Search

To investigate the dynamic recrystallization (DRX) behavior of forged 42CrMoA steel during hot deformation, the hot deformation experiments of forged 42CrMoA steel under different deformation conditions (strain rate, temperature, and strain) were carried out in this paper. The hot deformation activation energy of forged 42CrMoA steel was determined to be 413627.2 J · mol - 1 . The constitutive model and DRX kinetic model of the steel were established. Analyzing the reconstructed parent phase grains reveals that when the strain is constant, as the deformation temperature increases and the strain rate decreases, the average size and DRX volume fraction of the parent phase grains gradually increase, and the peak stress gradually decreases. When the deformation temperature and strain rate are constant, as the strain increases, the average size of the parent phase grains gradually decreases, and the volume fraction of DRX gradually increases. Based on the cellular automaton theory model and considering the influence of grain deformation on the DRX process, a cellular automaton dynamic recrystallization (T-DRX-CA) model for forged 42CrMoA steel based on topological deformation technology was established, and the microstructure evolution under different deformation conditions was simulated. The microstructure evolution under different deformation conditions was simulated, which was compared with experimental results. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. The hot deformation behavior of forged 42CrMoA steel under different deformation conditions was investigated by a cellular automaton dynamic recrystallization (T-DRX-CA) model based on topological deformation technique. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. [ABSTRACT FROM AUTHOR]

It is vital to reveal the effect of microstructure features on the corrosion behavior of pure aluminum anode in alkaline electrolyte for Al-air batteries. In this paper, we extensively studied the influence of mechanical deformation on the corrosion microstructure and then corrosion features of pure aluminum anode. The results demonstrate that the cold-rolling deformation could facilitate the grain size refinement of pure aluminum. Surprisingly, the aluminum anodes with smaller grain sizes and larger grain boundary areas could effectively improve the corrosion resistance. The further characterization of the microstructure indicates that the deformation is capable of causing the fracture of the cathodic secondary phase precipitate clusters thus weakening the galvanic corrosion effects. The results of this paper could gain insights into the design and processing of pure aluminum for Al-air battery. [ABSTRACT FROM AUTHOR]

Spherulite is the main microstructure feature of semicrystalline polymers, exhibiting a non-axisymmetric geometry with a sheaf structure in the center. In the initial stage of growth, spherulite is manifested initiation from the sheaf structure with a certain orientation. The size and orientation of sheaf structure are affected by various processing parameters. Previous research considered spherulite as completely radially symmetric structures, ignoring the effects of anisotropic sheaf on mechanical properties. In this paper, an anisotropic micromechanical model for evaluating the mechanical properties of semicrystalline polymers was proposed. The microstructure of single spherulite was modeled with different sheaf sizes, orientations, and crystallinities. The viscoplastic constitutive model together with the Arruda–Boyce model was used to describe the micromechanical behaviors of the crystalline lamellae and amorphous lamellae, respectively. The evolution of inhomogeneous plastic deformation, interlayer deformation and slip activities in spherulite was observed under tension. The results shown in this work enhance the understanding of the microstructure–property relationship of semicrystalline polymers, which, in turn, guides the development of advanced manufacturing techniques for tailoring mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, the deformation mechanisms of a Fe–2.25%Cr–1%Mo (P22) steel are studied after tensile tests at room temperature (RT) and 550 °C (HT), creep-fatigue tests at 550 °C and stress relaxation test at 550 °C (HTSR). The RT, HT and HTSR tests produced permanent strain of about 2.5% by different processes. Deformation features such as the orientation of the grains, local misorientation, grain boundary type and distribution, etc., were characterized using electron backscatter diffraction. Transmission electron microscopy was done subsequently to obtain greater insight into the dislocation substructures. The as-received sample had a ferritic–bainitic microstructure, and a large amount of local misorientation was found in the bainite, indicating plastic strain due to phase transformation. After tensile strain to 2.5% at room temperature, the dislocations formed very small substructures (~100–200 nm) in the ferrite grains, and most of the retained plastic strain seemed to be concentrated in the bainite after deformation. Both the ferrite and bainite showed much lower local misorientation and dislocation wall content after a tensile test to 2.5% strain at 550 °C. Compared to the RT tensile sample, after creep-fatigue at 550 °C, the substructures in ferrite opened up considerably and formed small-angle grain boundaries, with clean areas as large as 20–25 μm. After stress relaxation at 550 °C, the ferrite displayed even less substructure, while the bainite seemed to have greater amounts of local misorientation than in the creep-fatigue case. However, the degree of misorientation was less pronounced than in the room temperature tensile case. These results have been discussed with respect to the causes behind the phenomena observed herein and their possible effects on mechanical behaviour. [ABSTRACT FROM AUTHOR]

In this paper, the deformation behavior of a nickel-based single-crystal superalloy with [ 1 ¯ 40] and [ 3 ¯ 40] orientations was studied at room temperature by in situ electron backscattered diffraction (EBSD) tensile equipment. The mechanical properties, slip behavior and the corresponding Schmidt factor were analyzed. The deformation bands generated during the plastic deformation stage were found and characterized by using the electron backscattered diffraction (EBSD) technique. Furthermore, the formation and propagation of deformation bands played a softening effect on stress–strain curves; however, the secondary slip bands occurring after the propagation of deformation bands played a hardening effect. Finally, the formation of deformation band and its propagation on the mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

The impact of crushing on the macroscopic mechanical characteristics of granular materials from a microscopic perspective has recently been revealed using the discrete element method (DEM). The influence of the self-organized, mass conservation and volume conservation of daughter particles in the fragment replacement method (FRM) on particle breakage is complex and crucial. In this paper, 14-ball Apollo directly filling method (DFM) and expansion method are combined to keep balance among particles before and after crushing, considered to establish DEM to simulate granular material. By considering the influence of volume loss on the micro-fracture condition of the samples, the macro-responses of mechanical and deformation characteristics, the gradation change and the critical state are studied. The effect of inter-particle interaction on macroscopic properties is also analyzed from the microscopic perspective. The rationality of the volume expansion method is verified. The comparisons of samples with volume conservation and volume loss show that the stress development process and the volumetric strain are affected. The existence of the balance point of volume effect is related to the stress level which lead to the difference in stress and strain. Through analysis of relative breakage index (Br) and the statistical number of microscopic particles, it can be seen that the gradation deviation comes from the two-way influence of the volume loss on the crushing of particles. The volume loss has no effect on stress ratio in the critical state, but has a significant effect on stress change during shearing process, and results in the critical state void ratio to decrease with increasing confining pressure. The rationality of daughter particles' volume conservation are analyzed from the motion, displacement development and force chain evolution. [ABSTRACT FROM AUTHOR]

