scholarly journals Uniaxial Tensile Creep Behavior of Epoxy-Based Polymer Using Molecular Simulation

Polymers ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 261
Author(s):  
Xueliang Li ◽  
Xiaoyu Zhang ◽  
Jianzhong Chen ◽  
Li Huang ◽  
Yong Lv
Keyword(s):  
Epoxy Resin ◽  
Free Volume ◽  
Stress Level ◽  
Creep Behavior ◽  
High Stress ◽  
Dynamics Simulation ◽  
Tensile Creep ◽  
Creep Process ◽  
Uniaxial Tensile ◽  
Stress Levels

Based on the all-atomic molecular dynamics simulation method, the tensile creep behavior of epoxy-based polymer was discussed. The physical and mechanical properties of the model were characterized, such as glass transition temperature and yield strength. The simulation results are very close to the previous simulation and experimental results, and the correctness of the model is verified. On this basis, the tensile creep behavior and free volume evolution of polymer epoxy resin at different temperatures and stress levels were studied. The model fully predicted the three classical stages of epoxy resin creep (the primary, secondary and tertiary) and the dependent behavior of epoxy resin creep on temperature and stress level at the molecular level, and the creep rate increases with the increase of temperature and stress level. It was found that with the progress of the creep process, the proportion of free volume increases gradually under high stress levels, indicating that the effect of creep behavior on the structure of epoxy resin is that the interaction between atoms becomes weaker and weaker by increasing the distance between atoms, which finally induces creep failure in the material.

Modeling and Prediction of Creep Behavior of Polypropylene Packaging Belt

2011 ◽  
Vol 117-119 ◽  
pp. 1168-1171
Author(s):  
Zhao Yang Xu
Keyword(s):  
Stress Level ◽  
Creep Behavior ◽  
Creep Compliance ◽  
Element Model ◽  
Tensile Creep ◽  
Elastic Coefficient ◽  
Horizontal Shift ◽  
Stress Levels ◽  
Compliance Curve ◽  
Short Time

The short term tensile creep behaviors of polypropylene (PP) packaging belt under different stresses levels were studied through tensile creep test. The four-element model was applied to simulate the creep behaviors of the PP packaging belt. The results show that four-element model can be used to simulate the short time creep of PP packaging belt. The tensile creep behaviors of PP packaging belt have obviously correlation to the stress levels. The instantaneous elastic coefficient, delayed elastic coefficient and glutinous coefficient in Maxell model show a decreasing tendency with the increase of stress level. Based on the time-temperature-stress equivalence principle and take 15% stress level as a reference, the creep compliance master curve of 15% stress level was constructed by horizontal shift of the creep compliance curve of other stress levels, which can predict the creep behavior of PP packaging belt at the 15% stress level.

Prediction of Bending Creep Behavior of Rice Hull Flour/Polypropylene Composite

2012 ◽  
Vol 200 ◽  
pp. 203-206
Author(s):  
Zhao Yang Xu ◽  
Da Gang Li ◽  
Yan Wu
Keyword(s):  
Stress Level ◽  
Creep Behavior ◽  
Equivalence Principle ◽  
Master Curve ◽  
Creep Compliance ◽  
Bending Test ◽  
Rice Hull ◽  
Polypropylene Composite ◽  
Stress Levels ◽  
Compliance Curve

The creep behaviors of rice hull flour/PP composite under different stress levels were studied through bending test. The results show that the bending creep behaviors of rice hull flour/PP composite have obviously correlation to the stress levels. Based on the time-temperature-stress equivalence principle and 15% stress level as a reference, the creep compliance master curve of 15% stress level was constructed by horizontally shift the creep compliance curve of other stress levels, which can predict the creep behavior of rice hull flour/PP composite at the 15% stress level.

Tensile Creep Behavior of HPC at Early Ages under Different Curing Temperatures

2011 ◽  
Vol 250-253 ◽  
pp. 434-439 ◽  
Author(s):  
Yang Yang ◽  
Peng Li ◽  
Yan Ping Wu
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Strength Class ◽  
Concrete Specimen ◽  
Curing Temperature ◽  
Tensile Creep ◽  
Uniaxial Tensile ◽  
Creep Coefficient ◽  
The Difference ◽  
Uniaxial Tensile Creep

This paper presents an experimental investigation on tensile basic creep behavior of HPC at early ages by using a uniaxial tensile creep testing apparatus. Concrete specimens of 100×100×400mm with compressive strength class 60MPa was used, sealed and loaded at different curing temperature. The effects of the curing temperature and the age at loading on creep behavior are discussed. The results show that tensile specific creep and creep rate of HPC at early ages were governed by the age at loading. The specific creep, creep coefficient and creep rate were larger at earlier loading ages, and decreased exponentially with age at loading. The tensile specific creep decreased with curing temperature, but the difference in creep due to different curing temperatures decreased with the age at loading, and could be ignored while concrete specimen being loaded after the age of 7 days.

