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The knowledge on constitutive mechanical behavior at the temperatures close to the solidus is essential for predicting high-temperature deformation and fracture, e.g. cold and hot cracking of aluminum alloys. In this work we studied the tensile mechanical properties of an as-cast AA7050 alloy in a near-solidus temperature regime. Tensile tests were carried out using Gleeble-3800™ system at temperatures from 400 to 465 °C and at strain rates from 0.0005 to 0.05 s −1 . The results show that the strength decreases with increasing temperature and decreasing strain rate. Meanwhile, ductility decreases with the increase of temperature and strain rate. The constitutive parameters were extracted by fitting the test data to the extended-Ludwik and creep-law equations. The parameters for the extended-Ludwik equation are continuous with the values from a lower temperature regime obtained earlier, while the parameters for the creep-law equation are comparable with those obtained on other 7XXX aluminum alloys. We observed a change in fracture mode at 450 °C; from ductile transgranular to intergranular. This temperature coincides with the discontinuity point of the temperature-ductility slope. On the fracture surface of a sample that was deformed at 465 °C with a strain rate of 0.0005 s −1 , we observed features characteristic of micro-superplasticity. Considering the test conditions, viscous flows of incipient melt or liquid-like substances are suggested to be responsible for the formation of this feature. [ABSTRACT FROM AUTHOR]

The crystallographic texture and Charpy impact toughness have been investigated in American Petroleum Institute (API) X100 pipeline steel, and the different rolling processes are applied to adjust the crystallographic texture for the sake of improving impact toughness. It has been found that the very weak textures exist in the steel only rolled in the recrystallization region of austenite, but the intensity of the unfavorable {001} 〈110〉 component is quite high. The {001} 〈110〉 texture is harmful for impact toughness and needed to be decreased in most cases. It is confirmed that the appropriate controlled rolling processes effectively reduce the intensity of the {001} 〈110〉 texture. By contrast, low temperature finish rolling in the non-recrystallization region produces the fine grain structures, beneficial textures and superior impact toughness at the low temperature. In addition, the occurrence of delamination in the ductile region generates the unfavorable cleavage crack on the fracture surface of Charpy specimen and inevitably reduces the impact energy in the upper shelf region. The delamination will occur continuously with decreasing temperature due to the large volume fraction of {001} planes parallel to the rolling plane. [ABSTRACT FROM AUTHOR]

The sharing role of microstructural micro-constituents on hot deformation behavior of a 60/40 duplex brass was investigated through hot compression testing at predetermined temperatures in the range of 400–800 °C under the strain rates ranging from 0.001 to 0.1 s −1 . The hot working parameters (strain rate sensitivity, and apparent activation energy, Q ) were determined for different conditions of the applied thermomechanical processing. Assuming the Hyperbolic Sine functional behavior to analysis the deformation behavior of the alloy and also applying the rule of mixture in order to determine the share of each phase in strain accommodation, the interaction coefficients of alpha phase, P, and beta phase, R, were precisely estimated. The results indicate that the experimental material exhibits usual Dynamic Recrystallization (DRX) behavior such as single-phase materials; but in comparison to the conventional alloys DRX is postponed at 500 and 600 °C. Moreover, it is seen that the deformation mechanism at different temperatures has been severely depend on the order–disorder transformation of the beta phase in mixture. In fact this transformation is considered to play the main role in beta phase recrystallization retardation. However, at lower Zener Holloman ( Z ) values, the strain accommodation is mainly taken place in beta phase and the chief deformation mechanism is believed to be grain boundary sliding (GBS). Accordingly there crystallization of alpha phase is limited due to the lower strain accommodation. In contrast, at higher Z values, the alpha phase controls the governing deformation mechanism and the dynamic recrystallization of alpha grains may well lead to the microstructural grain refinement. [ABSTRACT FROM AUTHOR]

