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Showing papers on "Fractography published in 2006"


Journal ArticleDOI
TL;DR: In this paper, a comprehensive study was carried out on series of nanocomposites containing varying amounts of nanoparticles, either titanium dioxide (TiO 2 ) or aluminium oxide (Al 2 O 3 ).

766 citations


Journal ArticleDOI
TL;DR: In this article, the mechanism for the formation of the GBF area was proposed as the "dispersive decohesion of spherical carbide" model, in which during the fatigue process multiple microcracks are initiated dispersively by de-cohesion of the carbide from the matrix around a non-metallic inclusion.

358 citations


Book
24 Jan 2006
TL;DR: In this article, a failure investigation report of IMI 550 HPC-I (High Pressure COMPRESSOR (HPC-II) is reported. And the failure report is investigated.
Abstract: INTRODUCTION TO FRACTOGRAPHY Dimple Rupture Cleavage Fatigue Intergranular PHYSICAL METALLURGY OF TITANIUM ALLOYS Introduction Application of Titanium Alloys Effect of Alloying Elements Types of Titanium Alloys Alpha (alpha) Alloys Near alpha Alloys alpha + ss Alloys Metastable ss Alloys Beta Alloys Titanium Aluminides The Microstructure of Titanium Alloys Conventional Titanium Alloys Titanium Aluminides CHEMICAL COMPOSITIONS ALPHA ALLOYS NEAR-ALPHA ALLOYS ALPHA + BETA ALLOYS BETA ALLOYS TITANIUM ALUMINIDES Ti3Al-Based Alloys TiAl-Based Alloys CASE STUDY: FAILURE INVESTIGATION REPORT OF IMI 550 HIGH-PRESSURE COMPRESSOR (HPC-I) AERO ENGINE BLADE Introduction Investigation Chemical Analysis Microstructure Fractography Stress-Concentration Effects of a Notch Analysis of the Deposits Conclusion References Index

187 citations


Journal ArticleDOI
TL;DR: In this paper, the authors performed tensile tests on cylindrical specimens made of wet and dry concrete with different strain rates from 10 s−1 to 120 s−s−1 by means of a special experimental technique.

173 citations


Journal ArticleDOI
TL;DR: In this paper, an Mg AZ31 alloy with modified microstructures was investigated to determine microstructural effects on room temperature mechanical properties acquired from low strain rate (∼10 −3 ǫs −1 ) tensile testing to failure.
Abstract: An Mg AZ31 alloy with modified microstructures was investigated to determine microstructural effects on room temperature mechanical properties acquired from low strain rate (∼10 −3 s −1 ) tensile testing to failure. Three distinct microstructures were generated via heat treatment, viz.: (1) single phase, fine equiaxed grains; (2) single phase, coarse grains with twins; (3) fine, equiaxed grains decorated with Mg 17 (Al,Zn) 12 grain-boundary precipitates. Each microstructure was separately characterized with optical microscopy, X-ray crystallography, fractography, and hardness measurement prior to tensile testing. Tensile coupons fabricated from each microstructure were then elongated to failure in a miniature stage, and true stress–true strain curves were computed with the digital image correlation (DIC) technique. Initial yield point, ultimate tensile strength and maximum elongation were also computed and examined within the context of key features of each microstructure to infer the mechanism of plastic deformation in tension and whether or not the potential for improved room temperature formability exists.

145 citations


Journal ArticleDOI
TL;DR: In this paper, the orientation of fracture facets at the crack initiation site was determined using the electron backscattered diffraction (EBSD) technique in conjunction with the quantitative tilt fractography in a scanning electron microscope (SEM).
Abstract: A faceted initiation site is observed in Ti-6242 alloy for both the cyclic and static-loading test conditions. In this experimental study, the crystallographic orientation of the facets has been determined using the electron backscattered diffraction (EBSD) technique in conjunction with the quantitative tilt fractography in a scanning electron microscope (SEM). Quantitative tilt fractography analysis has been used to determine the spatial orientation of fracture facets. The results indicate that the normal-fatigue (no-dwell) fracture facets are oriented at ∼5 deg with respect to the basal plane; the dwell-fatigue fracture facets are oriented at ∼10 to 15 deg with respect to the basal plane and the static-loading fracture facets are oriented at ∼20 deg with respect to the basal plane. These crystallographic orientation determinations of the fracture facets at the crack-initiation site can be used to obtain an idea about the type of loading that produced them.

