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Showing papers on "Deformation (engineering) published in 2017"


Journal ArticleDOI
27 Apr 2017-Nature
TL;DR: A counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit, which enables a substantial reduction in cost compared to conventional maraging steels owing to the replacement of the essential but high-cost alloying elements cobalt and titanium with inexpensive and lightweight aluminium.
Abstract: Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands. Their outstanding strength originates from semi-coherent precipitates, which unavoidably exhibit a heterogeneous distribution that creates large coherency strains, which in turn may promote crack initiation under load. Here we report a counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit. We found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitates is almost the same as that of the surrounding matrix), showing very low lattice misfit with the matrix and high anti-phase boundary energy, strengthen alloys without sacrificing ductility. Such low lattice misfit (0.03 ± 0.04 per cent) decreases the nucleation barrier for precipitation, thus enabling and stabilizing nanoprecipitates with an extremely high number density (more than 1024 per cubic metre) and small size (about 2.7 ± 0.2 nanometres). The minimized elastic misfit strain around the particles does not contribute much to the dislocation interaction, which is typically needed for strength increase. Instead, our strengthening mechanism exploits the chemical ordering effect that creates backstresses (the forces opposing deformation) when precipitates are cut by dislocations. We create a class of steels, strengthened by Ni(Al,Fe) precipitates, with a strength of up to 2.2 gigapascals and good ductility (about 8.2 per cent). The chemical composition of the precipitates enables a substantial reduction in cost compared to conventional maraging steels owing to the replacement of the essential but high-cost alloying elements cobalt and titanium with inexpensive and lightweight aluminium. Strengthening of this class of steel alloy is based on minimal lattice misfit to achieve maximal precipitate dispersion and high cutting stress (the stress required for dislocations to cut through coherent precipitates and thus produce plastic deformation), and we envisage that this lattice misfit design concept may be applied to many other metallic alloys.

760 citations


Journal ArticleDOI
27 Sep 2017-Nature
TL;DR: The goal is to quantify the conditions under which the limits of dislocation-mediated plasticity are reached and to understand what happens to the metal beyond any such limit, and to address the complexity of crystal plasticity processes on the length scales and timescales that are examined.
Abstract: The limits of dislocation-mediated metal plasticity are studied by using in situ computational microscopy to reduce the enormous amount of data from fully dynamic atomistic simulations into a manageable form. Fully dynamic atomistic simulations of plastic deformation in metals are so computationally demanding that materials physicists have instead developed mesoscale proxies to model dislocation dynamics. In this paper, Vasily Bulatov and colleagues take on the challenge of modelling metal plasticity at the atomic level. Such simulations require models that contain many millions of atoms (the largest simulation in this study contains 268 million atoms), and algorithms are used to process the datasets down to a volume that allows human interpretation. The authors probe ultrahigh-strain-rate deformation in body-centred-cubic tantalum, a model metal, to investigate the limits of metal plasticity. They show that at certain limiting conditions, dislocations can no longer relieve metal loading and twinning takes over. At a strain rate lower than this limit, flow stress and dislocation density achieve a steady state and a sort of metal kneading is observed. The simulations support previous proposals of the maximum dislocation density that can be reached before a metal collapses. Ordinarily, the strength and plasticity properties of a metal are defined by dislocations—line defects in the crystal lattice whose motion results in material slippage along lattice planes1. Dislocation dynamics models are usually used as mesoscale proxies for true atomistic dynamics, which are computationally expensive to perform routinely2. However, atomistic simulations accurately capture every possible mechanism of material response, resolving every “jiggle and wiggle”3 of atomic motion, whereas dislocation dynamics models do not. Here we present fully dynamic atomistic simulations of bulk single-crystal plasticity in the body-centred-cubic metal tantalum. Our goal is to quantify the conditions under which the limits of dislocation-mediated plasticity are reached and to understand what happens to the metal beyond any such limit. In our simulations, the metal is compressed at ultrahigh strain rates along its [001] crystal axis under conditions of constant pressure, temperature and strain rate. To address the complexity of crystal plasticity processes on the length scales (85–340 nm) and timescales (1 ns–1μs) that we examine, we use recently developed methods of in situ computational microscopy4,5 to recast the enormous amount of transient trajectory data generated in our simulations into a form that can be analysed by a human. Our simulations predict that, on reaching certain limiting conditions of strain, dislocations alone can no longer relieve mechanical loads; instead, another mechanism, known as deformation twinning (the sudden re-orientation of the crystal lattice6), takes over as the dominant mode of dynamic response. Below this limit, the metal assumes a strain-path-independent steady state of plastic flow in which the flow stress and the dislocation density remain constant as long as the conditions of straining thereafter remain unchanged. In this distinct state, tantalum flows like a viscous fluid while retaining its crystal lattice and remaining a strong and stiff metal.