Small specimen test techniques (SSTTs), developed for scarce materials, industrial products, in-service equipment, etc., could be challenging to obtain sufficient materials for routine testing. This review focuses on the research on millimeter- and micron-scale SSTTs of metallic materials in the past decade. Mainstream small specimens are divided into similarity, penetration, and semi-penetration. Representative tests of the above three categories are analyzed in detail, including the small tensile test, small punch test, and indentation test. The macro- or micro-correlation methods of deformation and failure parameters between the SSTTs and conventional tests are discussed, including Young's modulus, yield strength, ultimate tensile strength, damage evolution, fracture strain, and the stress–strain full-history relationships. Meanwhile, the extensive requirements for material testing are also considered, such as anisotropy and strain rate, temperature, and stress triaxiality sensitivities. The characteristics and modification strategies of the SSTTs are described from the aspects of size effects, inhomogeneous structures, and manufacturing defects. Finally, this paper discusses the application of SSTTs in forging, stamping, welding, and additive manufacturing and highlights the potential development directions of SSTTs. [ABSTRACT FROM AUTHOR]

In this paper, the N back-migration and restoration behavior of duplex stainless steels (DSSs) 2101 and 2205 (DSS2205) were studied. Experimental findings indicated that the Cr2N in the ferrite (α) persistently decreased for both steels during the cooling process from 1200 °C to 1000 °C, and the disappearance rate of Cr2N in DSS2205 was significantly faster than that of lean duplex stainless steel 2101 (LDX2101). On the one hand, due to the severe partitioning behavior of N atoms in α migrating back to austenite (γ), on the other hand, the enriched Mn in LDX2101 and the enriched Ni in DSS2205 exerted an impact on N migration. Also, the cumulative thermal deformation at 1200 °C contributed to the N migration back into γ with the assistance of high-density dislocations and thermal deformation energy. Furthermore, the softening mechanism of constituent phases was dominated by discontinuous dynamic recrystallization (DDRX) mechanism in both steels at a strain rate of 10 s−1, which was characterized by strain-induced boundaries migration from low-density dislocations to high ones. [ABSTRACT FROM AUTHOR]

Advances in the use of in situ transmission electron microscopy (TEM) to study mechanical deformation have enabled a direct correlation of mechanical properties with microstructures, in particular, atomic-level defect dynamic processes. Shear deformation of metallic materials has been noticed to lead to unique microstructural features with superior properties that would be difficult to achieve by traditional metallurgical processes. However, in contrast to the case of in situ TEM studies of structural evolution under tension, compression, and bending, in situ TEM probing of dynamic processes during direct shear loading, especially at microscales and nanoscales, is very limited. This paper reviews recent progress on the development of in situ TEM for studying shear deformation in terms of both the technique and the scientific insights that have been gained. In addition, we discuss current challenges encountered in the use of in situ TEM for shear deformation, such as the limited total strain, strain rate, and spatial and temporal resolution. To provide perspective, we present promising opportunities for in situ TEM studies with pure shear loading by taking advantage of the integration of advanced imaging techniques both in TEM and scanning transmission electron microscopy domains, advanced electron detectors, highly efficient chemical analysis, data-driven machine learning, and environmental conditions. [ABSTRACT FROM AUTHOR]

The effects of hole shape and orientation on the mechanical properties of micro-scale 2D honeycomb structures, fabricated using a focused ion beam equipment, have been investigated using an in situ micro-mechanical testing machine inside the scanning electron microscope. The material used was single-crystal Ni oriented in the < 100 > direction, with the plane of the 2D micro-lattice having a {001} normal direction. The hole shapes explored were hexagonal and circular, while two different orientations of the hexagonal holes were also compared. One of these orientations had a horizontal arm (designated 0° orientation), while the other had a vertical arm (30° orientation) in each hexagon. The results indicate that there is substantial change in strength and ductility depending on the orientation and shape of the holes with respect to the tensile axis. The samples with 30° oriented hexagonal holes had the lowest strength and highest ductility, while the samples with circular holes showed the greatest yield and tensile strength. The samples with the 0° orientated hexagonal holes had much higher strength and lower ductility than the 30° orientated ones. Moreover, the samples with 0° orientated hexagonal holes, which had a similar hole pattern arrangement to the ones with circular holes, had a similar strength to those of the latter type. Thus, it is apparent from this study that the orientation or arrangement of the holes is more important in determining the properties of the 2D microlattice than the shape of the holes. Finite element simulation of the lattice structures utilised the GTN (Gurson, Tvergaard and Needleman) model to evaluate the failure modes under uniaxial tension. The lattice structure has been shown, in a previous paper by the authors, to exhibit composite like behaviour with strength differences in various parts arising from size effects. These size effect variations were incorporated into the model, and a generalised formulation for the GTN parameters was proposed on the basis of one of the experimental configurations and subsequently applied to the other geometries. The models were in good quantitative agreement with the experimental results with accurate representation of the flows stress and failure modes. [ABSTRACT FROM AUTHOR]

The article presents a list of articles related to materials science published in volumes 39, 40, and 41. The articles include "Adhesively-bonded joints and repairs in metallic alloys, polymers and composite materials," "Observations of common microstructural issues associated with dynamic deformation phenomena: Twins, microbands, grain size effects, shear bands, and dynamic recrystal," and "Role of entropy of fusion in phase transformation and selfdiffusion."

High-entropy alloys (HEAs) are multi-component alloys with a novel designed concept. These HEAs exhibit unique composition design and structural characteristics leading to excellent properties, which have attracted considerable attention in various fields. The extensively investigated HEAs exhibit excellent strength–ductility combination and excellent damage resistance at cryogenic temperature. Therefore, HEAs have potential applications in cryogenic temperature structural materials. It is important to study their deformation behavior and microstructural evolution at cryogenic temperature to provide the understanding needed for further alloy development. In this paper, the effects of different phase structure, grain size and stacking fault energy (SFE) on cryogenic temperature deformation behavior are reviewed. The research and development of tensile, compressive and fracture toughness of HEAs at cryogenic temperature are briefly reviewed. We discuss how individual deformation mechanisms can compete or operate synergistically with each other during cryogenic temperature plastic deformation, including dislocation slip, strain-induced twin formation and strain-induced phase transformation. In addition, the future trends and some problems faced by HEAs at cryogenic temperature are discussed, and prospects of HEAs are put forward. [ABSTRACT FROM AUTHOR]

