Showing papers on "Viscoplasticity published in 1985"
TL;DR: By assuming from the outset hyperelastic constitutive behavior, an alternative approach to finite deformation plasticity and viscoplasticity is proposed whereby the need for integration of spatial rate constitutive equations is entirely bypassed.
646 citations
TL;DR: In this paper, a general theory for the inelasticity of concrete is proposed, the main constituents being a new, rate independent model of distributed damage for mortar and the application of mixture theories to account for the composite nature of concrete.
604 citations
TL;DR: In this paper, the authors proposed two simple procedures to calculate the yield stress from the maximum torque and vane dimensions at the moment of yielding, and compared the proposed methods with the conventional procedure.
Abstract: In the vane method for measuring the yield stress, the conventional analysis assumes that the stress is uniformly distributed on a cylindrical sheared surface to calculate the yield stress from the maximum torque and vane dimensions. By using two simple procedures, the present work shows that this assumption is justified at the moment of yielding. The yield stress calculated using the proposed methods compares favorably with that obtained with the conventional procedure. A comparison with the yield stress independently determined by other methods again confirms the usefulness of the vane technique as a simple but accurate method for direct yield stress measurement.
532 citations
TL;DR: In this article, the authors focused on viscous-like behavior of solids during large-amplitude compressive stress-wave propagation and determined the maximum strain rate in the plastic wave for 30 steady or near steady wave profiles obtained with velocity interferometry methods.
Abstract: The present study is focused on viscouslike behavior of solids during large‐amplitude compressive stress‐wave propagation. Maximum strain rate in the plastic wave has been determined for 30 steady‐ or near steady‐wave profiles obtained with velocity interferometry methods. The materials include six metals, aluminum, beryllium, bismuth, copper, iron, and uranium, and two insulating solids, magnesium oxide and fused silica. A plot of Hugoniot stress versus maximum strain rate for each material is adequately described by η=aσmh. The exponent m is approximately 4 for all materials while the coefficient a is material dependent. A model is developed which incorporates the observed trends of the shock viscosity data in a three‐dimensional framework. Finite‐difference calculations using the model reproduce the experimental wave profile data.
338 citations
TL;DR: In this article, the viscoplastic response of metals at shear strain rates ranging from 105 s− 1 to 107 s−1 was investigated for two fcc metals: commercially pure aluminum and an aluminum alloy.
185 citations
TL;DR: In this article, a simple version of thermo/viscoplasticity theory is used to model the formation of adiabatic shear bands in high rate deformation of solids.
156 citations
01 Jun 1985
TL;DR: The state of the art of time temperature dependent elastic viscoplastic constitutive theories which are based on the unified approach werre assessed as discussed by the authors, which is characterized by the use of kinetic equations and internal variables with appropriate evolutionary equations for treating all aspects of inelastic deformation including plasticity, creep, and stress relaxation.
Abstract: The state of the art of time temperature dependent elastic viscoplastic constitutive theories which are based on the unified approach werre assessed. This class of constitutive theories is characterized by the use of kinetic equations and internal variables with appropriate evolutionary equations for treating all aspects of inelastic deformation including plasticity, creep, and stress relaxation. More than 10 such unified theories which are shown to satisfy the uniqueness and stability criteria imposed by Drucker's postulate and Ponter's inequalities are identified. The theories are compared for the types of flow law, kinetic equation, evolutionary equation of the internal variables, and treatment of temperature dependence. The similarities and differences of these theories are outlined in terms of mathematical formulations and illustrated by comparisons of theoretical calculations with experimental results which include monotonic stress-strain curves, cyclic hysteresis loops, creep and stress relaxation rates, and thermomechanical loops. Numerical methods used for integrating these stiff time temperature dependent constitutive equations are reviewed.
70 citations
TL;DR: An isotropic formulation of the viscoplasticity theory for small strain and based on overstress with a differential growth law for the equilibrium stress is introduced in this paper, where the four material constants and the two material functions of the theory are determined from uniaxial tensile tests involving strain-rate changes at room temperature and performed on a 6061 T6 Aluminum Alloy.
69 citations
01 Jan 1985
TL;DR: A comprehensive constitutive law for a sand-asphalt mixture subjected to either compressive or tensile cyclic loading is developed in this paper, where elastic, plastic, viscoelastic, and viscoplastic components are incorporated into the model as they are found to be simultaneously present during the loading process.
