Showing papers on "Strain hardening exponent published in 2007"
TL;DR: In this article, the structure of nacre is described over several length scales and the tablets were found to have wavy surfaces, which were observed and quantified using various experimental techniques.
Abstract: Mother-of-pearl, also known as nacre, is the iridescent material which forms the inner layer of seashells from gastropods and bivalves. It is mostly made of microscopic ceramic tablets densely packed and bonded together by a thin layer of biopolymer. The hierarchical microstructure of this biological material is the result of millions of years of evolution, and it is so well organized that its strength and toughness are far superior to the ceramic it is made of. In this work the structure of nacre is described over several length scales. The tablets were found to have wavy surfaces, which were observed and quantified using various experimental techniques. Tensile and shear tests performed on small samples revealed that nacre can withstand relatively large inelastic strains and exhibits strain hardening. In this article we argue that the inelastic mechanism responsible for this behavior is sliding of the tablets on one another accompanied by transverse expansion in the direction perpendicular to the tablet planes. Three dimensional representative volume elements, based on the identified nacre microstructure and incorporating cohesive elements with a constitutive response consistent with the interface material and nanoscale features were numerically analyzed. The simulations revealed that even in the absence of nanoscale hardening mechanism at the interfaces, the microscale waviness of the tablets could generate strain hardening, thereby spreading the inelastic deformation and suppressing damage localization leading to material instability. The formation of large regions of inelastic deformations around cracks and defects in nacre are believed to be an important contribution to its toughness. In addition, it was shown that the tablet junctions (vertical junctions between tablets) strengthen the microstructure but do not contribute to the overall material hardening. Statistical variations within the microstructure were found to be beneficial to hardening and to the overall mechanical stability of nacre. These results provide new insights into the microstructural features that make nacre tough and damage tolerant. Based on these findings, some design guidelines for composites mimicking nacre are proposed.
762 citations
Book•
01 Jan 2007
TL;DR: In this paper, the authors present an overview of Strengthening Mechanisms and the Lattice Resistance of Crystalline Solids and the Defect State of Polycrystals.
Abstract: 1. Structure of Crystalline Solids and the Defect State 2. Kinematics and Kinetics of Crystal Plasticity 3. Overview of Strengthening Mechanisms 4. The Lattice Resistance 5. Solid Solution Strengthening 6. Precipitation Strengthening 7. Strain Hardening 8. Deformation Instabilities, Polycrystals, Flow in Metals with Nano-structure and Superposition of Strengthening Mechanisms
573 citations
25 Jul 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the critical resolved shear strengths (CRSS) and hardening behaviors of deformation mechanisms were modelled using a viscoplastic self-consistent polycrystal model to model the changes in the flow stress profile, the strain anisotropy, and texture evolution.
Abstract: Uniaxial compression test data were obtained from magnesium alloy AZ31B sheet material tested along three sample directions (rolling, transverse and normal direction) over the temperature range T = 22–250 ◦ C. The yield point during in-plane compression is insensitive to temperature, up to 200 ◦ C, suggesting that athermal mechanisms are responsible for yielding. The in-plane compression samples exhibit very low r-values, which provides another signature of significant twinning activity in magnesium sheet, in addition to the characteristic sigmoidal strain hardening curve. By varying the critical resolved shear strengths (CRSS) and hardening behaviors of the deformation mechanisms, it is possible to model the changes in the flow stress profile, the strain anisotropy, and texture evolution using a viscoplastic self-consistent polycrystal model. Notably, the CRSS values for basal slip were observed to be constant, while that of twinning increased slightly, and the CRSS values of thermally activated slip
455 citations
TL;DR: In this paper, numerical algorithms for discrete dislocation dynamics simulations are investigated for the purpose of enabling strain hardening simulations of singlecrystals on massively parallel computers, and the authors propose a deterministic algorithm for single-crystal simulations.
