Fractography

About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.

The role of defects in the fracture of an Al–Si–Mg cast alloy

Abstract: A study of the tensile behaviour of test coupons that were extracted from cast plates of D357 aluminium is described. The effects of specimen thickness, heat treatment, structural integrity and hot isostatic pressing (HIP) were investigated. Chevron marks were found on the fracture surfaces of the specimens that failed under plane strain conditions. In most cases, structural defects, such as shrinkage pores and oxide films, were found at the initiation sites for fracture. It is shown that the structural defects that were found at the origin of the chevron patterns are large enough to explain the fractures, and that the tensile failure of cast Al–7Si–Mg alloys can be explained in terms of the principles of fracture mechanics. The influence of structural defects on the elongation to fracture is discussed, together with some implications for quality control programs involving cast Al–7Si–Mg components.

A fracture mechanics study of stress corrosion cracking of type-316 austenitic steel

Abstract: A new test specimen configuration, designated the T-notch double cantilever beam (TNDCB), was developed, calibrated and employed for a fracture mechanics study of stress corrosion cracking (SCC) of cold worked Type-316 austenitic stainless steel exposed to hot aqueous solutions of 44.7 wt pct MgCl2. The effects of stress intensity (K I ), temperature (T) and electrochemical potential (E) upon the crack velocity (v) and fractography were investigated. The stress intensity (K ISCC ) below whichv became immeasurably small was ∼12 MN·m−3/2. Above this value, three regions of behavior were observed. Region I exhibitedK I dependent cracking followed by Region II which exhibitedK I independent cracking and an apparent activation energy of 63 to 67 kJ/mol, followed by Region III where cracking again became dependent uponK I . The relative proportions of intergranular and transgranular crack paths were markedly dependent upon bothK I andE, and less sensitive toT. Crack velocity was insensitive to small changes inE with respect to the free corrosion potentials (E corr), but could be terminated by an applied active potential of ∼−0.35 VSCE. The pH within the propagating crack was estimated to be <1.0 atE corr, rising to ∼4.5 at −0.35 VSCE. The mechanism of SCC was discussed with respect to film rupture events caused by crack tip plastic deformation, adsorption controlled processes on the metal surface, and hydrogen diffusion in the metal lattice.