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Showing papers on "Deformation (engineering) published in 2006"


Journal ArticleDOI
23 Feb 2006-Nature
TL;DR: The magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy is reported, attributing this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase in the Ni45Co5Mn36.7In13.3 single crystal.
Abstract: Large magnetic-field-induced strains1 have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field1,2,3. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy4. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.

1,581 citations


Journal ArticleDOI
TL;DR: In this paper, a combined experimental and analytical investigation has been performed to understand the mechanical behavior of two amorphous polymers (polycarbonate and poly(methyl methacrylate) at strain rates ranging from 10−4 to 104−s−1.

611 citations


Journal ArticleDOI
TL;DR: In this article, the influence of texture and grain size on work hardening behavior and dynamic recovery of magnesium alloys was studied, in addition to the direct effect of texture through the change in the orientation factor for basal and prismatic slip, effects were found on dynamic recovery and the appearance of stage II of workhardening.

598 citations


Journal ArticleDOI
TL;DR: It is shown that both mineral nanoparticles and the enclosing mineralized fibril deform initially elastically, but to different degrees, which is consistent with a staggered model of load transfer in bone matrix, exemplifying the hierarchical nature of bone deformation.
Abstract: In biomineralized tissues such as bone, the recurring structural motif at the supramolecular level is an anisotropic stiff inorganic component reinforcing the soft organic matrix. The high toughness and defect tolerance of natural biomineralized composites is believed to arise from these nanometer scale structural motifs. Specifically, load transfer in bone has been proposed to occur by a transfer of tensile strains between the stiff inorganic (mineral apatite) particles via shearing in the intervening soft organic (collagen) layers. This raises the question as to how and to what extent do the mineral particles and fibrils deform concurrently in response to tissue deformation. Here we show that both mineral nanoparticles and the enclosing mineralized fibril deform initially elastically, but to different degrees. Using in situ tensile testing with combined high brilliance synchrotron X-ray diffraction and scattering on the same sample, we show that tissue, fibrils, and mineral particles take up successively lower levels of strain, in a ratio of 12:5:2. The maximum strain seen in mineral nanoparticles (≈0.15–0.20%) can reach up to twice the fracture strain calculated for bulk apatite. The results are consistent with a staggered model of load transfer in bone matrix, exemplifying the hierarchical nature of bone deformation. We believe this process results in a mechanism of fibril–matrix decoupling for protecting the brittle mineral phase in bone, while effectively redistributing the strain energy within the bone tissue.

594 citations


Journal ArticleDOI
TL;DR: The onset of a typical plastic event is studied with precision, and it is shown that the mode of the system which is responsible for the loss of stability has structure in real space which is consistent with a quadrupolar source acting on an elastic matrix.
Abstract: We present results on a series of two-dimensional atomistic computer simulations of amorphous systems subjected to simple shear in the athermal, quasistatic limit The athermal quasistatic trajectories are shown to separate into smooth, reversible elastic branches which are intermittently broken by discrete catastrophic plastic events The onset of a typical plastic event is studied with precision, and it is shown that the mode of the system which is responsible for the loss of stability has structure in real space which is consistent with a quadrupolar source acting on an elastic matrix The plastic events themselves are shown to be composed of localized shear transformations which organize into lines of slip which span the length of the simulation cell, and a mechanism for the organization is discussed Although within a single event there are strong spatial correlations in the deformation, we find little correlation from one event to the next, and these transient lines of slip are not to be confounded with the persistent regions of localized shear---so-called ``shear bands''---found in related studies The slip lines give rise to particular scalings with system length of various measures of event size Strikingly, data obtained using three differing interaction potentials can be brought into quantitative agreement after a simple rescaling, emphasizing the insensitivity of the emergent plastic behavior in these disordered systems to the precise details of the underlying interactions The results should be relevant to understanding plastic deformation in systems such as metallic glasses well below their glass temperature, soft glassy systems (such as dense emulsions), or compressed granular materials

531 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the tensile ductility of freestanding nanocrystalline Al films, where discontinuous grain growth results in a fundamental change in the way in which the material deforms.