Fracture is the ultimate continuum of a material. Hence, it is possible that the fracture features contain the signature of the whole deformation process undergone due to variation in triaxial state of stress under tensile deformation. The two dimensional fracture features were correlated with the stress triaxiality ratio where initial inclusion content was unaltered. In order to test that, many tensile experiments of a superalloy were carried out at different notch geometries and fractographic investigation was done extensively to correlate the fracture features (ie., fractured grain size, extent of tearing ridge, dimple diameter and dimple number density) with the tensile properties. [ABSTRACT FROM AUTHOR]

The effects of boron additions in an amount of 0.1–2 wt%, thermomechanical processing and heat treatment on microstructure and mechanical properties of a two-phase titanium alloy Ti–6.5Al–3.3Mo–0.3Si alloy have been investigated. Depending on the boron amount, the materials under study were divided into two groups: (1) boron modified alloys containing ~0.1 wt% of boron and (2) discontinuously reinforced metal matrix Ti–TiB based composites containing 1.5–2 wt% of boron. Boron additions led to formation of TiB whiskers, which were predominantly located along boundaries of prior β-grains and α-colonies resulting in refined as-cast microstructure. Multiple 3D forging at T =650–700 °C applied for the boron modified alloys resulted in formation of ultrafine-grained microstructure and intensive breaking of TiB whiskers. Tensile properties of the Ti–6.5Al–3.3Mo–0.3Si–0.2 wt% B alloy after multiple 3D forging followed by β-heat treatment were found to be appreciably higher than those of the alloy free of boron after the same processing route that was ascribed to better controlling the β-grain size during β heat treatment. The composite materials were subjected to multiple isothermal 2D forging at T =950 °C that provided effective alignment of TiB whiskers while retaining their high aspect ratio. The hot forged composites demonstrated appreciably higher strength, creep resistance in comparison with those of the base alloy without drastic reduction in ductility. The effect of TiB whiskers orientation and morphology on the tensile properties of the composite materials is discussed. [ABSTRACT FROM AUTHOR]

The deformation and fracture mechanisms of a low carbon microalloyed steel processed by asymmetric rolling (AsR) and symmetric rolling (SR) were compared by microstructural and texture evolutions during uniaxial tensile deformation. A realistic microstructure-based micromechanical modeling was involved as well. AsR provides more effective grain refinement and beneficial shear textures, leading to higher ductility and extraordinary strain hardening with improved yield and ultimate tensile stresses as well as promoting the occurrence of ductile fracture. This was verified and further explained by means of the different fracture modes during quasi-static uniaxial deformation, the preferred void nucleation sites and crack propagation behavior, and the change in the dislocation density based on the kernel average misorientation (KAM) distribution. The equivalent strain/stress partitioning during tensile deformation of AsR and SR specimens was modeled based on a two-dimensional (2D) representative volume element (RVE) approach. The trend of strain/stress partitioning in the ferrite matrix agrees well with the experimental results. [ABSTRACT FROM AUTHOR]

Repetitive upsetting (RU), a newly developed SPD technique, was employed to process AZ91D magnesium alloy plates at 400 °C for 0, 2, 4 and 8 passes. The microstructure and texture evolution of the plates after RU were investigated and correlated with the mechanical performances at room temperature. Results show that the initial coarse grains are effectively refined, however an abnormal grain coarsening appears after 8 passes of RU. A compression texture and a shear texture, induced by specific local strains, are observed within the RU-processed plates. Both the ultimate tensile strength (UTS) and elongation to fracture of the RU-processed AZ91D alloy are improved with the increase of RU passes, exhibiting a maximum increase of 35.8% and over 75%, respectively. The yield strength (YS) increases steadily in the first 4 RU passes and then decreases slightly after another 4 passes. The mechanical anisotropy is discussed from the perspective of texture and Schmid factor. [ABSTRACT FROM AUTHOR]

