Branching and Propagation Behaviors of Fatigue Crack in Precracked Specimen
Chobin MAKABE and Darrell F. SOCIE
Abstract:The growth behavior of crack was investigated under cyclic torsion with and without axial static stress using precracked steel. After shear mode crack growthCbranching of the crack was observed on both sides of the crack. The length between the branching points was dependent on loading conditions. This length was longer when the applied shear amplitude and the static axial stress level were higher. The crack propagation curves have turning points. Before the turning point, shear mode crack growth was observed and the crack propagation rate had good correlation with the branching behavior. It is found that the crack opening and the initiation of micro cracks help the shear mode crack growth After the branching of crack, loading method was changed from cyclic torsion to push-pull. When applied normal stress was higher, the crack grew under the condition of maximum shear stress criterion. On the other hand, when applied stress was lower, the crack grew under the condition of maximum principal stress criterion. Those behaviors are also related to slip band density and crack opening. Key Words:Low cycle fatigue, Torsional fatigue, Micro-crack, Crack