Viscoelastic stress relaxation in the hamstrings before and after a 10-week stretching program

2015 ◽  
Vol 51 (5) ◽  
pp. 761-764 ◽  
Author(s):  
Gustavo H. Peixoto ◽  
Andre G. Andrade ◽  
Hans J.K. Menzel ◽  
Silvia R.S. Araújo ◽  
Antônio E.M. Pertence ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Before And After ◽  
Viscoelastic Stress Relaxation

Predicting variations of the least principal stress with depth: Application to unconventional oil and gas reservoirs using a log-based viscoelastic stress relaxation model

Geophysics ◽  
2022 ◽  
pp. 1-56
Author(s):  
Ankush Singh ◽  
Mark D. Zoback
Keyword(s):  
Stress Relaxation ◽  
Principal Stress ◽  
Oil And Gas ◽  
Learning Technologies ◽  
Stress Profile ◽  
Gas Reservoirs ◽  
Midland Basin ◽  
Multi Stage ◽  
Viscoelastic Stress Relaxation ◽  
Geophysical Logs

Knowledge of layer-to-layer variations of the least principal stress, S hmin, with depth is essential for optimization of multi-stage hydraulic fracturing in unconventional reservoirs. Utilizing a geomechanical model based on viscoelastic stress relaxation in relatively clay rich rocks, we present a new method for predicting continuous S hmin variations with depth. The method utilizes geophysical log data and S hmin measurements from routine diagnostic fracture injection tests (DFITs) at several depths for calibration. We consider a case study in the Wolfcamp formation in the Midland Basin, where both geophysical logs and values of S hmin from DFITs are available. We compute a continuous stress profile as a function of the well logs that fits all of the DFITs well. We utilized several machine learning technologies, such as bootstrap aggregation (or bagging), to improve the generalization of the model and demonstrate that the excellent fit between predicted and observed stress values is not the result of over-fitting the calibration points. The model is then validated by accurately predicting hold-out stress measurements from four wells within the study area and, without recalibration, accurately predicting stress as a function of depth in an offset pad about 6 miles away.

scholarly journals Lung elastic recoil during breathing at increased lung volume

1999 ◽  
Vol 87 (4) ◽  
pp. 1491-1495 ◽  
Author(s):  
Joseph R. Rodarte ◽  
Gassan Noredin ◽  
Charles Miller ◽  
Vito Brusasco ◽  
Riccardo Pellegrino ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Tidal Volume ◽  
Lung Volume ◽  
Normal Subjects ◽  
Dynamic Hyperinflation ◽  
Airway Closure ◽  
Elastic Recoil ◽  
Volume Increase ◽  
Before And After ◽  
Residual Capacity

During dynamic hyperinflation with induced bronchoconstriction, there is a reduction in lung elastic recoil at constant lung volume (R. Pellegrino, O. Wilson, G. Jenouri, and J. R. Rodarte. J. Appl. Physiol. 81: 964–975, 1996). In the present study, lung elastic recoil at control end inspiration was measured in normal subjects in a volume displacement plethysmograph before and after voluntary increases in mean lung volume, which were achieved by one tidal volume increase in functional residual capacity (FRC) with constant tidal volume and by doubling tidal volume with constant FRC. Lung elastic recoil at control end inspiration was significantly decreased by ∼10% within four breaths of increasing FRC. When tidal volume was doubled, the decrease in computed lung recoil at control end inspiration was not significant. Because voluntary increases of lung volume should not produce airway closure, we conclude that stress relaxation was responsible for the decrease in lung recoil.

scholarly journals Data on tensile tests and NMR measurements of poly(vinilidene fluoride) before and after stress relaxation

Data in Brief ◽  
2018 ◽  
Vol 19 ◽  
pp. 55-58 ◽  
Author(s):  
Maria Marjorie Contreras ◽  
Christine Rabello Nascimento ◽  
Roberto Pinto Cucinelli Neto ◽  
Marysilvia F. Costa ◽  
Celio A. Costa
Keyword(s):  
Stress Relaxation ◽  
Tensile Tests ◽  
Before And After

scholarly journals ATR-FTIR Analysis and One-Week Stress Relaxation of Four Orthodontic Aligner Materials

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1868 ◽  
Author(s):  
Florina Jaggy ◽  
Spiros Zinelis ◽  
Georgios Polychronis ◽  
Raphael Patcas ◽  
Marc Schätzle ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Stress Relaxation ◽  
Optical Microscopy ◽  
Shear Bands ◽  
Attenuated Total Reflection ◽  
Ftir Microscopy ◽  
Similar Chemical ◽  
Before And After ◽  
Rectangular Strips ◽  
Level Of Significance

