Showing papers on "Strain rate published in 2003"
TL;DR: In this paper, fine-grained alloys of Mg-3Al-1Zn-0.2Mn in wt.% were obtained by an equal-channel angular extrusion technique and subsequent annealing at elevated temperatures.
1,193 citations
TL;DR: In this paper, the microstructural properties of advanced high strength and supra-ductile TRIP and TWIP steels with high-manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4mass%) were investigated as a function of temperature (−196 to 400°C) and strain rate (10−4≤e≤103 s−1).
Abstract: The microstructural properties of advanced high strength and supra-ductile TRIP and TWIP steels with high-manganese concentrations (15 to 25 mass%) and additions of aluminum and silicon (2 to 4mass%) were investigated as a function of temperature (−196 to 400°C) and strain rate (10−4≤e≤103 s−1). Multiple martensitic γfcc (austenie)→ehcpMs (hcp-martensite)→αbccMs (bcc-martensite)-transformations occurred in the TRIP steel when deformed at higher strain rates and ambient temperatures. This mechanism leads to a pronounced strain hardening and high tensile strength (>1 000 MPa) with improved elongations to failure of >50%. The austenitic TWIP steel reveals extensive twin formation when deformed below 150°C at low and high strain rates. Under these conditions extremely high tensile ductility (>80%) and energy absorption is achieved and no brittle fracture transition temperature occurs. The governing microstructural parameter is the stacking fault energy Γfcc of the fcc austenite and the phase stability determined by the Gibbs free energy ΔGγ→e. These factors are strongly influenced by the manganese content and additions of aluminum and silicon.The stacking fault energy Γfcc and the Gibbs free energy G were calculated using the regular solution model. The results show that aluminum increases Γfcc and suppresses the γfcc→ehcpMs transformation, whereas silicon sustains the γfcc→ehcpMs transformation and decreases the stacking fault energy. At the critical value of Γfcc≈25 mJ/mol and for ΔGγ→e>0, the twinning mechanism is favored. At lower stacking fault energy of (Γfcc 0, martensitic phase transformation will be the governing deformation mechanism.The excellent ductility and the enhanced impact properties enable complex deep drawing or stretch forming operations of sheets and the fabrication of crash absorbing frame structures.
893 citations
TL;DR: In this article, the stress-strain relations for the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (Vitreloy 1) over a broad range of temperatures and strain rates (10−5 to 103 s−1) were established in uniaxial compression using both quasi-static and dynamic Kolsky (split Hopkinson) pressure bar loading systems.
668 citations
TL;DR: In this paper, the authors investigated the plastic deformation of two Pd and two Zr-based bulk metallic glasses (BMGs) through the use of nanoindentation, which probes mechanical properties at the length scale of shear bands.
628 citations
TL;DR: In this article, a global model (GSRM-1) of both horizontal velocities on the Earth's surface and horizontal strain rates for almost all deforming plate boundary zones is presented.
Abstract: SUMMARY In this paper we present a global model (GSRM-1) of both horizontal velocities on the Earth’s surface and horizontal strain rates for almost all deforming plate boundary zones. A model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field. In our model we perform a least-squares fit between model velocities and observed geodetic velocities, as well as between model strain rates and observed geological strain rates. Model velocities and strain rates are interpolated over a spherical Earth using bi-cubic Bessel splines. We include 3000 geodetic velocities from 50 different, mostly published, studies. Geological strain rates are obtained for central Asia only and they are inferred from Quaternary fault slip rates. For all areas where no geological information is included a priori constraints are placed on the style and direction (but not magnitude) of the model strain rate field. These constraints are taken from a seismic strain rate field inferred from (normalized) focal mechanisms of shallow earthquakes. We present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones. Generally, the strain rate tensor field is consistent with geological and seismological data. With the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs. We find that in general there is a good agreement between the present-day plate motions we obtain and longterm plate motions, but a few significant differences exist. The rotation rates for the Indian, Arabian and Nubian plates relative to Eurasia are 30, 13 and 50 per cent slower than the NUVEL1A estimate, respectively, and the rotation rate for the Nazca Plate relative to South America is 17 per cent slower. On the other hand, Caribbean‐North America motion is 76 per cent faster than the NUVEL-1A estimate. While crustal blocks in the India‐Eurasia collision zone move significantly and self-consistently with respect to bounding plates, only a very small motion is predicted between the Nubian and Somalian plates. By integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in, for instance, redefining a no-net-rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation.
