The Experts below are selected from a list of 5574 Experts worldwide ranked by ideXlab platform
David P. Kihl - One of the best experts on this subject based on the ideXlab platform.
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Stochastic Fatigue Damage Accumulation in a T-welded joint accounting for the residual stress fields
International Journal of Fatigue, 2001Co-Authors: Shahram Sarkani, George Michaelov, David P. KihlAbstract:Abstract The residual stresses that occur as a result of nonhomogeneous heating and cooling during welding may have a significant effect on the Accumulation of Fatigue Damage in a welded joint. The problem is complicated not because of the complex spatial distribution of the residual stress fields, but because those fields typically change under an applied load. The present study considers the effect of residual stresses on Fatigue Damage Accumulation in a welded joint subjected to stochastic loading. The influence of residual stresses on stochastic Fatigue Damage Accumulation is accounted for by a simple approach based on an elastic–perfectly-plastic material model and the Gerber correction factor. The model assumes that the residual stress remaining at the critical location depends on the largest nominal stress ever endured by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic–plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of Fatigue Damage Accumulation.
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Stochastic Fatigue Damage Accumulation under broadband loadings
International Journal of Fatigue, 1999Co-Authors: David P. Kihl, Shahram Sarkani, Jeffrey E. BeachAbstract:Abstract Fatigue tests were conducted on 72 high-strength welded steel cruciform-shaped specimens subjected to stochastic loadings. Results of these tests are used to investigate experimentally the effects of loading non-normality and frequency bandwidth and truncation on the rate of Fatigue Damage Accumulation. Test results are compared with predictions made using Rayleigh approximation and rainflow analysis in terms of cycles and time to failure. Results indicate that non-normality can significantly increase the rate of Fatigue Damage Accumulation, and can result in non-conservative Fatigue life estimates if its effect is not accounted for, regardless of frequency content. Likewise, frequency content was also found to influence the rate of Fatigue Damage Accumulation, but to a lesser extent than non-normality. When higher-frequency components were included, shorter Fatigue lives were observed. Fatigue life predictions using rainflow analysis produced good agreement with experimental results; predictions made using Rayleigh approximation produced non-conservative Fatigue life estimates.
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Stochastic Fatigue Damage Accumulation of FRP Laminates and Joints
Journal of Structural Engineering, 1999Co-Authors: Shahram Sarkani, David P. Kihl, George Michaelov, Jeffrey E. BeachAbstract:Results are presented from a study on Fatigue Damage Accumulation in fiber-reinforced plastic coupons and joints. The main objective of the study is to investigate the effectiveness of the Palmgren-Miner linear Damage Accumulation model in predicting the Fatigue lives of FRP structures under stochastic loading histories. The coupon specimens used in the study are configured four ways: with the laminate laid up in two loading directions (0/90° and ±45°), and with the load transferred by two types of bearing (passive and active). The joint specimens considered represent bonded, bolted, and bonded-bolted butt-strap configurations. The results of the constant-amplitude Fatigue tests are fitted to two types of S-N curve models: power-law and exponential. Variable-amplitude Fatigue tests using narrow-band stochastic stress histories with various root-mean-square stresses are carried out. Rayleigh approximation formulas corresponding to both types of S-N curves are used to predict the Fatigue lives based on the S-N curve and loading parameters. The analytical Fatigue life predictions are compared with the experimental results. It is shown that the analytical predictions may overestimate or underestimate the actual Fatigue lives, depending on the specimen configuration and the root-mean-square stress level.
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Fatigue of welded steel joints under wideband loadings
Probabilistic Engineering Mechanics, 1996Co-Authors: Shahram Sarkani, David P. Kihl, George Michaelov, J. E. BeachAbstract:Abstract Fatigue tests were conducted on high-strength welded steel cruciform-shaped specimens subjected to random loadings to investigate the effects of loading intensity, nonnormality and frequency bandwidth on the rate of Fatigue Damage Accumulation. The test result are compared with predictions made using the Rayleigh approximation and rainflow analysis in terms of cycles and times to failure. Results indicate that nonnormality can significantly increase the rate of Fatigue Damage Accumulation and result in nonconservative Fatigue life estimates if it is effect is not accounted for properly. Likewise, frequency content was also found to influence the rate of Fatigue Damage Accumulation, but to a lesser extent than nonnormality.
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STOCHASTIC Fatigue OF WELDED STEEL JOINTS
1995Co-Authors: Shahram Sarkani, David P. Kihl, J. E. BeachAbstract:Fatigue tests were conducted on high strength welded steel cruciform shaped specimens subjected to random amplitude loadings. Results of these tests are used to experimentally investigate the effects of loading intensity, non-normality and frequency bandwidth on the rate of Fatigue Damage Accumulation. Test results are compared with predictions made using Rayleigh approximation and rainflow analysis in terms of cycles and times to failure. Results indicate non-normality can significantly increase the rate of Fatigue Damage Accumulation and result in non-conservative Fatigue life estimates if its effect is not accounted for. Likewise, frequency content was also found to influence the rate of Fatigue Damage Accumulation, but to a lesser extent than non-normality. When higher frequency components were included, shorter Fatigue lives were observed. Fatigue life predictions using rainflow analysis produced generally good agreement with experimental results.