scholarly journals The Differences in Stress Levels of Male and Female Nurses at Hospitals

2020 ◽  
Author(s):  
Sendhi Tristanti Puspitasari ◽  
Samsul Arifin ◽  
Anggaunitakiranantika . ◽  
Farah Farida Tantiani ◽  
Ludi Wishnu Wardhana
Keyword(s):  
Work Stress ◽  
Stress Level ◽  
High Stress ◽  
Male Nurses ◽  
P Value ◽  
Chi Square ◽  
Cross Sectional ◽  
Male And Female ◽  
Stress Levels ◽  
Female Nurses

A study conducted by Northwestern National Life stated that around 40% of workers experienced work-related stress. One of the professions who has a high risk of stress is nursing. This research aims to analyze the differences in stress levels of male and female nurses, employing a quantitative method and a cross sectional approach. There were 73 respondents, all of whom were nurses at X Hospital. Random sampling was used in this research. Chi Square test was carried out to determine the relationship between gender and work stress levels. The results showed that the majority of nurses were women (78.1% or 57 people) and male nurses accounted for the remaining 21.9% (16 people). A higher number of female nurses experience high stress (15.8%) compared to male nurses (12.5%). The result of the analysis of the gender effect on stress levels in X Hospital nurses generated p-value of 0.745 indicating that p value > 0.05. This result shows that there is no significant effect of gender on the stress level of nurses in Hospital X. Accordingly, from the hypothesis tested, it is proven that there is no significant relationship between the gender of nurses and work stress experienced. Keywords: Stress Level, Nurse, Hospital

scholarly journals Individual changes in stress-level predict non-suicidal self-injury

2019 ◽  
Keyword(s):  
Stress Level ◽  
High Stress ◽  
Self Injury ◽  
Stress Levels

In their latest study, Adam Miller and colleagues propose that these inconsistencies might be due to a reliance on “between-person” models that compare individuals with high stress levels to those with low stress levels.

scholarly journals Viscoelastic Damage Characteristics of Asphalt Mixtures Using Fractional Rheology

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5892
Author(s):  
Qipeng Zhang ◽  
Xingyu Gu ◽  
Zilu Yu ◽  
Jia Liang ◽  
Qiao Dong
Keyword(s):  
Damage Evolution ◽  
High Stress ◽  
Creep Damage ◽  
Asphalt Mixtures ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Tests ◽  
Steady Stage ◽  
Stress Levels ◽  
Different Temperatures

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

scholarly journals Experimental Study on Freeze-Thaw Effects on Creep Characteristics of Rubber Concrete

2022 ◽  
Vol 2022 ◽  
pp. 1-14
Author(s):  
Qi Li ◽  
Fei Xu ◽  
Hemin Zheng ◽  
Junhao Shi ◽  
Jianyu Zhang
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Stress Level ◽  
Creep Behavior ◽  
Mass Loss Rate ◽  
Crumb Rubber ◽  
Dynamic Elastic Modulus ◽  
Freeze Thaw ◽  
Stress Levels ◽  
Rubber Concrete

Crumb Rubber Concrete (CRC) can exhibit high freeze-thaw resistance, but its long-term creep behavior under various freeze-thaw conditions remains unclear, which is essential for the safety of pavement engineering in the severe cold zone. In this study, the freeze-thaw effects on the creep behavior of CRC under different stress levels were systematically analyzed by testing the compressive strength, the uniaxial creep under different stress levels, and the dynamic elastic modulus. To simulate real conditions of the road environment in the cold area, the lowest temperature of −20°C, six freeze-thaw cycles of 0, 30, 60, 90, 120, and 150, and seven different stress levels of 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9 of the compressive strength were employed in this study. The test results showed that the mass loss rate was 6%–11.2% and the compressive strength decreased by 6.51%–47% after 30–150 freeze-thaw cycles. When the stress level reached its critical value, the relative dynamic elastic modulus decreased with the number of freeze-thaw cycles. After 150 freeze-thaw cycles, failure did not appear when the stress level was lower than 50%, above which the creep failure was determined by the stress level and the number of the freeze-thaw cycles. Meanwhile, it was found that the cracking and interfacial debonding between the matrix and the crumb rubber particle were the main reasons for the degradation of CRC creep performance. Finally, a Weibull distribution-based empirical creep damage model was established to predict the failure of CRC, which can enhance its application to related engineering.