498 citations


Journal ArticleDOI
TL;DR: In this article, the deformation of ultrafine crystalline pure Cu with nanoscale growth twins is analyzed using the twin boundary as an internal interface and allowing special slip geometry arrangements that involve soft and hard modes of deformation.

453 citations


Journal ArticleDOI
TL;DR: In this paper, the deformation kinetics are controlled by the activities of dislocations, and the dominant thermally activated mechanism is suggested to originate from three possible processes, all involving interactions of mobile dislocation with grain boundaries.

416 citations


Journal ArticleDOI
TL;DR: In this article, the elastic deformation of poly(dimethylsiloxane) (PDMS) microchannels under imposed flow rates and the effect of this deformation on the laminar flow profile and pressure distribution within the channels were studied.
Abstract: We study the elastic deformation of poly(dimethylsiloxane) (PDMS) microchannels under imposed flow rates and the effect of this deformation on the laminar flow profile and pressure distribution within the channels. Deformation is demonstrated to be an important consideration in low aspect ratio (height to width) channels and the effect becomes increasingly pronounced for very shallow channels. Bulging channels are imaged under varying flow conditions by confocal microscopy. The deformation is related to the pressure and is thus non-uniform throughout the channel, with tapering occuring along the stream-wise axis. The measured pressure drop is monitored as a function of the imposed flow rate. For a given pressure drop, the corresponding flow rate in a deforming channel is found to be several times higher than expected in a non-deforming channel. The experimental results are supported by scaling analysis and computational fluid dynamics simulations coupled to materials deformation models.

331 citations


Journal ArticleDOI
27 Apr 2006-Nature
TL;DR: It is reported that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed ‘multi-junctions’, which are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals.
Abstract: At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects--dislocations. First theorized in 1934 to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed only two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening: a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions tying dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed hereafter multi-junctions. The existence of multi-junctions is first predicted by Dislocation Dynamics (DD) and atomistic simulations and then confirmed by the transmission electron microscopy (TEM) experiments in single crystal molybdenum. In large-scale Dislocation Dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in BCC crystals.

279 citations


Journal ArticleDOI
TL;DR: In this article, the effect of deformation twinning on the strain hardening behavior of polycrystalline AM30 Mg alloy was investigated, and the softening effect induced by double and contraction twinning was responsible for the abnormal strain-hardening behavior.

Journal ArticleDOI
TL;DR: In this paper, a new Pd-Si binary bulk metallic glass was developed, which exhibits a uniform plastic deformation and a large plastic engineering strain of 82% and a plastic true strain of 170%.
Abstract: Usually, monolithic bulk metallic glasses undergo inhomogeneous plastic deformation and exhibit poor ductility (<2%) at room temperature. We report a newly developed Pd–Si binary bulk metallic glass, which exhibits a uniform plastic deformation and a large plastic engineering strain of 82% and a plastic true strain of 170%, together with initial strain hardening, slight strain softening and final strain hardening characteristics. The uniform shear deformation and the ultrahigh plasticity are mainly attributed to strain hardening, which results from the nanoscale inhomogeneity due to liquid phase separation. The formed nanoscale inhomogeneity will hinder, deflect, and bifurcate the propagation of shear bands.

Journal ArticleDOI
TL;DR: In this article, the effect of the tool shape on the mechanical properties and microstructures of 5-mm thick welded aluminum plates was investigated, and the simplest shape, the ordinary shape (column with threads) and the triangular prism shape probes were used to weld three types of aluminum alloys.
Abstract: Prospecting the optimal tool design for welding steels, the effect of the tool shape on the mechanical properties and microstructures of 5-mm thick welded aluminum plates was investigated. The simplest shape (column without threads), the ordinary shape (column with threads) and the triangular prism shape probes were used to weld three types of aluminum alloys. For 1050-H24 whose deformation resistance is very low, a columnar tool without threads produces weld with the best mechanical properties; for 6061-T6 whose deformation resistance is relatively low, the tool shape does not significantly affect the microstructures and mechanical properties. For 5083-O whose deformation resistance is relatively high, the weldablity is significantly affected by the rotation speed. For a low rotation speed (600 rpm), the tool shape does not significantly affect the microstructures and mechanical properties of the joints.

