INVESTIGATION OF SIZE SCALE EFFECTS ON THE FATIGUE CRACK GROWTH CHARACTERISTICS OF AN ALUMINUM ALLOY

摘要

Size scale effect on the fatigue crack growth characteristics of 6063 aluminum alloy is examined in this paper. This is important, as often, a small scoop of material is removed from an in-service component or structure such as pressure vessels, chemical plants and pipe lines are used to decide on life extension. Constant amplitude fatigue crack growth tests were carried out using single edge notched (SENT) specimens and compact tension (CT) specimens to study the effect of size scale on the fatigue crack growth behavior of the material. The thicknesses of the specimens were varied from 10 mm to 0.36 mm. The size of the test specimens were varied from the ASTM standard size to miniature size of 20 mm × 5 mm × 0.36 mm. Tests were conducted at two different stress ratios in load control mode to study the effect of stress ratio on fatigue crack growth rate (da/dN). Seven point incremental polynomial methods was used to deduce the (da/dN) values to plot the fatigue crack growth curves for different specimens. The fracture surfaces were examined under a scanning electron microscope (SEM) to understand the nature of crack propagation at initial, intermediate and terminal stages of crack growth.