Showing papers on "Strain rate published in 1982"
01 Jan 1982
TL;DR: In this article, an experimental investigation into the behavior of short reinforced concrete columns is described, where 25 concrete units, each 450 mm (17.7 in.) square by 1200 mm (47.2 in.) high, were subjected to concentric or eccentric loads to failure at different strain rates.
Abstract: An experimental investigation into the behavior of short reinforced concrete columns is described. Twenty-five concrete units, each 450 mm (17.7 in.) square by 1200 mm (47.2 in.) high, containing either 8 or 12 longitudinal steel bars and different arrangements of square or octagonal steel hoops, were subjected to concentric or eccentric loads to failure at different strain rates. Results presented include an assessment of the effect of eccentricity of load, strain rate, amount and distribution of longitudinal steel, and amount and dis tribution of transverse steel. A stress-strain curve for concrete con fined by hoop reinforcement and loaded at a high strain rate (com parable with seismic loading) is proposed and compared with an existing curve based on previous tests conducted at low strain rates. The available ultimate compressive strain for concrete confined by hoop reinforcement is also discussed.
1,026 citations
TL;DR: In this article, a comparison of the spectral properties of turbulence spectra for both temperature gradient and velocity shear has been made using 10-15 m segments of vertical microstructure profiles (at depths of 5-100 m) obtained during the 1978 Joint Air Sea Interaction experiment (JASIN).
Abstract: Spectra of turbulence have been examined for both temperature gradient and velocity shear. The data for this comparison are 10–15 m segments of vertical microstructure profiles (at depths of 5–100 m) obtained during the 1978 Joint Air Sea Interaction experiment (JASIN). From the simultaneous measurement of them two microstructure quantities, the universal spectral constant q (the least principal rate of strain of the velocity spectrum) has been determined to be 3.7 ± 1.5. As well, the dissipation rate has been calculated from the high-wavenumber cut-off of the temperature microstructure spectra (ϵB) and from velocity shear (ϵSH). For a range of values from 8 × 10−9 to 5 × 10−7 m2 s−3 these two measures, ϵB and ϵSH, agree to within a factor of 2 on average. And finally, estimates of ξθ (temperature dissipation rate), ϵ and mean temperature gradient have been used to estimate a mixing efficiency, Γ = 0.24.
616 citations
TL;DR: In this paper, the von Mises effective strain criterion was used to measure the progress of the γ→α transformation in 304 stainless steel sheet loaded in uniaxial and biaxially tension at both low (10-3 per second and high (103 per second) strain rates.
Abstract: The γ→α transformation in 304 stainless steel can be induced by plastic deformation at room temperature. The kinetics of strain-induced transformations have been modeled recently by Olson and Cohen. We used magnetic techniques to monitor the progress of the γ→α transformation in 304 stainless steel sheet loaded in uniaxial and biaxial tension at both low (10-3 per second) and high (103 per second) strain rates. We found that using the von Mises effective strain criterion gives a reasonable correlation of transformation kinetics under general strain states. The principal effect of increased strain rate was observed at strains greater than 0.25. The temperature increase resulting from adiabatic heating was sufficient to suppress the γ→α transformation substantially at high rates. The consequences of the γ→α transformation on mechanical behavior were noted in uniaxial and biaxial tension. Uniaxial tension tests were conducted at temperatures ranging from 50 to -80°C. We found that both the strain hardening and transformation rates increased with decreasing temperature. However, the martensite transformation saturates at ≈85 pct volume fraction α. This can occur at strains less than 0.3 for conditions where the transformation is rapid. Once saturation occurs, the work hardening rate decreases rapidly and premature local plastic instability results. In biaxial tension, the same tendency toward plastic instability associated with high transformation rates provides a rationale for the low biaxial ductility of 304 stainless steel.
529 citations
TL;DR: The most effective influence on the amount of intracortical secondary osteal remodelling was also the maximum strain rate ratio, which could only explain 43% of the variance in the total number of secondary osteons formed.
475 citations
TL;DR: In this article, steady-state isothermal calculations appear to be consistent with the present-day experimental data and suggest that the flows of metals can be described by a single physical mechanism over a range of strain rates from 10 kHz to 1 THz.
Abstract: Recent experiments at strain rates reaching 0.1 GHz suggest a power-law dependence of solid-phase shear stress on strain rate. Novel nonequilibrium molecular dynamics simulations of plastic flow have been carried out. These steady-state isothermal calculations appear to be consistent with the present-day experimental data and suggest that the flows of metals can be described by a single physical mechanism over a range of strain rates from 10 kHz to 1 THz.