Shahram Sarkani - One of the best experts on this subject based on the ideXlab platform.
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Development and Application of a Model Using Center of Gravity of Hysteresis Loops to Predict Fatigue Damage Accumulation in Fiber-reinforced Plastic Laminates
Journal of Composite Materials, 2005Co-Authors: Kourosh Momenkhani, Shahram Sarkani, D. L. JonesAbstract:A new methodology for modeling Fatigue Damage Accumulation in fiber-reinforced plastic (FRP) laminates is introduced. This new model, termed the CG method, or the CG Model, utilizes the center of gravity (CG) of hysteresis loops (HL). It is inspired by previous investigations into Damage Accumulation models based on HL, such as maximum displacement (the width of the HL), energy dissipation (the area of the HL), plastic strain (the width of the interior part of the HL), and stiffness reduction. The CG method combines all these models, relates them to each other, and presents very consistent results. The CG model is especially helpful in cases where the other models cannot be used. This study shows that using the CG model a set of straight lines is created that present the evolution of the positions of the CG of the HLs during Fatigue tests. These ‘curves’ may then be employed to build the complete set of curves that, even for untested specimens at different stress levels, accurately predict Fatigue Damage ...
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Nondestructive Evaluation of Residual Stresses in Welded Joints with Application to Stochastic Fatigue Damage Accumulation
NDT Methods Applied to Fatigue Reliability Assessment of Structures, 2004Co-Authors: Shahram Sarkani, George Michaelov, Loren D. LutesAbstract:Some of the most popular techniques for nondestructive evaluation of residual stresses in welded joints are described. Particular attention is paid to the X-ray diffraction and neutron diffraction method. The neutron diffraction method is the only nondestructive technique that is able to provide a complete, through-thickness distribution of the residual stresses in welded joints. The information on residual stresses is particularly important for Fatigue Damage calculation under stochastic loadings. It is demonstrated that the influence of residual stresses on stochastic Fatigue Damage Accumulation may be incorporated by a simple approach based on elastic-perfectly-plastic material model and the Gerber correction factor. The model assumes that the remaining residual stress at the critical location depends on the largest nominal stress ever seen by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic-plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte-Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of Fatigue Damage Accumulation.
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Stochastic Fatigue Damage Accumulation in a T-welded joint accounting for the residual stress fields
International Journal of Fatigue, 2001Co-Authors: Shahram Sarkani, George Michaelov, David P. KihlAbstract:Abstract The residual stresses that occur as a result of nonhomogeneous heating and cooling during welding may have a significant effect on the Accumulation of Fatigue Damage in a welded joint. The problem is complicated not because of the complex spatial distribution of the residual stress fields, but because those fields typically change under an applied load. The present study considers the effect of residual stresses on Fatigue Damage Accumulation in a welded joint subjected to stochastic loading. The influence of residual stresses on stochastic Fatigue Damage Accumulation is accounted for by a simple approach based on an elastic–perfectly-plastic material model and the Gerber correction factor. The model assumes that the residual stress remaining at the critical location depends on the largest nominal stress ever endured by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic–plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of Fatigue Damage Accumulation.
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Stochastic Fatigue Damage Accumulation under broadband loadings
International Journal of Fatigue, 1999Co-Authors: David P. Kihl, Shahram Sarkani, Jeffrey E. BeachAbstract:Abstract Fatigue tests were conducted on 72 high-strength welded steel cruciform-shaped specimens subjected to stochastic loadings. Results of these tests are used to investigate experimentally the effects of loading non-normality and frequency bandwidth and truncation on the rate of Fatigue Damage Accumulation. Test results are compared with predictions made using Rayleigh approximation and rainflow analysis in terms of cycles and time to failure. Results indicate that non-normality can significantly increase the rate of Fatigue Damage Accumulation, and can result in non-conservative Fatigue life estimates if its effect is not accounted for, regardless of frequency content. Likewise, frequency content was also found to influence the rate of Fatigue Damage Accumulation, but to a lesser extent than non-normality. When higher-frequency components were included, shorter Fatigue lives were observed. Fatigue life predictions using rainflow analysis produced good agreement with experimental results; predictions made using Rayleigh approximation produced non-conservative Fatigue life estimates.