126 citations


Journal ArticleDOI
TL;DR: In this paper, the authors performed ultrasonic fatigue tests with smooth and notched bearing steel of two batches (JIS SUJ2-A and SUJ 2-B) and found that the S-N curves obtained from the smooth specimens were different and both did not show a distinct two-step.

119 citations


Journal Article
TL;DR: Examples of failure analysis in this study are intended to guide the researcher in using qualitative (descriptive) fractography as a tool for understanding the failure process in brittle restorative materials and also for assessing possible design inadequacies.
Abstract: PURPOSE To educate dental academic staff and clinicians on the application of descriptive (qualitative) fractography for analyses of clinical and laboratory failures of brittle materials such as glass and ceramic. MATERIALS AND METHODS The fracture surface topography of failed glass, glass fiber-reinforced composite, and ceramic restorations (Procera, Cerestore, In-Ceram, porcelain-fused-to-metal) was examined utilizing a scanning electron microscope. Replicas and original failed parts were scrutinized for classic fractographic features such as hackle, wake hackle, twist hackle, arrest lines, and mirrors. RESULTS Failed surfaces of the veneering porcelain of ceramic and porcelain-fused-to-metal crowns exhibited hackle, wake hackle, twist hackle, arrest lines, and compression curl, which were produced by the interaction of the advancing crack with the microstructure of the material. Fracture surfaces of glass and glass fiber-reinforced composite showed additional features, such as velocity hackle and mirrors. The observed features were good indicators of the local direction of crack propagation and were used to trace the crack back to an initial starting area (the origin). CONCLUSION Examples of failure analysis in this study are intended to guide the researcher in using qualitative (descriptive) fractography as a tool for understanding the failure process in brittle restorative materials and also for assessing possible design inadequacies.

116 citations


Journal ArticleDOI
TL;DR: In this paper, the mechanical properties of cold-sprayed aluminum and the effect of annealing on those properties were investigated and the results indicated good potential for cold spray as a bulkforming process.
Abstract: Cold spray, a new member of the thermal spray process family, can be used to prepare dense, thick metal coatings. It has tremendous potential as a spray-forming process. However, it is well known that significant cold work occurs during the cold spray deposition process. This cold work results in hard coatings but relatively brittle bulk deposits. This work investigates the mechanical properties of cold-sprayed aluminum and the effect of annealing on those properties. Cold spray coatings approximately 1 cm thick were prepared using three different feedstock powders: Valimet H-10: Valimet H-20: and Brodmann Flomaster. ASTM E8 tensile specimens were machined from these coatings and tested using standard tensile testing procedures. Each material was tested in two conditions: as-sprayed; and after a 300°C, 22h air anneal. The as-sprayed material showed high ultimate strength and low ductility, with <1% elongation. The annealed samples showed a reduction in ultimate strength but a dramatic increase in ductility, with up to 10% elongation. The annealed samples exhibited mechanical properties that were similar to those of wrought 1100 H14 aluminum. Microstructural examination and fractography clearly showed a change in fracture mechanism between the as-sprayed and annealed materials. These results indicate good potential for cold spray as a bulkforming process.

114 citations


Journal ArticleDOI
TL;DR: In this article, the development and failure of crack bridging ligaments were studied in detail in three dimensions using high-resolution X-ray microtomography, and direct comparison of these features has been made with scanning electron microscopy fractography.
Abstract: Intergranular stress corrosion cracking in a sensitised type 302 stainless steel wire has been observed in situ using high resolution X-ray microtomography. Tomography enables the development and failure of crack bridging ligaments to be studied in detail in three dimensions. Direct comparison of these features has been made with scanning electron microscopy fractography. The crack bridges failed in a ductile manner, with a morphology that is consistent with non-sensitised low energy grain boundaries.

