Showing papers on "Strain rate published in 1969"
TL;DR: In this article, a variational principle is established to characterize the flow field in an elastically rigid and incompressible plastic material containing an internal void or voids, and an approximate Rayleigh-Ritz procedure is developed and applied to the enlargement of an isolated spherical void in a nonhardening material.
Abstract: The fracture of ductile solids has frequently been observed to result from the large growth and coalescence of microscopic voids, a process enhanced by the superposition of hydrostatic tensile stresses on a plastic deformation field. The ductile growth of voids is treated here as a problem in continuum plasticity. First, a variational principle is established to characterize the flow field in an elastically rigid and incompressible plastic material containing an internal void or voids, and subjected to a remotely uniform stress and strain rate field. Then an approximate Rayleigh-Ritz procedure is developed and applied to the enlargement of an isolated spherical void in a nonhardening material. Growth is studied in some detail for the case of a remote tensile extension field with superposed hydrostatic stresses. The volume changing contribution to void growth is found to overwhelm the shape changing part when the mean remote normal stress is large, so that growth is essentially spherical. Further, it is found that for any remote strain rate field, the void enlargement rate is amplified over the remote strain rate by a factor rising exponentially with the ratio of mean normal stress to yield stress. Some related results are discussed, including the long cylindrical void considered by F.A. McClintock (1968, J. appl. Mech . 35 , 363), and an approximate relation is given to describe growth of a spherical void in a general remote field. The results suggest a rapidly decreasing fracture ductility with increasing hydrostatic tension.
4,156 citations
TL;DR: In this article, a fine grid scribed on the Mg-Al alloy of several grain sizes over a wide range of strain rates was used to measure the contribution of grain strain and the strain associated with grain boundary deformation.
137 citations
TL;DR: The mechanical behavior of OFHC copper at strain rates from 10−3 to 103 sec−1 at 300°, 420°, and 590°K was investigated in this paper.
Abstract: The mechanical behavior of OFHC copper at strain rates from 10−3 to 103 sec−1 at 300°, 420°, and 590°K was investigated. The strain rate behavior of copper can be divided into two regions. Below 10 sec−1 the dislocation motion is thermally activated over forest dislocation barriers. Above 103 sec−1, a linear relationship between stress and strain rate was observed indicating the presence of a viscous damping mechanism. The stress level τB that must be exceeded in order to obtain viscous behavior depends on the work‐hardened state of the copper. The mobile dislocation density in the viscous damping region was found to be (1) independent of strain rate, (b) only a small fraction (10−5) of the total dislocation density, (c) independent of strain, and (d) increased with increasing temperature. These deductions are discussed in terms of the dislocation multiplication and annihilation mechanism.
130 citations
TL;DR: In this article, a study of the stress-strain behavior, secondary slip geometry and slip line morphology of niobium single crystals purified by annealing in ultra-high vacuum was made.
Abstract: A study has been made of the stress-strain behaviour, secondary slip geometry and slip line morphology of niobium single crystals purified by annealing in ultra-high vacuum. Within favourable limits of orientation, temperature and strain rate the stress—strain curves exhibit well-defined three-stage hardening. The principal secondary slip system is not usually that bearing the highest proportion of the applied stress and this anomalous behaviour can account for the orientation dependence of overshoot. For temperatures below 250°K the stress-strain curve is non-linear and the initial hardening rate very high. The slip lines observed on crystals deformed at low temperatures belong to a {110} ⟨111⟩ system which, in extreme orientations, is only the sixth most highly stressed system. The slip appears as crystallographic lamellae, in contrast to the wavy slip observed for all other systems.
117 citations
TL;DR: In this paper, a theoretical solution was developed to enable the determination of the coefficient of consolidation, the compression index, and the preconsolidation pressure from this testing procedure, within established limits.
Abstract: Consolidation tests on three materials were conducted by inducing six different constant rates of strain on the samples. The total load on the sample, the pore pressure at the base and the deformation were measured. A theoretical solution was developed to enable the determination of the coefficient of consolidation, the compression index, and the preconsolidation pressure from this testing procedure. Within established limits, it is shown that the consolidation parameters determined by this method agree with parameters determined by the conventional testing method. The advantages of the proposed procedure are that a much shorter time is required to determine the consolidation parameters and that this procedure can be used to study the strain rate sensitivity of cohesive soils to consolidation loads.
113 citations
01 Jun 1969
TL;DR: In this paper, the authors measured the deformation in the zone of intense shear in which the removed chip is formed in orthogonal machining and showed that both the maximum and mean values of the maximum shear strain-rate in this zone are directly proportional to speed (shear velocity) and inversely proportional to scale.
Abstract: Experiments are described in which an explosive quick-stop device and printed grids (0.002 in square) were used to measure the deformation (streamlines of flow) in the zone of intense shear in which the removed chip is formed in orthogonal machining. A method is given for calculating the strain-rate from the experimental streamlines and it is shown that both the maximum and mean values of the maximum shear strain-rate in this zone are directly proportional to speed (shear velocity) and inversely proportional to scale (depth of cut).