Abstract: A comprehensive constitutive law for a sand-asphalt mixture subjected to either compressive or tensile cyclic loading is developed. The elastic, plastic, viscoelastic, and viscoplastic strain components are incorporated into the model as they are found to be simultaneously present during the loading process. The various parameters of the model are extracted from a series of repeated uniaxial creep and creep-recovery experiments performed under either compressive or tensile constant stress. The experiments are conducted at constant temperature and at various stress levels, time periods, and number of cycles. The material law presentation is followed by a parametric study that is intended to illustrate the relative quantitative influence of various parameters on the resilient and residual strain components.
58 citations
TL;DR: A comprehensive constitutive law for a sand-asphalt mixture subjected to either compressive or tensile cyclic loading is developed in this article, where elastic, plastic, viscoelastic, and viscoplastic components are incorporated into the model as they are found to be simultaneously present during the loading process.
Abstract: A comprehensive constitutive law for a sand-asphalt mixture subjected to either compressive or tensile cyclic loading is developed. The elastic, plastic, viscoelastic, and viscoplastic strain components are incorporated into the model as they are found to be simultaneously present during the loading process. The various parameters of the model are extracted from a series of repeated uniaxial creep and creep-recovery experiments performed under either compressive or tensile constant stress. The experiments are conducted at constant temperature and at various stress levels, time periods, and number of cycles. The material law presentation is followed by a parametric study that is intended to illustrate the relative quantitative influence of various parameters on the resilient and residual strain components.
53 citations
TL;DR: In this article, a class of plastic constitutive equations which show one-to-one correspondence between plastic strain increment dϵp and stress increment do is proposed from the viewpoint of tensor algebra.
TL;DR: In this article, a viscoplastic constitutive relation of the Perznya type is used to describe structural changes for a wide range of material behaviour from solid to liquid states.
Abstract: A viscoplastic constitutive relation of the Perznya type is used to describe structural changes for a wide range of material behaviour from solid to liquid states. Using the constitutive model, finite element simulations were carried out for two types of welding process: a circular plate welded in the centre and a butt-welded plate. The residual stress and temperature were calculated and compared with experimentally measured data.MST/24
TL;DR: In this paper, different mechanical formulations are employed for calculation of the large deformations occurring in metal forming processes, and the Eulerian and updated Lagrangian descriptions, valid for viscoplastic materials, are presented.
Abstract: Different mechanical formulations are employed for calculation of the large deformations occurring in metal forming processes. Eulerian and updated Lagrangian descriptions, valid for viscoplastic materials, are presented. In view of the numerical tests which were carried out, the Eulerian formulation, associated with an implicit integration scheme which proved to be numerically accurate and reliable, is shown to be preferable.
TL;DR: In this paper, the deformation of semi-solid dendritic alloys is studied from a mechanical standpoint using a compressible viscoplastic constitutive model and axisymmetric extrusion.
TL;DR: In this paper, Krieger et al. presented an evaluation of the local power law approximation for the Bingham and Casson plastic materials in dimensionless form, and the magnitude of the error in shear rate and the conditions under which the maximum error occurs, are shown to depend upon the gap width and location of the yield point as well as the rheological model.
Abstract: Prior studies have shown that the local power law approximation [I. M. Krieger, Trans. Soc. Rheol., 12, 5 (1968)] for calculation of the shear rate in a Couette viscometer provides accurate results for non‐Newtonian fluids which do not exhibit a yield stress, but is less accurate for those that do. An evaluation of this approximation is presented here for the Bingham and Casson plastic (yield) materials in dimensionless form. The magnitude of the error in shear rate, and the conditions under which the maximum error occurs, are shown to depend upon the gap width and location of the yield point as well as the rheological model. The error for a Casson fluid is less than half that for the Bingham material. Furthermore, the maximum error in the apparent viscosity function occurs under different conditions of gap width and yield point, and is considerably less than the error in shear rate for both materials.
TL;DR: In this article, a laser interferometer system is used to monitor the normal and transverse components of motion of a point at the rear surface of a target plate, and the experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material.
