Showing papers on "Fractography published in 1983"
TL;DR: In this paper, the micromechanics of failure emanating from machining-induced cracks in brittle materials are investigated and two components of residual stress have been identified: a crack-wedging force due to the plastic zone beneath the strength-controlling machining groove, and a compressive surface layer due to adjacent grooves.
Abstract: The micromechanics of failure emanating from machining-induced cracks in brittle materials is investigated. In situ monitoring of crack response during breaking tests (with use of acoustic wave scattering), strength measurements and post-failure fractography all indicate that the crack response is dominated by residual stresses. Two components of residual stress have been identified: a crack-wedging force due to the plastic zone beneath the strength-controlling machining groove, and a compressive surface layer due to adjacent grooves. The wedging force dominates and causes stable equilibrium crack extension during a breaking test. The implications of the results for non-destructive evaluation of surface damage by acoustic wave scattering is discussed.
175 citations
TL;DR: In this article, the authors examined hydrogen embrittlement in FeSi-and Ni-single crystals at low hydrogen pressures (10 mPa ⩽ pH2⩽ 100 kPa) and measured the crack tip opening angle α of a growing crack as a function of temperature, hydrogen pressure and rate.
143 citations
TL;DR: In this article, it is hypothesized that the cracklike internal surfaces are developed as a result of differential sintering of agglomerates relative to their surrounding powder compact, and isostatic hot-pressing of the sintered composites quickly eliminated the crack-like internal surface.
Abstract: Strengths of sintered Al2O3/ZrO2 composites are much lower than those of hot-pressed composites due to large flaws associated with the sintering process. Fractography has shown that cracklike internal surfaces are at the fracture origins of the sintered materials. It is hypothesized that the cracklike internal surfaces are developed as a result of differential sintering of agglomerates relative to their surrounding powder compact. Isostatic hot-pressing of the sintered composites quickly eliminated the cracklike internal surface. Flaws responsible for fracture of the isostatically hot-pressed composites were low-density regions that are not as easily eliminated.
143 citations
TL;DR: In this paper, the authors show that transgranular hydrogen embrittlement in 5.5Ni steel is primarily an interlath cracking phenomenon and that the fracture surface generally follows martensite lath boundaries.
Abstract: Quenched and tempered 5.5Ni steel was embrittled by hydrogen charging and broken in air at room temperature. The primary fracture mode was transgranular quasicleavage. The quasicleavage facets were studied by scanning electron fractography and by transmission electron microscopy of profile fractographic specimens. The latter were prepared by plating the fracture surface with nickel and thinning so that the fracture surface was contained within the region of the specimen that was transparent to the electron beam. The fracture surface generally followed martensite lath boundaries. In addition, interlath microcracks were frequently found in the material immediately beneath the fracture surface. These results suggest that transgranular hydrogen embrittlement in this steel is primarily an interlath cracking phenomenon. Since the lath boundary planes tend to lie in {110}, the results also explain the prevalence of {110} quasicleavage in the embrittled specimens, which contrasts with the {100} cleavage found in uncharged specimens broken below the ductile-to-brittle transition temperature.
83 citations
TL;DR: In this article, a study of the micro-mechanisms of tempered martensite embrittlement was made on a series of 4340-type steels in which the contents of manganese, silicon, and trace impurities, especially phosphorus and sulfur, were varied.
Abstract: A study of the micro-mechanisms of tempered martensite embrittlement was made on a series of 4340-type steels in which the contents of manganese, silicon, and trace impurities, especially phosphorus and sulfur, were varied. One plain-carbon steel was also examined. The study employed Charpy impact tests and four-point slow-bend tests coupled with an elastic-plastic stress analysis, as well as scanning electron fractography, Auger electron spectroscopy, transmission electron microscopy of extraction replicas, and magnetic measurements of the transformation of retained austenite. The results indicate that in these steels the TME phenomenon is an intergranular embrittlement problem caused by carbide precipitation on prior austenite grain boundaries which are already weakened by segregated phosphorus and sulfur. The transformation of intragranular retained austenite is concluded not to be of primary significance in the TME in these steels, although it may contribute to the magnitude of the TME toughness trough.