A novel approach for development of high strength and ductile beta titanium alloys was proposed and successfully applied. The microstructure of the designed alloys is fully composed of a bcc β-Ti phase exhibiting dendritic morphology. The new Ti 68.8 Nb 13.6 Cr 5.1 Co 6 Al 6.5 (at%) alloy (BETA tough alloy) exhibits a maximum tensile strength of 1290±50 MPa along with 21±3% of fracture strain. The specific energy absorption value upon mechanical deformation of the BETA tough alloy exceeds that of Ti-based metallic glass composites and commercial high strength Ti-based alloys. The deformation behavior of the new alloys was correlated with their microstructure by means of in-situ studies of the microstructure evolution upon tensile loading in a scanning electron microscope. [ABSTRACT FROM AUTHOR]

The deformation and failure mechanism of a multilayered thin film consisting of alternating soft Cu and hard TiN interlayers has been studied by in situ SEM compression of micro-pillars and finite element simulations. While the yielding of the multilayer is governed by the 'size-dependent' strength of Cu, the failure was found to occur by shearing of the columnar grains of TiN. At elevated temperatures of 200 and 400 °C, the yielding of the multilayers is governed by the stress-assisted diffusion of the Cu interlayers, which coalesce into microcrystals and grow into larger faceted crystals. [ABSTRACT FROM AUTHOR]

Abstract: The addition of nanoparticulate (NP) reinforcements to magnesium (Mg)-based materials is considered a promising technique in improving mechanical properties beyond what can be achieved through alloying and grain refinement. In this work, we have comprehensively collected the currently available experimental data for magnesium metal-matrix nanocomposites (Mg MMNCs) and performed analyses to determine the contribution of any Orowan-type strengthening, which is thought to be a primary mechanism in simultaneously improving both strength and ductility. Although studies are numerous, it was found that most of the individual reports in the literature do not provide sufficient data points to make quantitative conclusion on which mechanisms may be active. Of those that do, the analyses show that, in most cases, the enhanced strength can be accounted for by grain refinement and/or dislocation production through mechanical post-processing, such as hot-rolling, with little indication of Orowan strengthening. A comparison with hot-rolled Mg AZ31 alloy specimens demonstrates that the degree of grain refinement in Mg MMNCs is comparable to that achieved by traditional processing routes. In Mg MMNCs with higher yield strength than the AZ31 specimens of comparable grain size, the MMNC typically demonstrated significantly lower ductility indicating that yield strength improvements by mechanical post-processing have resulted in the expected decrease in ductility that accompanies increased dislocation density. [Copyright &y& Elsevier]

Abstract: The present study investigated hydrogen embrittlement (HE) cracking upon indentation of high-strength steel. When an indentation test was applied to high-strength steel that included absorbed hydrogen, radial cracks initiated and propagated at the corners of the indentation impression, whereas the as-received steel with no hydrogen absorption exhibited no cracking. In addition, the length of the hydrogen-induced indentation cracks was found to be dependent on the hydrogen content in the steel. A combined experimental and computational investigation was conducted for a mechanistic study of Vickers indentation cracking caused by hydrogen embrittlement. Crack propagation was simulated based on a cohesive zone model in the finite element method and the stress intensity factor for the crack was evaluated. It was found that the simulated crack initiates at loading, and then propagates upon unloading. The value of the stress intensity factor at the indentation crack was in agreement with the threshold resistance to crack propagation for HE cracking (threshold stress intensity factor, K ISCC). This suggests that the length of the cracks can be used to evaluate the susceptibility of the steel to HE cracking. [Copyright &y& Elsevier]

Abstract: Tensile fracture behaviors and mechanisms of 2D C/SiC-BC x composite were investigated. Results showed that the 2D C/SiC-BC x composite exhibited similar tensile strength (about 250MPa), but different fracture mode and damage evolution compared to that of 2D C/SiC composite under similar monotonic tensile stress condition at room temperature. The initial modulus and fracture modulus of 2D C/SiC-BC x composite obtained under tensile cyclic loading at RT were about 98.6GPa and 54.5GPa, respectively. At high temperatures, the tensile strengths were lower than that at room temperature and behaved as a step-like stress–strain curve. [Copyright &y& Elsevier]