Journal ArticleDOI
TL;DR: In this article, a serial sectioning process is followed by finite element method (FEM) simulation to reproduce, visualize, and model the 3D microstructure of particle-reinforced metal matrix composites.

Journal ArticleDOI
TL;DR: In this article, the compressive mechanical behavior of three common polymeric foams (expanded polystyrene, high-density polyethylene, and polyurethane) has been measured at strain rates ranging from 0.0087 to 2500/s.

Journal ArticleDOI
TL;DR: This paper studies the three-dimensional deformation of a vesicle membrane under the elastic bending energy, with prescribed bulk volume and surface area, with a newly developed energetic variational formulation.

Journal ArticleDOI
TL;DR: In this article, a 3D thermoviscoelastic model is proposed to represent the thermomechanical behavior of shape memory polymers, which is based on a physical understanding of the material behavior and a mechanical interpretation of the stress-strain-temperature changes observed during thermal loading.
Abstract: A 3D thermoviscoelastic model is proposed to represent the thermomechanical behavior of shape memory polymers. The model is based on a physical understanding of the material behavior and a mechanical interpretation of the stress–strain–temperature changes observed during thermomechanical loading. The model is thermodynamically motivated and is formulated in a finite strain framework in order to account for large strain deformations. Model predictions capture critical features of shape memory polymer deformation and, in some cases, provide very favorable comparisons with experimental results. POLYM. ENG. SCI. 46:486–492, 2006. © 2006 Society of Plastics Engineers.

Journal ArticleDOI
12 May 2006-Science
TL;DR: An x-ray diffraction method was presented that provided data on the dynamics of individual, deeply embedded dislocation structures, and during tensile deformation of pure copper, dislocation-free regions were identified.
Abstract: During plastic deformation of metals and alloys, dislocations arrange in ordered patterns. How and when these self-organization processes take place have remained elusive, because in situ observations have not been feasible. We present an x-ray diffraction method that provided data on the dynamics of individual, deeply embedded dislocation structures. During tensile deformation of pure copper, dislocation-free regions were identified. They showed an unexpected intermittent dynamics, for example, appearing and disappearing with proceeding deformation and even displaying transient splitting behavior. Insight into these processes is relevant for an understanding of the strength and work-hardening of deformed materials.

Journal ArticleDOI
Chongxiang Huang1, Ke Wang1, Si Wu1, Zhefeng Zhang1, G.Y. Li1, S.X. Li1 
TL;DR: In this article, the deformation twins were observed in polycrystalline Cu with grain sizes varying from micrometers to nanometers during the process of equal channel angular pressing at room temperature and low strain rate.

MonographDOI
01 Jan 2006
TL;DR: The Mechanics of Solids and Materials as mentioned in this paper provides a modern and integrated treatment of the foundations of solid mechanics as applied to the mathematical description of material behavior, including large strain, strain rate, temperature, time dependent deformation and localized plastic deformation.
Abstract: Mechanics of Solids and Materials intends to provide a modern and integrated treatment of the foundations of solid mechanics as applied to the mathematical description of material behavior. The 2006 book blends both innovative (large strain, strain rate, temperature, time dependent deformation and localized plastic deformation in crystalline solids, deformation of biological networks) and traditional (elastic theory of torsion, elastic beam and plate theories, contact mechanics) topics in a coherent theoretical framework. The extensive use of transform methods to generate solutions makes the book also of interest to structural, mechanical, and aerospace engineers. Plasticity theories, micromechanics, crystal plasticity, energetics of elastic systems, as well as an overall review of math and thermodynamics are also covered in the book.