70 citations
TL;DR: In this paper, the fracture behavior of thermoplastic poly(ethylene terephthalate) reinforced with short E-glass fiber was investigated using fractography and a fracture mechanics approach.
Abstract: The fracture behaviour of thermoplastic poly(ethylene terephthalate) reinforced with short E-glass fibre was investigated using fractography and a fracture mechanics approach. The observed microstructures, crack propagation and the stress-rupture lifetime data indicate a sudden breakdown induced by far-field effectS. The critical damage appears to be correlated with a ductile-to-brittle transition of matrix fracture. The calculation of fracture toughness for various fibre orientations indicates that the fibre pull-out energy is the dominant term in the case in which the fibre orientation is perpendicular to the notch tip.
59 citations
TL;DR: In this article, a mathematical model based on dynamic observations of intermittent crack growth was developed to support the concepts of intermittent cracks advance and decreased crack tip plasticity due to environmental water vapor.
Abstract: — Strains very near a growing fatigue crack have been computed from measured material displacements, both for a very dry environment and for humid air. Significant differences in crack tip strains arid crack tip opening displacements occur in these environments, with crack tip deformation in water vapor evidencing less plasticity than the dry environment. These quantitative results are incorporated into a previously developed mathematical model which is based, in part, on dynamic observations of intermittent crack growth. Fractography is shown to support the concepts of intermittent crack advance and decreased crack tip plasticity due to environmental water vapor.
56 citations
TL;DR: In this paper, the influence of ageing on relevant material properties (i.e., matrix plastic flow behavior, and morphology and chemistry of second-phase particles) was investigated, while a quantitative evaluation was made of the associated fractography.
32 citations
01 Jan 1983
22 citations
TL;DR: In order to examine the cause of the Zircaloy PEI failure, stress corrosion cracking (SCC) experiments under different types of corrosive agents (Iodine, iron iodide, aluminum, cesium iodide and cadmium) were conducted.
22 citations
01 Jul 1983
TL;DR: In this article, a wide-ranging fractographic research program, from the fundamental characterisation of test coupon fractures to the failure analysis of full-scale aerospace components, has been undertaken in Materials and Structures Department, RAE.
Abstract: : A wide-ranging fractographic research program, from the fundamental characterisation of test coupon fractures to the failure analysis of full-scale aerospace components, has been undertaken in Materials and Structures Department, RAE. This paper describes work on unidirectional CFRP test coupons in which a known mode of failure had been produced, the modes being longitudinal and transverse tension, compression and shear. From a fundamental understanding of the character of the different modes and of the mechanisms of fracture propagation it is shown how the qualitative significance of micro-defects occurring in good quality laminates may be assessed. The defects considered are fibre faults, fibre-matrix bond strength, fibre distribution, fibre alignment and voids and inclusions; these are illustrated and their individual and collective significance discussed.
TL;DR: In this article, cyclic striations, cleavage rivers and twist angle misorientations are measured and discussed in terms of geometrical and local stress considerations and a dislocation dynamics model is derived which qualitatively gives the correct ordering of power-law slopes (d a /d N vs ΔK ) and growth rate magnitudes as a function of test temperature.
TL;DR: In this paper, the authors used scanning electron fractography to evaluate the hydrogen embrittlement of three metallic glasses, Ni 40 Fe 40 B 20, Ni 39 Fe 39 Mo 4 Si 6 B 12 and Ni 40Fe 6 Co 20 Cr 12 Mo 6 B 16.
TL;DR: In this article, a new non-destructive technique for studying the sub-surface microstructure of cleaved samples which allows correlation with the associated surface morphology is described, based on Synchrotron X-ray Fractography (SXRF).
