Fatigue evaluation of ship structures considering change in mean stress condition

2017 ◽  
Vol 61 (5) ◽  
pp. 987-995 ◽  
Author(s):  
Norio Yamamoto
Keyword(s):  
Stress Condition ◽  
Mean Stress ◽  
Ship Structures ◽  
Fatigue Evaluation ◽  
Change In Mean

Trends in stress among pregnant and postpartum women during the COVID-19 pandemic (Preprint)

2021 ◽  
Author(s):  
Serwaa Omowale ◽  
Andrea Casas ◽  
Yu-Hsuan Lai ◽  
Sarah Sanders ◽  
Ashley Hill ◽  
...  
Keyword(s):  
Racial Differences ◽  
The United States ◽  
Mean Stress ◽  
Postpartum Health ◽  
Black And White ◽  
Pregnancy And Postpartum ◽  
Significant Difference ◽  
Stress Levels ◽  
Change In Mean ◽  
At Home

BACKGROUND Stress has been associated with adverse birth and postpartum health outcomes. Few studies have explored racial differences in maternal stress in a birthing population longitudinally in the United States (U.S.) during the ongoing COVID-19 pandemic. OBJECTIVE This study aimed to: (1) assess changes in reported stress before, during, and after initial emergency declarations (e.g., stay-at-home orders) were in place due to the COVID-19 pandemic and (2) assess Black-White differences in reported stress in a pregnant and postpartum population from Southwestern Pennsylvania. METHODS We leveraged data from the ongoing Postpartum Mothers Mobile Study (PMOMS) which surveys participants in real-time throughout the pregnancy and postpartum periods via ecological momentary assessment (EMA) and smartphone technology. We analyzed data from a subset of PMOMS participants (n=85) who were either Black or White, and who submitted EMA responses regarding stress between November 1, 2019 and August 31, 2020, the timeframe of this study. Data were divided into four phases based on significant events during the COVID-19 pandemic: a pre-phase (baseline), early-phase (first case of COVID-19 reported in U.S.), during-phase (stay-at-home orders), and post-phase (stay-at-home orders eased). We assessed mean stress levels at each phase using mixed-effects models and post-hoc contrasts based on the models. RESULTS Overall mean stress (min: 0, max: 4 as measured by a modified Cohen Perceived Stress Scale) during the pre-phase was 0.8 for Black and White participants [range for Black participants: 0-3.9, range for White participants: 0-2.8]. There was an increase of 0.26 points (t=5.19, d.f.=5649, p<.0001) in the during-phase as compared with the pre-phase, and an increase of 0.19 points (t=3.09, d.f.=5649, p=0.002) in the post-phase compared with the pre-phase (n=85). No difference was found between Black and White participants in the change in mean stress from the pre-phase to the during-phase (δ ̂= -0.016, p=0.867). There was a significant difference between Black and White participants in the change in mean stress from the during-phase to the post-phase (δ ̂ = -0.39, p<0.0001). CONCLUSIONS There was an overall increase in mean stress levels in this subset of pregnant and postpartum participants during the same time as the emergency declarations/stay-at-home orders in the US. Compared to baseline, mean stress levels remained elevated when stay-at-home orders eased. We found no significant difference in the mean stress levels by race. Given that stress is associated with adverse birth outcomes and postpartum health, stress induced by the ongoing COVID-19 pandemic may have adverse implications for birthing populations in the U.S. INTERNATIONAL REGISTERED REPORT RR2-10.2196/13569

Study on a New Design Fatigue Evaluation Method

2015 ◽  
Author(s):  
Seiji Asada ◽  
Takashi Hirano ◽  
Takehiko Sera
Keyword(s):  
Evaluation Method ◽  
Austenitic Stainless Steels ◽  
Carbon Steels ◽  
Design Evaluation ◽  
Low Alloy Steels ◽  
Mean Stress ◽  
Research Committee ◽  
Fatigue Design ◽  
Fatigue Evaluation ◽  
Design Factors

In order to develop new design fatigue curves for austenitic stainless steels, carbon steels and low alloy steels and a new design fatigue evaluation method that is rational and has a clear design basis, the Design Fatigue Curve (DFC) subcommittee was established in the Atomic Energy Research Committee in the Japan Welding Engineering Society. Tentative design fatigue curves were developed and studies on the effects of mean stress and design factors are ongoing. Design fatigue curves, including the effects of mean stress and design factors, are needed to establish a new fatigue design evaluation method. This paper describes the study on the new fatigue design evaluation method.

