Showing papers on "Pure shear published in 1974"

Instability and fracture in sheet metal

Abstract: The regime of sheet metal deformation extends from pure shear, 1= - 2, through plane strain, 2=0, to balanced biaxial tension, under which 1=2. During deformation a material passes into different states, termed (1) uniform straining, (2) diffuse straining, and (3) localized straining, respectively. Depending on the strain ratio, (1) alone, (1) & (2) & (3), (1) & (3) or (1) & (2) can be experienced by a sheet between zero strain and fracture. In this work the deformation behaviour, in tensile and hydraulic bulge testing, of steel, aluminium and 70-30 brass has been studied. The onset of state (3) has been correlated with strain measurements, taken from a cine film of the deformation, indicated by a grid electrochemically marked on the sheet surface. Various theories predict the major and minor strains at the initiation of these states, and the theoretical and experimental results are compared for the various materials; also the implications with respect to forming-limit diagrams are discussed.

The stress-strain curve of shear-banding polystyrene

Abstract: A zone of diffuse non-Hookean shear strain is shown by birefringence measurements to initiate before, and to propagate ahead of, shear bands in glassy polystyrene. A moire analysis of the displacements around the propagating shear band packet reveals that the shear band packet, although highly visible, contributes only a minor fraction of the total non-Hookean specimen strain while the diffuse shear zone contributes the major portion. The results also show conclusively that the polymer within the expanding shear zone undergoes strain softening. These facts allow one to properly interpret the existence of a load maximum in constant rate compression tests of polystyrene as due to the expansion and strain softening of the diffuse shear zone, rather than to propagation of the shear band packet or specimen buckling. The load maximum occurs when the shear zone has fully expanded across the specimen width.

Pressure dependence of the shear modulus of various polymers

Abstract: A torsion pendulum has been used to measure the shear modulus of a range of polymers as a function of applied hydrostatic pressure at 20° C. The pressure medium was usually nitrogen gas and the maximum pressure 20000 psi. The results show that the shear modulus of each polymer is increased by the application of pressure, and the magnitude of the increase is greatest for experiments carried out at temperatures just above an atmospheric relaxation temperature. The increase in shear modulus takes a finite time, of the order of minutes, to be achieved, the equilibrium value being reached in a shorter time at higher temperature.

Ultimate Static Strength of Plate Girders from Tests

Abstract: On the basis of 299 tests on plate girders, reported in the literature, some very simple formulas are given for the prediction of the ultimate static strength under pure shear, pure bending, and combined shear and bending, and of the web crippling load in case of very thin webs. The agreement between calculation and measurement is sufficient for average design purposes. All formulas can be evaluated using only a slide rule.

Constrained elastic recovery of a polymeric liquid after various shear flow histories

Abstract: The ultimate constrained elastic recovery of a polymeric liquid consisting of 2 gr. of polyisobutylene dissolved in 100 ml. of decalin was measured after two forms of shear flow history. The first consisted of a shear flow, of rateG, for a long time, after which the liquid was held stationary for a timeT1 before release. In the second the liquid, which had been stationary for a long time, was sheared for a timeT2 at a shear rateG and then released. The ultimate recovery in these experiments was measured as a function ofG, T1 andT2 and the results were compared with the predictions of two particular constitutive equations.

Deformation mechanisms of low density polyethylene with parallel lamellar morphology

Abstract: The mechanical anisotropy of low density polyethylene sheets possessing orthorhombic symmetry and parallel lamellae morphology has been studied by making measurements of the creep behavior in extension and shear at room temperature The behavior is interpreted in terms of two predominant deformation mechanisms taking place within and between the lamellae, ie, the c-shear process and interlamellar shear, respectively, the latter involving both simple and pure shear of the interlamellar regions Some of the creep compliances have unusually high time dependence and it is shown that this is related with intralamellar processes The determination of the three shear compliances involves the application of the St Venant relations for torsion of rectangular prisms This aspect has been thoroughly explored and is described in detail

Shear Strength and Polymer Friction

Abstract: The friction coefficient of thin polymer sheets under high loads can be accounted for by a simple extension of the adhesion theory of friction in which the pressure dependence of the shear strength of the polymer is taken into consideration. Recent measurements on polypropylene films, as well as earlier data on several other polymers, are used to illustrate these ideas.

Response of bulk polymer under motion with constant stretch histories

Abstract: In the investigation of non-Newtonian viscosity of polymeric materials both in solution and in melt, most experiments have been conducted under shearing flow, i. e., the velocity gradient of flow is perpendicular to the flow direction. One may consider other classes of flow, such as uniform flow, in that the velocity gradients of the flow are parallel to the flow direction. Uniform flow may include simple extensional flow, strip biaxial (pure shear) extensional flow and equal or nonequal biaxial extensional flow. It was reported by Ballman (1) that there is a large difference between viscosities in shear and simple extensional flow, thus it is pertinent to investigate the other kinds of uniform flow such as strip biaxial extensional flow.

Determination of the shear moduli of glass-reinforced plastics using ring specimens

Abstract: A description is given of a method of determining the interlaminar shear modulus and the shear modulus in the plane of the laminations of glass-reinforced plastics by testing part of a circular ring in torsion. The results of such tests are presented.

Waves on a shear flow

Abstract: The propogation of disturbance when a shear flow with a free surface, in a channel of infinite horizontal extent and finite depth, is disturbed by the application of time-oscillatory pressure, is studied. The initial value problem is solved by using transform techniques and the steady state solution is obtained therefrom in the limit t → ∞. The effect of the initial shear on the development of the wave system is investigated.

Solution of the problems of a perforated disk, a conical bar, and a flat wedge of nonlinear viscoelastic material in pure shear, torsion, and bending, respectively

Abstract: Exact solutions and approximations have been obtained for the problems of a disk with an opening twisted by opposite moments uniformly distributed over the inner and outer surfaces and of a conical bar twisted by a moment applied at the vertex of the cone. An approximate solution has been found for the problem of a flat wedge bent by pressure uniformly distributed along one of its sides. The disk is made of nonlinear viscoelastic material. In [1] it was proposed that problems for such a material be solved by the method of approximations. The rheological law of the nonlinear viscoelastic material of the cone and the wedge in Laplace—Carson transforms is the relation of the theory of small elastoplastic deformations with a power law of strain hardening.

The concept of shear stress in a solid material

Abstract: The author begins by looking at the difference between the supposed and the actual effects of the system of forces upon a rectangular block which are usually said to lead to a state of simple shear strain (the 'pack of cards' deformation). He then shows in an elementary way that the combination of compressive and tensile stresses, which lead to a state of pure shear strain by definition, imply a shear stress, as commonly understood. Finally, he shows that pure shear strain is implicit in the 'textbook' illustration of simple shear.

Periodic axial and shear deformation of polymers in the viscous-flow state

Abstract: Results are given of an experimental investigation of the combined periodic axial and shear deformation of polymers in the viscous-flow state. Specimens in the form of right cylinders were disposed between two parallel plates to which the material adhered completely. The experimental data are compared with those obtained under simple shear. The results indicate that, with combined periodic axial and shear deformation, nonlinear shear deformations affect the axial viscoelastic properties and nonlinear axial deformations affect the shear properties of the material.