This paper reports atomistic simulation studies of tensile and compressive behavior of nanowires of a model quinary high entropy face-centered cubic (FCC) alloy. The simulations employ empirical interatomic potentials and use massively parallel molecular dynamics techniques at the atomistic level to study the deformation mechanisms. The studies consider pristine cylindrical nanowires oriented along various crystallographic directions. The focus is the role that local composition fluctuations in the random alloy plays in the deformation response. The deformation behavior observed for the complex random alloy is compared with a corresponding "average atom" material that has the same average properties but no local compositional fluctuations. In all cases, deformation is governed by dislocations emitted from the free surface. Twinning was also found, depending on the crystallographic orientation and loading mode. We show that for all orientations, the high entropy alloy (HEA) wires show the onset of plasticity at lower stress levels than the average atom material. However, after the onset of plasticity, the HEA presents a higher strength, mostly driven by the fact that the dislocations emitted from the surface do not glide as easily in the random alloy as they do in the average atom material. [ABSTRACT FROM AUTHOR]

Al–Zn–Mg–Cu alloys can be fabricated by a series of thermo-mechanical processing methods (e.g., hot rolling, forging and extrusion), which is able to serve in aeronautic, automobile, and marine industries because of its excellent physical properties. However, reaching the balance between high strength and favorable ductility to present its high performance is still in progress, during which temperature and strain rate are two very important external variables. More importantly, the core lies in sophisticated microstructure evolution paths involved in hot deformation, which consists of different microstructure mechanisms and behaviors and can be expressed as various mechanical responses. Therefore, a fundamental review of microstructure mechanisms and behaviors, microstructure evolution and relevant mechanical responses of Al–Zn–Mg–Cu alloys during high-temperature deformation is of great significance. In present paper, first, various experimental methods have been introduced. Second, general trends of mechanical properties changing with temperature and strain rate have been summarized. Third, major microstructure mechanisms and behaviors have been discussed. Then, a schematic illustration originating from dislocations' movement has been depicted, which succeeding microstructure evolution and mechanical responses (including superplasticity) have been reviewed accordingly. Finally, further suggestions of hot deformation of Al–Zn–Mg–Cu alloys have been given. [ABSTRACT FROM AUTHOR]

Accurate flow stress data are essential for the design and optimization of thermo-mechanical processes for a wide range of metallic materials. Hot compression testing is generally used to establish the dependence of flow stress on temperature, strain and strain rate. Flow stress measurements have mostly used cylindrical specimens of different sizes. While the data has been corrected for friction and adiabatic heating, the measurements assume idealized uniform deformation in the test specimen when obtaining the flow stress data from the measured load and displacement. In this paper, it is shown that there is significant non-uniform deformation in the test specimen under practical testing conditions, and a methodology is developed to correct the flow stress data. This correction is generally more significant than the correction due to friction or adiabatic heating and is necessary to obtain more accurate flow stress data. The effect of specimen geometry is also investigated, and a geometry which results in more uniform strain distribution than a cylindrical specimen is used. Measurements are conducted for a prototype powder metallurgy nickel-base superalloy at a low strain rate over a deformation temperature range. Constitutive equations are constructed with the measured flow stress data. Finite element modeling of the tests using the corrected data provides a better agreement with the measured loads. The grain microstructures vary with the test parameters and are used to correlate the flow behavior. [ABSTRACT FROM AUTHOR]

Semi-crystalline polymers are now extensively used in various applications such as aircrafts, civilian structures, oil and gas platforms and electronics. They are, however, inherently damage prone, and over time, the formation of damages such as cavitation and crazing causes degradation in mechanical properties, which eventually results in the permanent failure of the materials. This paper provides an overview of the principal approaches to assess and characterize damage in semi-crystalline polymers. The damage characterization methods are divided into two categories: mechanical characterization methods, aiming at describing damage growth based on the measurement of mechanical or physical properties and structural characterization methods, focusing on the assessment of microdamage initiation and evolution. Special attention has been paid to in situ non-destructive damage characterization methods. For better understanding deformation/damage behavior in semi-crystalline polymers, two major damage theories currently used to describe damage development are also described. The paper concludes with a discussion of limitations and critical issues for characterizing damage in semi-crystalline polymers. [ABSTRACT FROM AUTHOR]

A methodology that accurately simulates the brittle behavior of epoxy polymers initiating at the molecular level due to bond elongation and subsequent bond dissociation is presented in this paper. The system investigated in this study comprises a combination of crystalline carbon nanotubes (CNTs) dispersed in epoxy polymer molecules. Molecular dynamics (MD) simulations are performed with an appropriate bond order-based force field to capture deformation-induced bond dissociation between atoms within the simulation volume. During deformation, the thermal vibration of molecules causes the elongated bonds to re-equilibrate; thus, the effect of mechanical deformation on bond elongation and scission cannot be captured effectively. This issue is overcome by deforming the simulation volume at zero temperature-a technique adopted from the concept of quasi-continuum and demonstrated successfully in the authors' previous work. Results showed that a combination of MD deformation tests with ultra-high strain rates at near-zero temperatures provides a computationally efficient alternative for the study of bond dissociation phenomenon in amorphous epoxy polymer. In this paper, the ultra-high strain rate deformation approach is extended to the CNT-epoxy system at various CNT weight fractions and the corresponding bond disassociation energy extracted from the simulation volume is used as input to a low-fidelity continuum damage mechanics (CDM) model to demonstrate the bridging of length scales and to study matrix failure at the microscale. The material parameters for the classical CDM model are directly obtained from physics-based atomistic simulations, thus improving the accuracy of the multiscale approach. [ABSTRACT FROM AUTHOR]

Although tension-shear coupling of weave fabrics in large deformation has been observed in experiments, most constitutive models for weave fabrics often ignore this coupling effect for simplicity. In this paper, a nonlinear anisotropic hyperelastic constitutive model is proposed to consider this tension-shear coupling effect. Draping experiments of a plain weave fabric over a tetrahedron mold are carried out to validate the proposed coupling constitutive model. Subsequently, the influences of tension-shear coupling on draping processes are investigated. Numerical simulation results indicate that the tension-shear coupling effect significantly changes fiber reorientation during draping process, which makes shear deformation tend to be uniform and reduces the local shear deformation concentration and should not be neglected in woven fabric stamping with salient double curvatures. [ABSTRACT FROM AUTHOR]

