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Peter B. Nagy - One of the best experts on this subject based on the ideXlab platform.
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Hall coefficient measurement for residual Stress Assessment in precipitation hardened IN718 nickel-base superalloy
2017Co-Authors: Dheeraj Velicheti, Peter B. Nagy, Waled HassanAbstract:We investigated the feasibility of residual Stress Assessment based on Hall coefficient measurements in precipitation hardened IN718 nickel-base superalloy. As a first step, we studied the influence of microstructural variations on the galvanomagnetic properties of IN718 nickel-base superalloy. We found that the Hall coefficient of IN718 increases from ≈ 8.0×10−11 m3/C in its fully annealed state of 15 HRC Rockwell hardness to ≈ 9.4×10−11 m3/C in its fully hardened state of 45 HRC. We also studied the influence of cold work, i.e., plastic deformation, at room temperature and found that cold work had negligible effect on the Hall coefficient of fully annealed IN718, but significantly reduced it in hardened states of the material. For example, measurements conducted on fully hardened IN718 specimens showed that the Hall coefficient decreased more or less linearly with cold work from its peak value of ≈ 9.4×10−11 m3/C in its intact state to ≈ 9.0×10−11 m3/C in its most deformed state of 22% plastic strain. We also studied the influence of applied Stress and found that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain was measured as a unitless gauge factor K that is defined as the ratio of the relative change of the Hall coefficient ΔRH/RH divided by the axial strain e = σ/E, where σ is the applied uniaxial Stress and E is the Young’s modulus of the material. We determined that the galvanomagnetic gauge factor of IN718 is κ ≈ 2.6 − 2.9 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive Stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements will not happen in this case. Additionally, the temperature dependence of the Hall coefficient was measured at three different hardness levels and the influence of thermal exposure was studied in fully hardened IN718 up to 700 °C.We investigated the feasibility of residual Stress Assessment based on Hall coefficient measurements in precipitation hardened IN718 nickel-base superalloy. As a first step, we studied the influence of microstructural variations on the galvanomagnetic properties of IN718 nickel-base superalloy. We found that the Hall coefficient of IN718 increases from ≈ 8.0×10−11 m3/C in its fully annealed state of 15 HRC Rockwell hardness to ≈ 9.4×10−11 m3/C in its fully hardened state of 45 HRC. We also studied the influence of cold work, i.e., plastic deformation, at room temperature and found that cold work had negligible effect on the Hall coefficient of fully annealed IN718, but significantly reduced it in hardened states of the material. For example, measurements conducted on fully hardened IN718 specimens showed that the Hall coefficient decreased more or less linearly with cold work from its peak value of ≈ 9.4×10−11 m3/C in its intact state to ≈ 9.0×10−11 m3/C in its most deformed state of 22% plastic strain. W...
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Stress Assessment in Precipitation Hardened IN718 Nickel-Base Superalloy Based on Hall Coefficient Measurements
Journal of Nondestructive Evaluation, 2017Co-Authors: Dheeraj Velicheti, Peter B. Nagy, Waled HassanAbstract:The feasibility of residual Stress Assessment in precipitation hardened IN718 nickel-base superalloy based on Hall coefficient measurement is investigated through studying the influence of thermal hardening, cold work, and applied Stress. Measurements in IN718 specimens of various hardness levels show that the Hall coefficient increases from 8 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully annealed state of 14 HRC to 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully hardened state of 45 HRC. Measurements in IN718 specimens of various cold work levels show that plastic deformation exerts negligible effect on the Hall coefficient of fully annealed IN718, while in fully hardened IN718 the Hall coefficient decreases more or less linearly with cold work from its peak value of 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its intact state to 8.9 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its most deformed state of 22% plastic strain. Measurements taken under applied Stress show that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain is called the galvanomagnetic gauge factor and defined as the ratio of the relative change of the Hall coefficient divided by the axial strain under applied uniaxial Stress. The gauge factor of IN718 is in the range of 2.6–2.9 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive Stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements does not happen in this case. In addition, the influence of thermal exposure up to 700 \({{}^{\circ }}\)C and the reversible temperature dependence of the Hall coefficient at room temperature are studied in IN718 at different hardness levels.
