Magnitude Of Stress Relaxation Research Articles

The Role of Clay in Limiting Frictional Healing in Fault Gouges

AbstractFrictional healing is fundamental to the seismic cycle and plays a role in the energy balance, dynamics, and recurrence interval of earthquakes and slow slip events. Although the healing behavior of quartz has been studied extensively, the role of clay content is less understood. We tested synthetic mixtures of quartz and smectite (10%–100% smectite) in a double‐direct shear configuration to measure frictional healing. We show that the magnitude and rate of healing decreases systematically with higher clay content (from 0.008/decade at 10% smectite to 0.002/decade at 100% smectite). Healing scales with both the magnitude of stress relaxation during holds and layer‐normal compaction of the gouge. We suggest this reflects the alignment of clay minerals, leading to saturation of the real area of contact that limits restrengthening during holds. The low healing rates of clay‐rich faults—together with rate‐neutral to rate‐strengthening friction—should promote frequent, small failures or stable sliding.

A micro-mechanism model of residual stress reduction by low frequency alternating magnetic field treatment

Low frequency alternating magnetic field treatment is a non-thermal method used to process welded samples with internal residual stress. The purpose of the paper is to investigate the quantitative correlation between magnetic treating parameters, magnitude of stress relaxation and the stress relaxation mechanism. The microstructure change of the material during magnetic treatment is also observed by TEM and discussed from the point of view of dislocation behavior in the processed material. The experimental results indicate that low frequency alternating magnetic field treatment is an effective method in reducing residual stress in steels. The main reason for the stress reduction is the even-distribution of dislocation due to magnetic treatment. A physical model of residual stress relaxation by magnetic treatment is raised based on the experimental results and microstructural observation that well explain the micro-mechanism of this method.

Micromechanism of residual stress reduction by low frequency alternating magnetic field treatment

Low frequency alternating magnetic field is used to process welded samples having internal residual stress. Magnetic treatment parameters and the magnitude of stress relaxation are investigated quantitatively. The microstructural change of the material during magnetic treatment is observed by TEM and discussed from the point of view of the dislocation behavior in the processed material. A physical model of residual stress relaxation produced by magnetic treatment is presented based on the experimental results and microstructural observation.

Stress relaxation in hematite nanoparticles-polystyrene composites

The viscoelastic behavior of a polystyrene matrix filled with hematite nanoparticles was investigated using the stress relaxation method. An increase in the elastic moduli of the composites, as well as in the magnitude of stress relaxation was found with increasing content of the inorganic phase. The obtained results are discussed in terms of a one-process model.

Involvement of the cytoskeleton in calcium-dependent stress relaxation of rat aortic smooth muscle.

Rat aortic smooth muscle exhibits a remarkable capacity for stress relaxation, the release of tension following tissue stretch. Stress relaxation was markedly enhanced in contracted aortic rings compared with unstimulated tissue. The magnitude of stress relaxation in contracted aortic rings correlated well with the passive tension imposed on the tissue by stretching, but showed little relationship to changes in tissue length or to the level of tension developed in response to agonist stimulation prior to stretch. The enhancement of stress relaxation in precontracted tissue was not affected by intimal rubbing or treatment with L-NAME. By comparison, the removal of extracellular calcium markedly attenuated stress relaxation. In addition, the use of cytochalasin B to block actin polymerization inhibited stress relaxation, whereas colchicine, a drug used to cause microtubule disassembly, had no effect on the phenomenon. The results indicate that the enhanced stress relaxation in contracted tissue is a calcium-dependent process and is not due to passive tissue elastic properties. We suggest that stress relaxation may not involve cross-bridge formation but could be explained by the remodelling of a portion of the tension-bearing actin cytoskeleton.

The Effect of Ultra-Low Temperature Treatments on the Stress in Aluminum Metallization on Silicon Wafers

ABSTRACTThe stresses in Al-0.75w%Si-0.5w%Cu unpatterned metallization on silicon wafers have been measured using substrate curvature and x-ray diffraction techniques after quenching in liquid nitrogen. Stresses were measured with and without phospho-silicate glass overlayers and SiO2 underlayers, and thermal cycling followed by relaxation at room temperature. It was found that cooling the substrates to 77 K and warming to room temperature caused the metallization stress to go from tensile to compressive. Subsequent heating of the substrates to above ∼70°C followed by cooling to room temperature caused the stress to become tensile. Both compressive and tensile stresses were found to relax at room temperature with a time constant of 2.3 ± 0.2 hours. The magnitude of stress relaxation was a function of temperature, being about 20 MPa after heating to 240°C. The metallization exhibited both compressive and tensile flow stresses of ∼100 MPa near room temperature.

Sealing characteristics of gland packing. 3rd report. Stress relaxation of packings and its modelling.

Tightening Pressure of gland packings decreases with an increasing time due to stress relaxation. From an engineering point of view, the prediction of stress relaxation of packings is very important, because the sealing characteristics are very much influenced by the tightening pressure. In this paper, the stress relaxation of asbestoid and graphitic packings after tightening has been experimentally investigated. The tightening pressure of packings decreases, rapidly just after tightening and gradually slows down with increasing time, and finally reaches an asymptotic value. The magni-tude of stress relaxation can be reduced very much by cyclic tightening. A visco-elastic model for the analysis of the stress relaxation has also been proposed. The numerical simulation by the model could well duplicate the experimental results of stress relaxation of packings.

Stress relaxation in hog carotid artery as related to contractile activity.

The purpose of this work was to test the hypothesis that stress relaxation (SR) in vascular smooth muscle is related to the amount of contractile activity (developed stress) and perhaps a property of the contractile element (CE). Using medial-intimal strips from the hog carotid artery, a strain (delta 1/l0, where l0 equals optimal length for force development) of 2% was applied at two different rates in the presence of various levels of developed or passive stress. Developed stress was altered either by changing the extracellular K-ion concentration with the strip length equal to l0 or by stimulating with a salt solution containing 30 mM KCl at various strip lengths. Passive stress was altered by varying strip length. At each level of developed or passive stress the magnitude of the increment in stress due to the strain (induced stress) and the SR were noted. SR varied directly with the magnitude of the developed stress, but there was a small and relatively unchanging amount of SR when passive stress was varied. At a given level of developed stress, the magnitude of SR was greater at a strain rate of 0.016 than at 0.001 l0/sec. When developed stress was altered, the magnitude of SR was essentially equal to the amount of induced stress; however, when passive stress was varied, SR was always less than induced stress. These observations are consistent with the hypothesis that, in the presence of developed stress, a large fraction of the SR represents the lengthening of the CE. This increased CE length allows a reequilibration of stress between the series elastic element and the contractile element. In the absence of developed stress, SR may represent a passive, physical property of this heterogeneous tissue.