Journal ArticleDOI
TL;DR: In this paper, four different ultrafine-grained (ufg) Al-7.5% Mg alloys were synthesized by consolidation of a mixture of as-received and cryomilled Al-Mg powders with a ratio of 1:9, yielding a bimodal microstructure consisting of coarse grains (grain sizes, d cg, typically of several micrometers).

Journal ArticleDOI
TL;DR: In this article, the authors carried out systematic creep tests after different times of rest and over sufficiently long times with pasty materials of various internal structures in a Couette geometry and showed that for a stress below the yield stress these materials remain solid but undergo residual, irreversible deformations over long time which exhibit some trends typical of aging in glassy systems.
Abstract: We carried out systematic creep tests after different times of rest and over sufficiently long times with pasty materials of various internal structures in a Couette geometry. From an analysis of the data taking into account the inertia of the system and the heterogeneous distribution of stress, we show that: (i) for a stress below the yield stress these materials remain solid but undergo residual, irreversible deformations over long time which exhibit some trends typical of aging in glassy systems; (ii) as a result of thixotropy (or aging) in the solid regime the elastic modulus increases logarithmically with the time of rest; (iii) in the liquid regime the effective behavior of the material can be well represented by a truncated power-law model; (iv) a fundamental parameter of the solid-liquid transition is a critical effective shear rate (associated with the yield stress) below which the material cannot flow steadily.

Journal ArticleDOI
TL;DR: In this paper, the spread in misorientation from the central grain orientation is measured and a parameter called the modified crystal deformation is determined from the spread of the misorientations.

Journal ArticleDOI
TL;DR: In this article, the indentation size effect (ISE) has been studied in single crystals, polycrystals and amorphous solids using the Vickers microhardness test and the results confirm the multifarious nature of the ISE contributed by the surface effect, strain gradient work hardening and non-dislocation mechanisms of deformation.

Journal ArticleDOI
TL;DR: Quasi-static and dynamic axial crushing tests were performed on thin-walled square tubes and spot-welded top-hat sections made of high-strength steel grade DP800 as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, the deformation and the fracture of porous solids from internal crystallization of salt are explored in the framework of the thermodynamics of unsaturated brittle poroelasticity.
Abstract: The deformation and the fracture of porous solids from internal crystallization of salt is explored in the framework of the thermodynamics of unsaturated brittle poroelasticity. In the first place the usual theory of crystal growth in confined conditions is further developed in order to include both the deformation and the drying of the porous solid. The thermodynamics reveals the existence of a dilation coefficient associated with the crystallization process, and provides a solute crystal equilibrium condition which involves the relative humidity, the supersaturation, and the salt characteristics. This thermodynamic condition and the mechanical equilibrium of the solution crystal interface combine to give the current crystallization pore radius. Upscaling this information at the macroscopic scale, and taking into account the salt mass supplied by the invading solution, the approach leads to a quantitative analysis of the role of the pore size distribution on the crystal growth under repeated imbibition drying cycles. The deformation and the fracture of the porous solid from drying-induced crystallization are then considered in the context of brittle poroelasticity. The current unsaturated macroscopic poroelastic properties are upscaled from the microscopic elastic properties of the solid matrix and from the current liquid, crystal and gas saturations. The adoption of a fracture criterion based on the elastic energy that the solid matrix can ultimately store finally leads to the determination of how long a stone can resist repeated cycles of drying-induced crystallization of salt.

Journal ArticleDOI
TL;DR: In this paper, the role of the excess free volume that is created during plastic deformation in strain softening of amorphous metals was conducted. But, their results can be explained by postulating the formation of nanovoids due to the coalescence of the extra free volume, which leads to the observation of reduced hardness.

