Creep Relaxation Time Research Articles

Extraordinary creep relaxation time in a La-based metallic glass

The structural relaxation times of metallic glasses (MGs) are generally believed to decrease with increasing flow rate, also known as shear thinning. In this work, an extraordinary loading rate-independent creep relaxation time, in contrast to the decreasing Maxwell relaxation time with increasing loading rate, is observed for a La-based MG with pronounced Johari–Goldstein relaxation under nanoindentation. The Johari–Goldstein relaxation in the flow of MGs is suggested to be a form of local Newtonian flow and may be not crucial in shear thinning, whereas the main α relaxation is proposed to predominate in the shear thinning of MGs, based on the disparity between the creep relaxation time and the Maxwell relaxation time. These results improve the current understandings on the structural relaxation and its role in the shear thinning and plastic deformation of MGs.

Creep analysis of silicone for podiatry applications

Purpose. This work shows an effective methodology to characterize the creep–recovery behavior of silicones before their application in podiatry. The aim is to characterize, model and compare the creep–recovery properties of different types of silicone used in podiatry orthotics.Methods. Creep–recovery phenomena of silicones used in podiatry orthotics is characterized by dynamic mechanical analysis (DMA). Silicones provided by Herbitas are compared by observing their viscoelastic properties by Functional Data Analysis (FDA) and nonlinear regression. The relationship between strain and time is modeled by fixed and mixed effects nonlinear regression to compare easily and intuitively podiatry silicones.Results. Functional ANOVA and Kohlrausch–Willians–Watts (KWW) model with fixed and mixed effects allows us to compare different silicones observing the values of fitting parameters and their physical meaning. The differences between silicones are related to the variations of breadth of creep–recovery time distribution and instantaneous deformation-permanent strain. Nevertheless, the mean creep-relaxation time is the same for all the studied silicones. Silicones used in palliative orthoses have higher instantaneous deformation-permanent strain and narrower creep–recovery distribution.Conclusions. The proposed methodology based on DMA, FDA and nonlinear regression is an useful tool to characterize and choose the proper silicone for each podiatry application according to their viscoelastic properties.

Anisotropic internal thermal stress in sea ice from the Canadian Arctic Archipelago

AbstractResults from an ice stress buoy deployed near the center of a multi‐year floe in the Viscount Melville Sound of the Canadian Arctic Archipelago between 10 October 2010 and 17 August 2011 are presented. The position record indicates the landlocked season was approximately 5 months, from 18 January to 22 June, when the sea ice was fast to Melville Island and Victoria Island. Thermal stresses (ranging from −84 to 66 kPa) dominate the internal stress record, with only a few dynamic stress events (∼50 kPa) recorded before the landlocked season. Intriguingly, the thermal stresses are isotropic before the landlocked ice onset and anisotropic during the landlocked season. Two possible causes to explain anisotropy in thermal stresses are considered: preferred c axis alignment of the ice crystal, and land confinement associated with the nearby coastline. The orientation of the principal stresses indicates that land confinement is responsible for the anisotropy. The stress record also clearly shows the presence of residual compressive stresses at the melt onset, suggesting a viscous creep relaxation time constant of several days. Finally, results show an interesting reversal in the sign of the correlation (from negative to positive) between surface air temperature and thermal stress after the onset of surface melt. We attribute this to the onset of water infiltration within sea ice after which colder night temperature leads to refreezing and compressive stresses. To the best of the authors' knowledge, this is the first time that anisotropic thermal stresses have been reported in sea ice.

Frequency, field, and temperature dependence of the AC penetration depth of a GdBa 2Cu 3O 7−δ film in the mixed state

We report on a systematic mutual induction measurement of the complex AC penetration depth λ of a sputtered high-quality GdBa 2Cu 3O 7−δ film in the mixed state by a very small coil system arranged near the sample surface. The complex penetration depth λ( B, T, ω) for DC inductions B ⩽ 0.65 T (perpendicular to the film), for temperatures 36 K ⩽ T ⩽ 81 K, and for frequencies 1 kHz ⩽ ω/2 π ⩽ 500 kHz was determined from the measured signal by a novel inversion scheme. The results are consistent with theoretical predictions based upon single vortex pinning. The Labusch parameter α, the flux creep relaxation time τ, as well as the effective activation energy U are simulateneously determined.

Age-related mechanical properties of human skin: An in vivo study

We have investigated in vivo how various viscoelastic parameters that describe the mechanical properties of the human skin may vary with age. Accordingly, we have used a mechanical device that records the torsional extensibility of the skin. When submitted to a low torque, the timeresponse curve of the skin affords the determination of the immediate extensibility (UE), the immediate recovery (UR), the viscoelastic part of the deformation (UV), the elastic recovery (UR/UE), and the creep relaxation time (τ). Because the skin thickness varies with age and primarily governs the mechanical properties, it was measured through an ultrasound technique at the same sites (forearm) where the torque was applied. The results show that the skin maintains its thickness and extensibility up to the seventh decade as opposed to its elasticity or recovery capacities, which decrease from an early age. The viscous part of the deformation is constant through life, whereas the creep relaxation time decreases linearily with age. Except for skin thickness, no differences in these parameters between men and women were detected. The significance of these results are discussed in terms of structure alterations. The determination of the elastic recovery (UR/UE) appears to be a parameter of choice for illustrating skin aging.

The loading problem for a linear viscoelastic earth: I. Compressible, non-gravitating models

A Legendre mode solution is given for deformation of a solid isotropic linear viscoelastic sphere under applied surface stresses. Under the simplifying assumptions that the sphere is elastic in compression and standard linear solid in shear two relaxation times appear; one the creep relaxation time of the material, the other depending on mode. It is shown formally how to reduce the case of a layered viscoelastic sphere to an equivalent unlayered one.