107 citations


Journal ArticleDOI
TL;DR: In this article, the HIPed superalloy Inconel 718 powder was consolidated by hot isostatic pressing (HIPing) at 1200°C under 120 MPa pressure for 3h.
Abstract: Inert gas atomized (IGA) superalloy Inconel 718 powder was consolidated by hot isostatic pressing (HIPing) at 1200 °C under 120 MPa pressure for 3 h. The HIPed alloy heat treated as per the aerospace materials specification (AMS) 5662J standard schedule, viz. solution treatment (ST) at 980 °C for 1 h/water quenching (WQ) to room temperature (RT) and a two-step ageing treatment (AT) at 720 °C for 8 h/furnace cooling (FC) at 55 °C h −1 to 620 °C and holding at 620 °C for 8 h and air cooling (AC) to room temperature has exhibited the yield strength (YS) and ultimate tensile strength (UTS) comparable to that of the conventionally processed (forged and heat treated) IN 718. However, its ductility and stress rupture properties at 650 °C were found to be poor due to the presence of prior particle boundary (PPB) networks decorated with highly stable oxides (Al 2 O 3 and TiO 2 ) and brittle MC (Nb, Ti)C carbides. To mitigate this problem, the HIPed alloy was subjected to solution treatment at 1270 °C for 1 h followed by re-HIPing at 1100 °C/130 MPa/3 h before heat-treating it as per AMS 5662J standard schedule. Optical and scanning electron microscopy (SEM) of the alloy processed under modified HIPing and heat treatment conditions have shown the dissolution of MC-carbides, breaking up of PPB networks and formation of equiaxed grains with an average diameter of about 50 μm. Transmission electron microscopy (TEM) of this alloy has revealed uniform distribution of γ″ and γ′ strengthening precipitates in the γ-matrix and the presence of δ(Ni 3 Nb) phase as well as very fine oxide particles near the grain boundaries. The tensile properties of the alloy processed under modified conditions have shown quite satisfactory levels of YS and UTS combined with a significantly improved elongation (EL) values at room temperature (19.5%) and at 650 °C (8.0%). The improvement in alloy ductility was found to correlate well with the fractography of the tensile tested specimens, which showed the predominance of transgranular fracture with fine dimples at room temperature and fine dimples together with the particle boundary facets at 650 °C. The stress rupture properties of modified processed alloy at 650 °C and at a stress level of 690 MPa have shown a vastly improved rupture life of 80 h combined with 5% ductility. The improvement in tensile and stress rupture properties accomplished by the modified processing makes it possible to explore the near net shape capability of HIP technology to its full potential in the development of alloy 718 components.

DOI
26 Sep 2006
TL;DR: In this paper, an expanded "fractography" guide for analyzing fractography of ceramics and glasses is presented. But it does not cover the analysis of brittle materials.
Abstract: nist recommended practice guide fractography of ceramics fractography of ceramics and glasses nist recommended fractography of ceramics and glasses nist recommended fractography of ceramics and glasses nist recommended nist recommended practice guide fractography of ceramics document about fractography of ceramics and glasses nist nist recommended practice guide fractography of ceramics fractography fractography of brittle materials:analysis of document about fractography of ceramics and glasses nist nist releases expanded 'fractography' guide for analyzing nist recommended practice guide fractography of ceramics professional resources link.springer errata sheet 4 as of: july 27, 2007 the words “fracture georgia statewide salary plan 2013 ebook | browserfame errata sheet 5 as of: october 30, 2007 the words “fracture fractographic failure analysis of a procera allceram crown cummins m11 shop manual 3666075 ebook | browserfame fractography of glasses and ceramics vi ceramic science and engineering programs duckoo faith in action discovering real life heroes faith rules honda frv user manual ekpbs document about advanced health assessment of womenclinical nih public access stereo and scanning electron microscopy study guide geometry houghton mifflin company answers golf outside service manual alisonlontay audi a4 convertible service manual adammaloyd singapore tax guide world strategic and business toff at the fair 1st edition uk herrnhut austalias first utopian commune by metcalf who fears the devil veencl home cooking around the world fiores environmental control of products volume 6 arcbc

Journal ArticleDOI
TL;DR: In this paper, the effect of nano-sized Al2O3 particulates as reinforcement and processing type with the micro-structural and tensile properties of magnesium was investigated, and the results showed that the overall combination of tensile property of these materials remained superior when compared to high strength magnesium alloy AZ91 reinforced with much higher weight percentage of SiC Fractography studies revealed that the typical brittle fracture of pure magnesium changed to ductile due to the incorporation of nanoAl2O 3 particulates, while powder metallurgy processed material exhibited superior yield strength and ultimate tensile strength