Proposed ASME Code High Cycle Fatigue Design Curves for Austenitic and Ferritic Steels

2017 ◽  
Author(s):  
Sampath Ranganath ◽  
Hardayal S. Mehta ◽  
Nathan A. Palm ◽  
John Hosler
Keyword(s):  
High Cycle Fatigue ◽  
Ferritic Steels ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Design Curve ◽  
Fatigue Design ◽  
Asme Code ◽  
The Mean ◽  
Number Of Cycles ◽  
Fatigue Evaluation

The ASME Code fatigue curves (S–N curves) are used in the fatigue evaluation of reactor components. For the assessment of high frequency cyclic loading (such as those produced by flow-induced vibrations), where the number of cycles is expected to be very large and cannot be estimated, the stresses are evaluated by comparison with the fatigue limit1 at 1011 cycles. Other high cycle events of finite time duration (e.g. safety relief loading), where the number of cycles is large but well defined, the fatigue evaluation is performed by comparing the calculated stress with the allowable values defined by the high cycle fatigue design curve. This paper discusses the development of fatigue design curves for austenitic and ferritic steels when the number of cycles is in the range 106 – 1011 cycles. The first part of the paper addresses austenitic stainless steel components which are used for reactor internals. Specifically, the approach described here uses temperature dependent properties (cyclic yield strength, cyclic ultimate strength) for the mean stress correction and the correction for the modulus of elasticity. The high cycle fatigue design curve is developed by applying the mean stress and the E correction on the reversing load mean data curve and applying a factor of 2 on stress. The generic methodology developed for austenitic steel was applied to carbon and low alloy steels also. The proposed fatigue design curves are part of a draft ASME Code Case being considered by the ASME Code Subgroup on Design Methods. This paper describes the technical basis for the proposed ASME Code Case for the high cycle fatigue design curves for austenitic and ferritic steels.

The Master S-N Curve Approach to Fatigue Evaluation of Offshore and Marine Structures

2004 ◽  
Author(s):  
P. Dong ◽  
J. K. Hong
Keyword(s):  
Stress Concentration ◽  
Fracture Mechanics ◽  
Plate Thickness ◽  
Offshore Structures ◽  
Theoretical Development ◽  
Structural Stress ◽  
Concentration Effects ◽  
Ship Structures ◽  
Loading Modes ◽  
Fatigue Evaluation

As reported in the last OMAE conference (Dong, 2003), a robust structural stress method has been developed and validated for fatigue evaluation of ship structures through a major joint industry project. The structural stress method not only provides a consistent method for characterizing stress concentration effects on fatigue in different joint types and loading modes, but also offers a rapid estimation procedure for stress intensity factors for arbitrary joint geometries and loading modes in fracture mechanics context. As a result, a master S-N curve approach has been recently developed by using the mesh-insensitive structural stress parameter and its direct linkage to fracture mechanics principles. The master S-N curve is described by an equivalent structural stress range parameter which provides a single parameter description of stress concentration effects, thickness effects, and loading mode effects on fatigue in welded joints. A massive amount of S-N data since 1947, encompassing drastically different joint types, plate thickness, and loading modes have been used to validate the effectiveness of the master S-N curve approach. With the master S-N curve method, plate joints in ship structures, tubular joints in offshore structures, as well as pipe joints for riser applications can be collapsed into a singe curve, referred to as the master S-N curve. This paper provides the detailed theoretical development, application examples, and validation results. The applications for the master S-N curve approach will be illustrated by using various offshore/marine examples.

scholarly journals Anisotropic nature of the capillary stress tensor

2021 ◽  
Vol 249 ◽  
pp. 11010
Author(s):  
Mojtaba Farahnak ◽  
Richard Wan ◽  
Mehdi Pouragha
Keyword(s):  
Stress Tensor ◽  
Relative Magnitude ◽  
Triaxial Tests ◽  
Mean Stress ◽  
Discrete Element Modeling ◽  
Capillary Stress ◽  
Micromechanical Approach ◽  
Characteristic Particle ◽  
Stress Transmission ◽  
Change In Mean

The paper describes a micromechanical approach that explores the anisotropic nature of the capillary stress tensor and its evolution in pendular granular materials via Discrete Element Modeling (DEM) simulations. Dimensionless parameters are used to address the conditions under which the contribution of capillarity (or cohesive interparticle forces) to the stress transmission within a Representative Elementary Volume (REV) is expected to be considerable. From a series of suction-controlled conventional triaxial tests, numerical results show that the significance of the capillary stress and the relative magnitude of its mean to deviatoric components is directly connected to the characteristic particle size and applied stress. In addition, it is shown that the anisotropic character of the capillary stress tensor intensifies with increasing suction. Furthermore, a simple shear test is conducted at constant mean stress to reveal the development of deviatoric capillary stresses in the absence of any change in mean stress, which cannot be captured by the commonly used Bishop’s stress expression.