TL;DR: In this paper, single-crystal subsize Charpy impact specimens of a model nickel-base superalloy were machined so as to propagate a crack in two directions through the lattice.
01 Sep 1983
TL;DR: AISI 4340 steel fracture under sustained load in hydrogen and in hydrogen sulfide over a range of temperatures and pressures, whose crack growth kinetics have been well characterized previously, was chosen for study.
Abstract: A study of the correlation and crack growth response was undertaken to better define the elemental processes involved in gaseous hydrogen embrittlement. AISI 4340 steel fracture under sustained load in hydrogen and in hydrogen sulfide over a range of temperatures and pressures, whose crack growth kinetics have been well characterized previously, was chosen for study. Fractographic results showed that crack growth followed predominantly along prior-austenite grain boundaries, with a small amount of quasi-cleavage, at low temperatures. At high temperatures, crack growth occurred primarily by microvoid coalescence. The fracture surface morphology, which is indicative of the micromechanisms for crack growth, was essentially the same for hydrogen and hydrogen sulfide. Changes in fracture morphology, i.e., crack paths, corresponded to changes in crack growth kinetics, both of which depended on pressure and temperature. There was no evidence for crack nucleation in advance of the main crack, and this suggests that the fracture process zone is located within one prior-austenite grain diameter from the crack tip.
TL;DR: In this article, the through-thickness tension test is used to assess resistance to lamellar tearing in steels produced for laminate-tearing-resistant applications.
Abstract: The through-thickness tension test is used to assess resistance to lamellar tearing. Observed through-thickness reduction-of-area (TTRA) values are usually well above the 20% minimum specification level in steels produced for lamellar-tearing-resistant applications. Low TTRA values, when encountered, indicate susceptibility to lamellar tearing but provide little indication of the source of premature fracture. Fractographic examination, especially with the scanning electron microscope, provides information about the origins of low ductility. Sources of premature fracture discussed herein are indigenous inclusions, exogenous inclusions, occluded hydrogen, undissolved alloy additions, and solidification microvoids.
TL;DR: Methode as discussed by the authors utilisant la technique de diffraction des rayons X for observer the surface fracturee en vue de l'analyse des micromecanismes and de la mecanique de la rupture.
Abstract: Methode utilisant la technique de diffraction des rayons X pour observer la surface fracturee en vue de l'analyse des micromecanismes et de la mecanique de la rupture. Application a la mesure de la distribution des tensions residuelles en dessous de la surface fracturee dans l'acier AISI 4340
TL;DR: In this paper, extensive electron fractographic studies were conducted on the previously generated fatigue fracture surfaces using both scanning and transmission electron microscopy, and the threshold micromorphology revealed crisp, cleavage-like facets.
01 Jan 1983
TL;DR: In this article, the authors describe the findings and interpretations of the fractographic survey conducted for the International Cyclic Crack Growth Rate (ICCGR) cooperative group round-robin specimens.
Abstract: This paper describes the findings and interpretations of the fractographic survey conducted for the International Cyclic Crack Growth Rate (ICCGR) cooperative group round-robin specimens. Specimens of A533B pressure vessel steel were tested at several laboratories in the United States and elsewhere with the same nominal test parameters. A rather wide scatter of the results was found. A fractographic and metallographic survey was carried out in order to clarify the scatter and to evaluate the micromechanism of the crack growth. The fractographic findings are reported in detail and correlated to the crack growth behavior. A hydrogen-assisted crack propagation mechanism based on the fractography is proposed and applied to the observed crack growth behavior.
TL;DR: In this paper, the effect of a local fiber distribution in the vicinity of a crack on the fracture toughness of glass fiber reinforced epoxy resins, which have ten kinds of fibre volume fraction including very low fraction, by means of fracture mechanics and fractography was made.
TL;DR: Grain oriented piezoelectric ceramics with bismuth-layer and tungsten-bronze structures were prepared by hot-pressing in this paper, where bend strength measurements in the direction parallel and perpendicular to the hotpressing direction were obtained.
