Creep Experiments Under Nonproportional Loadings With Stress Reversals for 2618 Aluminum

1984 ◽  
Vol 106 (4) ◽  
pp. 397-404 ◽  
Author(s):  
J. L. Ding ◽  
W. N. Findley
Keyword(s):  
Shear Stress ◽  
Strain Hardening ◽  
Synergistic Effects ◽  
Kinematic Hardening ◽  
High Stress ◽  
Creep Recovery ◽  
Flow Rule ◽  
Nonproportional Loading ◽  
Stress Levels ◽  
Stress Reversals

Experiments on creep of 2618-T61 aluminum under nonproportional loading steps combined with shear stress reversals, are reported. Compared to previous work, the stress levels, under which nonproportional loading steps were performed, were relatively low in the current work. In addition to the features of the material responses under nonproportional loadings such as anisotropy induced by creep strain, synergistic effects on creep and creep recovery, more findings related to stress reversals were a cyclic softening effect. The effect of shear stress reversal on tension creep was not significant because of the low stress levels. Isotropic strain hardening, kinematic hardening and independent strain hardening theories were evaluated. An auxiliary rule was developed for the isotropic and independent strain hardening approaches to extend the capabilities of the theories. Creep under stress reversals predicted by the kinematic flow rule was well described at low stresses but was too exagerated at high stress levels.

Ratcheting of Stainless Steel 304 Under Multiaxial Nonproportional Loading

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Kwang S. Kim ◽  
Rong Jiao ◽  
Xu Chen ◽  
Masao Sakane
Keyword(s):  
Stainless Steel ◽  
Shear Stress ◽  
Kinematic Hardening ◽  
Isotropic Hardening ◽  
Mean Stress ◽  
Nonproportional Loading ◽  
Torsional Strain ◽  
Ratcheting Strain ◽  
Stainless Steel 304 ◽  
Strain Cycling

Multiaxial ratcheting is often simulated by use of nonlinear kinematic hardening models, while in reality materials show cyclic hardening/softening and additional hardening under nonproportional loading. The effect of isotropic hardening on ratcheting needs to be addressed in simulation. In this study, ratcheting tests are conducted on stainless steel 304 under uniaxial, torsional, and combined axial-torsional loading. The ratcheting strain is predicted based on the constitutive theory that incorporates a modified Ohno–Wang kinematic hardening rule and Tanaka’s isotropic hardening model. The results show that the main features of the stress-strain response can be simulated with the constitutive model. Ratcheting strain under axial mean stress depends highly on the loading path and load level, and the degree of cyclic changes in shear stress under torsional strain control is not as influential. The torsional ratcheting strain under mean shear stress with (or without) fully reversed axial strain cycling is found close to the axial ratcheting strain under equivalent mean stress with (or without) torsional strain cycling. In all, the experimental and predicted ratcheting strains for nonproportional paths are found in decent correlation. However, overprediction still prevails for some loading paths, and ratcheting rates deviate considerably from experimental values.

Off-Axis Creep Recovery of Unidirectional Carbon/Epoxy Composites at High Temperature

2007 ◽  
Vol 334-335 ◽  
pp. 65-68 ◽  
Author(s):  
Masamichi Kawai ◽  
H. Kamioka ◽  
Jian Qi Zhang ◽  
Tetsuya Matsuda
Keyword(s):  
High Temperature ◽  
Creep Strain ◽  
Composite System ◽  
Kinematic Hardening ◽  
High Stress ◽  
Unidirectional Composite ◽  
Constant Stress ◽  
Creep Recovery ◽  
Creep Stress ◽  
Proposed Model

Off-axis creep recovery behavior after complete unloading during creep at a constant stress is examined for a unidirectional T800H/3631 carbon/epoxy composite laminate at high temperature. Creep and creep recovery tests are performed on plain coupon specimens with four kinds of fiber orientations: 10, 30, 45 and 90°. It is observed that the creep strain appeared at a high stress does not completely recover after full removal of the creep stress, indicating that an irrecoverable creep strain has developed under the prior constant stress loading. Variable stress creep simulations are attempted using the modified kinematic hardening model for homogenized anisotropic inelastic composites in which an accelerated change in kinematic hardening over a certain range of viscoplastic strain is considered. Comparison with experimental results demonstrates that the proposed model can adequately describe the off-axis creep and creep recovery behaviors of the unidirectional composite system under constant and variable stress conditions.