Journal ArticleDOI
TL;DR: In this paper, a collation of crack growth related data from a significant number of fatigue tests on commercial quality 7050-series aluminium alloy tested under various F/A-18 aircraft spectra is presented.
Abstract: This paper summarises a collation of crack growth related data from a significant number of fatigue tests on commercial quality 7050-series aluminium alloy tested under various F/A-18 aircraft spectra. The data presented consist of quantitative fractography measurements of the fracture surfaces including effective initiating defect size and type (mechanical, environmental or chemical). Three different surface conditions were considered: chemically etched, glass bead peened and machined. The purpose of providing these data was to facilitate analyses on the parameters governing the propagation of fatigue cracks in the 7050-series aluminium alloy. Here an investigation to determine whether surface finish or applied stress and spectra have any bearing on the initial defect size or the damage type is summarised. Based on this investigation, it appears that the applied stress and spectra have no correlation to the size of the equivalent initiating flaw; however, the surface finish appears to influence the various crack-initiating mechanisms and to govern the formation of the damage type.

Journal ArticleDOI
TL;DR: Very long life fatigue and near-threshold fatigue crack growth behavior of 7075 and 6061 Al-alloys in T6 condition were investigated using accelerated fatigue testing at 19.5 kHz on a piezoelectric machine as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the fracture toughness of an epoxy molding compound (EMC) has been enhanced over a wide temperature range by the addition of a very low volume fraction of silica nanoparticles to the EMC, which induces macroscopic crack deflection and plastic deformation in front of the crack tip.
Abstract: The fracture toughness of an epoxy molding compound (EMC) has been enhanced over a wide temperature range by the addition of a very low volume fraction of silica nanoparticles to the EMC filled with micro-silica particles, which induces macroscopic crack deflection and plastic deformation in front of the crack tip. To evaluate the fracture toughness (GIC) of these materials, the single edge notched bending (SENB) test was performed for a wide range of temperatures (from ambient temperature to 230°C). The fracture toughness of the nano-silica filled EMCs was found to be improved in this temperature range by as much as a factor of two. Investigation of the fracture surfaces revealed that the micro-silica particles are covered with deformed matrix materials, which implies that the silica nanoparticles induced the crack to move into the interface between the micro-silica particles. Fractography results suggest that the silica nanoparticles act as surface modifiers of the micro-silica particles, which results in crack deflection and plastic deformation.

Journal ArticleDOI
TL;DR: In this article, the elastic constants, hardness, fracture toughness and strength properties of polycrystalline yttrium aluminum garnet were measured using standard experimental procedures and fractography was used to gain insight into the fracture process and the nature of the flaws controlling the strength behavior.
Abstract: Polycrystalline neodymium-doped yttrium aluminum garnet (YAG), Nd: Y3Al5O12, has been produced in a transparent form and is being considered as a substitute for single crystal YAG in laser applications. To determine whether such a substitution could impact mechanical reliability, it is critical to compare the baseline mechanical properties of the single crystal and polycrystalline materials. In this study, elastic constants, hardness, fracture toughness and strength properties were measured using standard experimental procedures. In addition, fractography was used to gain insight into the fracture process and the nature of the flaws controlling the strength behavior. Overall, it was determined that the mechanical behavior of the polycrystalline YAG was very similar to that of the single crystal material. The elastic constants of polycrystalline YAG were almost the same as the single crystal and the polycrystalline material showed slight advantages in hardness and fracture toughness. Surface machining flaws were found to control the strength behavior with the single crystal material being the more sensitive to contact damage and, hence exhibiting a lower strength.

Journal ArticleDOI
TL;DR: In this paper, the variability in the tensile ductility of individually cast tensile test specimens of high-pressure die-cast AE44 Mg-alloy is examined at room temperature and at 394 K.
Abstract: Cast magnesium alloys often exhibit large variability in fracture related mechanical properties such as ductility and strength. In this contribution, the variability in the tensile ductility of individually cast tensile test specimens of high-pressure die-cast AE44 Mg-alloy is examined at room temperature and at 394 K. Significant specimen-to-specimen variations in the ductility are observed at both temperatures. The variability in the ductility does not quantitatively correlate to the average volume fraction of porosity (or any other microstructural parameters) in the bulk three-dimensional microstructure. The area fraction of porosity measured in the fracture surfaces of the tensile test specimens is much larger than the average volume fraction of the porosity in the corresponding bulk microstructure. Therefore, the fracture path preferentially goes through the regions of highly localized clusters of gas and shrinkage pores. Interestingly, at both test temperatures, the percent tensile ductility e shows a quantitative correlation with the area fraction of the porosity f in the corresponding fracture surfaces , which can be represented by the following simple equation e = e 0 [1 − f ] m , where e 0 and m are empirical constants.

