Evaluating fatigue crack propagation properties using a cylindrical rod specimen

In the evaluation of fatigue crack propagation properties, standard specimens such as the compact tension (CT) or center cracked specimens are commonly employed. However, these specimens are not applicable when the available material for testing is of a long axial length but small cross-sectional area. Surface cracked rod specimens may be used for this purpose. In the current work, to shed light on their applicability to the evaluation of fatigue crack propagation properties, surface cracked rod specimens were tested under axial tension. The development of the surface cracks was examined. Fatigue crack propagation data at the surface and in the deepest interior point of the surface cracks in different diameter rods were obtained. Comparison showed that rods with diameters of 8 mm and larger give fatigue crack propagation data similar to that given by compact tension specimens. For a 6 mm diameter rod specimen, growth rates were slightly higher than the standard if correlated in terms of ΔK but, fall in line with the standard, if crack closure was taken into account.