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Opportunities and Challenges for Nondestructive Residual Stress Assessment
Quantitative Nondestructive Evaluation, 2006Co-Authors: Peter B. NagyAbstract:For a long time, nondestructive residual Stress Assessment has been one of the greatest opportunities as well as one of the greatest challenges for the NDE community, and probably it will remain so in the foreseeable future. The most critical issue associated with nondestructive residual Stress Assessment seems to be that of selectivity. Numerous NDE methods have been found to be sufficiently sensitive to the presence of residual Stress, but unfortunately also rather sensitive to other spurious variations that usually accompany residual Stresses, such as anisotropic texture, microstructural inhomogeneity, plastic deformation, etc., which could interfere with, or even overshadow, the elastic strain caused by the sought residual Stress. The only sufficiently selective NDE method that is more or less immune from these spurious effects is X‐ray diffraction measurement, which however does not have the required penetration depth in most applications unless high‐energy neutron radiation is used. It is timely for...
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Near‐Surface Residual Stress Assessment in Inhomogeneous Nickel‐Base Superalloys
Quantitative Nondestructive Evaluation, 2006Co-Authors: F. Yu, Peter B. NagyAbstract:Recently, it has been shown that shot‐peened nickel‐base superalloys exhibit an approximately 1% increase in apparent eddy current conductivity at high inspection frequencies, which can be exploited for nondestructive subsurface residual Stress Assessment. Unfortunately, microstructural inhomogeneity in certain as‐forged and precipitation hardened nickel‐base superalloys, like Waspaloy, can lead to significantly larger electrical conductivity variations of as much as 4–6%. This intrinsic conductivity variation adversely affects the accuracy of residual Stress evaluation in shot‐peened and subsequently thermal‐relaxed specimens, but does not completely prevent it. Experimental results are presented to demonstrate that the conductivity variation resulting from volumetric inhomogeneities in as‐forged engine alloys do not display significant frequency dependence. This characteristic independence of frequency can be exploited to distinguish these inhomogeneities from near‐surface residual Stress and cold work ...
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Piezoresistive Effect for Near-Surface Eddy Current Residual Stress Assessment
AIP Conference Proceedings, 2005Co-Authors: Fengming Yu, Peter B. NagyAbstract:This paper discusses the relationship between isothermal and adiabatic piezoresistive properties of metals. The piezoresistive effect, i.e., Stress‐dependence of the electrical resistivity, can be exploited for nondestructive residual Stress Assessment using eddy current measurements. First, the paper establishes the relationship between the familiar isothermal piezoresistivity coefficients measured under uniaxial tension and hydrostatic pressure and the relevant isothermal electroelastic coefficients measured under uniaxial and biaxial Stress conditions either by non‐directional circular or directional elliptical eddy current coils. In order to quantitatively assess the prevailing residual Stress from eddy current conductivity measurements, the electroelastic coefficients must be first determined. These calibration measurements are usually conducted on a reference specimen of the material to be tested using cyclic uniaxial loads between 0.1 and 10 Hz, which is fast enough to produce adiabatic conditions....
F Deschamps - One of the best experts on this subject based on the ideXlab platform.