Abstract: Numerical algorithms for discrete dislocation dynamics simulations areinvestigated for the purpose of enabling strain hardening simulations of singlecrystals on massively parallel computers. The al ...
447 citations
TL;DR: In this paper, the evolution of twinning and texture in two Mg-based (+Al, Mn, Zn) alloys was investigated using uniaxial tension, unioxial compression and ring hoop tension testing at temperatures from ambient to 250°C and a strain rate of 0.1 s−1.
431 citations
TL;DR: The work hardening properties of a friction stir welded (FSWed) magnesium alloy were evaluated using two modified equations of hardening capacity and strain hardening exponent where the elastic deformation stage was excluded.
338 citations
15 Feb 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors performed uniaxial compression tests on samples cut along the extrusion direction from AZ31 Mg alloy tubes and found that the widespread formation of intersecting {10-12} extension twins is responsible for the increased strain hardening rate.
Abstract: Uniaxial compression tests were performed on samples cut along the extrusion direction from AZ31 Mg alloy tubes. A stage of increasing work hardening rate was observed on representative true sigma-epsilon curves. Specimens compressed to various strain levels were examined by optical microscopy and electron backscattered diffraction (EBSD) techniques. The results indicate that the widespread formation of intersecting {10-12} extension twins is responsible for the increased strain hardening rate. (c) 2006 Elsevier B.V. All rights reserved.
295 citations
TL;DR: In this paper, a physically based grain size dependent strain hardening model has been developed for the ferrite matrix, involving specific laws for the accumulation and saturation of dislocations along grain boundaries and for their net back stress contribution.
217 citations
TL;DR: In this article, a coupled thermo-mechanical finite element analysis of the forming process was performed for the temperature range 25-260°C (77-500°F) at different strain rates.
206 citations
TL;DR: In this paper, a constitutive model is developed to capture the rate-dependent stress-strain behavior of an amorphous polymer (poly(ethylene terephthalate)-glycol (PETG)) at temperatures in and above the glass transition (θg).
195 citations
TL;DR: In this article, a microstructure-based strain-hardening model for precipitate hardening materials is developed, accounting, in addition to the usual contributions, for the influence of a supersaturated solid solution as well as for a dependence of dynamic recovery on the yield strength and on the presence and stability of Orowan loops.
TL;DR: Haddadi et al. as mentioned in this paper evaluated the influence of work-hardening modeling in springback prediction in the first phase of the Numisheet’05 “Benchmark 3”: the U-shape “Channel Draw”.
TL;DR: In this article, the mechanical properties of unidirectional flax fibre reinforced unsaturated polyester resin composites were studied with particular emphasis on their tensile deformation behaviour.
Abstract: The mechanical properties of unidirectional flax fibre reinforced unsaturated polyester resin composites were studied with particular emphasis on their tensile deformation behaviour. These materials displayed characteristic non-linear behaviour when loaded parallel to the axis of the fibre, with a distinct knee preceding a drop in stiffness. Further deformation resulted in strain hardening behaviour. Load cycling and acoustic emissions analysis were used to investigate the nature of the knee and it was found that this corresponded with yielding behaviour in the composite. A well-defined yield point could be identified, which in composites of around 60% fibre volume fraction, occurred at a strain of some 0.12% and a tensile stress of 32 MPa. Varying the interfacial properties, through chemical modification of the fibre prior to lamination, was found to have a marked effect upon the onset of yielding and the yield point itself, as well as the deformation and fracture behaviour of the laminate. It is considered that this behaviour is intimately linked to the straining behaviour of the fibre as well as the fibre–matrix interaction and hypotheses to explain the observed behaviour are presented.
TL;DR: In this article, the authors reported an Fe-based bulk metallic glass which showed a plastic strain of ∼5.2%, together with high strength and distinct strain-hardening characteristics.