Abstract: T he pressure-shear plate impact technique is used to study material behavior at high rates of deformation. In this technique, plastic waves of combined pressure and shear stresses are produced by impact of parallel plates skewed relative to their direction of approach. Commercially pure alpha-titanium and 6061-T6 aluminum are tested under a variety of pressure and shear tractions by using different combinations of impact velocities and angles of inclination. A laser interferometer system is used to monitor simultaneously the normal and transverse components of motion of a point at the rear surface of the target plate. The experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material. Both isotropic and kinematic strain hardening models are used in the computations. The results indicate that unlike the normal velocity profiles, the transverse velocity profiles are sensitive to the dynamic plastic response and, thus, can be used to study material behavior at high strain rates. For the materials tested the results suggest that the flow stress required for plastic straining increases markedly with increasing strain rate at strain rates above 104s−1. Hydrostatic pressure of the order that exists in the tests (up to 2 GPa) does not affect the plastic flow in 6061-T6 aluminum and appears to have at most a minor effect on the deformation of the titanium.
TL;DR: In this paper, a general elasto/viscoplastic constitutive equation of a material with memory and internal variables is proposed based on the concept of generalized simple body. And the proposed theory can describe not only such rate-dependent behaviours as primary and secondary creep, but also accelerating (teritary) creep, in which strain rate increases under constant stress.
01 Mar 1985
TL;DR: In this article, a representation of thermoviscoplasticity is proposed to account for thermomechanical history dependence in the cyclic hardening behavior of some common high-temperature structural alloys.
Abstract: Experimental evidence of thermomechanical history dependence in the cyclic hardening behavior of some common high-temperature structural alloys is presented with special emphasis on dynamic metallurgical changes. The inadequacy of formulating nonisothermal constitutive equations solely on the basis of isothermal testing is discussed. A representation of thermoviscoplasticity is proposed that qualitatively accounts for the observed hereditary behavior. This is achieved by formulating the scalar evolutionary equation in an established viscoplasticity theory to reflect thermomechanical path dependence. To assess the importance of accounting for thermomechanical history dependence in practical structural analyses, two qualitative models are specified: (1) formulated as if based entirely on isothermal information; (2) to reflect thermomechanical path dependence using the proposed thermoviscoplastic representation. Predictions of the two models are compared and the impact the calculated differences in deformation behavior may have on subsequent lifetime predictions is discussed.
TL;DR: An elastic viscoplastic constitutive equation for steels at high temperature is calibrated on a set of torsion tests performed by IRSID for different temperatures, strain rates and steel qualities.
Abstract: An elastic viscoplastic constitutive equation for steels at high temperature is calibrated on a set of torsion tests performed by IRSID for different temperatures, strain rates and steel qualities. The integration of this equation in a computer code is examined and results for strip hot‐rolling are given.
AT&T1
TL;DR: In this paper, a scheme was introduced for generating a stress strain curve at any constant strain rate, temperature, pressure, in tension, shear or compression, and the annealing history, from a set of experimental stress-strain data by parametric scaling.
Abstract: A scheme is introduced for generating a stress strain curve at any constant strain rate, temperature, pressure, in tension, shear or compression, and the annealing history, from a set of experimental stress-strain data by parametric scaling. The parameters are determined for each polymer empirically first, but their study reveals much in terms of the structure-properties in glassy and crystalline polymers.
TL;DR: In this article, the authors present a mathematical model to describe dilatancy and/or compressibility of the rocks surrounding a horizontal tunnel, during their deformation by creep, and outline the boundaries of such areas.
Book•
01 Jun 1985
TL;DR: In this paper, high velocity deformation of metals has been studied in the context of Viscoplastic behavior and dynamic plasticity, and the effect of initial temperature and Neutron Irradiation on dynamic hardness.
Abstract: Introduction Shock Phenomena in Metals: Basic - Methos Shock Phenomena in Metals: Experimental Results High Velocity Deformation of Metals: Microphysical Interpretation of Viscoplastic Behavior High Velocity Deformation of Metals: Experimental Methods in Dynamic Plasticity High Velocity Deformation of Metals: High Strain-Rate Behavior of Polycrystals High Velocity Deformation of Metals: High Strain-Rate Behavior of Single Crystals High Velocity Deformation of Metals: Effect of Metallurgical Factors upon High Strain-Rate Behavior High Velocity Deformation of Metals: Influence of Initial Temperature and Neutron Irradiation Dynamic Hardness Conclusions and Problems for Future Study
TL;DR: In this article, an elasto-viscoplastic analysis of anisotropic plates and shells is undertaken by means of the finite element displacement method and a thick shell formulation accounting for shear deformation is considered and a layered approach is adopted in order to model property changes through the shell thickness.