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Stochastic Fatigue Damage Accumulation of FRP Laminates and Joints
Journal of Structural Engineering, 1999Co-Authors: Shahram Sarkani, David P. Kihl, George Michaelov, Jeffrey E. BeachAbstract:Results are presented from a study on Fatigue Damage Accumulation in fiber-reinforced plastic coupons and joints. The main objective of the study is to investigate the effectiveness of the Palmgren-Miner linear Damage Accumulation model in predicting the Fatigue lives of FRP structures under stochastic loading histories. The coupon specimens used in the study are configured four ways: with the laminate laid up in two loading directions (0/90° and ±45°), and with the load transferred by two types of bearing (passive and active). The joint specimens considered represent bonded, bolted, and bonded-bolted butt-strap configurations. The results of the constant-amplitude Fatigue tests are fitted to two types of S-N curve models: power-law and exponential. Variable-amplitude Fatigue tests using narrow-band stochastic stress histories with various root-mean-square stresses are carried out. Rayleigh approximation formulas corresponding to both types of S-N curves are used to predict the Fatigue lives based on the S-N curve and loading parameters. The analytical Fatigue life predictions are compared with the experimental results. It is shown that the analytical predictions may overestimate or underestimate the actual Fatigue lives, depending on the specimen configuration and the root-mean-square stress level.
George Michaelov - One of the best experts on this subject based on the ideXlab platform.
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Nondestructive Evaluation of Residual Stresses in Welded Joints with Application to Stochastic Fatigue Damage Accumulation
NDT Methods Applied to Fatigue Reliability Assessment of Structures, 2004Co-Authors: Shahram Sarkani, George Michaelov, Loren D. LutesAbstract:Some of the most popular techniques for nondestructive evaluation of residual stresses in welded joints are described. Particular attention is paid to the X-ray diffraction and neutron diffraction method. The neutron diffraction method is the only nondestructive technique that is able to provide a complete, through-thickness distribution of the residual stresses in welded joints. The information on residual stresses is particularly important for Fatigue Damage calculation under stochastic loadings. It is demonstrated that the influence of residual stresses on stochastic Fatigue Damage Accumulation may be incorporated by a simple approach based on elastic-perfectly-plastic material model and the Gerber correction factor. The model assumes that the remaining residual stress at the critical location depends on the largest nominal stress ever seen by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic-plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte-Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of Fatigue Damage Accumulation.
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Stochastic Fatigue Damage Accumulation in a T-welded joint accounting for the residual stress fields
International Journal of Fatigue, 2001Co-Authors: Shahram Sarkani, George Michaelov, David P. KihlAbstract:Abstract The residual stresses that occur as a result of nonhomogeneous heating and cooling during welding may have a significant effect on the Accumulation of Fatigue Damage in a welded joint. The problem is complicated not because of the complex spatial distribution of the residual stress fields, but because those fields typically change under an applied load. The present study considers the effect of residual stresses on Fatigue Damage Accumulation in a welded joint subjected to stochastic loading. The influence of residual stresses on stochastic Fatigue Damage Accumulation is accounted for by a simple approach based on an elastic–perfectly-plastic material model and the Gerber correction factor. The model assumes that the residual stress remaining at the critical location depends on the largest nominal stress ever endured by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic–plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of Fatigue Damage Accumulation.
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Stochastic Fatigue Damage Accumulation of FRP Laminates and Joints
Journal of Structural Engineering, 1999Co-Authors: Shahram Sarkani, David P. Kihl, George Michaelov, Jeffrey E. BeachAbstract:Results are presented from a study on Fatigue Damage Accumulation in fiber-reinforced plastic coupons and joints. The main objective of the study is to investigate the effectiveness of the Palmgren-Miner linear Damage Accumulation model in predicting the Fatigue lives of FRP structures under stochastic loading histories. The coupon specimens used in the study are configured four ways: with the laminate laid up in two loading directions (0/90° and ±45°), and with the load transferred by two types of bearing (passive and active). The joint specimens considered represent bonded, bolted, and bonded-bolted butt-strap configurations. The results of the constant-amplitude Fatigue tests are fitted to two types of S-N curve models: power-law and exponential. Variable-amplitude Fatigue tests using narrow-band stochastic stress histories with various root-mean-square stresses are carried out. Rayleigh approximation formulas corresponding to both types of S-N curves are used to predict the Fatigue lives based on the S-N curve and loading parameters. The analytical Fatigue life predictions are compared with the experimental results. It is shown that the analytical predictions may overestimate or underestimate the actual Fatigue lives, depending on the specimen configuration and the root-mean-square stress level.