305 citations


Journal ArticleDOI
TL;DR: In this paper, a non-linear elasto-viscoplastic model containing various deformation components is proposed, by connecting a Hooke body, a parallel combination of Hooke and plastic slide bodies, a Kelvin body, and a generalized Bingham body.

221 citations


Journal ArticleDOI
TL;DR: Through extensive computer simulations for a wide range of system sizes, it is demonstrated that cyclically deformed model glasses exhibit a sharply defined yielding transition with characteristics that are independent of preparation history.
Abstract: Amorphous solids are ubiquitous among natural and man-made materials. Often used as structural materials for their attractive mechanical properties, their utility depends critically on their response to applied stresses. Processes underlying such mechanical response, and in particular the yielding behaviour of amorphous solids, are not satisfactorily understood. Although studied extensively, observed yielding behaviour can be gradual and depend significantly on conditions of study, making it difficult to convincingly validate existing theoretical descriptions of a sharp yielding transition. Here we employ oscillatory deformation as a reliable probe of the yielding transition. Through extensive computer simulations for a wide range of system sizes, we demonstrate that cyclically deformed model glasses exhibit a sharply defined yielding transition with characteristics that are independent of preparation history. In contrast to prevailing expectations, the statistics of avalanches reveals no signature of the impending transition, but exhibit dramatic, qualitative, changes in character across the transition. The onset of yielding can be difficult to define unambiguously for amorphous materials. Here the authors undertake computer simulations of model glasses of varying system sizes and show that, under oscillatory shear, they exhibit a sharp transition independent of preparation history.

186 citations


Journal ArticleDOI
TL;DR: In this paper, the energy evolution characteristics of fine-to-medium-grained granite specimens from a quarry in Miluo city (China) were studied in the triaxial deformation and failure process of the rocks.

173 citations


Journal ArticleDOI
TL;DR: In this paper, a series of uniaxial compressive tests were conducted on prismatic marble specimens containing a circular or an elliptical hole using a servo-hydraulic machine synchronized with a charge-coupled device (CCD) camera.

156 citations


Journal ArticleDOI
TL;DR: In this paper, the experimental results about the thermal, mechanical and deformation properties of reactive powder concrete (RPC) at both test modalities are compiled and compared, and a comparison of compiled fire resistance data of RPC with existing code provisions is also presented.

142 citations


Journal ArticleDOI
TL;DR: In this article, the deformation behavior of Fe-29.8Mn-7.65Al-1.11C steel was investigated by means of TEM microstructure analysis and XRD texture measurements.

140 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed investigation into the anisotropic strain hardening, tension/compression yield asymmetry, and evolution of crystallographic texture of rolled WE43 rare earth magnesium alloy during quasi-static tension and compression at room temperature is presented.

136 citations


Journal ArticleDOI
TL;DR: In this paper, the critical resolved shear stress (CRSS) values of different slip modes are directly measured with an in-situ high energy X-ray diffraction microscopy (HEDM) experiment.

134 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of strain rate on hydrogen embrittlement behavior in a low-carbon martensitic steel and found that the deformation at a lower strain rate facilitated hydrogen to accumulate mainly on prior austenite grain boundaries.

Journal ArticleDOI
TL;DR: In this article, the authors synthesize high-entropy alloys by induction levitation melting with the aim of achieving a balanced combination of excellent strength at elevated temperature and reasonable ductility at room temperature.

Journal ArticleDOI
TL;DR: In this paper, the deformation behavior of three direct laser fabricated AlxCoCrFeNi high entropy alloys was examined by using x-ray diffraction, and it was found that the correlation between dislocation density, applied stress and compressive strain all benchmark closely with the behaviour of austenitic stainless steel.