Dual-phase high-carbon steels are of significant interest in mining industries particularly in comminution and rock handling applications where the strain rate varies from very low to very high. The effect of quasi-static strain rate on the deformation behaviour of austenite-martensite high-carbon low-alloy steel is investigated for compression loading in this paper. Experiments were conducted at different compressive strain rates (2.56 × 10−4 to 2.56 × 10−1 s−1), and the subsequent microstructural evolution was characterised by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy and electron backscatter diffraction (EBSD) techniques to establish the structure-property correlation. The experimental results indicated an increase in the yield strength (σy) with the increase in the strain rate due to the rate-dependent dislocation velocities. The strain hardening rate of the material exhibited a decreasing trend with an increase in the true strain values for all the applied strain rates. XRD results indicated the phenomenon of deformation-induced martensitic transformation (DIMT) to be rate dependent, whereas EBSD results showed an increase in the Kernel average misorientation values with increase in the strain rate. The volume fraction of retained austenite was observed to be decreasing with an increase in the engineering strain values irrespective of the applied strain rate. The microscopic features of the fracture surfaces showed the presence of transgranular cracking at low strain rates, whereas predominant intergranular cracks were found at higher strain rates. TEM results indicated the decrease in the lath martensites with increase in the strain rate. [ABSTRACT FROM AUTHOR]

This paper is the second of a two-part series assessing the feasibility of using the J-integral with full-field deformation data from digital image correlation (DIC) to characterize toughness in continuous fiber, SiC/SiC ceramic matrix composites (CMCs). In part I, line and area integral adaptations of the J-integral were validated with analytical and experimental deformation fields. It was found that variability in experimental data and contour truncation at the crack wake introduced error and path-dependency, but this could be mitigated through data filtering. In this paper, the line and area integral methods were evaluated for cross-ply and longitudinal CMC tensile specimens. It is demonstrated that these approaches cannot be used for quantitative characterization, but can be successfully used to examine qualitative trends. For both architectures, area integral measurements of the potential energy release rate, J, were larger (and arguably more accurate) than line integral measurements. Resistance curves were characteristic of tough materials, but the stress intensity magnitudes were larger in the longitudinal laminates than the cross-ply (for equivalent crack extension). Experimentally derived bridging laws showed that fiber bridging tractions were largest in the cross-ply laminates, which was attributed to a lower volume fraction of longitudinal fibers. Quantitative, single-value measurements of fracture toughness could not be established since (1) noise in the DIC data masked strain signals indicative of first matrix cracking, and (2) widespread matrix cracking rendered the J-integral invalid (regardless of size and position, the boundaries of the line and area contours inevitably intercepted microcracks). Rather, gross estimates of toughness and stress intensity factors were made under the assumption that the limitations in the spatial resolution of the DIC data essentially transforms regions with fine microcracking along the contour into continuous regions of elastic deformation. When evaluated with the J-integral, the smoothed deformation fields manifest as resistance curves indicative of a tough material. Thus, the J-integral was valuable for qualitative assessments of toughening mechanisms in the CMCs. [ABSTRACT FROM AUTHOR]

3D auxetic textile composite is a special type of auxetic materials which has attracted more attention in recent years. Its deformation behaviour and mechanical properties under quasi-static compression have been investigated in the previous studies. In this paper, a further study on its mechanical properties under low-velocity impact is presented. Both single and repeating impact tests were conducted at different impact energy levels ranging from 12.7 to 25.5 J. Results show that the 3D auxetic textile composite has better impact protective performance than the 3D non-auxetic textile composite due to better transmitted force reduction and higher energy absorption capacity under single-time impact and higher structural stability under repeating impacts. The results also show that the difference in protective performance between the auxetic and non-auxetic textile composites get increased with the increase in impact energy. [ABSTRACT FROM AUTHOR]

Oxide Dispersed Strengthened (ODS) ferritic stainless steels present well-known fine grains microstructures where dislocation movement is hindered by a dense precipitation of nano-oxides particles. Previous research, on the thermomechanical behavior at high temperature and strain rates, was focused on torsion tests (Karch in J Nucl Mater 459:53-61, 2014). Considering texture evolution and grain shape as indicators of the intragranular dislocation glide activity, it was shown that, for high temperature and strain rate, intragranular deformation was in competition with intergranular accommodation. The latter phenomenon was related to early damaging at grain boundaries. The occurrence of a transition phenomenon from an intragranular to an intergranular deformation mechanism, with increasing temperature, was recently confirmed by neutron diffraction spectroscopy (Stoica in Nature Commun 5:5178, 2014). In the present paper, hot extrusion (HE) tests are performed, avoiding damage due to the high stress triaxiality, and allowing further investigation of intragranular and intergranular plasticity at large strains. Three ferritic steels exhibiting various precipitation size and density were hot extruded. Microstructure evolution at different stages of deformation is investigated using the Electron Back-Scattered Diffraction (EBSD) technique. After extrusion at 1373 K (1100 °C), the microstructure of ODS steels consists of a mixture of small round shape grains and larger elongated grains containing low-angle grain boundaries. Texture measurements show the appearance of the α-fiber (<110>//extrusion direction) and an increase in its intensity during the extrusion process in the larger grains. The fragmentation of the large elongated grains by Continuous Dynamic Recrystallization (CDRX) partially occurs in ODS materials depending on precipitation reinforcement. For smaller grains, plastic deformation has no effect on crystallographic orientation and grain shape, indicating a grain boundary accommodation phenomenon as the major deformation mechanism. Precipitation density not only impacts the intragranular dislocation glide activity, but also reduces CDRX kinetics in coarse grains. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of the fracture behaviour of two industrial refractory materials thanks to the development of a new technique of digital image correlation (DIC). DIC, already known as a helpful and effective tool for the measurement of displacement and deformation fields in materials, has been adapted to take into account displacement discontinuities as cracks. The material transformation, usually assumed homogeneous inside each DIC subset, is thus more complex, while each subset can be cut in two parts with different kinematics. By this way, it is possible to automatically find the fracture paths and follow the crack geometries (length, opening) during the loading with a higher spatial resolution than the one obtained by standard DIC. After having presented the principle of the new technique, its metrological performances are assessed from synthetic images and the choice of crack detection criterion is discussed. The capacity of this new technique is shown through a comparative study with standard DIC. Its application is led on magnesia-spinel refractory materials, specifically to highlight and to characterize the evolution of kinematic fields (displacement and strain) observed at the surface of sample during a wedge splitting test typically used to quantify the work of fracture. We show that refractories with aggregates of iron aluminate spinel present a fracture mechanism with crack branching and can dissipate more energy thanks to a longer crack network. [ABSTRACT FROM AUTHOR]