Abstract: High dense tantalum sintering components with a hardness gradient within individual grains were synthesized successfully by means of spark plasma sintering (SPS) of the nitrided tantalum particles at a pressure of 400MPa and a temperature of 950°C. High yield strength up to 1350MPa combined with 12% fracture strain was achieved in the compression tests, which can be attributed to the novel gradient composition inside the grain structure. [Copyright &y& Elsevier]

Abstract: The (Zr48Cu36Al8Ag8)99.25Si0.75-based bulk metallic glass composite (BMGC) rods ex situ dispersed with Ta particles (with a diameter of 2–4mm) have been successfully fabricated by suction casting and characterized. These Ta-added BMGCs exhibit similar thermal properties in comparison with its base alloy counterpart, with relatively high glass forming ability (GFA). The results of compression test show that a superior mechanical performance with up to 22% compressive plastic strain, 1800MPa yield strength and 1850MPa fracture strength at room temperature can be obtained for the 2mm diameter rod of the ZrCu-based BMGC with 10vol.% Ta particles. These ex situ dispersed Ta particles (20±8μm) would arrange as semi-uniform confinement zones to restrict the shear band propagation. In addition, for a given Ta particle size, higher volume fraction particles would lead to more interfacial areas, shorter inter-particle spacings, smaller confinement zone sizes than the smaller volume fraction particles, and results in presenting larger compression plasticity. [Copyright &y& Elsevier]

Abstract: The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ΔK) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430Mpa, 530Mpa, 21J, 24Mpam1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ΔK The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation. [Copyright &y& Elsevier]

Abstract: To investigate the tensile properties and facture toughness of high-strength structural steel of Q420 under different conditions, tensile tests and crack tip opening displacement (CTOD) tests were conducted. The test results revealed that temperature significantly influenced the fracture toughness of structural steel and that fracture toughness was significantly reduced with the decrease in temperature, resulting in brittle fractures. Prestraining increased the yield stress and tensile strength of the structural steel. However, it significantly reduced the plasticity and fracture toughness, and further increased the probability of brittle fractures. As determined by FE-analysis, temperature and prestraining facilitated brittle fractures due to the activation of the resulting near crack tip stress fields. Based on the Weibull stress fracture criterion, the temperature and prestraining effects on the fracture toughness were predicted from fracture toughness results of the virgin material at room temperature by the local approach. The prediction was in good agreement with the experimental results. It certified that the critical Weibull stress obeys the two-parameter Weibull distribution in the local approach and the fracture behavior of the prestrained material at different temperatures can be characterized by the local approach. [Copyright &y& Elsevier]

Abstract: In this work, the role played by plastic straining on the FCC(γ)→HCP(ɛ) strain induced transformation (SIT) ɛ-martensite in a Co–Cr–Mo–0.05C alloy was investigated. It was found that alloy plastic deformation at room temperature promotes the development of ɛ-martensite giving rise to the formation of intragranular striations. Moreover, aging at 800°C of pre-strained specimens initially promotes SIT ɛ-martensite. This is followed by a time plateau (1h) delay after which isothermal ɛ-martensite develops. Apparently, prior plastic straining leads to increasing incubation times for the onset of the isothermal ɛ-martensite transformation. In addition, tensile specimens containing various amounts of isothermal ɛ-martensite were tested all the way to fracture and their respective stress–strain properties were experimentally determined. Comparisons between experimental and simulated flow curves using the rule of mixtures indicated some deviations in the simulations at volume fractions above 0.25 ɛ-martensite. In contrast, predictions of yield and tensile strength were in good agreement with the experimental outcome. In particular, linear trends were exhibited by both, the yield and tensile strength as a function of the volume fraction of ɛ-martensite. Finally, the alloy elongation remained nearly constant with the volume fraction of ɛ-martensite in the range of the 0.15