Abstract: Fe-based bulk metallic glasses usually exhibit very poor ductility (<0.5%), which has limited their applications. Here the authors report an Fe-based bulk metallic glass which shows a plastic strain of ∼5.2%, together with high strength and distinct strain-hardening characteristics. Its yield strength is ∼2.32GPa, while the ultimate strength is ∼2.80GPa due to the strain-hardening effect. Multiple shear bands and related shear ledges are observed on the deformed specimen. The high plasticity and strain hardening are attributed to the nanoscale inhomogeneity that resulted from liquid phase separation, which can hinder the propagation of shear bands and promote multiple shearing.
TL;DR: In this paper, a series of investigations on the effect of fiber reinforcement on the response of structural members in direct tension and flexure under reversed cyclic loading conditions is described. And the synergistic effects of composite deformation mechanisms in the ECC and structural members subjected to large shear reversals are identified.
TL;DR: In this article, the Fourier transform (FT)-rheology analysis of water-based dispersions and emulsions is used as model systems for a new rheological data analysis, in which the application of large amplitude oscillatory shear can be used to generate a high nonlinear response, which is analyzed by FT.
Abstract: Water-based dispersions and emulsions are used as model systems for a new rheological data analysis. The application of large amplitude oscillatory shear can be used to generate a high nonlinear response, which is analyzed by Fourier transform (FT)-rheology. The individual higher harmonics appearing in the shear stress response do not have a simple physical interpretation. Furthermore, in the FT analysis used so far the focus was mainly on the third harmonic relative to the fundamental I3/I1, even if multiple higher harmonics appear, as in the polystyrene dispersions examined here. As a consequence, we propose a new and simple method that considers the whole overtone spectra as a superposition of different overtone spectra of typical nonlinear rheological effects, like strain hardening, strain softening, and shear bands or wall slip. This novel analysis of FT-rheology experiments thus separates the nonlinear mechanical response into the underlying physical phenomena.
TL;DR: In this article, a simple approach based on the evolutionary laws of two dislocation densities related respectively to the forward and the backward straining was proposed to model the mechanical behavior of low carbon steels and aluminium alloys.
TL;DR: In this paper, a dimensionless parameter has been used to categorize the response into elastic, elastic-plastic-hardening, elasticplastic softening, rigid-PLS, rigidplastic hardening, and rigid-polysilicon softening.
TL;DR: Simulations are used to examine the microscopic origins of strain hardening in polymer glasses, finding that entangled and unentangled chains show the same strainhardening when plotted against the microscopic chain orientation rather than the macroscopic strain.
Abstract: Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While traditional entropic network models can be fit to the total stress, their underlying assumptions are inconsistent with simulation results. There is a substantial energetic contribution to the stress that rises rapidly as segments between entanglements are pulled taut. The thermal component of stress is less sensitive to entanglements, mostly irreversible, and directly related to the rate of local plastic rearrangements. Entangled and unentangled chains show the same strain hardening when plotted against the microscopic chain orientation rather than the macroscopic strain.
TL;DR: In this paper, the influence of various thermometallurgical and mechanical phenomena on stress evolution and to optimize the induction-assisted laser cladding process to get crack-free coatings of hard materials at high feed rates.
Abstract: In laser cladding thermal contraction of the initially liquid coating during cooling causes residual stresses and possibly cracks. Preweld or postweld heating using inductors can reduce the thermal strain difference between coating and substrate and thus reduce the resulting stress. The aim of this work is to better understand the influence of various thermometallurgical and mechanical phenomena on stress evolution and to optimize the induction-assisted laser cladding process to get crack-free coatings of hard materials at high feed rates. First, an analytical one-dimensional model is used to visualize the most important features of stress evolution for a Stellite coating on a steel substrate. For more accurate studies, laser cladding is simulated including the powder-beam interaction, the powder catchment by the melt pool, and the self-consistent calculation of temperature field and bead shape. A three-dimensional finite element model and the required equivalent heat sources are derived from the results and used for the transient thermomechanical analysis, taking into account phase transformations and the elastic-plastic material behavior with strain hardening. Results are presented for the influence of process parameters such as feed rate, heat input, and inductor size on the residual stresses at a single bead of Stellite coatings on steel.
