Fracture Behavior of 1/4-in-Thick 7075-T651 A1 Containing Semielliptical Surface Flaws

摘要

The static fracture behavior of surface-flawed and of center-through-crack specimens of 1/4-in.-thick 7075-T651 aluminum plate was investigated. The response of surface-flawed speciments to sustained tensile loading while exposed to aqueous 3-1/2% NaC1 solution was also studied. An equation was developed that yielded a constant value of fracture toughness for the surface-flawed specimens over a wide range of a/t and a/c ratios. Grain boundary delaminations ahead of the periphery were observed following exposure of specimens to the stress-salt water environment. The size of the delamination zone was found to increase with increasing applied stress intensity; the time of exposure was found to be of secondary importance in establishing the size of the delamination zone. Fracturing the specimens in air following exposure to the stress-salt water environment indicated that the delamination process sufficiently 'blunted' the flaws that in all cases except one the calculated fracture toughness increased as a result of the environmental exposure. (Author)