Abstract: A high Mn TWIP (TWinning Induced Plasticity) steel (0.6C–22Mn steel) and an Al-added TWIP steel (0.6C–18Mn–1.2Al steel) were fabricated, and their microstructures, tensile properties, and cup formability were analyzed to investigate effects of Al addition on deformation mechanisms in tensile and cup forming tests. The twinning was not only more homogenous but also less intense in the 0.6C–18Mn–1.2Al steel than in the 0.6C–22Mn steel. This aspect was confirmed by tensile stress-strain curves, where the strain hardening was lower in the 0.6C–18Mn–1.2Al steel. The tensile test results indicated that the 0.6C–22Mn steel had the better tensile strength and elongation than the 0.6C–18Mn–1.2Al steel. However, cracks were formed on cup sides of the 0.6C–22Mn steel when exposed to the air for seven days after the cup forming test. This was because a small amount of twinning took place as loads applied during the cup forming test were faster and larger than those of the tensile test, and because the stress was concentrated on the cup side. In the 18Mn–Al steel, on the other hand, the cracking did not occur due to lower stress concentration on the cup side because many twins were homogeneously formed inside most of austenite grains. [Copyright &y& Elsevier]

Abstract: The influence of ZrC content on the tensile deformation behavior and fracture strength of ZrCp/W composites in a temperature range of 800–1400°C was investigated. Both of the non-linear feature of the stress–strain curve and the rupture strain of the composites decreased with increasing ZrC content from 20 to 50vol% in all the tested temperatures. The maximum ultimate tensile strength of each ZrCp/W composite was found in the temperature range of 1000–1200°C. With increasing ZrC content from 20 to 50vol%, the maximum ultimate tensile strength of the ZrCp/W composite was decreased due to the porosity increase and the plasticity decrease of the composite although ZrC enhanced the tungsten matrix via load transferring and blocking dislocation movement in tungsten matrix. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an experimental investigation into the strength, deformation, and fracture behaviour of textile-reinforced concrete (TRC) subjected both to low and high-rate tensile loading ranging from 0.0001 to 50s−1. High strain rates were achieved using a high-rate servo-hydraulic testing machine. The effect of the addition of short fibres on the static and dynamic response of TRC has been investigated, and the microstructure of both composite and fibre was observed after the tests using an ESEM. An increase in tensile strength, strain capacity, and work-to-fracture was observed for strain rates up to 0.1s−1 with increasing strain rate. The addition of short glass fibres increased the tensile strength and first crack strength of the TRC. For high-speed tests (rates above 5s−1) an increase in the tensile strength, first crack strength and work-to-fracture was also observed, but at the same time there was a decrease in the strain capacity. The tests at high loading rates showed a pronounced effect of the specimen length on the measured mechanical properties: with increasing gauge length the tensile strength and strain capacity decreased, while the work-to-fracture increased. [Copyright &y& Elsevier]

Abstract: Nano-grain evolution in an austenitic stainless steel (SUS 316) during multidirectional forging (MDF) was investigated at temperatures of 77K and 300K. The flow stress during MDF and the room-temperature hardness increased significantly with increasing cumulative strain. The initial grains were subdivided by mechanical twinning and martensitic transformation. The formation of packets, which are composed of lamellar-structured mechanical twins with a spacing of 10–300nm, enhanced grain fragmentation. The packet size ranged from 40nm to 100nm depending on the MDF temperature and the cumulative strain. Tensile tests at ambient temperatures revealed a maximum proof strength of 2.1GPa. While the proof strength increased with cumulative strain, the plastic strain at fracture was approximately 10% independent of the cumulative strain over ∑Δɛ =2.4. [Copyright &y& Elsevier]

Abstract: Rolling unalloyed molybdenum, molybdenum alloys, and Oxide Dispersion Strengthened (ODS) molybdenum into sheet produces microstructures with elongated, pancake shaped grains that can result in anisotropic mechanical properties. In this work, unalloyed molybdenum, molybdenum alloys, and ODS molybdenum are rolled to thinner sheet and then subjected to tensile and fracture toughness testing and examination of the toughening mechanism. The ductile laminate toughening mechanism observed for wrought molybdenum results from a lower toughness in the short-transverse orientation that leads to separation of the layers of sheet-like grains of the microstructure along the grain boundaries in the regions of stress concentration. This splitting of the microstructure results in the formation of ligaments of grains, or non-constrained laminates, that are stretched to failure under a plane stress-state with large amounts of plastic deformation. The thinner specimens exhibit higher fracture toughness values and lower Ductile to Brittle Transition Temperature (DBTT) values than for thicker specimens machined from thicker starting material from the same alloy. The lower constraint of the thinner specimens tested in this work results in higher toughness and lower DBTT values. The finer grain size, finer precipitate size, and state of plane stress achieved for the thinner sheet specimens appears to enhance the ductile laminate toughening to result in higher fracture toughness and lower DBTT values. The detrimental effect of crack initiation from brittle carbides, oxides, and second phases is also observed to be diminished under a stress-state of plane stress. [Copyright &y& Elsevier]