98 citations
TL;DR: In this article, the authors investigated the mechanical properties, dislocation configurations and densities of single crystals of copper deformed in the strain-rate range 10−4 to 104 sec−1.
Abstract: The mechanical properties, dislocation configurations and densities have been investigated in single crystals of copper deformed in the strain-rate range 10−4 to 104 sec−1. It was found that the flow stress of copper exhibits two regions of strain-rate sensitivity. Below strain rates of 103 sec−1 the flow stress was relatively insensitive to strain rate but above 103 sec−1 the flow stress is a sensitive linear function of the strain rate. However, the dislocation density and configurations versus strain were found to be almost independent of strain rate throughout the range 10−4 to 104 sec−1. There was a straight line relationship between the flow stress and the square root of the dislocation density at all strain rates. However, at a strain rate of 6·5 X 103 sec−1 there is a positive intercept τ0 on the stress axis at zero dislocation density. The term τ0 can be related to the damping process retarding dislocation motion.
89 citations
TL;DR: The applicability of the following strain rate equation to high temperature deformation is examined in this paper, where it is shown that, as long as σ and v are independent of instantaneous changes in applied stress and temperature, a back stress term must be included if the equation is to be valid for transient as well as steady-state conditions.
69 citations
TL;DR: In this paper, the Cottrell theory relating the critical strain for serrated yielding, e0, to temperature and strain rate becomes inapplicable at temperatures above ∼0·3 T m.
Abstract: It is well established that at temperatures above ∼0·3 T m the Cottrell theory relating the critical strain for serrated yielding, e0, to temperature and strain rate becomes inapplicable. At these elevated temperatures e0 increases with increasing temperature and decreasing strain rate. These phenomena may be rationalized on the basis that during the high temperature critical strain dislocations move only in conjunction with a solute atmosphere.
55 citations
TL;DR: In this article, the fracture stress at the ductile-brittle transition temperature of polycrystalline molybdenum was found to be constant, 64± 2 kg mm−2, as the strain rate was raised from 5 × 10−6 to 5× 10−2sec−1.
52 citations
TL;DR: In this article, a general discussion of the failure modes which can occur in uniaxial tensile tests of a polyphase, polycrystalline material at various strain rates at elevated temperatures is presented.
Abstract: A general discussion is presented of the failure modes which can occur in uniaxial tensile tests of a polyphase, polycrystalline material at various strain rates at elevated temperatures. Specific results in the temperature range 0.56–0.70Tm are given using Type 316 stainless steel as a representative material. The intrinsic plastic failure is determined solely by plastic deformation, leading first to necking and concluding by separation at a point. However, this intrinsic plastic failure may be interrupted at relatively high strain rates by the formation of cracks at inclusions within the neck. At low strain rates the onset of appreciable necking is postponed and the whole failure process is determined by intergranular crack formation. At intermediate strain rates intergranular cracks form within the neck, and a shear mode of failure is possible. Some conclusions regarding future studies are included.
TL;DR: In this paper, tension and compression tests were conducted on single crystal samples of tantalum and tantalum-rhenium-base solid solutions as a function of temperature and strain rate.
TL;DR: In this article, a brief summary of the structure of keratin fibres is followed by a review of their mechanical and allied properties, including tensile stress-strain properties, stress relaxation, and creep, and torsional stress strain properties and stress relaxation.
Abstract: A brief summary of the structure of keratin fibres is followed by a review of their mechanical and allied properties. Among these properties are tensile stress–strain properties, stress relaxation, and creep, and torsional stress–strain properties and stress relaxation. The mechanism of supercontraction, properties of set fibres and disulphide-reduced fibres, and thermal transitions in keratin are also discussed. Finally, the various theoretical attempts that have been made to explain these properties are critically reviewed.
TL;DR: In this paper, the effect of grain size, strain rate and temperature on the lower yield stress of α-iron is discussed in terms of the theory of thermally activated flow.
TL;DR: In this article, a new consolidation test based upon maintaining a constant pattern of hydrostatic excess pressure in the test specimen is described, and the coefficient of consolidation is computed using a simple formula instead of by curve fitting schemes.
Abstract: A new consolidation test based upon maintaining a constant pattern of hydrostatic excess pressure in the test specimen is described. New apparatus and testing technique are developed for the test. The controlled gradient test can be performed at a slow rate strain that is practically constant for a particular test. The rate of strain can be selected from a fivefold range, permitting study of the effect of strain rate on the consolidation characteristics. These strain rates are still faster than the rates occurring in the field, but are closer to the field rates than the rates in the conventional test. In the new test the coefficient of consolidation is computed using a simple formula instead of by curve fitting schemes. Results of the new test are compared with those of the conventional test.
TL;DR: In this paper, the authors deal with slow processes of extension of an elasto-visoous cylinder under conditions where the theory of linear viscoelasticity is applicable.
Abstract: This paper deals with slow processes of extension of an elasto-visoous cylinder under conditions where the theory of linear viscoelasticity is applicable. Kinematic dependences are given and four nonstationary problems are solved concerning the extension of a cylinder when one of the following parameters is constant: strain rate, extension rate, stress, and tensile force.