Journal ArticleDOI
TL;DR: In this article, a tension-compression asymmetry of constitutive behavior is observed: the flow strength and ductility of these composites under tension are lower than those under compression, and the extent of asymmetry is larger for HIP composites.
Abstract: Aluminum 6092/(B 4 C) p metal matrix composites fabricated by two different powder consolidation routes, extrusion (EXTR) and sintering/hot isostatic-pressing (HIP), were made and tested over a wide range of strain rates (10 −4 to (3 × 10 2 ) s −1 ) under tension. A tension-compression asymmetry of constitutive behavior is observed: the flow strength and ductility of these composites under tension are lower than those under compression. Such asymmetry is reinforcement volume fraction dependent, and the extent of asymmetry is larger for HIP composites. Fractographic observations show different interfacial bonding characteristics (good bonding for the EXTR composites and relatively weak bonding for the HIP composites), indicating a strong effect of interfacial debonding on the constitutive and failure behavior of these composites. TEM observations reveal a weak amorphous layer composed mainly of aluminum, magnesium and carbon along Al/B 4 C interface in the HIP composites, which is consistent with the experimental observations.

Journal ArticleDOI
TL;DR: In this paper, the effect of boron on the fatigue crack growth rate in Inconel 718 (IN 718) was studied at room temperature (RT) and 650°C.
Abstract: The effect of boron on the fatigue crack growth rate (FCGR) in Inconel 718 (IN 718) was studied at room temperature (RT) and 650 °C The results showed that the addition of B improved the fatigue crack propagation resistance of IN 718 The higher the B concentration, higher was the fatigue threshold at 650 °C While the FCGRs increased as the test temperature increased from RT to 650 °C in the Paris regime, a rapid drop in the FCGRs in the near-threshold regime and a higher fatigue threshold at 650° were observed due to the oxide-induced crack closure The fracture surfaces were observed to exhibit transgranular cracking with fatigue striations in specimens tested at RT, and a mixture of transgranular and intergranular cracking at 650 °C The fracture mode changed from intergranular cracking to transgranular cracking and plastic deformation marks increased with increasing B concentration at 650 °C The micromechanism of improvement in the fatigue crack growth resistance due to B addition was further studied via observations of crack growth path, fractography and TEM examination of the plastic zone ahead of the crack tip The plastic deformation mode within the crack tip plastic zone was planar slip, along with twinning, on {1 1 1} planes A crystallographic cracking model was, thus, proposed on the basis of restricted slip or twinning The improvement in the fatigue crack growth resistance in IN 718 due to B addition was mainly attributed to the increase in the grain boundary cohesion via minimizing the deteriorative effect of oxygen and the increase in the resistance to the dislocation movement at the crack tip

Journal ArticleDOI
TL;DR: In this article, the phase composition of B 4 C, α-SiC, BN and TiB 2 was determined by means of XRD, SEM of surface thermally etched and TEM.

Journal ArticleDOI
TL;DR: In this article, a failure criterion for prediction of failure caused by kinking under multiaxial (axial compression and shear) loading has been adapted to a non-crimp fabric composite system.

Journal ArticleDOI
TL;DR: In this paper, the analysis of fracture toughness in the transition temperature region of API X70 pipeline steels according to ASTM E1921 standard test method was concerned with the application of a 3-point bend test of precracked Charpy V-notch specimens.
Abstract: This study is concerned with the analysis of fracture toughness in the transition temperature region of API X70 pipeline steels according to ASTM E1921 standard test method. Two kinds of steels were fabricated by varying finish rolling temperatures, and their microstructures and mechanical properties were examined. Elastic–plastic cleavage fracture toughness, KJc was determined by three-point bend tests of precracked Charpy V-notch specimens, and then the measured KJc values were interpreted by the three-parameter Weibull distribution. Fractographic observation indicated that the critical distance from a precrack tip to a cleavage initiation site linearly increased with increasing critical J value. Effects of martensite–austenite constituent (MA) and effective grain size on fracture toughness in the transition region were analyzed from the standpoint of cleavage crack initiation and propagation. The higher volume fraction of MA led to the lower resistance to cleavage crack initiation, and the larger effective grain size led to the lower resistance to cleavage crack propagation. Thus, the steel rolled in the two-phase region had the higher fracture toughness in the transition region and the lower reference temperature and energy transition temperature than the steel rolled in the single-phase region because of the lower volume fraction of MA and the smaller effective grain size.

