parts using bolts, rivets, etc. In other words, it inevitably requires generating holes in the mechanical structure. Because of such problems, CFRP has been attached with a normally used structural steel, to lighten the weight. It is quite difficult to understand the mechanical features of inhomogeneous composites. In order to increase the usage of inhomogeneous composites that contain multiple light weight mechanical parts, there is a necessity of mechanical basic data. This study used CFRP and SM45C that has the stacking angle [0/60/–60/0]. It has a form of a sandwich in which 5 mm thick SM45C acts as the core, with 2 mm thick unidirectional CFRP attached on both sides of it. Using inhomogeneous composites of such sandwich form, Compact Tension (CT) test and analysis took place. In the test, considering the actual material being used in mechanical industry, a hole was made on the edge of the crack and compared the results according to the location of the hole. SIMADZU corporation’s Universal Testing Machine was used in the test. Setting the test as the basis, we constructed a model for the analysis. In the analysis, like we did in the experiment, we kept in mind the fiber structure of unidirectional CFRP and the conditions of the analysis were identical to the test. As the test result, the magnitude was at its optimal when there was no hole. But if a hole had to be made, it is at its best when placed at the spot where the center of the hole is 20 mm from the edge of the crack. A model with no hole had the reaction force of 14 kN and the forced displacement was 4 mm. A model with a hole placed 20 mm from the edge of the crack had the reaction force of 11 kN with the forced displacement of 10 mm. Test results and analysis differ a lot, but the data after the section when the reaction force rapidly arises are reliable. In other words, in the process of destruction due to the crack propagation, the analysis is reliable.