Nonproportional Loading Steps in Multiaxial Creep of 2618 Aluminum

1985 ◽  
Vol 52 (3) ◽  
pp. 621-628 ◽  
Author(s):  
J. L. Ding ◽  
W. N. Findley
Keyword(s):  
Experimental Data ◽  
Strain Hardening ◽  
Kinematic Hardening ◽  
Superposition Principle ◽  
High Stress ◽  
Material Behavior ◽  
Time Dependent ◽  
Nonlinear Material ◽  
Strain Component ◽  
Dependent Strain

Experimental data on the creep behavior of 2618-T61 aluminum alloy under nonproportional loadings are presented. Among the important findings are the anisotropy induced by creep strain, synergistic effects during creep recovery, and strongly nonlinear material behavior at high stress levels. Data were compared with two theoretical models, a viscous-viscoelastic (VV) model and a viscoplastic (VP) model. In the VV model the time-dependent strain was decomposed into recoverable (viscoelastic) and nonrecoverable components. The VP model differs from the VV model in that all the time-dependent strain is assumed nonrecoverable. In each model, three viscoplastic flow rules based on different hardening natures, namely, isotropic strain hardening, kinematic hardening, and independent strain hardening were derived to describe the time-dependent nonrecoverable strain component, and compared with experiments. The viscoelastic component in the VV model was represented by the third-order multiple integral representation combined with the modified superposition principle. Predictions for all theories used material constants obtained from creep and recovery data only. Possible causes for the discrepancies between theories and experimental data were discussed. Further experimental and theoretical work necessary for the study of the time-dependent material behavior at high temperature were also suggested.

Multiaxial Creep of 2618 Aluminum Under Proportional Loading Steps

1984 ◽  
Vol 51 (1) ◽  
pp. 133-140 ◽  
Author(s):  
J.-L. Ding ◽  
W. N. Findley
Keyword(s):  
Strain Hardening ◽  
Kinematic Hardening ◽  
Superposition Principle ◽  
Viscoelastic Model ◽  
Creep Recovery ◽  
Strain Component ◽  
Proportional Loading ◽  
Dependent Strain ◽  
Stress States ◽  
Multiaxial Creep

Creep data of 2618-T61 aluminum alloy under multistep multiaxial proportional loadings at 200°C (392°F) are reported. Two viscoplastic flow rules were developed using constant stress creep and creep recovery data. One was based on the accumulated strain (isotropic strain hardening), and the other on a tensorial state varible (kinematic hardening). Data were represented by two models: a nonrecoverable viscoplastic model, and a viscous-viscoelastic model in which the time-dependent strain was resolved into recoverable (viscoelastic) and nonrecoverable components. The modified superposition principle was used to predict the viscoelastic strain component under variable stress states. The experiments showed that the viscous-viscoelastic model with either isotropic strain hardening or kinematic hardening gave very good predictions of the material responses. Isotropic strain hardening was best in some step-down stress states. The viscoelastic component accounted for not only the recovery strain but also the transient creep strain upon reloadings and step-up loadings.