578 citations
TL;DR: In this paper, a simple computational model, predicated on the assumption that a rate-sensitive grain boundary affected zone exists, is shown to explain the observed effect of grain size on the rate-dependent plastic response.
551 citations
TL;DR: In this paper, the authors studied the mechanical behavior of consolidated iron with average grain sizes from tens of nanometers to tens of microns under uniaxial compression over a wide range of strain rates.
496 citations
TL;DR: In this article, an expression for separation distance was derived from the force balance equations for the leading and trailing partials by considering the Peach-Koehler force from an applied stress field, repulsive force between leading and leading partial dislocations, attractive force due to the stacking fault energy, and resistance (or damping) force to the glide of the partials.
459 citations
TL;DR: In this paper, a model of metallic plastic flow suitable for numerical simulations of explosive loading and high velocity impacts is presented, where the dependence of the plastic strain rate on applied stress at low strain rates is of the Arrhenius form but with an activation energy that is singular at zero stress so that the deformation rate vanishes in that limit.
Abstract: We present a model of metallic plastic flow suitable for numerical simulations of explosive loading and high velocity impacts. The dependence of the plastic strain rate on applied stress at low strain rates is of the Arrhenius form but with an activation energy that is singular at zero stress so that the deformation rate vanishes in that limit. Work hardening is modeled as a generalized Voce law. At strain rates exceeding 109 s−1, work hardening is neglected, and the rate dependence of the flow stress is calculated using Wallace’s theory of overdriven shocks in metals [D.C. Wallace, Phys. Rev. B 24, 5597 (1981); 24, 5607 (1981)]. The thermal-activation regime is continuously merged into the strong shock limit, yielding a model applicable over the 15 decades in strain rate from 10−3 to 1012 s−1. The model represents all aspects of constitutive behavior seen in Hopkinson bar and low-rate data, including a rapid increase in the constant-strain rate sensitivity, with 10% accuracy. High-pressure behavior is co...
419 citations
TL;DR: In this paper, the role of deformation twinning in the strain-hardening behavior of high purity, polycrystalline α-titanium in a number of different deformation modes was investigated.
411 citations
TL;DR: In this article, the onset of dynamic recrystallization (DRX) can also be detected from inflections in plots of the strain hardening rate θ against stress a or, equivalently, from inflection in In θ-In a and In ǫ-E plots regardless the presence of stress peaks in flow curves.
Abstract: In constant strain rate tests, the occurrence of dynamic recrystallization (DRX) is traditionally identified from the presence of stress peaks in flow curves. However, not all materials display well-defined peaks when tested under these conditions. Using plain carbon, Nb-bearing and 321 austenitic stainless steels, it is shown that the onset of DRX can also be detected from inflections in plots of the strain hardening rate θ against stress a or, equivalently, from inflections in In θ-In a and In θ-e plots regardless the presence of stress peaks in the flow curves. These observations are verified by means of metallography. A unified description of the flow curve is introduced based on normalization of the stress and strain by the respective peak or steady state values. This approach reveals that, in a given material, the ratio of DRX critical stress to the peak or steady state stress is constant, as is that of the critical strain to the corresponding strain values. Furthermore, it is shown that the present technique can be used to establish the occurrence of DRX when this cannot be determined unambiguously from the shape of the flow curve.
TL;DR: In this paper, a series of hot-compression tests and Taylor-model simulations were carried out with the intention of developing a simple expression for the proof stress of magnesium alloy AZ31 during hot working.