Mean Stress Correction Procedure in Fatigue Evaluation for High Pressure Vessels

2004 ◽  
Author(s):  
Susumu Terada ◽  
Kenji Yamamoto
Keyword(s):  
Fatigue Tests ◽  
Pressure Vessels ◽  
High Ratio ◽  
Experimental Results ◽  
Mean Stress ◽  
Correction Procedure ◽  
The Mean ◽  
The Difference ◽  
Predicted Values ◽  
Fatigue Evaluation

One important issue in the fatigue evaluation that must be addressed is the mean stress correction procedure. ASME Div.3 is provided with the mean stress correction procedure. The predicted equivalent alternating stress intensities Seq are compared with the experimental results for push-pull fatigue tests with mean stress for JIS SCM440 and JIS SUS630 H1075. Seq per ASME Div.3 are not coincident with the experimental results. In case of high ratio of tensile mean stress to tensile strength, the difference becomes large and it is un-conservative. On the other hand Seq per KHK Standard are coincident with experimental results. The fatigue test results for pressurized cylinder tube by Davidson and Findley are also compared with predicted values per ASME Div.3 and KHK Standard. The results of comparison are same as that for above mentioned push-pull fatigue tests. Based on the experimental verification, the authors recommend that the mean stress correction procedure per KHK Standard be implemented in ASME Div.3.

Symptom Validity Testing

2018 ◽  
Vol 23 (6) ◽  
pp. 14-15
Author(s):  
Lee H. Ensalada
Keyword(s):  
Memory Deficits ◽  
Symptom Validity ◽  
Sensory Cues ◽  
Validity Testing ◽  
Symptom Validity Testing ◽  
Tunnel Vision ◽  
Blurry Vision ◽  
The Common ◽  
Fatigue Evaluation ◽  
Choice Testing

Abstract Symptom validity testing (SVT), also known as forced-choice testing, is a means of assessing the validity of sensory and memory deficits, including tactile anesthesias, paresthesias, blindness, color blindness, tunnel vision, blurry vision, and deafness. The common feature among these symptoms is a claimed inability to perceive or remember a sensory signal. SVT comprises two elements: a specific ability is assessed by presenting a large number of items in a multiple-choice format, and then the examinee's performance is compared to the statistical likelihood of success based on chance alone. These tests usually present two alternatives; thus the probability of simply guessing the correct response (equivalent to having no ability at all) is 50%. Thus, scores significantly below chance performance indicate that the sensory cues must have been perceived, but the examinee chose not to report the correct answer—alternative explanations are not apparent. SVT also has the capacity to demonstrate that the examinee performed below the probabilities of chance. Scoring below a norm can be explained by fatigue, evaluation anxiety, inattention, or limited intelligence. Scoring below the probabilities of chance alone most likely indicates deliberate deceptions and is evidence of malingering because it provides strong evidence that the examinee received the sensory cues and denied the perception. Even so, malingering must be evaluated from the total clinical context.

Impairment Questions and Answers

1999 ◽  
Vol 4 (4) ◽  
pp. 4-4
Keyword(s):  
Symptom Validity ◽  
Validity Testing ◽  
Symptom Validity Testing ◽  
Negative Results ◽  
Tunnel Vision ◽  
Questions And Answers ◽  
Blurry Vision ◽  
Fatigue Evaluation ◽  
Choice Testing ◽  
Rule Out

Abstract Symptom validity testing, also known as forced-choice testing, is a way to assess the validity of sensory and memory deficits, including tactile anesthesias, paresthesias, blindness, color blindness, tunnel vision, blurry vision, and deafness—the common feature of which is a claimed inability to perceive or remember a sensory signal. Symptom validity testing comprises two elements: A specific ability is assessed by presenting a large number of items in a multiple-choice format, and then the examinee's performance is compared with the statistical likelihood of success based on chance alone. Scoring below a norm can be explained in many different ways (eg, fatigue, evaluation anxiety, limited intelligence, and so on), but scoring below the probabilities of chance alone most likely indicates deliberate deception. The positive predictive value of the symptom validity technique likely is quite high because there is no alternative explanation to deliberate distortion when performance is below the probability of chance. The sensitivity of this technique is not likely to be good because, as with a thermometer, positive findings indicate that a problem is present, but negative results do not rule out a problem. Although a compelling conclusion is that the examinee who scores below probabilities is deliberately motivated to perform poorly, malingering must be concluded from the total clinical context.

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