TL;DR: In this paper, the authors present various durability properties of strain hardening fiber reinforced cementitious composites (SHFRCC) and argue that SHFRCC materials can be used in selected locations of reinforced concrete structural members to improve their overall durability performances.
Abstract: This paper reviews and presents various durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC). Published research results show that, due to its tight crack width properties compared to ordinary concrete and ordinary fibre reinforced concrete, SHFRCC significantly resists the migration of aggressive substances in to the concrete and improves the durability of reinforced concrete (RC). It is also reported that, due to the strain hardening and multiple cracking behaviours, SHFRCC meets the tight crack width limits for durability of RC structures proposed by different design codes. Based on the reviewed durability properties it is argued that SHFRCC materials can be used in selected locations of RC structural members to improve their overall durability performances.
25 Sep 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, stretch formability of AZ31 Mg alloy sheets was investigated by Erichsen tests at room temperature and stretch forming tests at 523 K. It is suggested that reduction of strain and plastic anisotropies related to texture intensity and texture distribution should be the dominant factor for excellent stretch forming.
Abstract: Stretch formability of AZ31 Mg alloy sheets was investigated by Erichsen tests at room temperature and stretch forming tests at 523 K. The as-received specimens with lower Lankford value (r-value) and higher strain hardening exponent coefficient (n-value) showed excellent stretch formability at room temperature. On the other hand, the as-received specimens with smaller grain size (higher ductility) exhibited excellent stretch formability at elevated temperature. It is suggested that reduction of strain and plastic anisotropies related to texture intensity and texture distribution should be dominant factor for excellent stretch formability at room temperature, and ductility related to fine grain size becomes important factor for stretch formability at elevated temperature, at which effects of strain and plastic anisotropies are negligibly small.
25 Aug 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of microporosity on the tensile properties of A356 alloy was investigated through systematic experimental approaches, with a constitutive prediction that takes into account the strain rate sensitivity and strain-hardening exponent.
Abstract: The effect of microporosity on the tensile properties of A356 alloy was investigated through systematic experimental approaches, with a constitutive prediction that takes into account the strain rate sensitivity and strain-hardening exponent. The strain rate sensitivity was measured through the incremental strain rate change method, and the volumetric porosity and fractographic porosity were obtained from the measurements of bulk density and the quantitative fractography analyses on the fractured surface, respectively. The UTS and elongation exhibit a strong dependence upon the variation in microporosity, with a linear and inverse parabolic relationship, respectively. The constitutive prediction based on the fractographic rather than the volumetric porosity can more accurately predict the overall tensile properties of A356 alloy. The constitutive model should necessarily take into account the strain rate sensitivity and strain-hardening exponent for an exact theoretical prediction of the tensile properties.
TL;DR: In this article, the authors investigated the strain path dependence of forming limit strains and stresses of a steel tube subjected to combined axial load and internal pressure using a tension-internal pressure testing machine.
TL;DR: In this paper, the beam deflection from a flexural test can be linearly related to tensile strain capacity, and a master curve relating this easily measured structural element property to material tensile capacity is constructed from parametric studies of a wide range of materials tensile and compressive properties.
Abstract: As emerging advanced construction materials, strain hardening cementitious composites (SHCCs) have seen increasing field applications recently to take advantage of its unique tensile strain hardening behavior, yet existing uniaxial tensile tests are relatively complicated and sometime difficult to implement, particularly for quality control purpose in field applications. This paper presents a new simple inverse method for quality control of tensile strain capacity by conducting beam bending test. It is shown through a theoretical model that the beam deflection from a flexural test can be linearly related to tensile strain capacity. A master curve relating this easily measured structural element property to material tensile strain capacity is constructed from parametric studies of a wide range of material tensile and compressive properties. This proposed method (UM method) has been validated with uniaxial tensile test results with reasonable agreement. In addition, this proposed method is also compared with the Japan Concrete Institute (JCI) method. Comparable accuracy is found, yet the present method is characterized with much simpler experiment setup requirement and data interpretation procedure. Therefore, it is expected that this proposed method can greatly simplify the quality control of SHCCs both in execution and interpretation phases, contributing to the wider acceptance of this type of new material in field applications.