Journal ArticleDOI
18 Jul 2006-Langmuir
TL;DR: The results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.
Abstract: We report herein the establishment of a single-cell compression method based on force measurements in atomic force microscopy (AFM). The high-resolution bright-field or confocal laser scanning microscopy guides the location of the AFM probe and then monitors the deformation of cell shape, while microsphere-modified AFM probes compress the cell and measure the force. Force and deformation profiles of living cells reveal a cubic relationship at small deformation (<30%), multiple peaks at 30-70% compression, and a rapid increase at over 80% deformation. The initial compression may be described qualitatively and quantitatively using a simple model of a nonpermeable balloon filled with incompressible fluid. Stress peaks reflect cell membrane rupture, followed by the deformation and rupture of intracellular components, beyond which the cell responses become irreversible. The Young's modulus and bending constant of living cell membranes are extracted from the balloon models, with 10-30 MPa and 17-52 kT, respectively. The initial compression of dead and fixed cells is modeled using Hertzian contact theory, assuming that the cell is a homogeneous sphere. Dead cells exhibit a cytoskeleton elasticity of 4-7.5 kPa, while fixation treatment leads to a dramatic increase in the cytoskeletal Young's modulus (150-230 kPa) due to protein cross-linking by imine bonds. These results demonstrate the high sensitivity of the single-cell compression method to the molecular-level structural changes of cells, which suggests a new generic platform for investigating cell mechanics in tissue engineering and cancer research.

Journal ArticleDOI
TL;DR: In this paper, deformation-induced phase transformation in a type 304 austenitic stainless steel has been studied in tension at room temperature and −50 °C. The evolution of transformation products was monitored using X-ray diffraction (XRD) line profile analysis of diffraction peaks from a single XRD scan employing the direct comparison method.
Abstract: Deformation-induced phase transformation in a type 304 austenitic stainless steel has been studied in tension at room temperature and −50 °C. The evolution of transformation products was monitored using X-ray diffraction (XRD) line profile analysis of diffraction peaks from a single XRD scan employing the direct comparison method. Crystallographic texture transitions due to deformation strain have been evaluated using (111) γ pole figures. The tensile stress-strain data have been analyzed to explain the influence of underlying deformation-induced microstructural changes and associated texture changes in the steel. It is found that the initial stage of rapidly decreasing strain hardening rate in type 304 steel is primarily influenced by hcp ɛ-martensite formation, and the second stage of increasing strain hardening rate is associated with an increase in the α′-martensite formation. The formation of ɛ-martensite is associated with a gradual strengthening of the copper-type texture components up to 15 pct strain and decreasing with further strain at −50 °C. Texture changes during low-temperature deformation not only change the mechanism of ɛ-martensite formation but also influence the strain rate sensitivity of the present steel.

Journal ArticleDOI
TL;DR: In this article, a method for measuring the modulus of soft polymer networks (E < 10 MPa) is presented, which utilizes compression-induced buckling of a sensor film applied to the surface of the specimen, where the periodic buckling wavelength, assessed by laser light diffraction or optical microscopy, yields the moduli of the network specimen.
Abstract: We present a new method for measuring the modulus of soft polymer networks (E < 10 MPa). This metrology utilizes compression-induced buckling of a sensor film applied to the surface of the specimen, where the periodic buckling wavelength, assessed rapidly by laser light diffraction or optical microscopy, yields the modulus of the network specimen. To guide the development of this new technique, we use classical mechanical analysis to calculate the sensitivity of the critical strain and resulting wavelength of the buckling instability to the modulus and thickness of the sensor film as well as the modulus of the soft material being probed. Experimental validation of our technique employed a series of model cross-linked poly(dimethylsiloxane) elastomers. To further demonstrate the versatility of this method, we measure the moduli of a set of pertinent biomaterials, i.e., cross-linked 2-hydroxyethyl methacrylate (HEMA) hydrogels. Using a hydrogel substrate possessing a gradient in the cross-link density, we a...