Fractography

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

Thermal-mechanical coupled effect on fracture mechanism and plastic characteristics of sandstone

Abstract: Scanning electronic microscopy (SEM) was employed to investigate fractographs of sandstone in mine roof strata under thermal-mechanical coupled effect. Based on the evolution of sandstone surface morphology in the failure process and fractography, the fracture mechanism was studied and classified under meso and micro scales, respectively. The differences between fractographs under different temperatures were examined in detail. Under high temperature, fatigue fracture and plastic deformation occurred in the fracture surface. Therefore, the temperature was manifested by these phenomena to influence strongly on micro failure mechanism of sandstone. In addition, the failure mechanism would transit from brittle failure mechanism at low temperature to coupled brittle-ductile failure mechanism at high temperature. The variation of sandstone strength under different temperature can be attributed to the occurrence of plastic deformation, fatigue fracture, and microcracking. The fatigue striations in the fracture surfaces under high temperature may be interpreted as micro fold. And the coupled effect of temperature and tensile stress may be another formation mechanism of micro fold in geology.

The effect of microstructure on fatigue crack propagation in iron-carbon alloys

Abstract: The dependence of fatigue crack growth rate on the cyclic stress intensity factor was determined for six iron-carbon alloys ranging in carbon content from 0.23 to 1.08 wt pct carbon. Both ferrite/pearlite and ferrite/free iron carbide microstructures were studied. Scanning electron microscope fractography studies correlated the fatigue mechanism with microstructure. It was found that when the predominant mode of crack growth was ductile, the crack growth rateda/dN could be related to the cyclic stress intensity factor ΔK by an equation of the formda/dN = (ΔK)m where andm are constants. The constantm was approximately equal to four when the crack growth mechanism presumably was the blunting and resharpening of the crack tip by slip processes. The constantm was greater than four when the crack growth mechanism was void coalescence in the interlamella ferrite of pearlite colonies. The preferred fatigue crack path through the pearlitic alloys was through the free ferrite phase.

Effect of Sulfide Ions on Caustic Cracking of Mild Steel

Abstract: Potentiostatically controlled slow strain rate tensile tests were conducted on AISI 1018 mild steel in hot (92°C) caustic solutions of and in a chemically inert cell. Reduction of area was used as a measure of susceptibility to stress corrosion cracking (SCC). The presence of sulfide ions raised the active‐passive transition potential to more noble values, and maximum susceptibility to SCC occurred at potentials near the active‐passive transition in each environment. Cracking at these potentials was further confirmed by conducting tests on prefatigue cracked double cantilever beam specimens at a known stress intensity, and crack fractography was studied by scanning electron microscopy. Crack liquid pH measurements were obtained with pH indicator paper using a freezing technique. A hydrogen embrittlement mechanism of SCC was eliminated from consideration in both environments on thermodynamic grounds. All observations were reasonably consistent with a dissolution mechanism of SCC involving film rupture events.