Journal ArticleDOI
Huajie Wang1, Fanglin Chen1, Z.Y. Gao1, W. Cai1, L.C. Zhao1 
TL;DR: In this paper, the effect of Fe content on hardness and toughness of Ni48.7Mn30.1Ga21.2 (x ǫ = 0) alloys is investigated and the relationship between the fracture toughness and fractography is discussed by observing the fracture morphology and analyzing the propagation of the crack.
Abstract: The effect of Fe content on hardness and toughness of Ni48.7Mn30.1−xFexGa21.2 (x = 0–11, number indicates at.%) alloys is investigated and the relationship between the fracture toughness and the fractography is discussed by observing the fracture morphology and analyzing the propagation of the crack. The micro-Vickers hardness results indicate that the hardness increases with increasing Fe content. The fracture toughness results indicate that Fe doping has improved the toughness of Ni–Mn–Ga alloys, and the toughness increases with increasing Fe content in Ni48.7Mn30.1−xFexGa21.2 (x = 0–11) alloys. Fracture morphology shows typical intergranular fracture with rock candy pattern in the Ni48.7Mn30.1Ga21.2 (x = 0) and river pattern cleavage fracture facets in the Ni48.7Mn19.1Fe11Ga21.2 (x = 11) alloy. The fracture type changing from intergranular fracture to transgranular fracture is the main reason for the improved toughness of Ni–Mn–Ga alloys by addition of Fe.

Journal ArticleDOI
TL;DR: In this paper, a surface treatment method which uses combined dispersant and a coupling agent is developed to treat the nano-SiO2 which is uniformly dispersed into the polypropylene matrix.
Abstract: In this study, polypropylene (PP)/nano-silica (nano-SiO2) composites were prepared by a melt blending process. Here, a novel surface treatment method which uses combined dispersant and a coupling agent is developed to treat the nano-SiO2 which is uniformly dispersed into the PP matrix. To treat the surface of nano-SiO2, the optimal content of the dispersant (SDBS) is 2.0% and the optimal amount of the coupling agent (KH-550) is 1.5%. The mechanism and synergistic effect of the combined dispersant and coupling agent are discussed based on their chemical structures. The fractography of PP/nano-SiO2 composites after notched impact testing observed by the scanning electron microscope (SEM) proves the uniform dispersion of nano-SiO2 in the PP phase. The mechanical testing results show that after surface treatment, both the tensile and notched impact strength of nanocomposites enhance markedly. The tensile strength reaches its maximum with the 4.0% of nano-SiO2 and the notched impact toughness achieves its maxi...

Journal ArticleDOI
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.

Journal ArticleDOI
TL;DR: High-resolution electron fractography (HEM) has been widely used for analysis of fracture surfaces as discussed by the authors and has been shown to be useful in failure analysis and in developing improved materials.
Abstract: Fracture surfaces have, no doubt, been studied throughout the history of mankind, probably starting with observations on stone-age tools. In the 16th to 18th centuries, the macroscopic appearance of fracture surfaces was used to assess the quality of metallic materials, with studies by Reaumur in 1722 being the most notable. However, it was not until 1943 that fracture surfaces were first examined at high magnifications (using optical microscopy up to 1000 ×), and that the first attempts were made to examine replicas of fracture surfaces using transmission electron microscopy (TEM). Early replicas had poor fidelity and resolution, and it was not until 1956 that Crussard et al. pioneered high-resolution TEM fractography using shadowed, direct-carbon replicas. This technique (and its subsequent variations) revolutionized fractography and led to a plethora of studies in the 1960's and 70's. It therefore seems appropriate to commemorate the 50th anniversary of high-resolution electron fractography with a review of how it, and subsequent scanning electron microscopy (SEM) and other techniques, have led to a better understanding of fracture processes. Such understanding has been invaluable in failure analysis and in developing improved materials. Milestone observations for a number of important models of fracture in inert environments including cleavage, brittle intergranular fracture, dimpled overload fractures, and fatigue fractures, are described first, followed by examples of key observations for fractures produced in embrittling environments.

