The Experts below are selected from a list of 13053 Experts worldwide ranked by ideXlab platform
Ali Fatemi - One of the best experts on this subject based on the ideXlab platform.
-
fatigue crack growth behavior in the presence of notches and multiaxial Nominal Stress states
Engineering Fracture Mechanics, 2016Co-Authors: Nicholas R. Gates, Ali FatemiAbstract:Abstract The primary focus of this study was to evaluate the effects of notches and multiaxial Nominal Stress states on mode I crack growth behavior under constant amplitude loading conditions. As a result, a variety of fatigue tests were performed using notched tubular and plate specimens made from 2024-T3 aluminum alloy. Because crack growth data were recorded for naturally initiated fatigue cracks, which can develop in different locations at the notch root, notch effects on crack growth were studied with respect to different initial crack geometry assumptions. By using an effective SIF model to account for Stress concentration and boundary condition effects on crack growth from notches, crack growth rate correlations were found to improve over those based on long crack assumptions. Additionally, tubular specimen tests performed using different Nominal loading paths allowed for the evaluation of multiaxial Stress state effects, including those from non-proportional loading, on the resulting mode I crack growth behavior. Crack growth rates for specimens subjected to multiaxial Nominal Stress states were observed to be higher than those for uniaxial loading conditions at the same Nominal mode I SIF range. While T-Stress corrections were able to account for the higher growth rates in some cases, they were unable to collapse all of the tubular specimen crack growth data into a single narrow band. Furthermore, the presence of mixed-mode crack growth effects was determined to be a likely cause for curvilinear crack paths and higher crack growth rates observed for longer cracks growing under 90° out-of-phase non-proportional loading conditions.
-
Notched fatigue behavior and Stress analysis under multiaxial states of Stress
International Journal of Fatigue, 2014Co-Authors: Nicholas R. Gates, Ali FatemiAbstract:Abstract The effect of notches on multiaxial fatigue behavior was studied using thin-walled tubular 2024-T3 aluminum specimens with a circular transverse hole. Constant amplitude fully reversed axial, torsion, and in-phase and 90° out-of-phase axial–torsion tests were performed in load control. Stress analysis was performed using both Neuber’s rule and FEA to study local Stress distributions. Neuber’s rule was found to be in reasonable agreement with FEA results for all loading conditions considered. Fatigue crack initiation for all loading cases examined was experimentally observed to occur on planes of maximum shear. For the same equivalent Nominal Stress, experimental lives in pure torsion were longer than those for pure axial loading. In-phase fatigue lives were also longer than out-of-phase lives at the same equivalent Stress. The Nominal Stress–life approach, applied by considering the fatigue notch factor along with both maximum principal Stress and von Mises equivalent (or effective) Stress, produced mostly non-conservative fatigue life predictions that varied by as much as a factor of 10 from experimental results. The local Stress and strain–life approaches, based on von Mises effective Stress or strain, resulted in reasonable correlation of test data at shorter fatigue lives, but became increasingly less accurate in the mid to high cycle fatigue regime, where predictions were in error by more than a factor of 10. The Fatemi–Socie critical plane parameter correlated all test data reasonably well (typically within a factor of 3) and is consistent with the experimentally observed damage mechanism for the tested material.
Patrick Ebermann - One of the best experts on this subject based on the ideXlab platform.
-
irreversible degradation of nb3sn rutherford cables due to transverse compressive Stress at room temperature
Superconductor Science and Technology, 2018Co-Authors: Patrick Ebermann, Johannes Bernardi, J Fleiter, Friedrich Lackner, Florian Meuter, Magdalena Pieler, C Scheuerlein, Daniel Schoerling, Felix WolfAbstract:In the framework of the Future Circular Collider design study for a 100 TeV circular collider, 16 T superconducting bending magnets based on Nb3Sn technology are being developed. A pre-Stress on the conductor during magnet assembly at room temperature (RT) is needed to counteract the Lorentz forces during operation. The superconducting properties of the brittle Nb3Sn superconductor are strain sensitive and excessive pre-Stress leads to an irreversible degradation of the superconductor. In order to determine the level of acceptable pre-Stress during the magnet assembly process, reacted and impregnated Nb3Sn cables were exposed to increasing transverse compressive Stress up to a maximum Stress level of 200 MPa at RT. After each Stress cycle, the critical current of the cable specimens were characterized at 4.3 K in the FRESCA cable test station. No significant critical current degradation was observed up to 150 MPa, followed by degradation less than 4% after a Nominal Stress of 175 MPa. A dramatic permanent critical current degradation occurred after applying a Nominal Stress of 200 MPa. A comprehensive post analysis consisting of non-destructive micro-tomography followed by microscopic characterization of metallographic cable cross sections was carried out after the critical current test to reveal cracks in the Nb3Sn sub-elements of the loaded specimen.
Nicholas R. Gates - One of the best experts on this subject based on the ideXlab platform.