448 citations
TL;DR: The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitive at intermediate strain rate (region II) where the material exhibits optimal super-plasticity as discussed by the authors.
Abstract: The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitivity at intermediate strain rates (region II) where the material exhibits optimal superplasticity This relationship is examined in detail, with reference both to the conflicting results reported for the Zn-22 pct Al eutectoid alloy and to the significance of the three regions of flow
378 citations
TL;DR: In this paper, the γ→α transformation in 304 stainless steel was induced by plastic deformation under various conditions of strain, strain state and strain rate, and the transformation microstructures were examined by transmission electron microscopy (TEM).
Abstract: The γ→α transformation in 304 stainless steel was induced by plastic deformation under various conditions of strain, strain state, and strain rate, and the transformation microstructures were examined by transmission electron microscopy (TEM). The nucleation of α martensite embryos was always confined to microscopic shear band (faults, twins, and e-martensite) intersections. In cases where shear bands consisted of bundles of intermixed faults, twins, and e-martensite, α nucleated preferentially only within specific portions of the intersection volume. At sufficiently large strains α appeared to grow into polyhedral shapes. We postulate that growth occurs by repeated nucleation of new α embryos and coalescence of such embryos into polyhedral shapes. These shapes can grow either within an active slip plane or out of it, depending on how many shear band intersections are produced during deformation. Actual measurements of the number of intersections indicated that more intersections are formed in biaxial tension per unit effective strain than in uniaxial tension. This accounts for the more irregular, blocky α morphology observed in biaxial tension. At high strain rates we also found an increase in the number of intersections. However, adiabatic heating at large strains and high rates restricts repeated nucleation and coalescence and limits the amount of α transformation product.
377 citations
TL;DR: In this article, the transition from high-temperature creep to brittle fracture in Maryland diabase was investigated as a function of confining pressure and strain rate, and experiments were conducted at 1000°C.
Abstract: The transition from high-temperature creep to brittle fracture in Maryland diabase was investigated as a function of confining pressure and strain rate. Experiments were conducted at 1000°C. Confining pressure was varied to 450 MPa and strain rates from 2×10−3 s−1 to 4×10−6 s−1 At fixed strain rate, the rock strength first increased with pressure, reached a maximum, and then decreased with increasing pressure. Finally, with high pressures, the strength reached an asymptotic value which was the steady state creep strength at that temperature and strain rate. The positive pressure sensitive domain corresponded to brittle behavior, the negative pressure sensitivity domain to a transitional behavior, and the pressure insensitive domain to dislocation creep. The boundary between the last two domains occurred where the strength of the rock was about equal to the confining pressure. Similar variations in strength have been reported in the literature for carbonates and silicates, although not associated with a transitional behavior. Unfaulted specimens deformed in the transitional field showed microcracks and plastically deformed minerals. The boundaries of the transitional domain were extrapolated to geological conditions corresponding to the oceanic lithosphere. The transition depth near ridges is in close agreement with the base of the seismogenic layer (Tapponnier and Francheteau, 1978). However, the old oceanic lithosphere is probably totally brittle over its whole thickness.
289 citations
TL;DR: In this article, a theoretical description of thermo-plastic instability in simple shear is presented in a system of equations describing plastic deformation, the first law of thermodynamics and Fourier's heat transfer rule.
Abstract: A theoretical description of thermo-plastic instability in simple shear is presented in a system of equations describing plastic deformation, the first law of thermodynamics and Fourier's heat transfer rule. Both mechanical and thermodynamical parameters influence instability and it is shown that two different modes of instability may exist. One of them is dominated by thermal softening and has a characteristic time and length, connected to each other by thermal diffusion.A criterion combining thermal softening, current stress, density, specific heat, work-hardening, thermal conductivity and current strain rate is obtained and practical implications are discussed.
278 citations
TL;DR: In this paper, a three dimensional constitutive equation is derived based on the Perzyna's elasto-viscoplastic theory and Cambridge theory, which can explain the behavior not only such timedependent behavior as creep, stress relaxation and strain rate effect, but also as secondary compression, aging and isotropic stress relaxation.
263 citations
TL;DR: In this article, a model of continental collision in which one of the continents acts as a rigid die indenting the other plate which flows as an incompressible viscoplastic medium was studied.