Abstract: Commercial purity titanium was processed through up to 8 passes by equal-channel angular pressing (ECAP) at room temperature using a die with a channel angle of 120°. The billets showed no evidence for any surface damage after ECAP. This processing reduced the grain size from ∼23μm in the unprocessed condition to ∼200nm after 6 or 8 passes. It also increased the yield strength and the ultimate tensile strength and increased the elongation to failure by comparison with CP Ti processed by ECAP at an elevated temperature. The results demonstrate the advantage of processing CP Ti by ECAP at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: A semi-circular specimen containing a vertical edge crack was used to assess mode I, mode II, and mixed mode fracture toughness of a marble rock. The specimen was subjected to three-point bending while the bottom supports were placed asymmetrically with respect to the crack position. Since the critical tangential stress should be the same in various fracture modes, it was shown that the first three terms of tangential stress infinite series in the vicinity of the crack tip should be used to satisfy this condition. Accordingly, a criterion was presented to predict the mixed mode fracture toughness of brittle materials which showed a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: The paper statistically studies fracture properties of an aluminum low-pressure die casting component on basis of 32 tensile tests on round bar specimens. It reveals that the probability distribution of both ultimate tensile strength and fracture strain can be described using either the Weibull or the Gaussian function. Goodness-of-fit tests based on the Anderson–Darling statistic fail to reject either of them. However, the extrapolation of the distribution of the fracture strain to a probability level of 0.01% gives an unrealistic low or even negative lower-bound value. This suggests that a pass of the goodness-of-fit tests is not sufficient for identifying a physically reasonable probability distribution. At the same time, three different methods for determining the tensile fracture strain are compared: the area reduction of the fracture surface, the critical elongation of the gauge section, and the combined experimental–numerical analysis. The first one gives the most reasonable estimate. It is also found that the ultimate tensile strength linearly correlates with the projected area of pores. [Copyright &y& Elsevier]

Abstract: The population and size of porosities in an A713 sand cast aluminum alloy were statistically measured and the pore size distribution could be quantified using a general extreme value (GEV) distribution function. The stress–number of cycles to failure (S–N) curve of the alloy was characterized using four-point bend fatigue testing at f =20Hz, R =0.1, and in ambient air. The fatigue strength of the alloy was measured to be 94.5MPa. Crack populations on the surfaces of the specimens fatigued at different stress levels were counted, and plotted against the applied maximum stress. It was found that the relationship between crack population and stress was a Weibull distribution function. By taking the derivative of the Weibull function, the density and strength distribution of fatigue weak links were derived. The strength distribution of fatigue weak links was profoundly different from the pore size distribution, indicating that the strength distribution of fatigue weak links, instead of the simple pore size distribution, should be used to evaluate the fatigue properties of this alloy. [Copyright &y& Elsevier]

Abstract: The crack-healing behavior of Si3N4/SiC composite under constant stress and low oxygen partial pressure was investigated. A semi-elliptical surface crack with a length of about 100μm was introduced at the center of the tensile surface by the indentation method. The specimens were crack-healed at 1200°C for 5h under tensile stress (σ app. =200–300MPa) and under low oxygen partial pressure and air (). The threshold constant stress for crack-healing was defined as 200MPa in oxygen partial pressure over 500Pa. The bending strengths of crack-healed specimens under tensile stress in showed almost the same value as a healed smooth specimen, and most specimens fractured outside the crack-healed zone. From these results, we conclude that crack-healing can be achieved under stress in low oxygen pressure and can lengthen lifetime and increase reliability in Si3N4/SiC composite ceramic. [Copyright &y& Elsevier]

