Browsing by Subject "Hysteresis"

Now showing 1 - 4 of 4
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    Developing an approach to improve beta-phase properties in ferroelectric pvd-hfp thin films
    (2020-05) Dale, Ashley S.; Cheng, Ruihua; Petrache, Horia; Wassall, Stephen
    Improved fabrication of poly(vinylindenefluoride)-hexafluoropropylene (PVDF-HFP) thin films is of particular interest due to the high electric coercivity found in the beta-phase structure of the thin film. We show that it is possible to obtain high-quality, beta-phase dominant PVDF-HFP thin films using a direct approach to Langmuir-Blodgett deposition without the use of annealing or additives. To improve sample quality, an automated Langmuir-Blodgett thin film deposition system was developed; a custom dipping trough was fabricated, a sample dipping mechanism was designed and constructed, and the system was automated using custom LabVIEW software. Samples were fabricated in the form of ferroelectric capacitors on substrates of glass and silicon, and implement a unique step design with a bottom electrode of copper with an aluminum wetting layer and a top electrode of gold with an aluminum wetting layer. Samples were then characterized using a custom ferroelectric measurement program implemented in LabVIEW with a Keithley picoammeter/voltage supply to confirm electric coercivity properties. Further characterization using scanning electron microscopy and atomic force microscopy confirmed the improvement in thin film fabrication over previous methods.
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    Nonlinear design, modeling and simulation of magneto rheological suspension: a control system and systems engineering approach
    (2017-12) Zambare, Hrishikesh B.; Razban, Ali; El-Mounayri, Hazim; Chen, Jie
    Suspension has been the most important subsystem of the vehicle viewed as a system. The ride comfort and vehicle handling performance are affected by the suspension design. Automotive technology has been continuously incorporating developments over the past few decades to provide the end users with a better comfort of driving. Multi-objective optimization of MR damper with objective function of maximizing damping force generated by MR damper with the geometrical parametric constraint function is achieved in this research using pattern search optimization technique. Research focuses on design, modeling, and simulation of active suspension using non-linear theory of the Magneto-Rheological (MR) damper with consideration of the hysteresis behavior for a quarter car model. The research is based on the assumption that each wheel experiences same disturbance excitation. Hysteresis is analyzed using Bingham, Dahl’s, and Bouc-Wen models. Research includes simulation of passive, Bingham, Dahl, and Bouc-wen models. Modeled systems are analyzed for the six road profiles, including road type C according to international standards ISO/TC108/SC2N67. Furthermore, the comparative study of the models for the highest comfort with less overshoot and settling time of vehicle sprung mass are executed. The Bouc-Wen model is 36.91 percent more comfortable than passive suspension in terms of damping force requirements and has a 26.16 percent less overshoot, and 88.31 percent less settling time. The simulation of the Bouc-Wen model yields a damping force requirement of 2003 N which is 97.63 percent in agreement with analytically calculated damping force generated by MR damper. PID controller implementation has improved the overshoot response of Bouc-Wen model in the range of 17.89 percent-81.96 percent for the different road profiles considered in this research without compromising on the settling time of system. PID controller implementation further improves the passenger comfort and vehicle ride handling capabilities. The interdisciplinary approach of systems engineering principles for the suspension design provides unique edge to this research. Classical systems engineering tools and MBSE approach are applied in the design of the MR damper. Requirement traceability successfully validates the optimized MR damper.
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    A rate insensitive linear viscoelastic model for soft tissues
    (Elsevier, 2007-08) Zhang, Wei; Chen, Henry Y.; Kassab, Ghassan S.; Department of Biomedical Engineering, School of Engineering and Technology
    It is well known that many biological soft tissues behave as viscoelastic materials with hysteresis curves being nearly independent of strain rate when loading frequency is varied over a large range. In this work, the rate insensitive feature of biological materials is taken into account by a generalized Maxwell model. To minimize the number of model parameters, it is assumed that the characteristic frequencies of Maxwell elements form a geometric series. As a result, the model is characterized by five material constants: μ0, τ, m, ρ and β, where μ0 is the relaxed elastic modulus, τ the characteristic relaxation time, m the number of Maxwell elements, ρ the gap between characteristic frequencies, and β = μ1/μ0 with μ1 being the elastic modulus of the Maxwell body that has relaxation time τ. The physical basis of the model is motivated by the microstructural architecture of typical soft tissues. The novel model shows excellent fit of relaxation data on the canine aorta and captures the salient features of vascular viscoelasticity with significantly fewer model parameters.
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    A rate-insensitive linear viscoelastic model for soft tissues
    (Elsevier, 2007-08) Zhang, Wei; Chen, Henry Y.; Kassab, Ghassan S.; Department of Biomedical Engineering, School of Engineering and Technology
    It is well known that many biological soft tissues behave as viscoelastic materials with hysteresis curves being nearly independent of strain rate when loading frequency is varied over a large range. In this work, the rate-insensitive feature of biological materials is taken into account by a generalized Maxwell model. To minimize the number of model parameters, it is assumed that the characteristic frequencies of Maxwell elements form a geometric series. As a result, the model is characterized by five material constants: micro(0), tau, m, rho and beta, where micro(0) is the relaxed elastic modulus, tau the characteristic relaxation time, m the number of Maxwell elements, rho the gap between characteristic frequencies, and beta=micro(1)/micro(0) with micro(1) being the elastic modulus of the Maxwell body that has relaxation time tau. The physical basis of the model is motivated by the microstructural architecture of typical soft tissues. The novel model shows excellent fit of relaxation data on the canine aorta and captures the salient features of vascular viscoelasticity with significantly fewer model parameters.