Abstract: We study a model of continental collision in which one of the continents acts as a rigid die indenting the other plate which flows as an incompressible viscoplastic medium. We consider two extreme cases of plane deformation: (1) plane strain which corresponds to an infinitely thick lithospheric plate, and (2) plane stress corresponding to a very thin plate. Deformation of the lithosphere, a thick plate, should be intermediate between those extremes. We found that the flow in the plane strain case is quite similar to that obtained by slip line, theory. The plane stress results are quite different, since in this case most of the plate shortening is taken up by the thickening of the lithosphere. We also explored the role of boundary conditions on the flow, in particular, the role of the side walls containing the flow of the lithosphere. In the case of a free lateral boundary the main feature is a flow of matter toward this free wall and a S-like pattern for the horizontal stress field. For a rigid wall, on the other hand, the plane strain and the plane stress results are quite different. In the first case, there is a large return flow on the sides of the punch, the material being extruded along the only free surface available. In the plane stress case, the return flow disappears, and the material displaced by the penetration of the die tends to thicken the plate. The role of a nonlinear constitutive relation is studied for power law creep. As the power of the flow limit increases, the flow retains its general features, but the deformation localizes creating sharper contrasts between high and low strain rate areas; in plane stress, the effect of nonlinearity is to increase the contrasts in vertical motion. Available data for Asia are discussed in the light of the new results.
TL;DR: In this paper, a fine-grained isotropic ice was tested in uniaxial compression at −5°C. Tests were made under: (1) constant strain rate, and (2) constant stress, with total axial strains up to about 7%.
TL;DR: In this article, the viscosity of soda-lime silica glass was measured at high strain rates and the data showed non-Newtonian viscous flow in this inorganic oxide glass with the visosity values below the expected Newtonian value.
Abstract: The viscosity of a soda‐lime silica glass was measured at high strain rates. The data show non‐Newtonian viscous flow in this inorganic oxide glass with the viscosity values below the expected Newtonian value. Following the imposition of large, steady strain rates, the observed stress increases with time to a maximum and then decreases to a time‐independent value. A comparison of the viscosity behavior of this glass with the molecular dynamics results in a ’’Lennard‐Jones’’ glass shows a number of points of correspondence and suggests the interpretation of the non‐Newtonian behavior as resulting from structural rearrangements in the material. The combined data show that the sustained, steady‐state stress asymptotically approaches a maximum at very high strain rates. This limiting stress is interpreted as the actual cohesive strength of the material and is calculated to be 1.4×108N/m2 (20,000 psi) for the glass under study.
TL;DR: In this article, the activation enthalpy of serrated flow is calculated by means of the conventional method (utilizing the critical strain for the onset of serrations) and by a newly developed method (starting from Δσ- and Δt-values).
TL;DR: The behavior of semi-solid Sn-Pb alloys was studied in compression between two parallel plates as discussed by the authors, where small dendritic samples were deformed at cross-head speeds leading to initial strain rates ranging from 13 × 10-3 s-1 to 12 × 103 s -1 in the semi solid state at a temperature just above the eutectic.
Abstract: The behavior of semi-solid Sn-Pb alloys was studied in compression between two parallel plates Small dendritic samples were deformed at cross-head speeds leading to initial strain rates ranging from 13 × 10-3 s-1 to 12 × 103 s-1 in the semi-solid state at a temperature just above the eutectic At the lower rates of deformation, breakdown of the dendrite structure occurs, at strains of 02 to 04, and a high degree of segregation of the liquid phase occurs For higher rates the segregation no longer occurs to such a great extent and the alloy deforms more homogeneously Some related experiments involving compression over a filter are presented to obtain stress-strain relations in bulk compression for later analysis The behavior in compression of alloys in the semi-solid state may be used as a refining process in the low strain-rate range where segregation of the liquid is large It may also prove useful in the high strain-rate range as a forming method
TL;DR: In this paper, the authors examined the plastic-flow behavior of plain carbon steels with a base composition of 0.8 Mn and 0.25 Si as a function of carbon content in the range 0.005 to 1.54 wt pct at strain rates from 6 x 10-6 to 2x 10-2 sec-1.
Abstract: The elevated-temperature plastic-flow behavior of plain carbon steels with a base composition of 0.8 Mn and 0.25 Si was examined as a function of carbon content in the range 0.005 to 1.54 wt pct at strain rates from 6 x 10-6 to 2 x 10-2 sec-1. Beyond 0.05 C the flow stress at a strain of 0.1 decreased with increasing carbon content at the rate of 13 MPa per pct carbon. However, the degree of softening depended on the strain level at which the flow stress was measured, because the increasing carbon content also decreased the rate of work hardening. The inferred increase in recovery processes with increasing carbon content is in agreement with the effects of carbon on diffusivity, elastic modulus, and lattice spacing, as well as the observed increase in grain growth with increasing carbon content. In the range 850 to 1300 °C (1562 to 2372 °F), the temperature dependence of the flow stress can be represented by σ= A exp (-BT) whereA depends on carbon content and strain, andB depends primarily on strain rate. Extrapolation to higher temperatures yields the carbon-content dependence of the flow stress at the austenite solidus.