The flow of glass at high stress levels

1970 ◽  
Vol 3 (1) ◽  
pp. 127-147 ◽  
Author(s):  
J.H. Li ◽  
D.R. Uhlmann
Keyword(s):  
High Stress ◽  
Stress Levels

scholarly journals On the effect of rheology on seasonal sea-ice simulations

1991 ◽  
Vol 15 ◽  
pp. 17-25 ◽  
Author(s):  
Chi F. Ip ◽  
William D. Hibler ◽  
Gregory M. Flato
Keyword(s):  
Shear Stress ◽  
Sea Ice ◽  
Correlation Coefficients ◽  
Arctic Basin ◽  
The Arctic ◽  
Flow Rule ◽  
Average Model ◽  
Ice Drift ◽  
Cavitating Fluid

A generalized numerical model which allows for a variety of non-linear rheologies is developed for the seasonal simulation of sea-ice circulation and thickness. The model is used to investigate the effects (such as the role of shear stress and the existence of a flow rule) of different rheologies on the ice-drift pattern and build-up in the Arctic Basin. Differences in local drift seem to be closely related to the amount of allowable shear stress. Similarities are found between the elliptical and square cases and between the Mohr-Coulomb and cavitating fluid cases. Comparisons between observed and simulated buoy drift are made for several buoy tracks in the Arctic Basin. Correlation coefficients to the observed buoy drift range from 0.83 for the cavitating fluid to 0.86 for the square rheology. The average ratio of buoy-drift distance to average model-drift distance for several buoys is 1.15 (square), 1.18 (elliptical), 1.30 (Mohr-Coulomb) and 1.40 (cavitating fluid).

An Application of Incremental Plasticity Theory to Fatigue Life Prediction of Steels

1991 ◽  
Vol 113 (4) ◽  
pp. 404-410 ◽  
Author(s):  
W. R. Chen ◽  
L. M. Keer
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Kinematic Hardening ◽  
Yield Condition ◽  
Strain Curve ◽  
Fatigue Life Prediction ◽  
304 Stainless Steel ◽  
Flow Rule ◽  
Stress Strain ◽  
Von Mises

An incremental plasticity model is proposed based on the von-Mises yield condition, associated flow rule, and nonlinear kinematic hardening rule. In the present model, fatigue life prediction requires only the uniaxial cycle stress-strain curve and the uniaxial fatigue test results on smooth specimens. Experimental data of 304 stainless steel and 1045 carbon steel were used to validate this analytical model. It is shown that a reasonable description of steady-state hysteresis stress-strain loops and prediction of fatigue lives under various combined axial-torsional loadings are given by this model

scholarly journals Occupational Stress and Job Burnout among Primary and Secondary School Teachers in Cuttack, Orissa, 2013

2017 ◽  
Vol 5 (1) ◽  
Author(s):  
Joyce Mathews
Keyword(s):  
Occupational Stress ◽  
Secondary School Teachers ◽  
Demographic Data ◽  
High Stress ◽  
Job Burnout ◽  
Stress Index ◽  
Stress Levels ◽  
Older Teachers ◽  
The Relationship ◽  
Primary And Secondary School

The purpose of this study was to explore the levels of occupational stress and job burnout among teachers working in primary and secondary schools and identify the relationship between the selected demographic data with the stress levels. The sample consisted of 100 teachers from 4 schools in Cuttack, Orissa. The instruments used to measure the variables were: 1.Headington Stress Index questionnaire, 2.Headingtacon Burnout Inventory, 3. Self care and Lifestyle Balance Inventory. The statistical techniques of descriptive statistics, ANOVA analysis and Pearson’s coefficient were employed to analyze the data. The findings of the study indicated that a major portion of the teachers’ population faced moderately low stress and burnout, and the remaining faced moderately high stress and burnout. Younger teachers are reported to have more stress than the older teachers. Higher the burnout among teachers, lower was the lifestyle balance among them. Experience, gender and grade did not affect the stress levels among teachers.

scholarly journals Psychological Impact of COVID-19 Pandemic on Healthcare Workers in Riyadh, Saudi Arabia: Perceived Stress Scale Measures

