Fatigue Crack Growth Life Prediction of an Extruded Thick-Walled Cylinder With Internal Axial Crack

Abstract

The integrity of nearly all engineering structures is threatened by the presence of cracks. Structural failure occurs if a crack larger than a critical size exists. Although most well designed structures initially contain no critical cracks, subcritical cracks can grow to failure under fatigue loading, called fatigue crack propagation. Fatigue failure, that is, failure under repeated or cyclic loading, is a serious concern of engineering design. Under fatigue loading, the component may fail at a stress level that is far below its yield strength. The extruded materials are extensively used in chemical, food and nuclear industry and generally offer a unique combination of strength and freedom with regard to design solutions. During extrusion, material flow occurs in the direction of applied force and as a result microstructure changes. The process ultimately induces variation in the mechanical properties when tested along or across the extrusion direction. In present study, the fatigue crack propagation in a thick-walled cylinder is analyzed through detailed experimental work and finite element analysis and the fatigue crack growth life of the cylinder, with internal axial crack, has been predicted. Fatigue crack growth tests were conducted on middle tension, M(T), samples. The fatigue crack growth data of the cylinder is obtained in the transverse direction which experiences the maximum tensile stress (hoop stress). The tests were conducted at ambient temperature in air atmosphere. The data thus obtained include the fatigue crack growth and the SN curves. The fatigue crack growth life of the thick-walled cylinder has been predicted with ANSYS structural software. An ANSYS Parametric Design Language (APDL) code has been written to simulate the crack growth process. The actual data obtained from the experimental work has been used for the simulation work.