Abstract: Grain oriented piezoelectric ceramics with bismuth-layer and tungsten-bronze structures were prepared by hot-pressing. Bend strength measurements in the direction parallel and perpendicular to the hot-pressing direction showed different anisotropic behaviors for SrBi2Nb2O9 and (Pb0.6Ba0.4)0.97La0.02Nb2O6 ceramics. Microindentation technique was applied and fhe crack propagation was examined with fractography.
01 Apr 1983
TL;DR: In this paper, the growth rates of fatigue crack growth were determined for a 508-2 steel in pressurized high-temperature, reactor-grade water, over a temperature range of 93/sup 0/C to 288/sup 1/O/C (200/sup 2/F to 550/Sup 0/F) and the fractography showed brittle-like features for all test temperatures.
Abstract: Fatigue crack growth rates were determined for A 508-2 steel in pressurized high-temperature, reactor-grade water, over a temperature range of 93/sup 0/C to 288/sup 0/C (200/sup 0/F to 550/sup 0/F) In addition, studies of the oxide layer on the fatigue fracture surface and of the fractography of these specimens were completed in order to provide information on corrosion-assisted, fatigue crack growth mechanisms The crack growth data show a distinct minimum in growth rate at approx 200/sup 0/C (approx 400/sup 0/F) Magnetite (Fe/sub 3/O/sub 4/) was found on the fatigue fracture surfaces at all temperatures The fractography shows brittle-like features for all test temperatures These observations suggest that hydrogen evolution may have occurred and that hydrogen-assisted crack growth may be responsible for the environmental effects observed
TL;DR: Fractography by scanning electron microscopy (SEM) of samples of a low molecular weight, high-density polyethylene from the melt isothermally crystallized at 125°C, together with SEM on these samples treated with p-xylene (including fracture surfaces), polarized light microscopy, differential scanning calorimetry and gel permeation chromatography have provided evidence that fracture preferentially develops along a weakest link path defined by regions of segregated low- molecular weight material.
Abstract: Fractography by scanning electron microscopy (SEM) of samples of a low molecular weight, high-density polyethylene from the melt isothermally crystallized at 125°C, together with SEM on these samples treated with p-xylene (including fracture surfaces), polarized light microscopy, differential scanning calorimetry and gel permeation chromatography have provided evidence that fracture preferentially develops along a weakest link path defined by regions of segregated low molecular weight material. The segregated material is to a considerable extent accumulated in the spherulite boundaries.
TL;DR: In this article, the authors studied the hydrogen embrittlement of a hardened and tempered plain carbon, eutectoid steel of 1930 MN m−2 tensile strength and showed that fracture initiated internally at oxide inclusions.
Abstract: The hydrogen embrittlement of a hardened and tempered plain carbon, eutectoid steel of 1930 MN m−2 tensile strength has been studied. Plain, unnotched specimens were electrolytically charged with hydrogen and then subjected to tensile tests and delayed failure tests at constant load. The test results showed a scatter characteristic of a stochastic process and it is shown that the distribution can be described by a modified form of the Weibull probability function. Fractographic results are reported which show that fracture initiated internally at oxide inclusions and it is suggested that the embrittlement can be explained by a pressure mechanism.
TL;DR: In this article, impact toughness, microstructure, and internal friction were examined for 0·3C-Cr-Mn-Si-2Ni steel with quenched, austempered, normalized, and annealed initial microstructures.
Abstract: Impact toughness, microstructure, and internal friction were examined for 0·3C–Cr–Mn–Si–2Ni steel with quenched, austempered, normalized, and annealed initial microstructures. It was found that the steel has appreciable susceptibility to temper brittleness with all these microstructures. The mechanism of temper brittleness in this steel was proved to be the result of an aging process of the α solid solution with precipitation of Fe3C(N) particles causing ‘dead pinning’ of dislocations.
01 Jan 1983