TL;DR: A new wrought magnesium alloy, AM30 (Mg-3 pct Al-0.4 pct Mn), has been developed in this article, which has 20 to 50 percent higher maximum extrusion speed, up to 50 pct ductility improvement at temperatures up to 200 °C, with similar yield and tensile strengths.
Abstract: A new wrought magnesium alloy, AM30 (Mg-3 pct Al-0.4 pct Mn), has been developed. Compared to the current workhorse commercial wrought magnesium alloy AZ31 (Mg-3 pct Al-1 pct Zn), the new AM30 alloy has 20 to 50 pct higher maximum extrusion speed, up to 50 pct ductility improvement at temperatures up to 200 °C, with similar yield and tensile strengths. The tensile behavior of AM30 and AZ31 magnesium alloy tubes suggests a moderate temperature forming range of 100 °C to 175 °C in which strain hardening offsets plastic instability until fracture by cavity coalescence occurs. The AM30 alloy has slightly better formability than AZ31 at room and moderate temperatures, due to higher strain-hardening rates (dσ/de) and exponents (n). Microstructural evaluation indicates that twinning is the major deformation mechanism for these alloys at room and moderate temperatures in addition to slip mechanisms. Dynamic recrystallization (DRX) is observed at temperatures greater than ∼150 °C, which causes local instabilities to occur, leading to failure.
25 Jul 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors analyzed the strain hardening behavior of randomly oriented polycrystals deformed in tension and compression using the Kocks-Mecking phenomenological approach and found that at low stresses, an extended regime of linear hardening consistent with an athermal forest hardening mechanism, akin to that observed in face-centered cubic metals, was observed.
Abstract: The strain hardening behaviour of randomly oriented polycrystals deformed in tension and compression is analysed using the Kocks-Mecking phenomenological approach. At low stresses, an extended regime of linear hardening consistent with an athermal forest hardening mechanism, akin to that observed in face-centered cubic metals, is observed. The increase in yield strength with decreasing grain size can also be accounted for by relating the mean free path of dislocations to the grain size. Profuse twinning in compression seems to have little or no effects on the overall strain hardening behaviour.
TL;DR: In this paper, the authors extended the indentation analysis to an elastoplastic thin film on an elastic substrate, and with the assistance of the substrate effect, the film elastic modulus, yield stress and work hardening exponent can be measured from one simple sharp indentation test with moderate penetration depth.
TL;DR: Flores, P., Rondia, E., Habraken, A.M., 2005a. as discussed by the authors investigated the material behavior with the help of classical tensile tests and the ones performed in his bi-axial machine in order to identify the yield locus and the hardening model.
TL;DR: In this article, a strain-induced evolution of ultrafine grains in pure copper was studied in multidirectional forging (MDF) at 195 K. The structural changes were associated with the development of high-density microshear bands crossed by MDF.
Abstract: Strain-induced evolution of ultrafine grains in pure copper was studied in multidirectional forging (MDF) at 195 K. The stress–strain behaviour was characterized by rapid strain hardening during early processing and the rate of strain hardening gradually decreased with straining, leading to an apparent steady-state flow at large cumulative strains of more than 5. The structural changes were associated with the development of high-density microshear bands crossed by MDF. The new fine grains 0.16 µm in size, which was smaller than the subgrain size evolved during early deformation, were evolved primarily at microshear band intersections, and then the new fine grains filled out the whole sample as the number of microshear band intersections increased at large strains. This is essentially similar to continuous dynamic recrystallization. The size of new grains can be expressed by a power law function of flow stress with a grain size exponent of about –0.3. The kinetics of the strain-induced grain evolution is ...