Showing papers on "Viscoplasticity published in 1973"
01 Jan 1973
TL;DR: In this article, the authors deal with the application of thermodynamics to materials which exhibit plastic deformations (either purely plastic or viscoplastic), focusing on the definition of the thermodynamic state and on the expression of the second law.
Abstract: This study deals with the application of thermodynamics to materials which, besides viscoelastic deformations, exhibit plastic deformations (either purely plastic or viscoplastic). Attention is focussed on the definition of the thermodynamic state and on the expression of the second law. Three different formulations are presented
(1)
With hidden variables and using an intermediate, released, configuration.
(2)
With hidden variables and using a fixed reference configuration.
(3)
In functional representation.
Finally an hypothesis about the dissipativity is investigated.
172 citations
TL;DR: An alternative to the currently used Perzyna's theory of viscoplasticity for small strains is presented in this paper, where the plastic strain rate vector is normal to the quasistatic yield surface which in turn may not include the origin.
60 citations
TL;DR: Based on the observation that plastic behavior is a macroscopic manifestation of the motion and interaction of dislocations, a plasticity theory is proposed that represents a connecting link between solid state physics and the conventional plasticity and viscoplasticity theories.
20 citations
TL;DR: In this article, the velocity and stress fields behind the shock wave front were investigated by a ray method in a three-dimensional elastic viscoplastic medium with hardening, and an analytical solution was obtained for the velocity to second order accuracy in the distance along the normal from the wave front.
8 citations
01 Feb 1973
TL;DR: In this paper, a new analytical approach was developed for establishing the local stress state and temperature (including regions near the surface) in axisymmetric extrusions, and a numerical method (finite differences) for solving the plasticity equations and thereby predicting the flow lines has been developed.
Abstract: : A new analytical approach was developed for establishing the local stress state and temperature (including regions near the surface) in axisymmetric extrusions. Also a numerical method (finite differences) for solving the plasticity equations and thereby predicting the flow lines has been developed. The plastic deformation kinetics derived from hot extrusion tests on Ti-50A and Ti-5Al-2.5 Sn are in good accord with those for the high temperature deformation of these materials in simple tension or compression and it was deduced that the rate-controlling mechanism is glide and climb in Ti-50A and viscous glide in Ti-5Al-2.5 Sn. Further, the change from the single maximum type of visioplasticity pattern to the double maximum type appears to be governed mainly by the plastic flow behavior of the material. Friction studies employing the ring forging test indicate that for effective lubrication during the hot working of titanium alloys the ratio of viscosity eta of a glass lubricant to the flow stress sigma should be in the range 0.0001 < eta/sigma < 0.01 (poise/dyne/sq cm) at interface velocities of 0.5 - 1.0 in./min. (Modified author abstract)
7 citations
TL;DR: In this article, the authors considered the dynamic buckling of thin viscoplastic cylindrical shells and derived the stability effect of the viscous properties of the material on the buckling process.
Abstract: The dynamic buckling of thin viscoplastic cylindrical shells is considered in the formulation developed by Abrahamson and Goodier [1]. The constitutive equations employed describe the rate sensitive plastic material and a biaxial state of stress is considered. The influence of the viscosity parameter on the buckling process is discussed in detail and in the limiting case the solution for a perfectly plastic material is obtained. From the analysis of the final deflections as a function of the applied impulse the “stability effect” of the viscous properties of the material on the buckling process is determined.
7 citations
01 Sep 1973
TL;DR: In this article, a method of analyzing nonlinear static and dynamic responses of deformable solids has been developed based on an incremental variational formulation using the Lagrangian mode of description.
Abstract: : A method of analyzing nonlinear static and dynamic responses of deformable solids has been developed based on an incremental variational formulation using the Lagrangian mode of description. The material nonlinearity due to plasticity or viscoplasticity as well as the geometric nonlinearity due to large displacements are considered. The equations of motion are obtained in a linearized incremental form using the principle of virtual work and solved using step-by-step numerical integration procedures. Equilibrium check is made at the end of each step and the residual forces are added to the next increment for improved accuracy over the pure incremental method. For elastic-plastic solutions the flow theory of plasticity is used along with the von Mises yield condition for isotropically hardening materials. The viscoplastic constitutive theory is also in the form of an associated flow law and capable of considering strain rate sensitive behavior. The viscoplastic strains are taken into account using an initial strain formulation. The discretization of the structure is achieved by the use of degenerate isoparametric finite elements and the computer codes that have been developed are capable of analyzing large axisymmetric deformations of shells of revolution. (Modified author abstract)
7 citations
TL;DR: In this paper, the authors derived stress-rate and strain-rate variational principles for a viscoplastic material characterized by additive elastic and inelastic strain rates, where elastic, viscous and plastic properties are assumed to be temperature dependent but all coupling effects are neglected.
6 citations
TL;DR: In this article, a finite-difference representation of the equations of motion of a continuous medium in Lagrange coordinates and the differential equations governing the behavior of the medium were proposed.
Abstract: Models of elastoplastic media are applied to soils and rocks [1, 2]. In conformity with experimental data [3–5] a model of soils and rocks as a viscoplastic medium has been proposed [6]. Below we give a solution, based on this model, of the problem on the propagation of a plane one-dimensional wave. As the basis of computer programs we propose a finite-difference representation of the equations of motion of a continuous medium in Lagrange coordinates and the differential equations governing the behavior of the medium. A “direct calculation” procedure with pseudoviscosity is applied. It is shown that the damping of plane waves is connected with two energy-dissipating mechanisms, determined by the viscous and plastic properties of the medium. The washing out of a discontinuity can occur in the absence of a segment of the dynamical compression curve that is concave to the strain axis. Under certain conditions the maximum strain is attained during the phase of decreasing stress. These results agree with the experimental data [3].
6 citations
TL;DR: In this paper, an analytical expression for the upper yield stress is developed which is an upper bound to the actual upper-yield stress in a material, and the implications of the inclusion of an upper limit to the dislocation velocity are explored with reference to the phenomenon of upper yield point and subsequent yield drop.
3 citations
TL;DR: In this paper, the influence of strain-hardening and viscosity on the cylindrical elastic/viscoplastic wave propagation was discussed and it was shown by computer analysis that work hardening and viscosity affect the results considerably and that at a certain time after the impact load is applied an elastic region appears within the viscoplastically deforming medium.
Abstract: This paper discusses the influence of strain-hardening and of viscosity on the cylindrical elastic/viscoplastic wave-propagation. Perzyna's model is used with linear viscosity dependence, bilinear quasi-static stressstrain curve and a radial stress is assumed to be suddenly applied on the surface of a cylindrical cavity and maintained constant. It is shown by computer analysis that work-hardening and viscosity affect the results considerably and that at a certain time after the impact load is applied an elastic region appears within the viscoplastically deforming medium.
TL;DR: In this paper, the problem of a thin circular plate under uniformly distributed transverse pressure is solved by means of a theory of viscoplasticity, in which the dynamic yield surface is defined as the surface which encloses the quasistatic yield surface.
Abstract: In a previous paper a theory of viscoplasticity was developed in which the dynamic yield surface is defined as the surface which encloses the quasistatic yield surface and has a constant distance from it. In the present paper, by means of the above theory, the problem of a thin circular plate under uniformly distributed transverse pressure is solved. The material of the plate is assumed to be rigidviscoplastic. The solution is compared with previous solutions of the same problem.