Evidence for the effect of serotoninergic and dopaminergic gene variants on stress levels in horses participating in dressage and harness racing

2019 ◽  
Vol 59 (12) ◽  
pp. 2206
Author(s):  
S. Negro ◽  
M. J. Sánchez-Guerrero ◽  
E. Bartolomé ◽  
M. Solé ◽  
M. D. Gómez ◽  
...  
Keyword(s):  
Stress Level ◽  
Mixed Model ◽  
High Stress ◽  
Comt Gene ◽  
Gene Variants ◽  
Gene Variant ◽  
Association Analyses ◽  
Relative Contribution ◽  
Stress Levels ◽  
Eye Temperature

Eye temperature assessed with infrared thermography is an adequate tool for stress level assessment in sport horses’ competitions having a moderate heritability. Serotonin and dopamine signal transduction-linked gene variants have been associated with anxiety-related traits in several species. In this study we examined the association between 10 gene variants in BDNF, COMT, HTR1A, TPH2 and SLC6A4 genes (and the haplotypes at SLC6A4 gene) with stress level (measured with eye temperature and heart rate) in 270 animals, 135 Spanish Trotter Horses (STH) participating in trotting races and 135 ‘Pura Raza Español’ (PRE) horses in dressage. Association analyses were performed using a unified mixed model (counting for population structure and individual relatedness) for the whole population and for each horse breed. The g.43865600G > A intronic gene variant located 11.0 kb downstream from the transcription start site of SLC6A4 gene was associated with an increase in eye temperature before competition with a relative contribution of this gene variant of 38.8% (P = 0.001), 31.8% just after (P = 0.001) and 29.8% 2 h after the competition (P = 0.003). In STH, the g.43865600G > A gene variant showed the same association with eye temperature before (P = 0.001, contribution 27.2%), just after (P = 0.0003, 29.0%) and after the competition (P = 0.002, 17.5%); and the c.*111G > A gene variant located at the 3′UTR region of COMT gene was associated with eye temperature 2 h after the competition (P = 0.001, 22.3%). These results showed that SLC6A4 and COMT gene variants are associated with stress level measured as eye temperature increase during competitions, and may be promising tools for genetic testing against resistance at high stress levels in trotter horses.

Creep Behavior of PB-Free Solders

2001 ◽  
Author(s):  
F. Hua ◽  
C. M. Garner ◽  
H. G. Song ◽  
J. W. Morris
Keyword(s):  
Activation Energy ◽  
Creep Behavior ◽  
Solder Joints ◽  
Creep Process ◽  
Diffusion Activation Energy ◽  
Air Cooling ◽  
Shear Creep ◽  
Self Diffusion ◽  
Intermetallic Particles ◽  
Stress Levels

Abstract This study reports results of shear creep behavior of four Pb-free solders, Sn-3Ag-0.5Cu, Sn-3.5Ag, Sn-0.7Cu and Sn-10In-3.1Ag at 95θC and 130θC. At the stress levels tested, all the four solders showed the stress components close or larger than 5, typical for matrix creep. The calculated activation energies for Sn-0.7Cu, Sn-3.5Ag and Sn-3Ag-0.5Cu are from 103kJ/mol to 117kJ/mol, which are very close to the pure Sn self-diffusion activation energy (107kJ/mol). It suggested that the creep process is controlled by Sn bulk self-diffusion rate. The creep activation energy for Sn-10In-3.1Ag is higher in the range of 173–193kJ/mol. The Sn-0.7Cu, Sn-3Ag-0.5Cu and Sn-10In-3.1Ag solder joints were also prepared with two different cooling rates, 3.5θC/min. (furnace-cooling) and 2.7θC/S (air-cooling) and tested at 130θC. It was observed that faster cooled solder joints have faster creep strain rates than slower cooled solder joints at the stress levels tested for all three solders, due to the fine and even distribution of intermetallic particles.

Team Stress and Adverse Events during Neonatal Tracheal Intubations: A Report from NEAR4NEOS

2019 ◽  
Vol 37 (14) ◽  
pp. 1417-1424 ◽  
Author(s):  
Rachel A. Umoren ◽  
Taylor L. Sawyer ◽  
Anne Ades ◽  
Stephen DeMeo ◽  
Elizabeth E. Foglia ◽  
...  
Keyword(s):  
Adverse Events ◽  
Stress Level ◽  
Neonatal Intensive Care ◽  
High Stress ◽  
Hemodynamic Instability ◽  
Neonatal Intensive Care Units ◽  
Family Presence ◽  
Stress Levels ◽  
High Stress Level ◽  
Event Rates

Objective This study aimed to examine the association between team stress level and adverse tracheal intubation (TI)-associated events during neonatal intubations. Study Design TIs from 10 academic neonatal intensive care units were analyzed. Team stress level was rated immediately after TI using a 7-point Likert scale (1 = high stress). Associations among team stress, adverse TI-associated events, and TI characteristics were evaluated. Result In this study, 208 of 2,009 TIs (10%) had high stress levels (score < 4). Oxygenation failure, hemodynamic instability, and family presence were associated with high stress level. Video laryngoscopy and premedication were associated with lower stress levels. High stress level TIs were associated with adverse TI-associated event rates (31 vs. 16%, p < 0.001), which remained significant after adjusting for potential confounders including patient, provider, and practice factors associated with high stress (odds ratio: 1.90, 96% confidence interval: 1.36–2.67, p < 0.001). Conclusion High team stress levels during TI were more frequently reported among TIs with adverse events.

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