This paper presents a review of the mechanical characterisation of thin film and coated systems using indentation tests. The potential in assessing mechanical properties of films and coatings using indentation tests has received a great deal of attention since this knowledge is vital for predicting their performance. The relevant theoretical background is discussed. Experimental work, numerical studies and data interpretation techniques for indentation on single bulk materials and thin films are discussed. Surface conditions, indentation depths and indentation size effects for indentation tests on thin films and coated systems are discussed. Data interpretation methods for indentation on films and coated systems are reviewed with a discussion on their limitations. Other studies in this field concerning the substrate effects and critical indentation depth ratios are also discussed. Suggestions for future experimental work and data interpretation are provided. [ABSTRACT FROM AUTHOR]

Stacking fault energy (SFE) is an intrinsic material property whose value is crucial in determining different secondary deformation mechanisms in austenitic (face-centered cubic, fcc) steels. Considerable experimental and computational work suggests that the SFE itself is highly dependent-in a complex manner-on chemical composition and temperature. Over the past decades, there have been a large number of efforts focused on determining the composition dependence of SFE in austenitic steel alloys by means of experimental, theoretical or computational methods. Unfortunately, experimental methods suffer from the indirect nature of the methodologies used to estimate the value of SFE, while computational and/or theoretical approaches are either limited by the physics that they can incorporate into the predictions or have more practical limitations associated, for example, to the size of the systems that can be modeled or the assumptions that must be made. In this paper, we review the major experimental and computational approaches to determine SFE in austenitic steel alloys, and we discuss their limitations. We then demonstrate a data-driven machine learning technique to mine the literature of experimental SFE data in steels, while algorithms at the fore-front of machine learning have been used to visualize the SFE data and then construct a three-class classifier. The classifier is used then to predict likely secondary deformation mechanisms of untested compositions, while the classifier itself is presented as a valuable tool for the further development of austenitic steel alloys in which the specific secondary plastic deformation mechanisms are a feature to design for. The data as well as the entire analysis workflow are made available to the wider community through a public github repository. [ABSTRACT FROM AUTHOR]

AgSn and CuSn are important intermetallic compounds formed in lead-free solders and dental amalgams. In this paper, we present a study on the microstructural stability in a AgCuSn alloy using a combination of scanning and transmission electron microscopy experiments. The as-cast microstructure comprises the D0 phases θ-AgSn and ε-CuSn, plus a small amount of η-CuSn. There is topotaxial precipitation of AgSn within the CuSn phase, which coarsens with heat treatment at 450 °C. For extended low-temperature aging (1000 h at 100 °C), there is also precipitation of CuSn within the AgSn phase. All the heat-treatments result in the formation of secondary defects in the near-surface region. These defects are dislocations in the AgSn and {011}-type twins in the CuSn. The same defect types are observed in these phases for as-cast samples deformed in compression suggesting that different deformation mechanisms are operating in these isostructural phases. [ABSTRACT FROM AUTHOR]

A new nucleation mechanism is proposed for $$ \{ 10\bar{1}1\} $$ deformation twin in hcp materials. The mechanism is based on the results of atomistic computer simulations. It was found that under high shear stress applied on $$ \{ 10\bar{1}1\} $$ plane (the stress level is about 7 % of shear modulus), the core of a slip dislocation can transform to a twin embryo. The transformation and subsequent twin growth are accompanied by nucleation and migration of interfacial defects including disconnections and stacking faults. The paper provides the analysis of the nature of these defects and describes the reactions between them. [ABSTRACT FROM AUTHOR]

A new method is developed in this paper to deal with the thermomechanical response of continuous fiber-reinforced composites. Treating the matrix as an elastic-perfectly plastic solid, the analytical formulae of the deformations and stresses of the matrix are obtained from the plasticity theory, axisymmetric equilibrium equation, and stress–strain and strain–displacement relations. The fiber is taken to be an anisotropic, elastic material, and the formulae calculating its deformations and stresses are also presented. The boundary conditions and the consistence of deformations and stresses between the fiber and matrix, and between elastic and plastic regions of the matrix are employed to determine the unknown constants in the analytical formulae. With the developed method, the thermomechanical stress distributions in composites reinforced with circumferentially orthotropic, radially orthotropic and transversely isotropic fibers are investigated, and how the elastic-perfectly plastic property and different materials of the matrix affect the thermomechanical response of the composites is discussed. For the thermomechanical loads and composite systems given in this paper, the elastic-perfectly plastic property of the matrix can reduce the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix. A strong matrix can raise the compressive stresses in the fiber, and the tensile circumferential and axial stresses in the matrix. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue properties and deformation behavior of the T6-treated Mg-2.99Nd-0.18Zn-0.38Zr (NZ30K) and an AZ91D-T6 magnesium alloys with the same grain size. Compared with the AZ91-T6 alloy, the NZ30K-T6 alloy shows significant increases in mechanical properties, achieving 17 MPa in YS, 51 MPa in UTS, 2.4 % in elongation, and 15 MPa in FS, respectively. The NZ30K-T6 alloy also shows higher cyclic stress amplitudes in comparison with the AZ91-T6 alloy. This is attributed to increased matrix strength from the higher precipitate strengthening in the NZ30K-T6 alloy. The cyclic stress amplitude of the AZ91-T6 alloy increases with increasing the number of cycles. For the NZ30K-T6 alloy, the cyclic stress amplitude first increases and then decreases during cyclic deformation. Hysteresis loops were symmetrical at all total strain amplitudes due to the lessened extents of texture in these cast magnesium alloys and the absence of twinning-detwinning during cyclic deformation. For both AZ91-T6 and NZ30K-T6 alloys, the cracked slip bands initiate the fatigue cracks and also assist the crack propagation. The Coffin-Manson law and Basquin equation can be used to evaluate the fatigue parameters and predict the LCF lives of both AZ91-T6 and NZ30K-T6 alloys. The multi-scale fatigue (MSF) life models and the same model parameters were also used to predict the HCF lives of these alloys. [ABSTRACT FROM AUTHOR]

The complex nature of damage in ceramic matrix composites (CMCs) renders conventional methods of measuring quantitative fracture properties impractical. This paper is the first of two-part series that assesses the feasibility of using the J-integral with full-field deformation data from digital image correlation (DIC) to characterize toughness in continuous fiber SiC/SiC CMC laminates. It provides a resource for best practices when incorporating experimentally measured, full-field deformation data into J-integral evaluations of toughness. The techniques discussed are important for researchers attempting to measure fracture properties in advanced materials with damage mechanisms that have yet to be well characterized. Two methods for evaluating potential energy release rates J are presented: (1) numerical integration over a line contour and (2) Gaussian integration over an area contour. Accuracy and path independency for both methods were verified using analytically derived deformation fields for a center-cracked, infinite plate of isotropic material under equi-biaxial tension. Inherent noise in the deformation data and necessary contour truncation at the crack surfaces reduced accuracy and introduced path dependency. However, this was mitigated by careful noise filtering of the deformation data prior to the evaluation of J. Applying the line and area integrals to DIC data from tapered, double-cantilever beam, acrylic compact tension specimens resulted in the findings that (1) both integrals measured fracture toughness within a range of published values; (2) both integrals captured the constant stress intensity factor behavior that is characteristic of the tapered beam geometry; and (3) the area integral measurements were consistently larger than line integral measurements. The area integral is more accurate than the line integral as it samples more data points, reducing its sensitivity to experimental noise. Although variability in experimental data can be minimized, it cannot be eliminated. Measurement error is inevitable; thus, the line and area integrals must be used with caution when characterizing quantitative properties including fracture toughness. [ABSTRACT FROM AUTHOR]

