Proportional Loading Tests Research Articles

Temperature‐dependent mechanical properties and constitutive equation of cellulose nitrate

AbstractThe strain‐time response under tensile loading (creep tests) and the stress strain response under constant tensile stress rate (proportional loading tests) have been evaluated at 4 temperatures 20, 45, 55, and 65°C, for samples of cellulose nitrate. A time‐dependent constitutive equation (or stress‐strain relation) for the nonlinear visco‐elastic material is deduced from invariant theory with a hypothesis of a creep potential. The procedure for determining the seven material constants involved in the deduced constitutive equation is described for the creep and proportional loading tests and the variation of these constants with temperature is presented. The deduced constitutive equation gives good agreement with the actual observations for the creep and proportional loading tests, independent of the values of temperature, creep stress, or stress rate.

Continuum mechanics studies of plastic instabilities

The continuum mechanics framevork for analyzing necking and shear band instabilities is discussed. The predicted onset of instability depends sensitively on the material’s constitutive characterization, not only through properties, such as strain hardening and strain rate sensitivity, that can be measured in proportional loading tests, but also through the material’s response to a change in loading path. A specific problem is discussed that illustrates the influence of the curvature of flow potential surfaces even when a softening mechanism plays a major role in precipitating localization.

プラスチックねじの強度に関する研究 組合せ荷重下におけるプラスチックねじの挙動

This paper deals with the experimental consideration on a method to estimate the strength of plastics screws under the combined load of tension and torsion. First, a testing machine is designed so that the three different tests (i.e. tensile, tightening and proportional loading tests) can be carried out for this purpose. Second, it is proposed that the equivalent stress-equivalent plastic strain curve obtained from combined loading should be compared with the stress-strain curve in the uniaxial tension to clarify the strength under such the combined load corresponding to the proof stress under the uniaxial tension. Third, the strength ofthe screws made of polycarbonate (PC) is considered by use of the testing machine. The results obtained are as follows. (1) The equivalent stressequivalent plastic strain curves of the screws under the combined load agree approximately with the stress-strain curve of cylindrical test piece under uniaxial tension. (2) The tendencies of the stress under the combined load corresponding to the proof stress of PC screw gives fairly good agreement with the failure curve based on Maximum Distorsion Energy Theory. (3) The strength of PC screws in tightening can be predicted from the proof stress of cylindrical test piece under uniaxial tension since the shearing stress can be assumed approximately to be distributed linearly in the radial direction within the range of actual tightening.

Deformation of Yield Surface by means of Proportional Loading Tests

Deformation of Yield Surface by means of Proportional Loading Tests

Mechanical Property of Celluloid under Proportional Loading

In order to investigate the effects of loading history and variation of temperature on the deformation behavior of softened celluloid by heating, the proportional loading tests were made at a constant temperature on specimens made of a celluloid plate and a thin walled cylindrical celluloid tube for various periods of heating time. The effect of heating time on the mechanical property of the material was examined, and the Poisson's ratio and the stress-strain relations under tensile and torsional loadings were discussed. The conclusions obtained are summarized as follows:(1) The mechanical property of celluloid is not affected by heating time.(2) The residual stress appearing in the thin walled cylindrical tube specimen is small and an isotropy in a plane is maintained.(3) The Poisson's ratio is 0.47 and the incompressible condition is satisfied still for the inelastic deformation within the range of 6 percent error.(4) The deformation resistance of torsional loading is larger than that of tensile loading. This may be attributed to the effect of a first invariant of stress tensor.

On Proportional Combined Loading Tests of an Aluminum Alloy and Its Analytical Formulation

Proportional combined loading tests using axial load and torque were conducted on thin-walled tubular specimens of annealed isotropic aluminum alloy 5056. The experimental results showed that the third invariant of stress deviator affects considerably the plastic deformation of the material; that is, an equivalent stress-equivalent strain curve for simple tension or compression appears higher than that for pure torsion and the plastic strain vector is generally noncoaxial with the deviatoric stress vector. These results were formulated in the form of a nonlinear tensor relation between stress deviator and plastic strain on the basis of the general relation between coaxial tensors. The tensor equation derived was found to represent well the experimental results.