Fractography

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

The use of laser surface-annealed treatment to retard fatigue crack growth of austenitic stainless steel

Abstract: Fatigue crack growth behavior of an AISI 316 austenitic stainless steel (SS) annealed using a CO2 laser was evaluated under various environments—lab air, gaseous hydrogen and saturated hydrogen sulfide solution. The laser-annealed specimen revealed no change in microstructures in various regions of the specimen. The results of fatigue crack growth tests indicated the laser-annealed specimen had a higher resistance to fatigue crack growth in the region preceding the laser-annealed zone (LAZ) independent of the test environments. Meanwhile, crack growth results also suggested that AISI 316 SS showed a low level of sensitivity to hydrogen-accelerated crack growth. X-ray diffraction pattern of the fatigue-cracked surface revealed that partial austenite to martensite transformation occurred within a narrow depth. The presence of residual austenite in the highly strained region trapped a large amount of hydrogen, which helped reduce hydrogen embrittlement susceptibility and hydrogen-accelerated crack growth in the alloy. Fatigue fractography of the specimens tested in air showed predominantly transgranular fatigue fracture with some flat facets (FFs). In case of specimens tested in the H2S solution or gaseous hydrogen at low loading frequency, quasi-cleavage (QC) fracture was correlated with hydrogen-enhanced crack growth. Moreover, the presence of obvious striations on the fracture surface of embrittled specimens could be attributed to the hydrogen-activated slip processes ahead of the crack front.

Analysis and Testing of Mixed-Mode Interlaminar Fracture Behavior of Glass-Cloth∕Epoxy Laminates at Cryogenic Temperatures

Abstract: This paper presents results from an analytical and experimental study of the effect of temperature and mixed-mode ratio on the interlaminar fracture toughness in glass-cloth/ epoxy laminates. Mode I, mode II, and mixed-mode tests were conducted by the double-cantilever beam, end-notched flexure, and mixed-mode bending lest methods at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K). A finite element model was used to perform the delamination crack analysis. Mode I, mode II, and mixed-mode energy release rates at the onset of delamination crack propagation were computed using the virtual crack closure technique. The fracture surfaces were examined by scanning electron microscopy to correlate with the interlaminar fracture properties.

Effect of the welding profile generated by the modified indirect electric arc technique on the fatigue behavior of 6061-T6 aluminum alloy

Abstract: This paper reports the effect of the welding profile generated by the modified indirect electric arc (MIEA) technique on the fatigue behavior of 6061-T6 welded joints. The calculations are based on the effect of the stress concentration factor produced by the characteristic geometry of the welding profile formed during the welding process. It was found that the fatigue life of welded samples using this welding technique was larger in comparison with data reported in the literature. Also, measurements of microhardness and tension testing were performed to account for the effect of different levels of fatigue damage on the mechanical properties of these welds. Experimental findings reveal that, with reference to undamaged samples, fatigue damage increases the microhardness in the weld metal and heat affected zone (HAZ) whereas it only produces a moderate increase in yield strength of approximately 14% for a 75% of fatigue damage. Tensile and fatigue tests indicate that the thermal affection undergone by the plates during fusion welding dictates failure in the HAZ under tension stress but not under fatigue. The failure mechanism under fatigue is discussed in terms of theoretical analyses and fractography.