The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Shuai Liu - One of the best experts on this subject based on the ideXlab platform.
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Serrated flow and failure behaviors of a Hadfield steel at various Strain rates under extensometer-Measured Strain control tensile load
Journal of Materials Research and Technology, 2020Co-Authors: Liqiang Zhang, Pengcheng Guo, Guan Wang, Shuai LiuAbstract:Abstract A Hadfield steel has been investigated to clarify the serrated flow and to explore the failure behavior at room temperature. The tensile experiments were performed under extensometer-Measured Strain control, rather than under conventional cross-head displacement control, at Strain rates ranging from 6 × 10−3 s−1 to 6 × 10−6 s−1. Three types of serrations, including type A, B and C ones, are observed. The occurrence of different types of serrations depends on both Strain rate and Strain level. The type C serration is identified in Hadfield steels at room temperature for the first time. At high Strain rates, there is substantially higher serration density and reduction in stress compared with that observed at low Strain rates. Furthermore, two different initiation modes of deformation bands are revealed. The fracture crack nucleates at a position with dense twins, and propagates primarily in the direction perpendicular to the tensile axis and deflects frequently due to the interaction with the boundary of grains and twins.
Alexis Mendez - One of the best experts on this subject based on the ideXlab platform.
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Accurate Temperature Compensation and Characterization of Overall System Thermal Response Using Total Measured Strain in FBG Sensors
Structural Health Monitoring-an International Journal, 2013Co-Authors: Todd Haber, Stephen K. Ferguson, D. Guthrie, T. Graver, B. J. Soller, Alexis MendezAbstract:One of the most common fiber optic sensor (FOS) types used are fiber Bragg gratings (FBG) -based Strain sensors are simultaneously sensitive to both temperature and Strain. Thus it is essential to utilize sensors that are either fully temperature insensitive or, alternatively, properly temperature compensated to avoid erroneous measurements. In this paper, we introduce the concept of Measured “total Strain”, which is inherent and unique to optical Strain sensors. We review and analyze the temperature and Strain sensitivities of FBG Strain sensors and decompose the total Measured Strain into thermal and non-thermal components. We explore the differences between substrate CTE and System Thermal Response Coefficients, which govern the type and quality of thermal Strain decomposition analysis.
Chan-gi Pak - One of the best experts on this subject based on the ideXlab platform.
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Unsteady Aerodynamic Force Sensing from Measured Strain
2016Co-Authors: Chan-gi PakAbstract:A simple approach for computing unsteady aerodynamic forces from simulated Measured Strain data is proposed in this study. First, the deflection and slope of the structure are computed from the unsteady Strain using the two-step approach. Velocities and accelerations of the structure are computed using the autoregressive moving average model, on-line parameter estimator, low-pass filter, and a least-squares curve fitting method together with analytical derivatives with respect to time. Finally, aerodynamic forces over the wing are computed using modal aerodynamic influence coefficient matrices, a rational function approximation, and a time-marching algorithm. A cantilevered rectangular wing built and tested at the NASA Langley Research Center (Hampton, Virginia, USA) in 1959 is used to validate the simple approach. Unsteady aerodynamic forces as well as wing deflections, velocities, accelerations, and Strains are computed using the CFL3D computational fluid dynamics (CFD) code and an MSC/NASTRAN code (MSC Software Corporation, Newport Beach, California, USA), and these CFL3D-based results are assumed as Measured quantities. Based on the Measured Strains, wing deflections, velocities, accelerations, and aerodynamic forces are computed using the proposed approach. These computed deflections, velocities, accelerations, and unsteady aerodynamic forces are compared with the CFL3D/NASTRAN-based results. In general, computed aerodynamic forces based on the lifting surface theory in subsonic speeds are in good agreement with the target aerodynamic forces generated using CFL3D code with the Euler equation. Excellent aeroelastic responses are obtained even with unsteady Strain data under the signal to noise ratio of -9.8dB. The deflections, velocities, and accelerations at each sensor location are independent of structural and aerodynamic models. Therefore, the distributed Strain data together with the current proposed approaches can be used as distributed deflection, velocity, and acceleration sensors. This research demonstrates the feasibility of obtaining induced drag and lift forces through the use of distributed sensor technology with Measured Strain data. An active induced drag control system thus can be designed using the two computed aerodynamic forces, induced drag and lift, to improve the fuel efficiency of an aircraft. Interpolation elements between structural finite element grids and the CFD grids and centroids are successfully incorporated with the unsteady aeroelastic computation scheme. The most critical technology for the success of the proposed approach is the robust on-line parameter estimator, since the least-squares curve fitting method depends heavily on aeroelastic system frequencies and damping factors.