Abstract: An elasto‐viscoplastic analysis of anisotropic plates and shells is undertaken by means of the finite element displacement method. A thick shell formulation accounting for shear deformation is considered and a layered approach is adopted in order to model property changes through the shell thickness. In order to avoid ‘locking’ behaviour as the shell thickness is reduced, the nine‐node Lagrangian and heterosis elements are introduced into the present model. Viscoplastic yielding is based on the Huber—Mises criterion extended by Hill for anisotropic materials. Time integration of the strain rate equations is accomplished by both explicit and implicit algorithms and special consideration is given to the evaluation of the viscoplastic strain increment for anisotropic situations. The computer code developed is demonstrated by application to a range of numerical examples.
01 Dec 1985
TL;DR: In this paper, the state variable based viscoplastic constitutive model of Bodner and Partom was considered for material modeling and a unique iterative algorithm was developed to evaluate the model constants from both tensile SHB and plate impact test data.
Abstract: : High strain rate material behavior of 1020, C1008, HY100 steels, OFHC copper, 7039-T64 aluminum, and BeO was characterized. Data were obtained from split Hopkinson bar (SHB) and plate impact test configurations. A high speed photographic system was used to obtain dynamic stress-strain data from necking Hopkinson bar specimens. The state variable based viscoplastic constitutive model of Bodner and Partom was considered for the material modeling. Computer programs and special purpose subroutines were developed to use the Bodner-Partom model in the STEALTH finite difference code. A unique iterative algorithm was developed to evaluate the model constants from both tensile SHB and plate impact test data. The model constants were determined for the five metals. Both tension and compression SHB and plate impact tests were successfully simulated using Bodner-Partom model constants.
TL;DR: In this paper, the Fatigue behavior of a viscoplastic compact tension specimen is analyzed using the finite element method using a constant strain, triangular element computer program called VISCO to calculate the stress and strain fields ahead of the crack tip under cyclic loading at a load ratio of 0.1.
TL;DR: An elastic/viscoplastic constitutive equation for rock-like materials which is able to describe, besides creep, an irreversible compressibility and/or dilatancy of the volume is formulated in this article.
TL;DR: In this paper, a simple approximate method is introduced and compared with experimental results, which enables the estimation of the uniaxial creep behaviour of asphalt or asphalt-like materials under arbitrary alternating tension-compression loading histories with a comparatively small mathematical and experimental effort.
TL;DR: In this paper, the authors estimate the mechanical behavior of the material under multiaxial dynamic loading constitutive equations must be worked out, which have to be valid over wide ranges of strain rate and temperature.
Abstract: Under dynamic loading shock waves propagate in metallic materials and may be concentrated after reflection from fixed boundaries. In these cases high strain rate gradients are initiated in the material, which are accompanied by a change in temperature due to the adiabatic character of high rate deformation processes. In order to estimate the mechanical behaviour of the material under multiaxial dynamic loading constitutive equations must be worked out, which have to be valid over wide ranges of strain rate and temperature. Often a viscoplastic behaviour is assumed using the equation of Perzyna:
TL;DR: In this paper, an elastic-viscoplastic constitutive law is implemented in the formulations of a curved quadrilateral element based on thin shell theory, and the element surface is defined using variable-order polynomials allowing representation of a wide range of shell geometries.
Abstract: An elastic–viscoplastic constitutive law is implemented in the formulations of a curved quadrilateral element based on thin shell theory. The element surface is defined using variable-order polynomials allowing representation of a wide range of shell geometries. The large displacement effects are included by using an incremental stiffness procedure together with the Lagrangian mode of description of motion. The time rate effects may be treated by using explicit, semi-explicit or implicit time marching schemes. A scheme for automatic calculation of time step is used. By allowing steady-state conditions to be reached, plasticity solutions are obtained. Both perfect plasticity and strain hardening are considered. The Von Mises yield rule and the associated flow rule are used to determine plastic deformation. The spread of plasticity in the thickness direction is allowed by using a layered model. The procedures developed are applied to solve elastic-plastic, small and large displacement problems of thin plates and shells and the results obtained are compared with existing solutions to illustrate the validity and accuracy of the present developments.