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Fatigue of welded steel joints under wideband loadings
Probabilistic Engineering Mechanics, 1996Co-Authors: Shahram Sarkani, David P. Kihl, George Michaelov, J. E. BeachAbstract:Abstract Fatigue tests were conducted on high-strength welded steel cruciform-shaped specimens subjected to random loadings to investigate the effects of loading intensity, nonnormality and frequency bandwidth on the rate of Fatigue Damage Accumulation. The test result are compared with predictions made using the Rayleigh approximation and rainflow analysis in terms of cycles and times to failure. Results indicate that nonnormality can significantly increase the rate of Fatigue Damage Accumulation and result in nonconservative Fatigue life estimates if it is effect is not accounted for properly. Likewise, frequency content was also found to influence the rate of Fatigue Damage Accumulation, but to a lesser extent than nonnormality.
Huifeng Tan - One of the best experts on this subject based on the ideXlab platform.
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Fatigue Damage Accumulation of Steel/rubber Composite
Journal of Materials Science & Technology, 2006Co-Authors: Zhenhui Tian, Huifeng TanAbstract:The Fatigue Damage Accumulation of [§20 ‐ ] laminated steel cord reinforced rubber composite under T-T loading was studied. Results indicate that the increase in the cyclic maximum strain exhibits three-stage tendency in the process of Fatigue. The macroscopic Fatigue Damage initiates from the ends of steel cords in the form of cylindrical crack. Damage propagates along with the increase in crack numbers, the cord/matrix interface debonding and the growth of interply cracks. By using the dynamic creep as parameter, a linear Fatigue Damage Accumulation model was established. This model can be used under dual loading conditions to estimate the residual Fatigue life of the specimen.
Dimitrios G. Pavlou - One of the best experts on this subject based on the ideXlab platform.
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a one parameter nonlinear Fatigue Damage Accumulation model
International Journal of Fatigue, 2017Co-Authors: Kristen Rege, Dimitrios G. PavlouAbstract:Abstract A nonlinear model for Fatigue Damage Accumulation under variable amplitude loading is presented. The known assumption that the isoDamage curves are converging at the knee point of the S-N curve of the material, has been adopted. The proposed model does only require one parameter, in addition to the S-N curve of the material, in order to calculate the remaining Fatigue life. A single value for the parameter has been found to give satisfying agreement with experimental data for four arbitrary selected steels, indicating a general trend.
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A Phenomenological Approach for Fatigue Damage Accumulation of CF/PEEK Laminates Under Two-Stage Loading
International Review of Mechanical Engineering-IREME, 2013Co-Authors: Dimitrios G. Pavlou, Kyriakos I KourousisAbstract:The life of composite materials (CM) subjected to Fatigue conditions is associated with the gradual Damage of their structure. Since the Damage Accumulation is reflected by changes in CM properties, the derivation of Damage Accumulation curves may be based on test results providing the reduction of the residual strength. Examined in this work is a non-linear Fatigue Damage Accumulation function for cross-ply CF/PEEK laminates. This Damage function is specified with respect to Damage parameters derived by the strength decrease during Fatigue for the CF/PEEK. Taking into account this concept, an improvement of the theory of isoDamage lines is proposed. Since the nonlinearity of the derived Damage function depends on an exponent that is a function of the Fatigue stress amplitude, the effect of the loading order and the previous Damage history on the total Fatigue life is investigated. Numerical examples of Fatigue life prediction under two-stage loading conditions and a Damage Accumulation map for the CP/PEEK are presented and discussed.
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Derivation of Fatigue Damage Accumulation curves based on changes in composite material properties
2013Co-Authors: Dimitrios G. Pavlou, Kyriakos I KourousisAbstract:The life of composite materials (CM) subjected to Fatigue conditions is associated with the gradual Damage of their structure. Since the Damage Accumulation is reflected by changes in CM properties, the derivation of Damage Accumulation curves may be based on test results providing the reduction of the residual strength. Examined in this work is a non-linear Fatigue Damage Accumulation function for cross-ply CF/PEEK laminates. This Damage function is specified with respect to Damage parameters derived by the strength decrease during Fatigue for the CF/PEEK. Taking into account this concept, an improvement of the theory of isoDamage lines is proposed. Since the nonlinearity of the derived Damage function depends on an exponent that is a function of the Fatigue stress amplitude, the effect of the loading order and the previous Damage history on the total Fatigue life is investigated. Numerical examples of Fatigue life prediction under two-stage loading conditions and a Damage Accumulation map for the CP/PEEK are presented and discussed.
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A phenomenological Fatigue Damage Accumulation rule based on hardness increasing, for the 2024-T42 aluminum
Engineering Structures, 2002Co-Authors: Dimitrios G. PavlouAbstract:Abstract In this paper the problem of cummulative Fatigue Damage is considered. A non-linear Fatigue Damage Accumulation rule, suitable for stepwise constant amplitude Fatigue loading, is presented for the aerospace material Al-2024-T42. The proposed rule takes into account the previous Damage history as well as the loading order effect. This Damage function is specified with respect to Damage parameters derived by the hardness increase during Fatigue of the material Al-2024-T42. Theoretical results are correlated with experimental data for specimens subjected to two stage Fatigue loading.