The aim of this study was to estimate possible differences in the chemical composition and relaxation of orthodontic aligner materials. Four commercially available thermoplastic materials CAM (Scheu-Dental, Iserlohn, Germany), COP (Essix, Dentsply Raintree Essix Sarasota, FL, USA), DUR (Great Lakes Dental Technologies, Tonawanda, NY) and ERK (Erkodent Erich Kopp, Pfalzgrafenweiler Germany) were included in this study. Rectangular strips from each material were prepared according to the manufacturer’s instructions and subjected to attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and stress relaxation characterization. The reduction in applied stress (RAS) after one week was estimated and statistically analyzed by one-way ANOVA at the 0.05 level of significance. All specimens were subjected to optical microscopy before and after stress relaxation testing under transmittance polarized illumination. ATR-FTIR microscopy revealed that all materials are made of polyethylene terephthalate glycol (PETG) while no significant differences were identified in RAS values among materials tested, which ranged from 6%–10% (p ≥ 0.05). All samples illustrated the developments of shear bands during relaxation testing according to optical microscopy findings. The tested materials illustrated similar chemical composition and relaxation behavior and thus no differences in their clinical efficacy are anticipated.

Effect of Residual Stress on High Temperature Deformation in a Weld Stainless Steel

2006 ◽  
Vol 524-525 ◽  
pp. 311-316 ◽  
Author(s):  
Robert C. Wimpory ◽  
Farid R. Biglari ◽  
Rainer Schneider ◽  
Kamran M. Nikbin ◽  
N.P. O'Dowd
Keyword(s):  
Stainless Steel ◽  
High Temperature ◽  
Stress Relaxation ◽  
Residual Stresses ◽  
Imperial College ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Collaborative Effort ◽  
Specific Objective ◽  
Before And After

This paper considers the measurement of residual stresses induced by mechanical loading in a weld Type 347 stainless steel. The work is based in part on an ongoing Round Robin collaborative effort by the Versailles Agreement on Materials and Standards, Technical Working Area 31, (VAMAS TWA 31) working on ‘Crack Growth of Components Containing Residual Stresses’. The specific objective of the work at Imperial College London and HMI, Berlin is to examine how residual stresses and prior straining and subsequent relaxation at high temperature contribute to creep crack initiation and growth for steels relevant to power plant applications. Tensile residual stresses have been introduced in the weld by pre-compression and neutron diffraction measurements have been carried out before and after stress relaxation at 650 oC. Significant relaxation of the residual stresses has been observed, in agreement with earlier work on a stainless steel. Preliminary results suggest that the strains local to the crack drop by over 60% after 1000 h relaxation at 650 oC for the weld steel. The results have been compared with finite element studies of elastic-plastic pre-compression and stress relaxation due to creep.

Wandering of Crosslinks in Rubber at High Temperature

1959 ◽  
Vol 32 (3) ◽  
pp. 696-700
Author(s):  
M. J. Voorn ◽  
J. J. Hermans
Keyword(s):  
Stress Relaxation ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Crosslinking Density ◽  
Heat Treated Sample ◽  
Equilibrium Degree ◽  
Heat Treated ◽  
Before And After ◽  
Final Stress ◽  
Different Temperatures

Abstract There are strong reasons to believe that on heating a crosslinked rubber crosslinks are broken and new ones formed. This has been established by the well-known work on stress relaxation of Tobolsky and his school, and others. In the following we will discuss some experiments which give further support to these views, both of a qualitative and quantitative nature. In the first place, we carried out a few preliminary experiments on stress relaxation at elevated temperatures. This stress relaxation may be due to either or both of two effects : (a) a displacement of the crosslinks, (b) a change in the number of crosslinks per unit of volume (crosslinking density p). A measure of ρ can be obtained from the equilibrium degree of swelling at room temperature, and this gives us a means of comparing changes of ρ in a stretched sample with those occurring in the unstretched state. To this end commercial rubber strips were heated in the stretched state in the absence of oxygen at three different temperatures (80, 106, 122° C) for times varying from 2 to 72 hours. The degree of stretch, i.e., the length of the stretched rubber divided by the original length was α=1 (unstretched) in one series, and α=3 in a second series. The initial stress τ0 (for α=3) and the final stress τ at the end of the heating period were read from the stress-strain diagrams, taking into account that for the heat-treated strips there was a permanent set. In other words, τ is the stress needed to give the heat-treated sample at room temperature a length 3 times the length of the original untreated sample; the ratio τ/τ0 is therefore essentially the ratio between the moduli of elasticity. The cross-linking densities ρ0 and ρ before and after heating were derived from swelling experiments (for details see the sections on swelling).

Viscoelastic stress relaxation in film/substrate systems—Kelvin model

2003 ◽  
Vol 93 (5) ◽  
pp. 2453-2457 ◽  
Author(s):  
Sun-Chien Ko ◽  
Sanboh Lee ◽  
Chun-Hway Hsueh
Keyword(s):  
Stress Relaxation ◽  
Kelvin Model ◽  
Viscoelastic Stress Relaxation ◽  
Film Substrate
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