2021 ◽  
Vol 11 (4) ◽  
pp. 377-388
Author(s):  
Nuha Alwaqdani ◽  
Hala A. Amer ◽  
Reem Alwaqdani ◽  
Fahad AlMansour ◽  
Hind A. Alzoman ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Perceived Stress ◽  
Online Survey ◽  
High Stress ◽  
Post Traumatic Stress ◽  
Perceived Stress Scale ◽  
Health Crisis ◽  
Stress Scale ◽  
Increased Risk ◽  
Stress Levels

Abstract Background The COVID-19 pandemic has been stressful and of considerable concern among health care workers (HCWs). Being particularly at increased risk for exposure, HCWs worry about becoming infected as well as infecting co-workers, patients and family members. Such distress and panic may have destructive effects on individuals and may last long after the pandemic situation leading to depression or post-traumatic stress disorder. Therefore, the aim of the current study is to measure and investigate the prevalence of the factors affecting psychological stress during the COVID-19 pandemic among HCWs. Methods A self-administered online survey—including perceived stress scale (PSS) questions—was disseminated among HCWs in Riyadh, Saudi Arabia (SA) between1st June and 30th July 2020. Results A total of 469 HCWs responded to the survey for a high response rate (93.8%). The PSS revealed that 15.8% of the respondents were suffering from high stress levels, 77.2% were suffering from moderate stress levels and 7% with low stress levels. Females and junior frontline staff reported more severe stress levels. Participation on the pandemic team shows significant impact on stress levels. Conclusion COVID-19 pandemic has increased stress levels among HCWs and affects their psychological wellbeing. Designing programs promoting HCWs mental health are crucial and emotional and psychological support strategies should be part of every public health crisis management plan.

scholarly journals The major worldwide stress of healthcare professionals during the first wave of the COVID-19 pandemic – the international COVISTRESS survey

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0257840
Author(s):  
Sébastien Couarraze ◽  
Louis Delamarre ◽  
Fouad Marhar ◽  
Binh Quach ◽  
Jiao Jiao ◽  
...  
Keyword(s):  
Healthcare Workers ◽  
Protective Factor ◽  
Healthcare Professionals ◽  
High Stress ◽  
Medical Doctors ◽  
Health Crisis ◽  
Paramedical Staff ◽  
Increased Risk ◽  
Stress Levels ◽  
Very High

Introduction The COVID-19 pandemic has initiated an upheaval in society and has been the cause of considerable stress during this period. Healthcare professionals have been on the front line during this health crisis, particularly paramedical staff. The aim of this study was to assess the high level of stress of healthcare workers during the first wave of the pandemic. Materials and methods The COVISTRESS international study is a questionnaire disseminated online collecting demographic and stress-related data over the globe, during the pandemic. Stress levels were evaluated using non-calibrated visual analog scale, from 0 (no stress) to 100 (maximal stress). Results Among the 13,537 individuals from 44 countries who completed the survey from January to June 2020, we included 10,051 workers (including 1379 healthcare workers, 631 medical doctors and 748 paramedical staff). The stress levels during the first wave of the pandemic were 57.8 ± 33 in the whole cohort, 65.3 ± 29.1 in medical doctors, and 73.6 ± 27.7 in paramedical staff. Healthcare professionals and especially paramedical staff had the highest levels of stress (p < 0.001 vs non-healthcare workers). Across all occupational categories, women had systematically significantly higher levels of work-related stress than men (p < 0.001). There was a negative correlation between age and stress level (r = -0.098, p < 0.001). Healthcare professionals demonstrated an increased risk of very-high stress levels (>80) compared to other workers (OR = 2.13, 95% CI 1.87–2.41). Paramedical staff risk for very-high levels of stress was higher than doctors’ (1.88, 1.50–2.34). The risk of high levels of stress also increased in women (1.83, 1.61–2.09; p < 0.001 vs. men) and in people aged <50 (1.45, 1.26–1.66; p < 0.001 vs. aged >50). Conclusions The first wave of the pandemic was a major stressful event for healthcare workers, especially paramedical staff. Among individuals, women were the most at risk while age was a protective factor.

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