Influence of geometry of composite cruciform specimen under biaxial loading on coefficients of central testing zone

Based on the features of composite cruciform specimens under biaxial tensile loading, we analyzed the rules of how stress concentration factors and loading coefficients of the central testing zone in the cruciform specimens of different geometric shapes, change with different thickness ratios and load ratio conditions. The biaxial tensile tests with different load ratios were implemented for verification. The results show that the coefficients of the central testing zone have nothing to do with the loading magnitude, but are related to geometric shapes, thickness ratios and loading ratios. Smaller width of equal-width loading arms and larger thickness ratio contribute to smaller stress concentration factors, and different load ratios mean different stress concentration factors. Generally, the loading coefficients increase along with the increase of thickness ratios. The x-axis loading coefficient β_x rises nonlinearly while the y-axis coefficient β_y decreases linearly with the increase of load ratios. In addition, for the D-shaped cruciform specimen under biaxial tensile loading, the y-axis stress component of the central testing zone is negative when the load ratio f=4/1, and the central area shows a state of compressive stress.