Journal ArticleDOI
TL;DR: In this article, the deformation incompatibility between grains during polycrystalline deformation was investigated using high-resolution digital image correlation (HRDIC) supported by electron backscatter diffraction (EBSD) to study quantitatively and at the microstructural scale the accommodation of deformation compatibility in an AZ31 magnesium alloy.

Journal ArticleDOI
01 Mar 2017-Vacuum
TL;DR: In this paper, the authors investigated the hot deformation behaviors of a nickel-based superalloy, and the hot compressive tests were conducted at the deformation temperature range of 920-1040°C and strain rate range of 0.001-1s−1.

Journal ArticleDOI
TL;DR: In this article, the authors proposed fracture-based forming limit criteria for anisotropic materials in sheet metal forming to predict the sudden fracture in complicated forming processes, where the Lou-Huh ductile fracture criterion was modified using the Hill's 48 yield function instead of the von Mises isotropic yield function to account of the influence of anisotropy on the equivalent plastic strain at the onset of fracture.

Journal ArticleDOI
Ziguang Zhao1, Kangjun Zhang1, Yuxia Liu1, Jiajia Zhou1, Mingjie Liu1 
TL;DR: This study reports a general and synergistic strategy to fabricate high-strain and tough shape memory organohydrogels that feature binary cooperative phase and are nonswellable in water and oil, which is important for multimedia applications.
Abstract: Shape memory effect in polymer materials has attracted considerable attention due to its promising applications in a variety of fields. However, shape memory polymers prepared by conventional strategy suffer from a common problem, in which high strain capacity and excellent shape memory behavior cannot be simultaneously achieved. This study reports a general and synergistic strategy to fabricate high-strain and tough shape memory organohydrogels that feature binary cooperative phase. The phase- transition micro-organogels and elastic hydrogel framework act synergistically to provide excellent thermomechanical performance and shape memory effect. During shape memory process, the organohydrogels exhibit high strain capacity, featuring fully recoverable stretching deformation by up to 2600% and compression by up to 85% beneath a load ≈20 times the organohydrogel's weight. Furthermore, owing to the micro-organogel and hydrogel heterostructures, the interfacial tension derived from heterophases dominates the shape recovery of the organohydrogel material. Simple processing and smart surface patterning of the shape memory behavior and multiple shape memory effects can also be realized. Meanwhile, these organohydrogels are also nonswellable in water and oil, which is important for multimedia applications.

Journal ArticleDOI
TL;DR: In this paper, the effect of texture and temperature on reorientation of martensite variants was investigated, and the authors used a thermodynamic approach involving the elastic strain energy associated with the growth of reoriented martensites to rationalize these temperature dependencies.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated hydrogen embrittlement in Ni-based superalloy 718 by tensile testing at slow strain rate (10 −4 s −1 ) under continuous electrochemical hydrogen charging.

Journal ArticleDOI
TL;DR: In this paper, a series of uniaxial compressive tests were conducted on saturated frozen Helin loess under five different strain rates (1,×10 −-2 /s, 1,× 10 −-3 /s), 1, × 10 −−4 /s and 5 × 10−5 −5 /s).

Journal ArticleDOI
TL;DR: Based on the Split Hopkinson Pressure Bar (SHPB) system, dynamic compressive tests were done on red-sandstone specimens, which were free from freeze-thaw (F-T) or suffered from 5, 10, 15, 25 F-T cycles.

Journal ArticleDOI
TL;DR: In this article, the deformation mechanisms of LM and BM were systematically investigated by studying dislocation structures of the plastic deformation region (including UDR and NR) of tensile specimens.

