Showing papers on "Viscoplasticity published in 1977"

Theory of spall damage accumulation in ductile metals

Abstract: S pall damage is a type of fracture produced when large tensile stresses are developed in material bodies as a result of the interaction of stress waves. The damage develops independently at various points in the body because of the short duration of stress application, but interacts in a complicated way with the stress wave. A theory of these phenomena is presented for the case where the basic response of the material is viscoplastic, and where the damage takes the form of a distribution of small rounded voids. This theory is specialized to the case of rectilinear motion and an example problem solved numerically.

The time dependence of friction of rock joints

Abstract: For the determination of the time dependent friction behaviour on rock joints laboratory tests (in principle direct shear test) are conducted. “Opalinuston” as a weak rock was used as test material. The tests are carried out under controlled strain conditions at different shear rates. The results show that the friction resistance depends on shear rate and relative movements. For constant relative movements and a constant normal stress a logarithmic relation between friction resistance and shear rate results. By determining the dependence of the viscoplastic friction on relative movement a creep curve can be deduced describing the friction behaviour of a joint in the examined time range.

Relationship between anelastic and nonlinear viscoplastic behavior of 316 stainless steel at low homologous temperature

Abstract: At low homologous temperature the plastic strain rate seems to be controlled largely by dislocation glide friction. However, since a sizeable fraction of the applied stress σ is dissipated in overcoming the strong barriers due to dislocation tangles generated by strain hardening, only a portion of the applied stress is actually expended against the frictional resistance. A recent model for this process, proposed by Hart, includes the role of dislocation pile-ups at the strong barriers. The pile-ups provide a mechanism for producing the internal back stress that reflects the barrier penetration stress. They also appear in the deformation as a stored anelastic strain component. The resultant behavior at low temperature and high stress is similar to that proposed by Gupta and Li. The same model also predicts an anelastic behavior at low stress. Measurements at both high and low stress levels on 316 Stainless Steel have now shown that the predictions of the model are quantitatively consistent at both stress levels.

Linearly viscoplastic material

Abstract: Viscoplastic material models which are based upon dislocation dynamics are so complex mathematically that they seldom yield closed‐form solutions to boundary value problems. Here we examine a material having a linear dependence of dislocation speed on stress. The boundary value problem corresponding to a constant crosshead speed tension test of this material remains highly nonlinear. However, an analytic solution to the problem is found in terms of tabulated functions and this solution is used to demonstrate some of the features of the response of the material during tension testing.

An ideally viscoplastic analysis of shock profiles

Abstract: In previous work the authors have shown examples of the concept of ideal viscoplasticity applied to the analysis of rate sensitive material response. The aim of these idealizations has been to generate reasonably simple solutions that exhibit the essential features found experimentally. In this paper a closed form solution is developed for the problem of a shock wave propagating without change of shape. A very simple approximate expression is found that is in excellent agreement with the exact solution, and simple approximations are obtained for the largest strain rate and the shock thickness. The solution implies that dislocation behavior rather than non-linearity in the material pressure, volume relation is primarily responsible for the decrease of shock thickness with impact intensity.

Photoplastic slope deformation models.

Abstract: Block-type slope deformation models were investigated using viscous and viscoplastic optically sensitive materials loaded by body weight beyond yield and strength limits.

Nonisothermal structural regime of motion of a nonlinear viscoplastic medium in a plane channel

Abstract: The motions of Newtonian and non-Newtonian media with consideration of the heat of friction and temperature dependence of the rheological characteristics of the medium have been examined by many authors [1–6]. A detailed bibliography of these works is given in [3, 5], In the dissertation of one of the authors* an attempt was made to investigate heat transfer during movement of a nonlinear viscoplastic medium with consideration of the temperature dependence of plastic viscosity at a constant value of the ultimate shear stress to. The last assumption is not always justified, since more often cases are found when not only plastic viscosity but also the ultimate shear stress changes with change in temperature. In this article we will examine the effect of the heat of internal friction with consideration of the temperature dependence of plastic viscosity and ultimate shear stress on the hydraulic characteristics of a laminar regime of motion in a plane channel of nonlinear viscoplastic media whose rheological behavior is described by the generalized Casson equation [5]. The upper and lower estimates are found for nonlinear differential equations describing the indicated processes.

Birefringence of non-linear viscoelastic-plastic polymers

Abstract: The observation of photoelastic-plastic states of stress is well known as one of the valuable methods of experimental stress analysis in an infinitesimal elastic-plastic deformation. Photorheology is a comparatively new method for the measurement of non-steady inelastic deformation. Several investigations have been reported of birefringent properties in the elastic-plastic or in the viscoelastic-plastic region. In these, however, the birefringence relations are regarded as empirical or semi-empirical. A birefringence relation for a non-linear viscoelastic-plastic polymer is deduced mathematically from the view-point of continuum mechanics. The birefringent effect is the product of the principal strain difference and a scalar function of the invariants of the elastic and the viscoplastic strains.