TL;DR: In this paper, a temperature change test was used to determine the temperature dependence of τ ∗ on individual specimens, the temperature at which τ∗ becomes zero, and absolute values of τ ∼ 0.
TL;DR: In this article, single crystals of uranium dioxide were deformed in compression to nominal strains of 1 and i %, and the dislocation density of the as-grown crystals was 2 × 10 6 / cm 2.
TL;DR: In this article, a comparative study of the deformation behavior of mechanically and chemically polished ice crystals is described for single crystals, showing that mechanically disturbed surface layers and sub-boundaries do not act as strong barriers to dislocation movement in ice crystals, but rather serve as sources of dislocations.
Abstract: A comparative study of the deformation behaviour of mechanically and chemically polished ice crystals is described For single crystals, mechanical disturbance of the surface layer greatly reduces the maximum stress for basal glide in constant strain rate tests in compression Single crystals with sub-boundaries do not show any prominent surface effect, but exhibit quite a low maximum stress The results indicate that mechanically disturbed surface layers and sub-boundaries do not appear to act as strong barriers to dislocation movement in ice crystals, but rather as sources of dislocations Surface condition does not appear to affect the maximum stress for polycrystals The influence of strain rate (range 21 × 10−5 to 17 × 10−4 s−1) and temperature (range −10 to −30°C) upon the maximum stress was also investigated for both single crystals and polycrystals of ice
01 Jan 1969
TL;DR: In this paper, a double-resonator method for measuring the complex modulus (kHz-range) of a crystal during plastic flow in tensile or creep tests is described.
TL;DR: In this article, an experimental study of the strain rate behavior of technically pure iron in pure shear is reported, and the basic assumptions of the visco-plasticity theory for complex states of stress have been examined in the light of this experimental evidence.
TL;DR: In this article, the effects of sinusoidal internal stresses on average dislocation velocities are examined for the power law stress dependence, v = V 1 τ e m∗ ; the exponential stress dependence and the hyperbolic started that when the magnitude of the internal stresses is comparable with the applied stress, the stress dependence of the velocity becomes anomalously high.
TL;DR: In this paper, the authors applied the time-temperature superposition principle to yield stress, initial tangent moduli, and relaxation moduli data for all three types of loading.
Abstract: Epoxy–Versamid specimens were loaded in tension, compression, and flexure at different strain rates and temperatures to determine mode of failure, yield stress and strain, and tangent and relaxation moduli. Stress-strain curves were used to define brittle, ductile, ductile-rubbery, and rubbery modes of behavior which prevailed in different temperature-strain rate regions. The time-temperature superposition principle was applied to yield stress, initial tangent moduli, and relaxation moduli data for all three types of loading.
The transition regions, tangent and relaxation moduli, and shift factors were the same in tension, compression, and flexure. Thus the most convenient mode of loading can be used to determine the general time-temperature dependence. The ratio of compressive-to-tensile yield stress was almost constant over the entire ductile region. Flexural yielding data were used to predict yield stress in tension and compression, and stress relaxation master curves were shown to be related to elastic modulus vs. strain rate curves. The yielding phenomenon was interpreted using Eyring's theory of non-Newtonian viscoplastic flow. The apparent activation energy and activation volume were larger for tension than compression. A theory is offered to explain why yielding can occur in a cross-linked system.
TL;DR: In this article, the authors examined the plastic strain region from 3 × 10 −5 through macroscopic yielding in Ferrovac-E iron from room temperature to 77°K.
TL;DR: The Hopkinson split bar as discussed by the authors is a split bar instrumented with both a set of piezoelectric X-cut quartz crystal pressure transducers and a pair of strain gauge transducers to enable investigation of the stress-strain rate behavior in compression of brittle and low strength materials.
Abstract: The Hopkinson split bar, instrumented with both a set of piezoelectric X‐cut quartz crystal pressure transducers and a set of strain gauge transducers, was developed to enable investigation of the stress—strain—strain rate behavior in compression of brittle and/or low strength materials. The approach was applied to the study of a brittle, strain rate sensitive, polycrystalline, organic solid, and for purposes of comparison a relatively ductile, highly filled polymer. Comparison and discussion of data from the two materials illustrate the advantage of the technique to obtain valid, more accurate stress and modulus information at strain levels significantly lower than those satisfactorily obtained by using the split bar instrumented with strain gauges alone.
TL;DR: In this article, the theory of the plastic potential including the convexity of the yield surface was derived based on the principle of maximal specific rate of dissipation work, which yields the theory that the stress and the strain rate always have a common system of principal axes.
Abstract: The paper is based on the principle of maximal specific rate of dissipation work, which yields the theory of the plastic potential including the convexity of the yield surface. The author shows that in isotropic bodies the stress and the strain rate always have a common system of principal axes. He further demonstrates that, for soils with a sufficiently slender conical yield surface, the principal stress corresponding to a zero principal extension rate is always the intermediate one. It follows that a large class of yield surfaces are equivalent in plane flow.
TL;DR: In this article, the significance of the log creep rate versus log stress plot is examined in detail for results on a Cr-Mo steel and it is shown how errors may readily arise in measurement of creep rates at very low stresses.