Stress relaxation

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

On the damping function of shear relaxation modulus for entangled polymers

Abstract: Published data of the damping function of the shear relaxation modulus, h(γ), are reviewed. This is the ratio of the relaxation modulus measured at a finite magnitude of shear, γ, to that at the limit of γ = 0. Majority of the data are in accord with the universal function of the Doi-Edwards tube model theory, in which the damping or the decrease of h(γ) is attributed to the contraction along the tube of extended polymer chains. The weaker damping seems to be attributed to 1) comb-branching such as in LDPE; 2) lack of entanglement in too short chains; 3) bimodal molecular weight distribution. However, a star-branching does not cause a deviation from the tube model theory and a broadness of molecular weight distribution is not a major origin of a weaker damping. A star-branched polystyrene with 15 arms exhibits no strain dependence: h(γ) = 1. For highly entangled systems with more than 50 entanglement points per molecule, the strain dependence is stronger than that of the Doi-Edwards theory. This could be due to a slip or an instability of deformation in the material.

Characterization of Models for Time-Dependent Behavior of Soils

Abstract: Different classes of constitutive models have been developed to capture the time-dependent viscous phenomena (creep, stress relaxation, and rate effects) observed in soils. Models based on empirica...

Cell wall yield properties of growing tissue : evaluation by in vivo stress relaxation.

Abstract: Growing pea stem tissue, when isolated from an external supply of water, undegoes stress relaxation because of continued loosening of the cell wall. A theoretical analysis is presented to show that such stress relaxation should result in an exponential decrease in turgor pressure down to the yield threshold ( Y ), with a rate constant given by φe where φ is the metabolically maintained irreversible extensibility of the cell wall and e is the volumetric elastic modulus of the cell. This theory represents a new method to determine φ in growing tissues. Stress relaxation was measured in pea ( Pisum sativus L.) stem segments using the pressure microprobe technique. From the rate of stress relaxation, φ of segments pretreated with water was calculated to be 0.08 per megapascal per hour while that of auxin-pretreated tissue was 0.24 per megapascal per hour. These values agreed closely with estimates of φ made by a steady-state technique. The yield threshold (0.29 megapascal) was not affected by auxin. Technical difficulties with measuring φ by stress relaxation may arise due to an internal water reserve or due to changes in φ subsequent to excision. These difficulties are discussed and evaluated. A theoretical analysis is also presented to show that the tissue hydraulic conductance may be estimated from the T ½ of tissue swelling. Experimentally, pea stems had a swelling T ½ of 2.0 minutes, corresponding to a relative hydraulic conductance of about 2.0 per megapascal per hour. This value is at least 8 times larger than φ. From these data and from computer modeling, it appears that the radial gradient in water potential which sustains water uptake in growing pea segments is small (0.04 megapascal). This means that hydraulic conductance does not substantially restrict growth. The results also demonstrate that the stimulation of growth by auxin can be entirely accounted for by the change in φ.