This study investigates the influence of geometric discontinuities specifically, circular holes – on the fracture behavior of fiber-reinforced polymer composite plates containing edge cracks. Using the Finite Element Method (FEM) as a non-destructive numerical tool, we analyze how variations in hole size and positioning affect the stress distribution σ _yy and the J-integral near the crack tip. The J-integral, used both as a fracture toughness parameter and a crack detection indicator, effectively captures the energy release rate and the severity of crack-tip conditions in anisotropic composite materials. Reference models without holes were first validated before introducing circular holes at varying distances from the crack front. The results reveal that strategically placed holes can reduce local stress concentrations and lower the J-integral values, mitigating the driving force behind crack propagation. These findings highlight the importance of geometric optimization and advanced simulation in improving damage tolerance and fracture resistance of composite structural components. Furthermore, the insights gained are particularly relevant to the aerospace industry, where fiber-reinforced polymer composites are increasingly used in aircraft structures due to their high strength-to-weight ratio and fatigue performance. Understanding fracture behavior under geometrical modifications enhances the structural reliability of such lightweight components under operational conditions.

To study the effect of the variable amplitude on the carburised 17CrNi high-strength steel, very high cycle fatigue tests were performed on smooth specimens under the stress ratios of 0 and −1. After the experiment, the characteristics of the fracture surfaces were investigated by means of an optical microscope and a scanning electron microscope. Circular-formed marks were found around the inclusion inside the fisheye. Finally, based on five damage models, the fatigue life of the carburised 17CrNi high-strength steel was predicted. The comparison of the calculated lives with the experimental data shows that the modified Miner's criterion is the most accurate and it can adequately characterise the fatigue life of the 17CrNi steel.