TL;DR: In this paper, the effects of thermal history, strain rate and fracture mode on hot ductility in steels were studied, in order to clarify the sensitivity of surface cracking during both continuous casting operation and direct hot rolling.
Abstract: Hot ductility in steels was studied. Special emphases were placed on the effects of thermal history, strain rate and fracture mode in order to clarify the sensitivity of surface cracking during both continuous casting operation and direct hot rolling.There exist three temperature regions where typical embrittlement is noticed, i.e., Tm-1200°C (I), 1200-900°C (II), and 900-600°C (III). The cause of the embrittlement in the region I is the existence of residual liquid film along the dendritic interfaces. The ductility is found to be independent of the strain rate. In the region II, the precipitation of finely distributed oxy-sulfides at the austenite grain boundary weakens the boundary strength, and thus overaging treatments such as slow cooling, holding for certain time, or slow rate of straining result in good ductility. On the other hand, the embrittlement in the III region is manifested by the slower strain rate of test. Controlling factors of this embrittlement are precipitation of oxides, sulfides and nitrides, precipitation of proeutectoid ferrite film along austenite grain boundary as well as grain boundary sliding. Detailed mechanism is discussed.
TL;DR: In this paper, the effect of concurrent deformation on the kinetics of pearlite spheroidisation in three eutectoid plain carbon steels with three interlamellar spacings, ranging from 0.14μm to 0.9μm.
TL;DR: In this paper, failure and post-failure behavior of Westerly granite were investigated at pressures up to 400 MPa and temperatures up to 700°C in an internally heated gas apparatus.
TL;DR: In this paper, the authors investigated the relationship between the stretching tensor D and the logarithmic (Hencky) strain In V, with V the left stretch tensor.
TL;DR: In this article, a model of shear banding is presented which shows how a wide band develops from a narrow imperfection in an elasto-viscoplastic material subjected to dynamic shear strain.
Abstract: A model of shear banding is presented which shows how a wide shear band develops from a narrow imperfection in an elasto-viscoplastic material subjected to dynamic shear strain. The model predicts that the width of the shear band is (i) independent of the properties of the initial imperfection and (ii) dependent upon thermal conductivity and strain rate. The dependence upon strain rate is verified qualitatively and quantitatively from experimental results. Finally, the model predicts narrowing of the region of rapid straining with ongoing deformation as is observed in experiment.
TL;DR: In this article, an expression derived from microscopic first principles for the strain rate increase at constant stress or the stress drop at constant strain rate of solids driven through a phase transition was proposed.
Abstract: After a short review of transformation plasticity and of the extant models, we propose an expression derived from microscopic first principles for the strain rate increase at constant stress or the stress drop at constant strain rate of solids driven through a phase transition. We also suggest the possibility of a premonitory contribution to transformation plasticity due to a weakening of elastic constants before the transition.
TL;DR: Slow strain rate stress corrosion tests on notched or pre-cracked specimens of pre-stressing steel immersed in Ca(OH)2 solutions, to which HCl was added where the pH needed to be reduced, have shown that enhanced cracking results at potentials below about − 900 mV, irrespective of pH, with an intermediate region in which cracking is absent or less severe than at other potentials.
TL;DR: In this paper, an improved split-Hopkinson pressure bar system for materials testing at high rates of loading is described, which has a preloading bar together with a pulse-shaping dummy specimen of the same material as the test specimen.
Abstract: An improved version of the split-Hopkinson pressure bar system for materials testing at high rates of loading is described. This new system has a preloading bar together with a pulse-shaping dummy specimen of the same material as the test specimen. Using the transmitted pulse through the pulse shaper as a tailored incident pulse for loading the test specimen enables testing to be carried out at virtually constant rates of strain, from about 100 s-1 to 300 s -1. This represents a significant improvement over the normal method where there can be considerable variation in strain rate throughout a test with a consequent uncertainty in the interpretation of the results.
TL;DR: In this article, the development of shear bands is closely related to the onset of dynamic recrystallisation during deformation, and a change of bulk deformation within the mylonites from relatively homogeneous to inhomogeneous.