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clinical Stress Assessment using a visual analogue scale
Occupational Medicine, 2012Co-Authors: Francoisxavier Lesage, Sophie Berjot, F DeschampsAbstract:Background Clinicians increasingly require short, efficient methods for assessing diStress, both in applied research and clinical settings. Most of the available questionnaires are unsuitable for busy clinical settings. The visual analogue scale (VAS) is widely but empirically used to assess perceived Stress. Aims To provide evidence on two of the psychometric properties of the VAS: its discriminative sensitivity (capacity to highlight a difference between groups) and its interconcept validity (the relationship between VAS Stress Assessment and the Assessment of different, but similar concepts). Methods Employees attending occupational health centres were randomly selected and completed the VAS and also either the Perceived Stress Scale (PSS) or the Hospital Anxiety and Depression Scale (HADS). Analyses of variance were performed to study group effects (age, sex, marital status, parental status, occupational status) on Stress scores (PSS and VAS). Results In total, 763 employees participated of whom 501 completed the PSS and 262 the HADS. P-values obtained for the effects of sex, age and occupational status were lower with the VAS than with the PSS. Correlations between the VAS and the anxiety subscale, depression subscale and total score of the HADS were 0.66, 0.45 and 0.65, respectively. Other tools used to assess aspects of psychological diStress are known to have similar correlations. Conclusions Our findings provide evidence that the VAS is at least as discriminating as a questionnaire when it comes to highlighting differences in Stress levels between two groups, and the observed correlations with related constructs support its construct validity.
Francoisxavier Lesage - One of the best experts on this subject based on the ideXlab platform.
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clinical Stress Assessment using a visual analogue scale
Occupational Medicine, 2012Co-Authors: Francoisxavier Lesage, Sophie Berjot, F DeschampsAbstract:Background Clinicians increasingly require short, efficient methods for assessing diStress, both in applied research and clinical settings. Most of the available questionnaires are unsuitable for busy clinical settings. The visual analogue scale (VAS) is widely but empirically used to assess perceived Stress. Aims To provide evidence on two of the psychometric properties of the VAS: its discriminative sensitivity (capacity to highlight a difference between groups) and its interconcept validity (the relationship between VAS Stress Assessment and the Assessment of different, but similar concepts). Methods Employees attending occupational health centres were randomly selected and completed the VAS and also either the Perceived Stress Scale (PSS) or the Hospital Anxiety and Depression Scale (HADS). Analyses of variance were performed to study group effects (age, sex, marital status, parental status, occupational status) on Stress scores (PSS and VAS). Results In total, 763 employees participated of whom 501 completed the PSS and 262 the HADS. P-values obtained for the effects of sex, age and occupational status were lower with the VAS than with the PSS. Correlations between the VAS and the anxiety subscale, depression subscale and total score of the HADS were 0.66, 0.45 and 0.65, respectively. Other tools used to assess aspects of psychological diStress are known to have similar correlations. Conclusions Our findings provide evidence that the VAS is at least as discriminating as a questionnaire when it comes to highlighting differences in Stress levels between two groups, and the observed correlations with related constructs support its construct validity.
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Validity of occupational Stress Assessment using a visual analogue scale
Occupational Medicine, 2011Co-Authors: Francoisxavier Lesage, Sophie BerjotAbstract:BACKGROUND: The visual analogue scale (VAS) is empirically used by occupational physicians to assess Stress but very few studies have been published about its quantitative validation. AIMS: To assess the external validity of the VAS for the Assessment of Stress in the clinical occupational health setting by comparing its scores with the Perceived Stress Scale (PSS) of Cohen. METHODS: An anonymous self-completed questionnaire (PSS14) and the VAS were filled in by a random sample of 360 workers from several occupational health centres. RESULTS: No difference between the mean scores of PSS14 and Stress VAS was found. The equation of the linear regression was 'VAS score = -0.18 + 1008 × PSS14 score'. A VAS score of 7.0 was identified as having the best sensitivity/specificity ratio (0.74 and 0.93, respectively) for identifying those with 'high Stress' using the PSS cut-off score of 7.2, using a receiver operator curve approach. CONCLUSIONS: Our results support an acceptable agreement between the two tests, meaning that the two tools assess the same psychological construct. The good sensitivity/specificity ratio and the area under the curve close to 1 provide evidence that a VAS is suitable to help the occupational physician detect a high level of Stress. The use of a VAS for Stress Assessment seems to be meaningful, suitable and useful for occupational physicians.
Oscar Mayora - One of the best experts on this subject based on the ideXlab platform.