-
fatigue crack growth behavior in the presence of notches and multiaxial Nominal Stress states
Engineering Fracture Mechanics, 2016Co-Authors: Nicholas R. Gates, Ali FatemiAbstract:Abstract The primary focus of this study was to evaluate the effects of notches and multiaxial Nominal Stress states on mode I crack growth behavior under constant amplitude loading conditions. As a result, a variety of fatigue tests were performed using notched tubular and plate specimens made from 2024-T3 aluminum alloy. Because crack growth data were recorded for naturally initiated fatigue cracks, which can develop in different locations at the notch root, notch effects on crack growth were studied with respect to different initial crack geometry assumptions. By using an effective SIF model to account for Stress concentration and boundary condition effects on crack growth from notches, crack growth rate correlations were found to improve over those based on long crack assumptions. Additionally, tubular specimen tests performed using different Nominal loading paths allowed for the evaluation of multiaxial Stress state effects, including those from non-proportional loading, on the resulting mode I crack growth behavior. Crack growth rates for specimens subjected to multiaxial Nominal Stress states were observed to be higher than those for uniaxial loading conditions at the same Nominal mode I SIF range. While T-Stress corrections were able to account for the higher growth rates in some cases, they were unable to collapse all of the tubular specimen crack growth data into a single narrow band. Furthermore, the presence of mixed-mode crack growth effects was determined to be a likely cause for curvilinear crack paths and higher crack growth rates observed for longer cracks growing under 90° out-of-phase non-proportional loading conditions.
-
Notched fatigue behavior and Stress analysis under multiaxial states of Stress
International Journal of Fatigue, 2014Co-Authors: Nicholas R. Gates, Ali FatemiAbstract:Abstract The effect of notches on multiaxial fatigue behavior was studied using thin-walled tubular 2024-T3 aluminum specimens with a circular transverse hole. Constant amplitude fully reversed axial, torsion, and in-phase and 90° out-of-phase axial–torsion tests were performed in load control. Stress analysis was performed using both Neuber’s rule and FEA to study local Stress distributions. Neuber’s rule was found to be in reasonable agreement with FEA results for all loading conditions considered. Fatigue crack initiation for all loading cases examined was experimentally observed to occur on planes of maximum shear. For the same equivalent Nominal Stress, experimental lives in pure torsion were longer than those for pure axial loading. In-phase fatigue lives were also longer than out-of-phase lives at the same equivalent Stress. The Nominal Stress–life approach, applied by considering the fatigue notch factor along with both maximum principal Stress and von Mises equivalent (or effective) Stress, produced mostly non-conservative fatigue life predictions that varied by as much as a factor of 10 from experimental results. The local Stress and strain–life approaches, based on von Mises effective Stress or strain, resulted in reasonable correlation of test data at shorter fatigue lives, but became increasingly less accurate in the mid to high cycle fatigue regime, where predictions were in error by more than a factor of 10. The Fatemi–Socie critical plane parameter correlated all test data reasonably well (typically within a factor of 3) and is consistent with the experimentally observed damage mechanism for the tested material.
Felix Wolf - One of the best experts on this subject based on the ideXlab platform.
-
irreversible degradation of nb3sn rutherford cables due to transverse compressive Stress at room temperature
Superconductor Science and Technology, 2018Co-Authors: Patrick Ebermann, Johannes Bernardi, J Fleiter, Friedrich Lackner, Florian Meuter, Magdalena Pieler, C Scheuerlein, Daniel Schoerling, Felix WolfAbstract:In the framework of the Future Circular Collider design study for a 100 TeV circular collider, 16 T superconducting bending magnets based on Nb3Sn technology are being developed. A pre-Stress on the conductor during magnet assembly at room temperature (RT) is needed to counteract the Lorentz forces during operation. The superconducting properties of the brittle Nb3Sn superconductor are strain sensitive and excessive pre-Stress leads to an irreversible degradation of the superconductor. In order to determine the level of acceptable pre-Stress during the magnet assembly process, reacted and impregnated Nb3Sn cables were exposed to increasing transverse compressive Stress up to a maximum Stress level of 200 MPa at RT. After each Stress cycle, the critical current of the cable specimens were characterized at 4.3 K in the FRESCA cable test station. No significant critical current degradation was observed up to 150 MPa, followed by degradation less than 4% after a Nominal Stress of 175 MPa. A dramatic permanent critical current degradation occurred after applying a Nominal Stress of 200 MPa. A comprehensive post analysis consisting of non-destructive micro-tomography followed by microscopic characterization of metallographic cable cross sections was carried out after the critical current test to reveal cracks in the Nb3Sn sub-elements of the loaded specimen.
Bashir S Shariat - One of the best experts on this subject based on the ideXlab platform.
-
pseudoelastic behaviour of perforated niti shape memory plates under tension
Intermetallics, 2014Co-Authors: Bashir S ShariatAbstract:Abstract This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with circular, elliptical and square holes. The investigation is done both experimentally and by mathematical modelling. It is found that the Nominal Stress–strain curve of such structures deviates from typical Stress–strain variation of NiTi with flat Stress plateaus, by exhibiting Stress gradients over the forward and reverse transformations of the hole-affected areas. The hole-affected length is nearly triple the lateral dimension of the hole, and when 33% of the gauge length is covered by (circular) holes, the entire sample behaves like a functionally graded material. Such mechanical behaviour is advantageous for achieving better load–displacement controllability and wider Stress window for shape memory actuation and sensing.