Determination of Stress Intensity Factor and Interaction Behavior of Radial Cracks in an Un-notched Round Bar

摘要

Cracks emanating from the surface of a bar, power transmission shafts, and pressure vessels when undergoing cyclic loading. Multiple radial cracks also originating from the inner surface of cylinders when undergoing cyclic internal pressure. In general, surface cracks in structural components are often approximated by elliptical, semi elliptical cracks, circular or semi circular cracks. Due to complexities in analysis of multiple cracks, many researchers have studied the damage tolerance analysis of single crack in rectangular plate, notched and unnotched round bar and thus the effect of crack interaction has been neglected. In order to predict safe-life of such cracked components, it is important to know the individual stress intensity factors (SIF) under mixed mode loading. This paper presents the SIF and interaction behavior of multiple radial cracks in an un notched round bar subjected to far filed tension loading. Three surface cracks of same dimensions (crack depth and aspect ratios) were introduced around the circumference of the cylindrical rod specimen. The crack depth ratio (a/d) ranging between 0.1 and 0.3 was considered for two different crack aspect ratios (a/c = 0.6 and 1.0). The crack tip region was meshed with isoparametric singular elements to incorporate the singularity of stress and strain fields. The SIF values of single and multiple cracks are compared to determine the interaction behaviour of radial cracks on SIF. Comparison SIF of radial cracks with published SIF of single crack showed a good agreement at short crack depths ((a/d) <0.3). Beyond the crack depth ratio of 0.3 higher SIF is observed. This is due to interaction effect of radial cracks which increases with crack depth ratio. SIF are higher at the surface (S/S0 = ±1) of a semi-circular crack whereas SIF are higher at the crack middle region (S/S0 =0) for semi elliptic cracks independent of crack depth ratios.