Journal ArticleDOI
TL;DR: In this paper, the effects of rolling deformation, rolling temperature and aging treatment on microstructure and mechanical properties of Cu-Cr-Zr alloy were investigated and the relevant influencing mechanism was also discussed.
Abstract: The effects of rolling deformation, rolling temperature and aging treatment on microstructure and mechanical properties of Cu-Cr-Zr alloy were investigated and the relevant influencing mechanism was also discussed in this study. The results showed that the tensile strength of the Cu-Cr-Zr alloy increased with an increase of rolling deformation at room temperature. The elongation to failure of the alloy decreased until the rolling reduction is up to 80% and then increased with the reduction, which is related to the grain orientation change from Copper texture with poor plasticity to the Goss/Brass texture with good plasticity. A large amount of Cr precipitates were identified during rolling at 300 °C in Cu-Cr-Zr alloy, which resulted in much higher electrical conductivity and tensile strength exceeded that of the room-temperature rolling with the rolling reduction over 80%. Aging treatment of 450 °C for 1 h led to the formation of massive Cr and Cu 4 Zr precipitates, which can significantly improve the tensile strength from 591.1 MPa to 669.1 MPa and electrical conductivity from 30.3%IACS to 74.5%IACS of the room-temperature rolled alloy. These results provide a guideline for exploring efficient preparation methods of high-performance Cu-Cr-Zr alloys.

Journal ArticleDOI
Zhen Zhang1, S.J. Qu1, A.H. Feng1, Jun Shen1, Daolun Chen2 
TL;DR: In this article, the authors identify plastic flow behavior and microstructural evolution during sub-transus hot deformation of a Ti-6Al-4V alloy with three initial microstructures through compressive deformation at different strain rates in a Gleeble simulator and via SEM and TEM examinations.

Journal ArticleDOI
25 Oct 2017-Nature
TL;DR: X-ray diffraction experiments with femtosecond resolution are presented that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation, and find a transition from twinning to dislocation-slip-dominated plasticity at high pressure.
Abstract: Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum-an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

Journal ArticleDOI
TL;DR: In this paper, the deformation behavior of the FDM samples in general and individual rasters of different thicknesses (layer thickness), in particular, laid at different directions under uniaxial tension is revealed.

Journal ArticleDOI
TL;DR: In this paper, a constitutive equation was formulated for describing interdependency between deformation temperature, strain rate, flow stress and strain, and the estimated apparent activation energy (Q) ∼350 kJmol-1 for the hot deformation was approximately similar to the activation energy for diffusion of the slowest diffusing element Ni in this alloy.

Journal ArticleDOI
TL;DR: In this article, the contribution of micro-twinning mechanism to the creep deformation behavior of single crystal superalloy MD2 is studied. But the authors do not consider diffusion-controlled growth of twins.

Journal ArticleDOI
TL;DR: In this paper, the hydromechanical coupling tests with various differential water pressures and confining pressures were performed to clarify mechanical and permeability characteristics of fractured limestone in complete stress-strain process.
Abstract: To clarify mechanical and permeability characteristics of fractured limestone in complete stress–strain process, the hydromechanical coupling tests with various differential water pressures and confining pressures were performed. The mechanical characteristics of fractured limestone specimens are sensitive to confining pressure, differential water pressure, and effective stress. The increasing differential water pressure weakens the rock strength and deformation modulus by activating the lateral deformation of fractured limestone, which is attributed to the decrease in the effective minimum principal stress. The experimental results verify the validity of Mohr–Coulomb yield criterion considering the effective stress effect under hydromechanical coupling condition. The permeability values display four stages of decrease–gradual increase–rapid increase–small drop in complete stress–strain process, which roughly correspond to volumetric compression stage, elastic deformation stage, yield, and post-peak stage, as well as residual strength stage, respectively. At a low differential water pressure in the range of 2–5 MPa, the corresponding relationship mentioned above is obvious. However, at high differential water pressures up to 8–14 MPa, there is a deviation from the correspondence above, i.e., permeability reduction stage is shorter than the stage of volumetric compression. A cubic polynomial is used to describe the relationship between permeability and volumetric strain at volumetric compression stage. However, it is difficult to describe the relationship between the permeability and volumetric strain by a uniform fitting equation at the dilatancy stage.

Journal ArticleDOI
TL;DR: In this paper, a temperature-dependent micromechanical behavior of medium-Mn transformation-inducedplasticity (TRIP) steel with a nominal chemical composition of Fe-0.1C-10Mn-2Al (mass%) fabricated by intercritical annealing 650°C for 1 1/h after cold-rolling was investigated using in situ high-energy X-ray diffraction (HE-XRD) with uniaxial tensile tests at temperatures of 100, 25 and 50°C.