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Acceleration and Velocity Sensing from Measured Strain
AIAA Infotech @ Aerospace, 2016Co-Authors: Chan-gi Pak, Roger A. TruaxAbstract:A simple approach for computing acceleration and velocity of a structure from the Strain is proposed in this study. First, deflection and slope of the structure are computed from the Strain using a two-step theory. Frequencies of the structure are computed from the time histories of Strain using a parameter estimation technique together with an autoregressive moving average model. From deflection, slope, and frequencies of the structure, acceleration and velocity of the structure can be obtained using the proposed approach. Simple harmonic motion is assumed for the acceleration computations, and the central difference equation with a linear autoregressive model is used for the computations of velocity. A cantilevered rectangular wing model is used to validate the simple approach. Quality of the computed deflection, acceleration, and velocity values are independent of the number of fibers. The central difference equation with a linear autoregressive model proposed in this study follows the target response with reasonable accuracy. Therefore, the handicap of the backward difference equation, phase shift, is successfully overcome.
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Wing Shape Sensing from Measured Strain
AIAA Journal, 2016Co-Authors: Chan-gi PakAbstract:A new two-step theory is investigated for predicting the deflection and slope of an entire structure using Measured Strain at discrete locations. In the first step, a Measured Strain is fitted using a piecewise least-squares curve fitting method together with the cubic spline technique. These fitted Strains are integrated twice to obtain deflection data along the optical fibers. In the second step, computed deflection along the optical fibers is combined with a finite-element model of the structure in order to interpolate and extrapolate the deflection and slope of the entire structure through the use of the System Equivalent Reduction and Expansion Process. The theory is first validated on a computational model, a cantilevered rectangular plate wing. The theory is then applied to test data from a cantilevered swept-plate wing model. Computed results are compared with finite-element results, results using another Strain-based method, and photogrammetry data. In general, excellent matching between the targ...
Liqiang Zhang - One of the best experts on this subject based on the ideXlab platform.
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Serrated flow and failure behaviors of a Hadfield steel at various Strain rates under extensometer-Measured Strain control tensile load
Journal of Materials Research and Technology, 2020Co-Authors: Liqiang Zhang, Pengcheng Guo, Guan Wang, Shuai LiuAbstract:Abstract A Hadfield steel has been investigated to clarify the serrated flow and to explore the failure behavior at room temperature. The tensile experiments were performed under extensometer-Measured Strain control, rather than under conventional cross-head displacement control, at Strain rates ranging from 6 × 10−3 s−1 to 6 × 10−6 s−1. Three types of serrations, including type A, B and C ones, are observed. The occurrence of different types of serrations depends on both Strain rate and Strain level. The type C serration is identified in Hadfield steels at room temperature for the first time. At high Strain rates, there is substantially higher serration density and reduction in stress compared with that observed at low Strain rates. Furthermore, two different initiation modes of deformation bands are revealed. The fracture crack nucleates at a position with dense twins, and propagates primarily in the direction perpendicular to the tensile axis and deflects frequently due to the interaction with the boundary of grains and twins.
Todd Haber - One of the best experts on this subject based on the ideXlab platform.
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Accurate Temperature Compensation and Characterization of Overall System Thermal Response Using Total Measured Strain in FBG Sensors
Structural Health Monitoring-an International Journal, 2013Co-Authors: Todd Haber, Stephen K. Ferguson, D. Guthrie, T. Graver, B. J. Soller, Alexis MendezAbstract:One of the most common fiber optic sensor (FOS) types used are fiber Bragg gratings (FBG) -based Strain sensors are simultaneously sensitive to both temperature and Strain. Thus it is essential to utilize sensors that are either fully temperature insensitive or, alternatively, properly temperature compensated to avoid erroneous measurements. In this paper, we introduce the concept of Measured “total Strain”, which is inherent and unique to optical Strain sensors. We review and analyze the temperature and Strain sensitivities of FBG Strain sensors and decompose the total Measured Strain into thermal and non-thermal components. We explore the differences between substrate CTE and System Thermal Response Coefficients, which govern the type and quality of thermal Strain decomposition analysis.