Strain rate

About: Strain rate is a research topic. Over the lifetime, 29156 publications have been published within this topic receiving 667347 citations.

Modeling of dynamic material behavior in hot deformation: Forging of Ti-6242

Abstract: A new method of modeling material behavior which accounts for the dynamic metallurgical processes occurring during hot deformation is presented. The approach in this method is to consider the workpiece as a dissipator of power in the total processing system and to evaluate the dissipated power co-contentJ = ∫o σ e ⋅dσ from the constitutive equation relating the strain rate (e) to the flow stress (σ). The optimum processing conditions of temperature and strain rate are those corresponding to the maximum or peak inJ. It is shown thatJ is related to the strain-rate sensitivity (m) of the material and reaches a maximum value(J max) whenm = 1. The efficiency of the power dissipation(J/J max) through metallurgical processes is shown to be an index of the dynamic behavior of the material and is useful in obtaining a unique combination of temperature and strain rate for processing and also in delineating the regions of internal fracture. In this method of modeling, noa priori knowledge or evaluation of the atomistic mechanisms is required, and the method is effective even when more than one dissipation process occurs, which is particularly advantageous in the hot processing of commercial alloys having complex microstructures. This method has been applied to modeling of the behavior of Ti-6242 during hot forging. The behavior of α+ β andβ preform microstructures has been exam-ined, and the results show that the optimum condition for hot forging of these preforms is obtained at 927 °C (1200 K) and a strain rate of 1CT•3 s•1. Variations in the efficiency of dissipation with temperature and strain rate are correlated with the dynamic microstructural changes occurring in the material.

Stress-strain behavior of concrete confined by overlapping hoops at low and high 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.

Finite strain calculations of continental deformation .2. comparison with the india-asia collision zone

Abstract: Numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness, of stress and strain rate, and of latitudinal displacements that may be compared with observations in the India-Asia collision zone. A simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations, provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2×1013 (±5 × 1012) N m−1 in regions in front of the indenter. Under these conditions, the calculated deformation shows accommodation of convergence primarily by crustal thickening, to produce a plateau in front of the indenter. Palaeomagnetic data from India and Tibet, and the observed distribution of topography, suggest that much of the post-Eocene convergence of India with Asia has been taken up by deformation within Asia that involved crustal thickening. The principal difference between calculation and observation is the absence from the calculated strain rate fields of east-west extension of the plateau in front of the indenting boundary. The calculations show that once such a plateau is formed, the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings. Seismically determined regional strain rates exhibit a similar distribution, with the Tibetan plateau straining at about one quarter the rate of the Tien Shan and Ningxia-Gansu regions. Calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the Mongolia-Baikal, Tien Shan, Tibet, and Ningxia-Gansu regions of Asia, to within the uncertainty of the latter. The vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a Theologically stratified continental lithosphere obeying laboratory-determined flow laws. We suggest that the thin viscous sheet model, described in this paper and its companion, gives a simple and physically plausible description of the observed deformation in central Asia; in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening, with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established.

Hyperbolic Stress-Strain Response: Cohesive Soils

Abstract: The divergent concepts of a stability analysis, as compared with a load-deformation approach to soil mechanics, are shown to be compatible within the framework of a hyperbolic stress-strain relation. The two-constant hyperbolic form of the stress-strain response is such that the ultimate shear strength of the soil is contained within the general formulation and appears in the mathematical limit of the stress as the strain becomes excessive. This is quantiatively demonstrated for a remolded cohesive soil tested in consolidated-undrained triaxial compression. The variables contained in the hyperbolic stress-strain relation include the preconsolidation pressure, rebound stress, lateral pressure during the test, vertical normal stress, strain, and rate of strain. History effects are included in terms of the overconsolidation ratio. The general formulations obtained for the consolidated-undrained triaxial tests are compared with the results reported in the literature by other investigators for both drained and undrained consolidated triaxial tests under various conditions.