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Fractography
About: Fractography is a research topic. Over the lifetime, 5043 publications have been published within this topic receiving 86068 citations.
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TL;DR: In this article, the elastic constants, fracture toughness, fracture morphology, and crack-tip plastic zone of a bulk amorphous alloy (bulk metallic glass), with the composition Zr-10Al-5Ti-17.9Cu-14.6Ni (at. pct), were investigated.
Abstract: The elastic constants, fracture toughness, fracture morphology, and crack-tip plastic zone of a bulk amorphous alloy (bulk metallic glass), with the composition Zr-10Al-5Ti-17.9Cu-14.6Ni (at. pct), were investigated. The room-temperature fracture toughness reached values as high as 69 MPa&mrm. However, it showed considerable scatter, which is, at least in part, due to microcrystalline regions in the castings. Controlled crack propagation could not be obtained in chevron-notched specimens. The fracture-surface morphologies of chevron-notched specimens varied as the crack advanced, and this effect is probably related to differences in the crack propagation rate. Controlled fracture resulting in featureless fracture surfaces was observed during in-situ transmission electron microscope (TEM) fracture experiments. The plastic zone of a fatigue-precracked bulk flexure specimen was examined in situ in an atomic-force microscope (AFM). Shear displacements up to 2 &gmm were found. The AFM observations did not reveal any cracks associated with the shear steps. Sectioning of shear steps using a focused ion beam (FIB) with a diameter of 5 nm also did not reveal any cracks.
47 citations
TL;DR: In this paper, the authors describe the room-temperature and hightemperature mechanical properties and failure modes of series Nb-W-Si alloys (Nb-10W, Nb10Si-5W, nb10W-5Si, and Nb 10W-10Si) prepared by arc melting.
Abstract: This article describes the room-temperature and high-temperature mechanical properties and failure modes of series Nb-W-Si alloys—Nb-10W, Nb-10Si, Nb-10Si-5W, Nb-10W-5Si, and Nb-10W-10Si—prepared by arc melting. For the Nb-10W alloy, the microstructure was a monolithic Nb solid solution (Nbss) with a grain size up to a few hundred microns, while the other four alloys consisted of primary Nbss and a eutectic of Nbss/Nb5Si3 (5-3 silicide) as a result of replacing Nb with Si. Among all alloys, the Nb-10W showed the highest fracture toughness of about 15.3 MPa√m1/2 and the lowest 0.2 pct yield compressive strength of 90 MPa at 1670 K. Conversely, the Nb-10Si-10W had the highest 0.2 pct yield strength of about 330 MPa at 1670 K and the lowest fracture toughness of 8.2 MPa√m1/2. It is suggested that toughness is supplied by the metallic Nbss phase, while high-temperature strength is mainly provided by the brittle silicide phase. For the Nb-10W alloy with the monolithic Nbss, intergranular cleavagelike crack propagation is the fracture mode at room temperature, and dislocation movement within the grains and grain-boundary sliding are the dominant modes of high-temperature failure. With two-phase Nbss/Nb5Si3 microstructures, the compressive damage of all four alloys at high temperature was dominated by debonding of the interfaces between the Nbss and the silicide; however, the fracture mode at room temperature is transgranular, controlled by the primary Nbss cleavage.
47 citations
TL;DR: In this article, the fatigue behavior of friction stir spot welds in magnesium AZ31 alloy is experimentally investigated and modeled, and it is shown that the size of the interfacial hook, which comes about from the speed, depth of plunge, dwell time, and tool configuration, is a major contributor to the fatigue life of the joint.
Abstract: The fatigue behavior of friction stir spot welds in magnesium AZ31 alloy is experimentally investigated and modeled. The friction stir spot welds employed in this study are representative of preliminary welds made in developing the joining process for potential use in automobile manufacturing. Load control cyclic tests were conducted on single weld lap-shear coupons to determine fatigue life properties. Optical fractography of the failed fatigue coupons revealed that fatigue cracks initiated from the interfacial "hook" and eventually failed by either nugget pullout or full width separation, depending on the cyclic load amplitude. The failure modes of the magnesium AZ31 alloy were similar to the aluminum alloys of comparable friction stir spot welds. To predict the fatigue life of the lap-joint coupons, a crack growth modeling approach based on a kinked crack stress intensity solution was used. The fatigue model predictions compared well to the experimental fatigue life results, despite an approximate stress intensity factor solution for this weld geometry. The experiments and modeling conducted in this study suggest that the size of the interfacial hook, which comes about from the speed, depth of plunge, dwell time, and tool configuration of the friction stir spot weld process, is a major contributor to the fatigue life of the joint.
47 citations
15 Feb 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the average size of voids developed at fracture under various conditions were measured using the fractography of the sheets and the average void sizes were also correlated with the ratio of Mohr's circle shear strain ǫ31 to effective strain.
Abstract: In this work, forming limit diagrams with fracture limit have been evaluated for various steel sheets namely interstitial free (IF) steel with thickness 0.6, 0.85, 0.9, 1.2 and 1.6 mm, 0.85 mm noncoated and 0.85 mm coated, high strength low alloy (HSLA) steel with thickness 1.6 mm, extra deep drawing quality (EDDQ) steel with thickness of 1.2 mm and stainless steel 430 grade of 1.2 mm. The fractography of the sheets were taken using scanning electron microscope for the above said steel sheets under various conditions namely tension–tension strain condition, plane strain condition and tension–compression strain condition. Using the fractography, the average size of voids developed at fracture under the above said conditions were measured. The average size of voids for various sheets mentioned above were correlated with various shear strains, the ratio of mean strain to effective strain and other factors involving various shear strains, strain hardening exponent and normal anisotropy values. The ratio of height of the dome to punch radius (H/R) for various sheets mentioned above was correlated with the mean strain and also with the ratio of mean strain to effective strain. The average void sizes were also correlated with the ratio of Mohr's circle shear strain ɛ31 to effective strain.
47 citations
17 Feb 2012
TL;DR: In this article, the authors present an approach to predict the reliability of crack growth in an environment with an Environmentally Enhanced Crack Growth (EEDCG) test. But they do not discuss the results of the test.
Abstract: Preface ix Acknowledgments xi 1. Introduction 1 2. Fracture Mechanics Background 6 3. Environmentally Enhanced Crack Growth 19 4. Fracture Mechanics Tests 32 5. Strength Testing 68 6. Quantitative Fractography 99 7. Microstructural Effects 131 8. Predicting Reliability 145 9. Concluding Remarks 158 References 161 Name Index 175 Subject Index 179
47 citations