Torsional Creep Tests Research Articles

Screening Test for Torsional Creep Performance of Plastics

Abstract The objective of this project was to determine the usefulness and limitations of a modified indentation hardness test in determining the creep resistance of plastics. Tests were run on 13 different materials and correlations were made between the modified hardness test and torsional creep tests at a 1000-psi (6895-kPa) stress level up to 500 h. The modified hardness test may be used as a screening test for creep performance as it allows determination of expected creep performance at a very early stage of material evaluation, where there are usually limited amounts of material available. Equations were developed to allow the prediction of creep performance. The correlations developed are not applicable to anisotropic materials.

Nonlinear creep of a glass fabric-reinforced plastic in several complex states of stress

Tensile, compressive, torsional, and combined creep tests have been performed on tubular specimens of a glass fabric-reinforced plastic. The sign of the normal stress has been found to have an important influence on the development of the shear creep strains. The rheological parameters of the material necessary for approximating the test curves have been determined and the results of the calculations compared with experiment.

A Comparison of Creep Theories for Multiaxial Loading of Polyethylene

Several creep theories are investigated for multiaxial loading of high-density polyethylene, a slightly cross-linked polymer demonstrating a nonlinear stress-strain-time relationship. Among the theories considered are nonlinear viscoelastic models, isochronous stress-strain diagrams employing a hyperbolic sine relationship, and multiple integral representations. The material parameters for these theories were determined from simple tension, compression, torsion and biaxial creep tests using single step loading. These theories were then analyzed for multiple step pressure-tension loading of a thin walled cylinder, in which the internal pressure and the axial load were varied independently of each other to check the effect of stress history on theory accuracy.

A Linear Compressibility Assumption for the Multiple Integral Representation of Nonlinear Creep of Polyurethane

The assumption that volume changes associated with creep of a nonlinear viscoelastic material are only linearly dependent on the stress history is incorporated into a third-order multiple integral representation. This assumption reduces the number of independent kernel functions in the representation from 12 to 7. The traces of these independent kernels may be determined from two tension, two torsion, and one combined tension and torsion creep tests. Experiments on polyurethane are well represented by this method. The time-dependence of the kernel functions is expressed by time raised to a power with the power differing for different-order kernel functions.

Relationship between the Torsion or Bending Creep Strength and the Tension Creep Strength of 13%Cr Steel

In order to find the correlation of the torsion or bending creep strength with the tensile creep strength for hardened and tempered 13%Cr steel, creep tests in tension, torsion and pure bending have been made at temperatures 400°C and 500°C. And then, these experimental results were compared with the analytical results by calculation based on von Mises or Tresca criterion. The tensile creep tests were conducted on 8mmφ cylindrical specimens, the torsion creep tests on 10mmφ/8.5mmφ thin-walled and 8mmφ solid cylindrical specimens, and the bending creep tests with 6mmt×10mm plate specimens. The apparatus employed in the torsion or bending creep tests were made in our laboratory. The creep test continued altogether for 400 hours. The results obtained can be summarized as follows:(1) The ratio of the shear creep strength to the tensile creep strength of 13%Cr steel corresponding to a mean creep rate of 0.2 or 1.0 per cent per 1000 hours for 300 to 400 hours is respectively 0.48 for 400°C, and 0.43, 0.46 for 500°C. On the other hand, the ratio derieved from the calculations due to von Mises or Tresca criterion is respectively 0.48 and 0.43 for 400°C, and 0.51, 0.45 for 500°C.(2) The ratio of the torsion creep strength of solid cylindrical specimen to the tensile creep strength for same creep rates is respectively 0.68, 0.70 for 400°C and for 500°C, 0.49, 0.50.(3) The ratio of the bending creep strength to the tensile creep strength for same creep rates is respectively 1.37, 1.55 for 400°C, and 1.47, 1.35 for 500°C, while the ratios obtained by calculation are 1.29 for 400°C and 1.34 for 500°C.

Rheololgical Properties of Asphalt Manufactured from Petroleum Oils of Different Origins

Torsional creep test and volume dilatometry are carried out for five kinds of straight asphalt manufactured from petroleum oils of different origins. The equilibrium elastic compliance varies from sample to sample and increases very rapidly with increasing number average molecular weight. This is reasonable because the equilibrium compliance Je(∞) is proportional to a higher order average of the molecular weight distribution. This average and hence Je(∞) are almost unchanged through blowing process and depend mostly on chemical compositions of the mineral oil from which the asphalt has been separated.