The paper examines the roughening along a metal-polymer interface, to find out whether the relevant length scale is on a sub-grain level or on the grain-size level. This is relevant for understanding the possible delamination of a polymer coating on a metallic substrate. Therefore we have investigated the local lattice orientation in heavily strained ferritic steel using electron back-scatter diffraction. From that data we have calculated the components of the local orientation gradient tensor as well as the local Schmid factor for deformation along [100] and [001] on {101} and {112} slip systems. The curvature of the draw-and-redraw steel- polyethylene terephthalate (PET) laminate interface as well as the curvature of the underlying steel lattice was examined in detail. It is concluded that roughening at a sub-grain length scale along the interface is due to plasticity in the interior of the grains. [ABSTRACT FROM AUTHOR]

This paper describes fabrication of Si nanograins through allotropic phase transformation by concurrent application of high pressure and intense straining using high-pressure torsion (HPT). Single-crystalline Si(100) wafers were processed by HPT under a pressure of 24 GPa at room temperature. X-ray diffraction and Raman analysis revealed that the HPT-processed samples were composed of metastable Si-III and Si-XII phases and amorphous phases in addition to the original diamond-cubic Si-I phase. It was found that nanograins formed because the Si-I diamond phase had transformed to high-pressure phases (Si-II, Si-XI, and Si-V) having metallic nature, and it then became easier to generate a high density of dislocations to form grain boundaries. The high-pressure phases were further transformed to the Si-XII and Si-III phases via the Si-II phase upon unloading and they existed as metastable phases at ambient pressure. Subsequent annealing at 873 K gave rise to reverse transformation to Si-I but with nanograin sizes. Although no appreciable photoluminescence (PL) peak was observed from the HPT-processed sample, a broad PL peak centered around 600 nm was detected from the annealed sample due to quantum confinement in the Si-I nanograins. [ABSTRACT FROM AUTHOR]

All the five independent elastic properties/constants of micro- and nano-structured hierarchical and self-similar random irregular honeycombs with different degrees of cell regularity are obtained by analysis and computer simulation in this paper. Cell wall bending, stretching, and transverse shearing are the main deformation mechanisms of hierarchical honeycombs. The strain gradient effects at the micro-meter scale, and the surface elasticity and initial stress effects at the nano-meter scale are incorporated into all the deformation mechanisms in the analysis and finite element simulations. The results show that the elastic properties of hierarchical random irregular honeycombs strongly depend on the thickness of the first-order cell walls if it is at the micro-meter scale, and that if the thickness of the first-order cell walls is at the nano-meter scale, the elastic properties of hierarchical random irregular honeycombs are not only size-dependent, but are also tunable and controllable over large ranges. In addition, the geometrical properties of nano-structured hierarchical random irregular honeycombs are also tunable and controllable. [ABSTRACT FROM AUTHOR]

In the present paper, the influence of grain morphology on the textures of multiphase steels measured after phase transformation is investigated. Especially, it is shown that the presence of very elongated grains in the product phase can strongly influence the classical quantitative determination of the texture of this phase from surface measurements (in X-ray diffraction or EBSD). Thus, a method is proposed to deduce the 'real' texture from the 'apparent' one, measured within a plane. It is then shown that for the investigated multiphase steel, for which phase transformation has occurred either from deformed or recrystallized austenite, this correction provides a very good quantitative agreement between corrected experimental product (ferrite) textures and those obtained from the parent (austenite) phase, assuming a KS or slightly different orientation relationship, without considering any variant selection. [ABSTRACT FROM AUTHOR]

In the first part of this two-part paper, the effect of increasing Ce in solid solution on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated in the as-deformed and annealed state. In this second part, the effect of rolling speed on the microstructure and texture development of these alloys is evaluated. The effect of rolling speed on the recrystallization and texture evolution of four Mg–Zn–Ce sheets was investigated at as-deformed and different stages of annealing. The deformation microstructure was obtained through two stages that can be characterised as rough rolling and finish rolling. To study the effect of finish rolling temperature, one rolling pass with a 65 % reduction in thickness was performed at 300 and 450 °C and at rolling speeds of 15 and 1000 m/min. The results showed that by increasing the rolling speed, more secondary and compression twins were activated, which leads to the formation of more numerous local shear bands and a more uniform microstructure. Annealing secondary twins (S-twins) and their vicinity were observed to be the preferential sites for nucleation, and it seems that recrystallization on S-twins contributes to basal texture weakening. Therefore, an increasing number of such twins increase the texture weakening. In this way, the combination of these RE additions and HSR resulted in a weaker deformed and annealed texture. [ABSTRACT FROM AUTHOR]

Different mechanisms have been suggested by many authors as controlling the rate of superplastic flow in different materials. From the viewpoint of computational effort and aesthetics, it is highly desirable to explain the phenomenon, independent of the material/system considered, on a common basis. With this aim, a mesoscopic grain boundary sliding-controlled deformation model was proposed sometime ago as being responsible for superplastic flow in materials of different kinds. In this paper, a rigorous numerical computational procedure for the experimental validation of the model, which takes into account all the physical requirements of the model, is presented. The soundness of the new procedure is established by analysing the experimental data pertaining to many systems belonging to different classes of materials, and matching the results of the analysis with the experimental findings. [ABSTRACT FROM AUTHOR]

