Stress relaxation

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

Sorbitan tristearate layers at the air/water interface studied by shear and dilatational interfacial rheology.

Abstract: The shear and dilatational rheology of condensed interfacial layers of the water-insoluble surfactant sorbitan tristearate at the air/water interface is investigated. A new interfacial shear rheometer allows measurements in both stress- and strain-controlled modes, providing comprehensive interfacial rheological information such as the interfacial dynamic shear moduli, the creep response to a stress pulse, the stress relaxation response to a strain step, or steady shear curves. Our experiments show that the interfacial films are both viscoelastic and brittle in nature and subject to fracture at small deformations, as was supported by in-situ Brewster angle microscopy performed during the rheological experiments. Although any large-deformation test is destructive to the sample, it is still possible to study the linear viscoelastic regime if the deformations involved are controlled carefully. Complementary results for the dilatational rheology in area step compression/expansion experiments are reported. The dilatational behavior is predominantly elastic throughout the frequency spectrum measured, whereas the layers exhibit generalized Maxwell behavior in shear mode within a deformation frequency regime as narrow as two decades, indicating the presence of additional relaxation mechanisms in shear as opposed to expansion/compression. If the transient rheological response from stress relaxation experiments is considered, then the data can be described well with a stretched exponential model both in the shear and dilatational deformations.

A Model for stress generation and relief in oxide — Metal systems during a temperature change

Abstract: When an oxidized metal is cooled from a high temperature, stresses are produced at the metal-scale interface, owing to the difference in thermal expansion rates of the oxide and metal. Such stresses become time- and temperature-dependent if the scale or underlying metal creeps as cooling occurs. A model is presented which describes thermally induced stresses in the scale and accounts for partial stress relaxation by creep of the metal substrate and/ or the scale. The expected stresses are a function of the material parameters: thermal expansion coefficients, elastic modulii, and creep rates of both metal and scale. To illustrate a range of behaviors, we have presented example calculations for three Cr2O3 forming metals, Ni-30Cr, pure Cr, and MA-754. The effect of stress relaxation during thermal cycling was also examined briefly. In these examples, creep of the Cr2O3 scale was not expected to be important.

Stress Relaxation in Solids

Abstract: THE purpose of this communication is to direct attention to a similarity in the shape of stress–log time graphs relating to static stress relaxation in solid materials. For a number of high polymers and metals the following relation between the inflexion slope F of the stress–log time curves and the total decrease in stress Δσ was found: F is defined as (dσ/d ln t)inflexion. A condition for the applicability of equation (1) seemed to be absence of internal stresses, that is, careful annealing. The substances investigated were rubber hydrochloride1, polyethylene2,3, cellulose and paper4, polycrystalline and single crystal cadmium, indium, lead and tin5, and polycrystalline molybdenum6. Experiments have also been carried out on a number of other substances including polyisobutylene, polyvinyl acetate, beryllium, aluminium, Lipowitz's alloy, cetyl alcohol, and single crystals of lithium fluoride7.