Effect Of Temperature Cycling Research Articles

Sound Propagation in Near-Stoichiometric Ti-Ni Alloys

Experimental data on sound velocity illustrate the unusual velocity-temperature relationship of near-stoichiometric nickel-titanium alloys. The effect of temperature cycling, annealing, pressure, minimum exposure temperature, and time is also shown.

Paper 39: Exploratory Tests on the Effects of Temperature and Load Cycling on the Creep Resistance and Micro-Structure of Two Austenitic Steels

Paper 39: Exploratory Tests on the Effects of Temperature and Load Cycling on the Creep Resistance and Micro-Structure of Two Austenitic Steels

Paper 16: Effect of Thermal Cycling on Pre-Stressed Steam Pipelines

Investigations into the effect of temperature and pressure cycling on a pre-loaded model main steam line of 0·5% Cr-0·5% Mo-0·25% V steel have shown that a relatively large increase in length occurred over a few cycles at 100 per cent cold pull, and a decrease in length occurred at 50 per cent cold pull. Using high temperature platinum-tungsten strain gauges, it has been found that large changes in strain occur round an expansion loop in the model pipeline. It is suggested that large changes in the design stress distribution in a main steam line occur during the commissioning stages of a generating unit, making creep behaviour of the line during base loading difficult to predict. It is further suggested that failure in pipelines when a unit is working under a twoshift system is due to low cycle fatigue, as the strain changes occurring do not appear to approach an equilibrium minimum under cycling conditions. It would appear that strain changes, and hence the effect of low cycle fatigue, can be minimized by choosing a level of cold pull between 50 and 100 per cent, the actual level depending upon the physical characteristics of the pipe material, the more important ones being thermal expansion and the change of yield stress with temperature. Using the plastic strain range measured in the test a prediction can be made regarding the time to failure.

Incremental collapse in α-uranium subjected to thermal cycles while undergoing creep

Experiments are reported which were carried out in order to study the effects of temperature cycling upon α-uranium polycrystals undergoing steady-state creep. The results of these experiments are discussed in terms of the internal stresses generated by anisotropic expansion of individual crystals in the aggregate; a theory which was developed earlier is extended to cover the case of large temperature cycles when the physical properties of uranium polycrystals vary during the cycle. An analogy between this theory and Parkes' theory of thermally-induced stresses in redundant engineering structures is pointed out, and it is shown that deformations caused by thermal transients may comprehensively be understood in terms of elastic cycling, shakedown and incremental collapse.

Recovery of cold-worked aluminium at low temperatures

The attenuation of high-frequency sound was measured in single crystals of superpure and zone refined aluminum to study the nature of point defects. Separate attenuation curves were obtained for the temperature range 4.2 to 90 deg K for specimens subjected to a cooling rate effect, cold work effect, and temperature cycling effect. A sharp rise in the attenuation at 50 deg K is associated with a decrease in the number of point defects, and the formation of the defects is attributed to plastic deformation at low temperntures. (H.D.R.)

Effects of ultrahigh temperature on magnetic properties of core materials

An experimental study has been made of the effects of temperature on the magnetic properties of the following ferromagnetic alloys: Orthonol, 4-79 Mo Permalloy, AEM 4750, L and Z Silectron, Transformer A, Audio Transformer A, 11.7 Alfenol, 15.5 Alfenol, 3 Mo Thermenol, 7-70 Perminvar, and Supermendur. Measurements were made of the d-c and 60 cps (cycles per second) magnetic properties in the temperature range of 24r-800 C (degrees centigrade). The materials were also evaluated after several temperature cycles between 24-500 C. The results indicate that, in general, high temperature decreased the maximum induction and the residual induction from their 24 C values. For all materials tested, with the exception of Supermendur and 11.7 Alfenol, the coercive force decreased with increase in temperature. The maximum permeability increased with increasing temperature until the Curie temperature was approached, then it started to decrease. The initial permeability also increased with increasing temperature, but unlike the maximum permeability, it generally started to decrease at a greater rate and at a lower temperature. Grain-oriented materials were more affected by temperature cycling than were unoriented materials. The effects of temperature cycling on the magnetic properties generally appeared as an increase in the coercive force, a decrease in the maximum permeability, a decrease in the residual flux density, and a decrease in the squareness ratio.

The Structure of the F Region of the Ionosphere

The effects of temperature cycles, of a decay coefficient non-uniform with height, and of vertical tidal drifts upon the structure of the F region of the ionosphere are considered. Special attention is devoted to the behaviour of the level at which the maximum electron density occurs.