Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Dynamics of viscoelastic flow in ion tracks: origin of plastic deformation of amorphous materials

Abstract: In the present paper, track formation and plastic deformation (creep and anisotropic growth) of amorphous solids under heavy ion bombardment are discussed in terms of viscoelastic shear stress relaxation in thermal spike regions and the subsequent freezing-in of the associated strain increments. The resulting strained tracks are considered to represent the (symmetry-breaking) mesoscopic defects responsible for anisotropic macroscopic deformation. Recent theoretical approaches to the problem are critically reviewed. A system of viscoelastic continuum equations is proposed which includes the recently used “effective flow temperature approach” as a limiting case. General solutions of this system are presented and discussed. These solutions, completed by a model for the ion beam induced reduction of the viscosity, appears to be suited to fully describe the deformation characteristics of amorphous materials including the threshold behaviour with respect to electronic stopping power and ion fluence (“incubation dose”) as well as the target temperature dependence. An evaluation of appropriate experimental studies on the basis of the presented theory is expected to provide valuable information on the (ion beam reduced) viscosity of amorphous materials around ambient and thermal spike temperatures.

Stress relaxation of passivated aluminum line metallizations on silicon substrates

Abstract: In the present study, the Eshelby theory of inclusions is applied to model the stresses arising after heat treatment at 400 °C in aluminum line metallizations, embedded in silicon/passivation matrix. The stresses obtained are about 200 MPa higher than the ones previously reported. Moreover, the stresses in the axial and width directions of the lines are shown to be on the same order, while the normal stress is smaller, especially in the lines of low thickness‐to‐width ratio. A modification of the familiar sin2 ψ method of x‐ray stress measurement is presented to deal more accurately with the [111]‐fiber texture present in the aluminum lines studied. The lateral and normal stresses in the aluminum metallizations after a heat treatment at 400 °C are measured in room temperature by x‐ray diffraction from 4 h after the heat treatment at 400 °C up to 3 months. The experimental results are well in accord with predictions obtained from the Eshelby model. Particularly, the lateral stresses are found to be about equal, while the initial normal stress is smaller, but eventually becomes the largest stress component. Dislocation mechanisms to rationalize the present observations are discussed: at longer times, diffusion‐controlled dislocation climb and void growth connected to it appear to be the most important mechanisms to relieve the stress, while during cooling dislocation glide is also significant.

Short term flexural creep behavior of wood‐fiber/polypropylene composites

Abstract: Short term flexural creep tests were conducted to investigate the creep behavior of wood-fiber polypropylene composites. Three experimental parameters were selected : the addition of a wetting agent, temperature, and wood-fiber concentration. All creep curves are presented in terms of relative creep as a percentage of instantaneous (initial) strain. The creep power law model was used to accurately fit the creep data. The addition of a wetting agent greatly reduced the creep at high stress, but had little effect at a lower stress level. The extent of relative creep increased with increasing temperature. It was found that the slope of the power law model was directly proportional to the temperature. The addition of wood-fibers into pure polymer greatly improved the creep resistance of the matrix polymer. The relative creep of the composites decreased with an increase in wood-fiber concentration. However, the composite showed relatively large creep compared with that of solid wood. It was found that both the time exponent and slope of the power law model were inversely related to wood-fiber concentration. The flexural modulus of the composites also had an inverse relationship with the time exponent.

Relaxation processes in vulcanized rubber. I. Relation among stress relaxation, creep, recovery, and hysteresis

Abstract: An experimental study is described of stress relaxation, creep, recovery, and hysteresis in vulcanized rubbers under moderate deformations. The measurements indicate that the rate of stress relaxation is substantially independent of the amount or type of deformation for moderate deformations, and is simply related to the hysteresis. The rates of creep and recovery are found to be in good agreement with values calculated from the form of the load—deformation relationship and the (constant) value of the relaxation rate.

Dynamic Yield Behavior of Explosively Loaded Metals Determined by a Quartz Transducer Technique

Abstract: Explosively generated plane waves were passed through plates of duraluminum, iron, and steels of various compositions and heat treatments. X-cut quartz disks of large diameter-to-thickness ratios (≥5) were used to obtain continuous stress-time profiles of elastic-plastic wave structures associated with yielding. For times less than wave transit time through the disk, the short-circuit current output is directly proportional to the specimen-to-quartz interface stress up to 21 kbar. The incident wave profile in the specimen is then determined from the interface stress-time profile on the basis of an assumed model. Advantages of the technique are excellent time resolution, high sensitivity, and relative simplicity of use. The profiles for duraluminum, normalized SAE 1018 steel, and normalized Armco iron exhibit a relatively slow rise to the yield stress, subsequent stress relaxation, except in duraluminum, and then a gradual rising transition into the plastic wave. In comparison, SAE 4340 and other tool stee...