Abstract: Microscale shear bands are features that often occur oblique to the mylonitic foliation in
mylonites. This paper is concerned with such structures within a quartz-mylonite. Geometrical
features, microstructures and fabrics associated with shear bands are described. Both optical
and transmission electron microscopy have been used. It was observed that the development
of shear bands is closely related to (i) the onset of dynamic recrystallisation during deformation,
(ii) a change of bulk deformation within the mylonites from relatively homogeneous to inhomogeneous
and (iii) a marked softening of the mylonite. Across shear bands, dominant deformation
mechanisms change from a dislocation creep type to grain boundary sliding. This induces strong
modification of quartz lattice preferred orientations. The asymmetry of quartz fabrics due to
shear should generally be favoured by the development of shear band structures. Our results
indicate that the production of ductile shear band structures helps to accommodate large strain
deformations at low temperatures. Results also indicate that grain and sub-grain sizes are not
affected by variations in strain rate.
TL;DR: In this paper, an extensive experimental investigation comprising tensile testing and high voltage electron microscopy studies of interstitial-free α-Fe was carried out and the results were compared with the empirically derived Ludwik-Hollomon and Ludwik relationships for the σ-ϵ behaviour of metals.
TL;DR: In this paper, the effects of hydrogen on the plastic deformation of nickel and nickel-carbon alloys were studied using a wide range of strain rates at about 300 K. The emphasis of the study was on the behavior at very low strains and low strain rates.
TL;DR: In this article, two single-crystal clinopyroxenes: chrome diopside and hedenbergite were tested in a Griggs solid medium, triaxial, hot creep tester.
Abstract: Laboratory deformation experiments were carried out on two single-crystal clinopyroxenes: chrome diopside and hedenbergite. Tests were made in a Griggs solid medium, triaxial, hot creep tester. A confining pressure of 1000 MPa was applied in all experiments. Crystals were deformed at strain rates from 10−4 to 10−8 s−1 and at temperatures from 400°C to 1200°C. Two orientations of the crystals with respect to the maximum principal compressive stress were tested. The first orientation subjects the (100), [001] and (001), [100] mechanical twinning systems in clinopyroxene to a high resolved shear stress in the sense appropriate for mechanical twinning to occur. The second orientation subjects these systems to an equal resolved shear stress but in the opposite sense so that mechanical twinning is not possible. Effects of temperature and strain rate on the flow stress are observed for the two clinopyroxene compositions. Mechanical twinning on the system (100), [001] is observed to be the primary deformation mechanism in crystals oriented favorably for twinning. The resolved shear stress required for mechanical twinning on this system is 140 MPa for hedenbergite and 100 MPa for chrome diopside. The smaller twinning stresses for diopside are considered to be due to abundant inclusions in the crystals. The mechanical twinning stress is nearly independent of temperature from 400°C to 850°C and strain rate from 10−4 to 10−8 s−1. Above 850°–1000°C for diopside and 1000°C for hedenbergite, deformation occurs by dislocation glide and is strongly temperature and strain rate dependent. Crystals tested in the orientation for which mechanical twinning is not possible deform by two different dislocation glide mechanisms depending on temperature. Details of these experiments are reported in part 2. Results for mechanical twinning predict that this is not an important deformation mechanism in the earth unless resolved shear stress on the twinning system exceeds 140 MPa. Lack of dependence of twinning stress on strain rate implies that large, rapid strains will occur in this mineral if the twinning stress is reached. Independence of twinning stress in clinopyroxenes from temperature, strain rate, or composition allows use of this mineral as a geopiezometer. At plate margins where stresses are high, presence of mechanically twinned clinopyroxene grains allows determination of the orientation and magnitude of stresses responsible for the deformation.
TL;DR: In this article, the microstructural changes associated with dynamic recovery and dynamic recrystallization were investigated by thin foil TEM observation and related to the results of hardness measurements.
Abstract: Dynamic recrystallization behavior of austenite in Nb-bearing HSLA steels as well as 18-8 stainless steel was investigated by hot compression testing. The hot deformation equipment, incorporating a rapid cooling system and an on-line data analysis system, made it possible to investigate the microstructural changes associated with the restoration process by fully suppressing the static recovery and recrystallization. The stress-strain behavior to a strain of 0.70 was investigated in the range of strain rate from 5×10-4 to 10s-1 and of temperature from 900 to 1200°C. Dynamic recrystallization was observed in all the steels deformed under the condition of the Zener-Hollomon parameter being less than 1015s-1, but it was not observed with the highest strain rate of 10s-1. An increase of Nb content in the HSLA steels increased the flow stress for any deformation condition and also increased the strain at onset of dynamic recrystallization. Dynamically recrystallized grain size was primarily related to the value of the Zener-Hollomon parameter, but was not influenced by the initial grain size. The microstructural changes accompanying dynamic recovery and dynamic recrystallization were investigated by thin foil TEM observation and related to the results of hardness measurements.
TL;DR: Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress, and the number of cycles to fatigue failure was more strongly controlled by strain amplitude than stress amplitude.
Abstract: Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.