Abstract: A series of hot-compression tests and Taylor-model simulations were carried out with the intention of developing a simple expression for the proof stress of magnesium alloy AZ31 during hot working. A crude approximation of wrought textures as a mixture of a single ideal texture component and a random background was employed. The shears carried by each deformation system were calculated using a full-constraint Taylor model for a selection of ideal orientations as well as for random textures. These shears, in combination with the measured proof stresses, were employed to estimate the critical resolved shear stresses for basal slip, prismatic slip, 〈c+a〉 second-order pyramidal slip, and {\(10\bar 12\)} twinning. The model thus established provides a semianalytical estimation of the proof stress (a one-off Taylor simulation is required) and also indicates whether or not twinning is expected. The approach is valid for temperatures between ∼150 °C and ∼450 °C, depending on the texture, strain rate, and strain path.
TL;DR: In this paper, an experimentally validated computational model for titanium alloys accounting for plastic anisotropy and time-dependent plasticity for analyzing creep and dwell phenomena was developed for hcp crystalline structure, with the inclusion of microstructural crystallographic orientation distribution.
TL;DR: In this paper, the authors demonstrate that all solid polymers are intrinsically brittle and will undergo a ductile to brittle fracture transition based on the nature of their bonding alone, and that the most effective way of avoiding a brittle to brittle transition is to reduce the plastic resistance to delay reaching the brittle strength which is governed by intrinsic cavitation.
TL;DR: In this paper, the tensile properties of fully dense nanocrystalline cobalt electrodeposits with an average grain size of 12 nm were studied at different strain rates.
TL;DR: In this paper, a finite element method was used to verify the differences between the dynamic and static tensile strengths and the strain-rate dependency of the dynamic tensile strength of rock.
TL;DR: In this article, the lateral growth strain is modeled using a dislocation climb process in which "unlucky" counter-diffusing cations and anions are trapped at cores of dislocations.
15 Jul 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the uniaxial tensile deformation behavior of three aluminum sheet alloys (Al 5182+1% Mn, Al 5754 and Al 6111-T4) was studied in the warm forming temperature range of 200-350°C and in the strain rate range of 0.015-1.5 s −1.
Abstract: Uniaxial tensile deformation behavior of three aluminum sheet alloys, Al 5182+1% Mn, Al 5754 and Al 6111-T4, are studied in the warm forming temperature range of 200–350 °C and in the strain rate range of 0.015–1.5 s −1 . Approaches have been made to process the selected aluminum sheet alloys so that the microstructural change during warm forming provides adequate recovery favorable to formability but does not deteriorate the post-forming properties. The total elongation in uniaxial tension is found to increase with increasing temperature and to decrease with increasing strain rate. The enhanced ductility at elevated temperatures is contributed primarily from the post-uniform elongation which becomes dominant at elevated temperatures and/or at slow strain rates. The enhancement of strain rate sensitivity ( m value) with increasing temperature accounts for the ductility improvement at elevated temperatures. The uniaxial tensile test is identified to serve as a screening test for ranking relative formability among different sheet alloys. Based on this criterion, the strain hardened 5xxx alloys (Al 5182+Mn and Al 5754) have shown better formabilities than the precipitation hardened alloy (Al 6111-T4).
TL;DR: The underlying principles of TDE, strain, and strain rate echocardiography are reviewed and currently available quantification tools and clinical applications are discussed.
Abstract: Tissue Doppler (TDE), strain, and strain rate echocardiography are emerging real time ultrasound techniques that provide a measure of wall motion. They offer an objective means to quantify global and regional left and right ventricular function and to improve the accuracy and reproducibility of conventional echocardiography studies. Radial and longitudinal ventricular function can be assessed by the analysis of myocardial wall velocity and displacement indices, or by the analysis of wall deformation using the rate of deformation of a myocardial segment (strain rate) and its deformation over time (strain). A quick and easy assessment of left ventricular ejection fraction is obtained by mitral annular velocity measurement during a routine study, especially in patients with poor endocardial definition or abnormal septal motion. Strain rate and strain are less affected by passive myocardial motion and tend to be uniform throughout the left ventricle in normal subjects. This paper reviews the underlying principles of TDE, strain, and strain rate echocardiography and discusses currently available quantification tools and clinical applications.
25 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a novel technique for producing high-strain-rate superplastic (HSRS) microstructure via friction stir processing (FSP) in a commercial 2024 Al has been demonstrated.