This paper highlights the observation that the Wilshire equations for failure times and times to various strains, as reported in the original literature, may not be the most appropriate ones for all materials—including the one selected in this study. Further, such appropriateness can be determined by looking at the consistencies between the parameter estimates obtained using minimum creep rates in comparison to using failure times. It is shown, using 1CrMoV steel as an illustration, that the parameter consistency can be achieved by generalising the Monkman–Grant relation so that it contains a temperature correction. Indeed, the ability of the Wilshire equations to produce meaningful physical parameters, such as the activation energy, is shown to be highly dependent upon a valid specification for the Monkman–Grant relation. It is shown that variations in the measured values for some of the Wilshire parameters ( w and k3) with strain indicate that the causes of deformation are different at different strains and different stresses. Finally, the measured variations in the parameters of the Monkman–Grant relation with strain enable accurate interpolated and extrapolated creep curves to be calculated for any test condition. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) is an attractive processing method in severe plastic deformation techniques involving the application of high compressive pressure with concurrent torsional straining. Excellent grain refinement is anticipated when using this technique to average grain sizes of the submicrometer or even nanometer ranges. Because of the significant microstructural changes during processing, there are numerous reports showing evolution in local hardness toward homogeneity throughout a disk diameter with increasing numbers of revolutions. The achieved hardness after HPT is mostly much higher than that in the as-received condition because of exceptional grain refinement although there are a limited number of metals and alloys showing softening or weakening after HPT processing. This paper was initiated to review recent discoveries in the experimental results on hardness evolution toward homogeneity during HPT processing and discuss the different models of hardness developments with respect to imposed equivalent strain by HPT processing for a range of metals and alloys. Moreover, recent results of hardness homogeneity and heterogeneity through thicknesses of the processed disks are discussed toward a complete understanding of hardness evolution in the UFG metals processed by HPT. [ABSTRACT FROM AUTHOR]

The overall objective of the investigation presented in this paper was to study the effect of dispersion of core-shell polymer (CSP) particles within the ply interfaces on damage evolution of glass/epoxy laminates under impact loading. These laminates were fabricated with the CSP particle dispersion controlled to 14 % of the total weight of the used prepreg. A series of impact experiments were done with instrumental drop tower device at all probable impact energies within a practical low velocity impact range. The damage phenomena occurring in the internal microstructure of the laminates were analysed with the help of scanning electron microscope and correlated to the structural response of the laminate. The predominant damage modes were dependent on the magnitude of the applied impact energy. The CSP particle incorporation does not change the sequence of the fracture events but it delays and mitigates the damage creation. The deformation of the CSP particles and the tearing of their outer shells absorb most of the impact energy thereby preventing initiation of matrix cracks at lower impact energies and delaying fibre damage at higher energies. The crushed particles along with their nano-size rubber cores impede crack propagation requiring the cracks to follow torturous paths consequently dissipating additional amount of energy. These particles also promote elastic energy absorption of the laminates minimizing their tendency to fracture easily under impact. The ultimate load bearing capability of the modified laminate showed 60 % improvement and the deflection characteristics indicated lower proneness to impact. [ABSTRACT FROM AUTHOR]

The Poisson's ratio describes an extent of transverse deformation of a material when an axial strain is applied. A change of the Poisson's ratio from positive to negative can equip a material with a set of specific properties. In this paper, a study of a composite material with a tunable Poisson's ratio is presented. Samples of such a composite were first fabricated with two different polymers based on a composite structure proposed in our previous work using a multi-material additive-manufacturing system. Using both experimental and numerical methods, deformation mechanisms and mechanical properties of this composite material were analyzed. The obtained results demonstrate that its Poisson's ratio can be reduced by increasing the difference in stiffness of constituent materials and turned from positive to negative when this difference is sufficiently high. Additionally, the study also validates a possible method to fabricate composites with designed structures and multi-constituent materials using additive-manufacturing techniques. [ABSTRACT FROM AUTHOR]

This paper describes the mechanical properties of B2/L21 two-phase Fe30Ni20Mn20Al30 (at.%) in both the as-cast condition and after a 72 h anneal at 823 K. The temperature dependence of the compressive strength of Fe30Ni20Mn20Al30 showed three distinct regions: (1) brittle fracture at low temperature, (2) plastic flow with a rapid decline in yield strength from 1500 to 250 MPa from the brittle-to-ductile transition temperature (BDTT) to 873 K, and (3) a slight decrease in yield strength to ~150 MPa from 873 to 1073 K. Interestingly, the BDTT (573 K) exhibited by the coarser microstructure present in 72 h annealed material was lower than that of the as-cast alloy (623 K). Using both differential scanning calorimetry and in situ heating in a transmission electron microscope, an L21-to-B2 transition was found at 750 ± 25 K. A mixture of intergranular fracture and transgranular cleavage was observed after room temperature compression while only cleavage was found at 673 K. All the specimens deformed extensively without fracture when tested at temperatures higher than 673 K. The strain rate had little effect on the strength at 573 K and a moderate effect at 873 K with a strain-rate sensitivity exponent value of 0.1. [ABSTRACT FROM AUTHOR]

The hot working behaviour of duplex stainless steels has been studied in the literature mainly through hot torsion or hot compression tests. The aim of this paper is to investigate the hot deformation behaviour of a duplex stainless steel type 2205 (F51) through hot tension tests, which are easier to carry out and can offer some additional information about the maximum sustainable strain in tension before starting of irreversible damage. In fact, even under the uniaxial compressive action of a forging press, tensile stresses may develop in some zones of the forged product. These zones become most critical and the knowledge of the limiting conditions are important. Three different test temperatures were selected, namely 900, 1000, and 1100 °C. The hot working behaviour was characterised by fitting the mean flow stress, strain rate, and temperature relationship with the hyperbolic sine function defined by Sellars and Tegart. An activation energy Q equal to 430 kJ/mol was obtained for plastic straining at high temperature. It corresponds to values, obtained with hot torsion or hot compression tests, reported in the literature where a large variation in activation energy is also found for duplex stainless steels. It was explained by considering the intrinsic two-phase nature of the investigated steel. The ductility in the different hot working conditions was characterised by the true strain at the onset of damage formation under prevailing tensile stress conditions. The role of the microstructure as well as of damage formation during deformation on the shape of the flow stress curves was analyzed. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) techniques have recently been developed for producing bulk ultrafine grained metallic materials. High pressure torsion (HPT) produces finer microstructures than those achieved by other SPD processes because of the higher imposed strain and hydrostatic pressure. It is known that HPT-processed metals show a highly heterogeneous microstructure not only along the radius due to the nature of torsional deformation but also through the thickness. Since the sample size for HPT is small, the local properties of HPT-processed specimens have not been investigated yet. In this paper, we propose a method to obtain stress-strain curves from nanoindenting curves by combining the finite element method and the recursion method. The nanoindentation technique was employed to elucidate the local mechanical properties, especially the stress-strain behavior. The method to extract the stress-strain curves from the load-displacement curves obtained by nanoindentation tests was applied to the edge region of the HPT-processed sample. The extracted properties correlated well with experimental results qualitatively.` [ABSTRACT FROM AUTHOR]

