ROLE OF WIRE ASPECT RATIO AND CRACK ASPECT RATIO ON FRACTURE BEHAVIOR OF WIRE SPECIMEN

Accurate stress intensity factor (SIF) solutions for cylindrical specimens with different wire aspect ratios and crack aspect ratios are required to determine the fracture toughness of rods and wires. The mode I geometric factor solutions of various crack configurations in a cylindrical fracture specimen in tension have been determined using liner elastic fracture mechanics. Finite element analysis (FEA) is applied to compute this as a function of wire aspect ratio (𝐻/𝐷), crack aspect ratio (𝑎/𝑏), and relative crack depth (𝑎/𝐷). It is found that the geometric factor is independent of wire aspect ratio for shallow cracks but has a major influence for deeper cracks. Also, the geometric factor is higher for concave cracks which facilitates the crack propagation. The mechanistic causes of the same are explained. Fracture toughness measurements on polymethylmethacrylate (PMMA) were carried out for the experimental validation of the solutions. The application of these solutions to fracture toughness measurements at the micro- and nanoscale, particularly in ceramic fibers and high strength metallic wires, is discussed.
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