Abstract: The fracture behavior of two metal matrix composites (MMCs) at different aging conditions is investigated both at the global and local levels. The study is focused on the processes of void initiation near the crack tip by either particle fracture or particle/matrix decohesion, and on fracture initiation. The global fracture properties are determined by conventional fracture mechanics tests. The local conditions for void and fracture initiation are determined using fractographic analyses and subsequent analytical computations, based on the HRR-field equations, mean-field theory, and a simple analytical model from literature. The correlation between the global and local fracture properties is studied. The applicability of existing models to predict the fracture toughness of MMCs is discussed. The results of the analyses suggest that the maximum principal stresses in the particles at the moment of void initiation are not constant, but exhibit a dependency on the composite yield strength. [Copyright &y& Elsevier]

Abstract: Using a commercial, electrodeposited copper film of 12μm thickness, tensile tests, fatigue tests and static loading tests were performed. The elastic modulus, two types of yield strengths, tensile strength and strain-hardening exponent were obtained. Fatigue tests were performed at four levels of mean stresses and cyclic plastic strain and ratcheting strain (monotonic plastic strain) were measured continuously during the tests. Irrespective of mean stress, fatigue life can be well represented by the maximum stress. The monotonic plastic strain at fracture is nearly constant, irrespective of fatigue life or mean stress. Based on the results obtained, the reason why fatigue life can be well represented by the maximum stress is discussed. [Copyright &y& Elsevier]

Abstract: The creep behavior of novel magnesium-base alloys was investigated in the temperature interval between 473 and 623K. The alloy Mg96Ni3Y1.5CeMM1.5 (wt.%) was produced by two different processing techniques: (i) casting and subsequent hot extrusion at 673K, and (ii) a casting and powder metallurgy procedure involving cold isostatic pressing of atomized powders and hot extrusion at 673K. Compressive creep tests with stepwise loading were used for analyses of the creep behavior. The treatment procedure of the alloy does not influence its creep resistance substantially. Detailed analyses of the stress dependences of the creep rate have shown that they can be described by the Garofalo sinh relationship modified for the back stress concept. [Copyright &y& Elsevier]

Abstract: New relationships, incorporating the activation energy for matrix diffusion (300kJmol−1) and the ultimate tensile strength values at the creep temperature, allow effective rationalization of the multi-batch stress rupture properties for Grade 92 steel (9Cr–0.5Mo–1.8W–V–Nb). These approaches lead to straightforward procedures for extrapolation of short-term results, with creep life measurements from tests lasting up to only 5000h providing reasonable estimates of 100,000h rupture strengths. Validation of this new methodology would therefore offer the prospect of cost-effective acquisition of long-term creep design data. [Copyright &y& Elsevier]

Abstract: The roles of specimen thickness and hardening behavior of the material on the ductile tearing resistance of a 6056 aluminum alloy are investigated separately as a function of stress triaxiality, by varying both the heat treatment (overaging or annealing + slow cooling) and the specimen geometry. The fracture path can be slanted or flat. Results show that increasing hardening capability and specimen thickness favors flat fracture. For the overaged material, the energy dissipation rate, measured on Kahn specimens, reaches a maximum value for an intermediate value of thickness (3.2 mm), whereas for the annealed material, a change in the fracture mode (from slanted to flat) induces a continuous increase in toughness with increasing thickness up to 6 mm. [Copyright &y& Elsevier]

In this study, fracture toughness (J-integral) values in cracked welded nodular iron were determined experimentally, and stress–strain analyses were done by the finite element method, for different crack sizes and locations with various strength levels. As a result, the effect of yield strength mismatch on the constraint around crack tip was discussed by means of stress triaxiality (ST) and plastic strain. It was found that ST values increase with crack length. Different regions in the weldment affect the extent of plastic deformation in the material. [Copyright &y& Elsevier]