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Unobtrusive Stress Assessment Using Smartphones
IEEE Transactions on Mobile Computing, 1Co-Authors: Alban Maxhuni, Pablo Hernadez-leal, Eduardo F. Morales, Enrique Sucar, Venet Osmani, Oscar MayoraAbstract:Stress Assessment is a complex issue and numerous studies have examined factors that influence Stress in working environments. Research studies have shown that monitoring individuals' behaviour parameters during daily life can also help assess Stress levels. In this study, we examine Assessment of work-related Stress using features derived from sensors in smartphones. In particular, we use information from physical activity levels, location, social-interactions, social-activity and application usage during working days. Our study included 30 employees chosen from two different private companies, monitored over a period of 8 weeks in real work environments. The findings suggest that information from phone sensors shows important correlation with employees perceived Stress level. Secondly, we used machine learning methods to classify perceived Stress levels based on the analysis of information provided by smartphones. We used decision trees obtaining 67.57% accuracy and 71.73% after applying a semi-supervised method. Our results show that Stress levels can be monitored in unobtrusive manner, through analysis of smartphone data.
Sophie Berjot - One of the best experts on this subject based on the ideXlab platform.
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clinical Stress Assessment using a visual analogue scale
Occupational Medicine, 2012Co-Authors: Francoisxavier Lesage, Sophie Berjot, F DeschampsAbstract:Background Clinicians increasingly require short, efficient methods for assessing diStress, both in applied research and clinical settings. Most of the available questionnaires are unsuitable for busy clinical settings. The visual analogue scale (VAS) is widely but empirically used to assess perceived Stress. Aims To provide evidence on two of the psychometric properties of the VAS: its discriminative sensitivity (capacity to highlight a difference between groups) and its interconcept validity (the relationship between VAS Stress Assessment and the Assessment of different, but similar concepts). Methods Employees attending occupational health centres were randomly selected and completed the VAS and also either the Perceived Stress Scale (PSS) or the Hospital Anxiety and Depression Scale (HADS). Analyses of variance were performed to study group effects (age, sex, marital status, parental status, occupational status) on Stress scores (PSS and VAS). Results In total, 763 employees participated of whom 501 completed the PSS and 262 the HADS. P-values obtained for the effects of sex, age and occupational status were lower with the VAS than with the PSS. Correlations between the VAS and the anxiety subscale, depression subscale and total score of the HADS were 0.66, 0.45 and 0.65, respectively. Other tools used to assess aspects of psychological diStress are known to have similar correlations. Conclusions Our findings provide evidence that the VAS is at least as discriminating as a questionnaire when it comes to highlighting differences in Stress levels between two groups, and the observed correlations with related constructs support its construct validity.
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Validity of occupational Stress Assessment using a visual analogue scale
Occupational Medicine, 2011Co-Authors: Francoisxavier Lesage, Sophie BerjotAbstract:BACKGROUND: The visual analogue scale (VAS) is empirically used by occupational physicians to assess Stress but very few studies have been published about its quantitative validation. AIMS: To assess the external validity of the VAS for the Assessment of Stress in the clinical occupational health setting by comparing its scores with the Perceived Stress Scale (PSS) of Cohen. METHODS: An anonymous self-completed questionnaire (PSS14) and the VAS were filled in by a random sample of 360 workers from several occupational health centres. RESULTS: No difference between the mean scores of PSS14 and Stress VAS was found. The equation of the linear regression was 'VAS score = -0.18 + 1008 × PSS14 score'. A VAS score of 7.0 was identified as having the best sensitivity/specificity ratio (0.74 and 0.93, respectively) for identifying those with 'high Stress' using the PSS cut-off score of 7.2, using a receiver operator curve approach. CONCLUSIONS: Our results support an acceptable agreement between the two tests, meaning that the two tools assess the same psychological construct. The good sensitivity/specificity ratio and the area under the curve close to 1 provide evidence that a VAS is suitable to help the occupational physician detect a high level of Stress. The use of a VAS for Stress Assessment seems to be meaningful, suitable and useful for occupational physicians.