Complex Stress Creep Fracture of an Aluminium Alloy

The purpose of the investigation was to examine the tertiary creep and the creep fracture characteristics of an aluminium alloy to specification B.S.2L42, subject to complex stressing at 200 dog. C. The scope of the work involved seven pure torsion, pure tension, and combined tension and torsion creep tests, of durations between 300 hrs. and 3,000 hrs., on the aluminium alloy at 200 deg. C., and analysis of the results.

軟鋼の変動荷重における捩りクリープ試験

Torsional creep tests of a mild steel were carried out under varying stress levels at 500°C by using thin walled tubular test pieces. In the present test conditions under constant stress, buckling occurs within the range of primary creep, where the relation between strain γ and time t is expressed by Andrade's equation, γ=γ0+βtn, like as in tensile creep tests. For varying stress tests, stress level is varied to the lower stress of τu=-12.8, -6.4, 0kg/mm2 and is maintained for 60min after the upper stress τ0=12.8kg/mm2 for 60min, and the cycle is repeated. The instantaneous strain, creep rate, and total creep are greater when the previous stresses are higher in the reverse direction. Accordingly, the creep resistance is increasing with test time, and yet the increase is smaller when the stress returns to the constant τ0 from higher τu. The instantaneous recovery of strain in releasing of stresses is constant if the stresses were in the same height, and is not varied by the number of cycles. The rate of recovery strain under τu=0, i.e. during the rest of load, is in linear relation with time when the both are shown by logarithmic coordinate, and is not affected by the number of cycles.

引張り予歪をうけた耐熱鋼の捩りクリープ特性について

The authors had reported the transition phenomenon of the increasing creep rate with the augment of prestrain, in the torsional creep test of previously twisted mild steel. In this report, we investigated the same phenomenon in the torsional creep test to HCM steel previously tensioned.From. Figs. 6-8, We know that, on increasing the prestrain of the steel, creep rate increases abruptly, after the prestrain exceeds the ultimate-point, to about two times of creep rate before that point and appears to remain constant approximately before and after this transition zone.Fig. 9 shows the relation between strain rate γ (as to γ1 and γ2, see Fig. 6-8) and the value of stress τ ; on the while, Fig. 10 shows the experimental results concerning the following relation, { γ=KPnP=γ⋅e- /RT, where K and n are the constants, T is the absolute temperature, Q is the activation energy and R is the gas constant. From these relations, we know that the ratio γ2/γ1 is constant (about1/2) independently of the value of shear stress.

捩り予歪軟鋼材の捩りクリープ特性について

In order to investigate the effect of prestrain, especially large amount of prestrain on the creep phenomena the authors performed the torsional creep test, in the direction of working, of the small round solid bar of mild steel previously twisted at room temperature.1. The transition phenomenon in the creep rate (measured after one hour) vs. prestrain relation was observed, and the creep rate of material above the transition prestrain range is about 2 times larger than below the range (see Figs. 4-6).2. The ratio of two creep rates above and below the transition range is approximately constant independent of stress and temperature. And on these creep rates the general equationr= KPn, P=τ⋅e-Q/RTwhere K and n are the constants, γ is the creep rate, τ is the shear stress, T is the absolute temperature, Q is the activation energy and R is the gas constant, is satisfied in this experiment.3. It was found that both the decreasing point of the strain hardening rate in a torsional test and the ultimate point in a tensile test correspond to the begining point of the transition.

Rheology of metals at elevated temperatures

An account is given of the outline and progress of an examination of the general stress, time, and temperature dependence of the creep, plastic strain, and relaxation properties of several metals and metallic alloys, which, while being typical practical engineering materials, are different in their basic structures. The temperature range examined for each of these materials has been in each case chosen as the practical temperature range of use at elevated temperatures in actual engineering practice. The work involves simple tensile, torsion, and combined stress creep tests, and similar varieties of short period plastic strain tests and relaxation tests. The results, so far obtained in the work, and the inferences drawn from them, are discussed in relation to such appropriate theory as has currently been advanced, and in several cases it has been possible to suggest relations modifying or replacing those implicit in such theory.