Journal ArticleDOI
TL;DR: The hypothesis that the KA of the adhesion zone of resin/ceramic systems is affected by the ceramic microstructure is tested andimation of interfacial toughness was feasible by fracture mechanics and fractography.
Abstract: We suggest that the apparent interfacial fracture toughness (KA) may be estimated by fracture mechanics and fractography This study tested the hypothesis that the KA of the adhesion zone of resin/ceramic systems is affected by the ceramic microstructure Lithia disilicate-based (Empress2-E2) and leucite-based (Empress-E1) ceramics were surface-treated with hydrofluoric acid (HF) and/or silane (S), followed by an adhesive resin Microtensile test specimens (n = 30; area of 1 ± 001 mm2) were indented (98 N) at the interface and loaded to failure in tension We used tensile strength (σ) and the critical crack size (c) to calculate KA (KA = Yσc1/2) (Y = 165) ANOVA and Weibull analyses were used for statistical analyses Mean KA (MPa·m1/2) values were: (E1HF) 026 ± 006; (E1S) 023 ± 006; (E1HFS) 030 ± 006; (E2HF) 031 ± 006; (E2S) 013 ± 005; and (E2HFS) 041 ± 007 All fractures originated from indentation sites Estimation of interfacial toughness was feasible by fracture mechanics and fractogra

Journal ArticleDOI
TL;DR: In this paper, the authors describe a series of experiments and analyses that were used to examine crack growth near sapphire/epoxy interfaces, where they used a new biaxial loading device was used to conduct mixed-mode fracture experiments.
Abstract: This paper describes a series of experiments and analyses that were used to examine crack growth near sapphire/epoxy interfaces. Adhesion of the epoxy to the sapphire was enhanced by coating the sapphire with mixtures of two silane coupling agents that form self-assembled monolayers. A new biaxial loading device was used to conduct a series of mixed-mode fracture experiments. Crack opening interferometry, atomic force microscopy, and angle-resolved X-ray photoelectron spectroscopy allowed cohesive zone sizes, fracture surface topographies, and loci of fracture to be established. The experiments were complemented by finite element analyses that accounted for the rate- and pressure-dependent yielding of the epoxy. The analyses also made use of traction-separation laws to represent the various interphases that were produced by the mixed monolayers. The intrinsic toughness (defined as the area underneath the traction-separation curve) of the bare sapphire interfaces was independent of mode-mix and lower than values from previous experiments with glass/epoxy and quartz/epoxy specimens. The increase in overall toughness with mode-mix was completely accounted for by viscoplastic dissipation in the epoxy outside the cohesive zone. The minimum toughness of the coated sapphire interfaces was about five times higher than the mode-mix independent intrinsic toughness of the uncoated specimens. The increase in overall toughness with mode-mix was almost completely accounted for by increases in the intrinsic toughness as the traction-separation law varied with mode-mix. As a result, viscoplastic dissipation outside the cohesive zone was minimal. Atomic force fractography and X-ray photoelectron spectroscopy indicated that the crack growth mechanisms and the loci of fracture in the coated and uncoated specimens were quite different.

Journal ArticleDOI
TL;DR: In this article, the effect of porosity on the fatigue crack growth rate in Ti-6Al-4V laser welds was investigated, and it was shown that porosity was present in partial penetration welds over a narrow fusion zone (FZ) with martensite structure.
Abstract: The effect of porosity––a common welding defect––on the fatigue crack growth rate (FCGR) in Ti–6Al–4V laser welds was investigated. The experimental results reveal that porosity was present in partial penetration welds over a narrow fusion zone (FZ) with martensite structure. The FCGR of the FZ was lower than that of the base plate. The fracture surface morphology of weld metal was much rougher as compared to that of the base plate. Randomly oriented martensite in the FZ led to local cleavage fracture along a preferred plane, thus, altering the crack growth direction significantly out of the primary crack plane. The zigzag crack path in the FZ resulted in a reduced FCGR at a given ΔK compared to the base plate. Besides, the porous weld showed a serration on the crack growth curve, and behaved the similar crack growth characteristics as the defect free one. SEM fractography revealed that the deflection of crack path around porosity together with local notch blunting as the crack tip pierced into porosity, balanced the increased FCGR for the occurrence of instant crack advance as the crack front reached the porosity at a low stress ratio. In contrast, the serration and drop in FCGR occurred sparingly at a high stress ratio as the crack front met the porosity.