Abstract: A novel technique for producing high-strain-rate-superplastic (HSRS) microstructure via friction stir processing (FSP) in a commercial 2024 Al has been demonstrated. A maximum ductility of ∼525% has been achieved at a strain rate of 10 −2 s −1 and 430 °C. Current results suggest that friction stir processing can be developed as a simple yet effective technique for producing microstructure amenable for superplasticity at high strain rates and/or lower temperatures and at lower flow stresses.
TL;DR: In this paper, a method for estimating dislocation densities is proposed, based on nucleation of loops at the shock front and their extension due to residual shear stresses behind the front.
TL;DR: In this article, a transition state theory based predictive model is developed for the tensile failure of nanotubes based on the parameters fitted from high-strain rate and temperature dependent molecular dynamics simulations.
Abstract: Strain rate and temperature dependence of the tensile strength of single-wall carbon nanotubes has been investigated with molecular dynamics simulations. The tensile failure or yield strain is found to be strongly dependent on the temperature and strain rate. A transition state theory based predictive model is developed for the tensile failure of nanotubes. Based on the parameters fitted from high-strain rate and temperature dependent molecular dynamics simulations, the model predicts that a defect free micrometer long single-wall nanotube at 300 K, stretched with a strain rate of 1%/hour, fails at about 9 plus or minus 1% tensile strain. This is in good agreement with recent experimental findings.
TL;DR: In this article, a combined experimental and numerical investigation on the effects of H2 addition to lean-premixed CH4 flames in highly strained counterflow fields using preheated flows indicate significant enhancement of lean flammability limits and extinction strain rates for relatively small amounts of H 2 addition.
TL;DR: In this article, the thermomechanical response of DH-36 Naval structural steel was analyzed using uniaxial compression tests on cylindrical samples, using an Instron servohydraulic testing machine and UCSD's enhanced Hopkinson technique.
TL;DR: In this article, the authors show that the yield strength for Cu with ultrafine grain sizes becomes obviously temperature and strain-rate dependent, in contrast to the temperature/rate insensitive behavior of conventional face-centered-cubic metals.
Abstract: We show that the yield strength for Cu with ultrafine grain sizes becomes obviously temperature and strain-rate dependent, in contrast to the temperature/rate insensitive behavior of conventional face-centered-cubic metals. A thermally activated deformation mechanism is operative at room temperature and especially at slow strain rates, but not at 77 K. In addition to the gain in strength, the tensile ductility and particularly uniform strains also increase at cryogenic temperatures and with increasing strain rate, as a result of improved strain hardening due to suppressed dynamic recovery.
TL;DR: In this paper, a number of special experiments are described in the paper that support the transport of microcracks across the shear plane, and the important role compressive stress plays on the Shear plane.
Abstract: When metal is removed by machining there is substantial increase in the specific energy required with decrease in chip size. It is generally believed this is due to the fact that all metals contain defects (grain boundaries, missing and impurity atoms, etc.), and when the size of the material removed decreases, the probability of encountering a stress-reducing defect decreases. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the metal-cutting shear plane. If the material being cut is very brittle, or the compressive stress on the shear plane is relatively low, microcracks grow into gross cracks giving rise to discontinuous chip formation. When discontinuous microcracks form on the shear plane they weld and reform as strain proceeds, thus joining the transport of dislocations in accounting for the total slip of the shear plane. In the presence of a contaminant, such as CCI4 vapour at a low cutting speed, the rewelding of microcracks decreases, resulting in decrease in the cutting force required for chip formation. A number of special experiments are described in the paper that support the transport of microcracks across the shear plane, and the important role compressive stress plays on the shear plane. Relatively recently, an alternative explanation for the size effect in cutting was provided based on the premise that shear stress increases with increase in strain rate. When an attempt is made to apply this to metal cutting by Dineshet al (2001) it is assumed in the analysis that the von Mises criterion pertains to the shear plane. This is inconsistent with the experimental findings of Merchant. Until this difficulty is taken care of, together with the promised experimental verification of the strain rate approach, it should be assumed that the strain rate effect may be responsible for some notion of the size effect in metal cutting. However, based on the many experiments discussed here, it is very unlikely that it is totally responsible for the size effect in metal cutting as inferred in Dineshet al (2001).