In this paper, rapid solidified MgZnY (at.%) alloy powders produced by an inert gas atomizer were consolidated using a severe plastic deformation technique of high pressure torsion (HPT) at room temperature and 373 K. The behavior of powder consolidation, matrix microstructural evolution, and mechanical properties of the powders and compacts were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, microhardness, and tensile testing. As the HPT processing temperature increases, the powders are more plastically deformed due to decreased deformation resistance, grain boundaries are more in equilibrium, powder bonding is enhanced due to increased interparticle diffusion, hence, tensile ductility and strength increases. On the other hand, hardness decreases with the increased processing temperature, due to less dislocation density. [ABSTRACT FROM AUTHOR]

Magnesium alloy (AZ31) based metal matrix composite reinforced with carbon nanotubes (CNTs) was fabricated using the technique of disintegrated melt deposition followed by hot extrusion. In this research paper, the microstructure, hardness, tensile properties, tensile fracture, high cycle fatigue characteristics, and final fracture behavior of CNTs-reinforced magnesium alloy composite (denoted as AZ31/1.0 vol.% CNT or AZ31/CNT) is presented, discussed, and compared with the unreinforced counterpart (AZ31). The elastic modulus, yield strength, tensile strength of the reinforced magnesium alloy was noticeably higher compared to the unreinforced counterpart. The ductility, quantified both by elongation-to-failure and reduction in cross-section area of the composite was higher than the monolithic counterpart. A comparison of the CNT-reinforced magnesium alloy with the unreinforced counterpart revealed a noticeable improvement in cyclic fatigue life at the load ratios tested. At all values of maximum stress, both the reinforced and unreinforced magnesium alloy was found to degrade the cyclic fatigue life at a lower ratio, i.e., under conditions of fully reversed loading. The viable mechanisms responsible for the enhanced cyclic fatigue life and tensile behavior of the composite are rationalized in light of macroscopic fracture mode and intrinsic microscopic mechanisms governing fracture. [ABSTRACT FROM AUTHOR]

This paper presents a study of microscale plastic deformation at the crack tip and the effect of microstructure feature on the local deformation of aluminum specimen during fracture test. Three-point bending test of aluminum specimen was conducted inside a scanning electron microscopy (SEM) imaging system. The crack tip deformation was measured in situ utilizing SEM imaging capabilities and the digital image correlation (DIC) full-field deformation measurement technique. The microstructure feature at the crack tip was examined to understand its effect on the local deformation fields. Microscale pattern that was suitable for the DIC technique was generated on the specimen surface using sputter coating through a copper mesh before the fracture test. A series of SEM images of the specimen surface were acquired using in situ backscattered electronic imaging (BEI) mode during the test. The DIC technique was then applied to these SEM images to calculate the full-field deformation around the crack tip. The grain orientation map at the same location was obtained from electron backscattered diffraction (EBSD), which was superimposed on a DIC strain map to study the relationship between the microstructure feature and the evolution of plastic deformation at the crack tip. This approach enables to track the initiation and evolution of plastic deformation in grains adjacent to the crack tip. Furthermore, bifurcation of the crack due to intragranular and intergranular crack growth was observed. There was also localization of strain along a grain boundary ahead of and parallel to the crack after the maximum load was reached, which was a characteristic of Dugdale-Barenblatt strip-yield zone. Thus, it appears that there is a mixture of effects in the fracture process zone at the crack tip where the weaker aspects of the grain boundary controls the growth of the crack and the more ductile aspects of the grains themselves dissipate the energy and the corresponding strain level available for these processes through plastic work. [ABSTRACT FROM AUTHOR]

This paper develops a modification of the shared frailty model that allows for the distribution of the response and the random effects to be determined by the data (from within the exponential family of distributions). A simulated maximum likelihood and a computationally simpler simulated linear least squares approach to estimating this model are also presented. These generalizations are important for modelling high-temperature deformation because they allow life time predictions to be made with levels of confidence attached to them, for the real world situation where repeated experimental observations are not normally distributed and not independent of each other. An application to a commonly used material in power generation revealed that ignoring these characteristics lead to an underestimate of the minimum safe life when operating at 773 K and stresses above 235 MPa. [ABSTRACT FROM AUTHOR]

This paper describes some technical limitations encountered in joining ceramics–ceramics or ceramics–metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina–alumina or alumina and the nickel base alloy HAYNES® 214™ using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic–plastic and elastic–plastic–creep behavior have also been used to better design the joints and to predict their performance. It was found that the residual stresses caused by the thermal expansion mismatch between alumina (Al2O3) and the Ni-based superalloy (HAYNES® 214™) have severely deteriorated the joints compared to Al2O3–Al2O3 joint fabricated with the same solid-state bonding parameters. The high residual stresses zones obtained through the FEA simulation fitted well with the fractographic observations of the Al2O3/Ni/HAYNES® 214™ joints. Also, in order to use the joint material as a structural material, the study about the effect of geometrical parameters has been performed. Optimal geometries have been determined. [ABSTRACT FROM AUTHOR]

The aim of this paper is to establish the correlation among sintering process, porosity, and important thermo-mechanical property of refractory concrete, i.e., creep. Creep deformation was investigated according to the standard laboratory procedure applied at three temperatures: 1200, 1300, and 1400 °C. Corundum and bauxite-based refractory concretes were investigated. The concretes are varying in chemical and mineralogical composition. Both loss of strength and degradation of material occur when refractory concrete is subjected to increased temperature and compressive static load. Measuring of thermo-mechanical properties can indicate and monitor the changes within microstructure. Variation of refractory concrete microstructure, as a consequence of sintering process, during exposure to constant compressive load and constant elevated temperature during certain time-intervals was investigated using scanning electron microscope and Image Pro Plus program for image analysis. Obtained results of the investigation proved that creep can be useful method when type of refractory concrete is to be chosen for an application. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) of titanium creates an ultrafine-grained (UFG) microstructure which results in significantly enhanced mechanical properties, including increasing the high cycle fatigue strength. This work addresses the challenge of maintaining the high level of properties as SPD processing techniques are evolved from methods suitable for producing laboratory scale samples to methods suitable for commercial scale production of titanium semi-products. Various ways to optimize the strength and fatigue endurance limit in long-length Grade 4 titanium rod processed by equal channel angular pressing (ECAP) with subsequent thermal mechanical treatments are considered in this paper. Low-temperature annealing of rods is found to increase the fatigue limit, simultaneously enhancing UFG titanium strength and ductility. The UFG structure in titanium provides an optimum combination of properties when its microstructure includes mostly equiaxed grains with high-angle boundaries, the volume fraction of which is no less than 50%. [ABSTRACT FROM AUTHOR]