Study of Fatigue Crack-hole Interaction and Prediction of Crack Path

Abstract

Engineering components contain several defects. These defects are introduced during the extraction of the alloys and at various stages of manufacturing. Existence of defects such as, blow holes, slag inclusions, quench cracks, weld defects, notches, mechanical holes etc. are common in engineering materials and components. Their presence may reduce the load carrying capacity of the component and may cause immature failure in the both under monotonic and dynamic loading. These defects also interact with a propagating fatigue crack and may cause crack deflection, crack growth acceleration and even retardation. This investigation aims to study fatigue crack-hole interaction and prediction of crack path. The study has been made using 25×25 mm2 cross section aluminium beam of span length 300 mm with circular hole of 3 mm diameter located at different positions. All fatigue tests were conducted using a 100 kN BiSS servo-hydraulic UTM. The tests were conducted under constant load amplitude condition maintaining a stress ratio, R=0.3. The monitoring of crack path was done by tip tracking method (TTM) using 10x magnification travelling microscope. The beams were subjected to constant amplitude load cycle under four-point bending loading condition. Presence of the hole deflected cracks from their normal paths. In some cases the cracks merged into the hole and resulted crack arrest. In the present work an attempt has been made to develop a model to predict the fatigue crack path.