25 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of temperature and strain rate on the resulting recrystallised grain size was investigated and it was shown that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 μm) can be easily produced by DRX during high-temperature extrusion of the AZ91 alloy.
Abstract: Microstructural changes during high-temperature extrusion and torsion of an AZ91 alloy (Mg–9Al–1Zn, wt.%) were investigated. In the experimental domain studied, dynamic recrystallisation (DRX) occurs and the effect of temperature and strain rate on the resulting recrystallised grain size was investigated. Complete recrystallisation in torsion is associated with the development of a stress plateau after softening from the peak stress, which is systematically observed in the first steps of straining. The resulting grain size can be related to the value of the peak stress. It appears that the precipitation of the Mg 17 Al 12 phase does not affect significantly the torsion behaviour of the alloy in the experimental domain investigated here. This study supports the idea that very fine-scale microstructures (i.e. with a mean grain size smaller than 5 μm) can be easily produced by DRX during high-temperature extrusion of the AZ91 alloy.
TL;DR: In this article, an ultrasound system and method for calculation and display of tissue deformation parameters are disclosed, which can be used for applications such as stress echo, where the deformation parameter strain is determined by an accumulation of strain rate estimates for consecutive frames over an interval.
Abstract: An ultrasound system and method for calculation and display of tissue deformation parameters are disclosed. The tissue deformation parameter strain is determined by an accumulation of strain rate estimates for consecutive frames over an interval. The interval may be a triggered interval generated by, for example, an R-wave in an ECG trace. Three quantitative tissue deformation parameters, such as tissue velocity, tissue velocity integrals, strain rate and/or strain, may be presented as functions of time and/or spatial position for applications such as stress echo. For example, strain rate or strain values for three different stress levels may be plotted together with respect to time over a cardiac cycle. Parameters which are derived from strain rate or strain velocity, such as peak systolic wall thickening percentage, may be plotted with respect to various stress levels.
TL;DR: Shear yielding and steady state flow of glassy materials with molecular dynamics simulations of two standard models: amorphous polymers and bidisperse Lennard-Jones glasses show that rate dependence is nearly independent of temperature.
Abstract: We study shear yielding and steady state flow of glassy materials with molecular dynamics simulations of two standard models: amorphous polymers and bidisperse Lennard-Jones glasses. For a fixed strain rate, the maximum shear yield stress and the steady state flow stress in simple shear both drop linearly with increasing temperature. The dependence on strain rate can be described by either a logarithm or a power law added to a constant. In marked contrast to predictions of traditional thermal activation models, the rate dependence is nearly independent of temperature. The relation to more recent models of plastic deformation and glassy rheology is discussed, and the dynamics of particles and stress in small regions is examined in light of these findings.
TL;DR: In this article, the influence of interface scattering on finite-amplitude shock waves was experimentally investigated by impacting flyer plates onto periodically layered polycarbonate/6061 aluminum, poly carbonate/304 stainless steel and polycarbonates/glass composites.
Abstract: In heterogeneous media, scattering due to interfaces/microstructure between dissimilar materials could play an important role in shock wave dissipation and dispersion. In this work, the influence of interface scattering on finite-amplitude shock waves was experimentally investigated by impacting flyer plates onto periodically layered polycarbonate/6061 aluminum, polycarbonate/304 stainless steel and polycarbonate/glass composites. Experimental results (obtained using velocity interferometer and stress gage) show that these periodically layered composites can support steady structured shock waves. Due to interface scattering, the effective shock viscosity increases with the increase of interface impedance mismatch, and decreases with the increase of interface density (interface area per unit volume) and loading amplitude. For the composites studied here, the strain rate within the shock front is roughly proportional to the square of the shock stress. This indicates that layered composites have much larger shock viscosity due to the interface/microstructure scattering in comparison with the increase of shock strain rate by the fourth power of the shock stress for homogeneous metals. Experimental results also show that due to the scattering effects, shock propagation in the layered composites is dramatically slowed down and the shock speed in composites can be lower than that either of its components.