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Characterization of rapidly consolidated γ-TiAl
Kothari, Kunal,Radhakrishnan, Ramachandran,Sudarshan, Tirumalai S.,Wereley, Norman M. Techno-Press 2012 Advances in materials research Vol.1 No.1
A powder metallurgy-based rapid consolidation technique, Plasma Pressure Compaction ($P^2C^{(R)}$), was utilized to produce near-net shape parts of gamma titanium aluminides (${\gamma}$-TiAl). Micron-sized ${\gamma}$-TiAl powders, composed of Ti-50%Al and Ti-48%Al-2%Cr-2%Nb (at%), were rapidly consolidated to form near-net shape ${\gamma}$-TiAl parts in the form of 1.0" (25.4 mm) diameter discs, as well as $3"{\times}2.25"$ ($76.2mm{\times}57.2mm$) tiles, having a thickness of 0.25" (6.35 mm). The ${\gamma}$-TiAl parts were consolidated to near theoretical density. The microstructural morphology of the consolidated parts was found to vary with consolidation conditions. Mechanical properties exhibited a strong dependence on microstructural morphology and grain size. Because of the rapid consolidation process used here, grain growth during consolidation was minimal, which in turn led to enhanced mechanical properties. Consolidated ${\gamma}$-TiAl samples corresponding to Ti-48%Al-2%Cr-2%Nb composition with a duplex microstructure (with an average grain size of $5{\mu}m$) exhibited superior mechanical properties. Flexural strength, ductility, elastic modulus and fracture toughness for these samples were as high as 1238 MPa, 2.3%, 154.58 GPa and 17.95 MPa $m^{1/2}$, respectively. The high temperature mechanical properties of the consolidated ${\gamma}$-TiAl samples were characterized in air and vacuum and were found to retain flexural strength and elastic modulus for temperatures up to $700^{\circ}C$. At high temperatures, the flexural strength of ${\gamma}$-TiAl samples with Ti-50%Al composition deteriorated in air by 10% as compared to that in vacuum. ${\gamma}$-TiAl samples with Ti-48%Al-2%Nb-2%Cr composition exhibited better if not equal flexural strength in air than in vacuum at high temperatures.
Magnetorheological Isolators Using Multiple Fluid Modes
Brigley, Mikel,Choi, Young-Tai,Wereley, Norman M.,Choi, Seung-Bok Sage Science Press (UK) 2007 Journal of intelligent material systems and struct Vol. No.
<P>This study presents the experimental and theoretical evaluation of an MR (magnetorheological) isolator using multiple fluid modes including shear, flow and squeeze. For doing so, a novel type of multi-mode MR isolator against multi-degree-of-freedom excitations is proposed and fabricated. The experimental testing of the proposed MR isolator is conducted by an MTS machine and its damper characteristics are experimentally evaluated by equivalent damping and complex stiffness methods. To construct a theoretical model of the MR isolator, its dynamic equation is derived and important model parameters are identified by the force averaging method using the forceU2014;displacement or the force-velocity plots. Using the theoretical model, the damper characteristics of the MR isolator are also predicted and compared to those computed using the experimental data.</P>
Frontal Crash Mitigation using MR Impact Damper for Controllable Bumper
Woo, David,Choi, Seung-Bok,Choi, Young Tae,Wereley, Norman M. Sage Science Press (UK) 2007 Journal of intelligent material systems and struct Vol. No.
<P>This study presents performance characteristics of a magnetorheological (MR) impact damper for controllable bumper in vehicle systems. Recently, several mechanisms are proposed in order to minimize the injury of vehicle occupants during frontal collision. One of the promising candidates is the MR fluid which undergoes significant instantaneous reversible changes in material characteristics when subjected to a magnetic field. Using this salient property, a new type of MR impact damper is devised in this work. The proposed damper is integrated with bellows to induce the flow motion and the motion is operated under flow mode. The field-dependent damping force is evaluated by computer simulation with various conditions. In order to investigate the effectiveness of the proposed impact damper, a lumped parameter mathematical model of frontal vehicle crash system including MR impact damper is developed and realized in order to evaluate acceleration peak reductions and transmitted force in the frontal collision.</P>
Design of frequency-tunable mesh washer isolators using shape memory alloy actuators
Jeong, Ho-Kyeong,Lee, Juho,Han, Jae-Hung,Wereley, Norman M SAGE Publications 2016 Journal of intelligent material systems and struct Vol.27 No.9
<P>This article introduces a novel frequency-tunable isolator that uses shape memory alloy wires as actuators and as an isolation material. The isolation material is a compressed mesh washer using the pseudoelasticity of the shape memory alloy. Frequency tuning of the isolator can easily be achieved using a simple electric circuit. Two improved models of frequency-tunable isolator, based on the authors' previous model, were proposed and fabricated. This article presents detailed design procedures for adaptive shock isolators for launch vehicles that are able to achieve both shock attenuation performance and avoidance of vibration amplification. Launch vehicles experience a severe dynamic environment during the flight phase. In particular, pyroshock generated from several separation events could result in malfunctions of electrical components. Moreover, low-frequency vibration (<100Hz) at the maximum dynamic-pressure phase could reduce the structural integrity of payloads. With this system, the resonant frequencies of the isolators are selectively controlled in two states using an adaptive mechanical system with compression of the isolation materials. Successful designs for the isolators and various test results regarding frequency tuning are presented.</P>
Geometry optimization of MR valves constrained in a specific volume using the finite element method
Nguyen, Quoc-Hung,Han, Young-Min,Choi, Seung-Bok,Wereley, Norman M Institute of Physics Publishing 2007 Smart materials & structures Vol.16 No.6
<P>This paper presents the geometric optimal design of magnetorheological (MR) valves in order to improve valve performance, such as pressure drop. The optimization problem is to find the optimal geometric dimensions of MR valves constrained in a specific volume. After describing the configuration of MR valves, their pressure drops are investigated on the basis of the Bingham model of an MR fluid. Then, the valve ratio, which is an objective function, is derived by considering the field-dependent (controllable) and viscous (uncontrollable) pressure drops of the MR valves. Subsequently, the optimization procedure using a golden-section algorithm and a local quadratic fitting technique is constructed via a commercial finite element method (FEM) parametric design language. From the constructed optimization tool, optimal solutions of the MR valves, which are constrained in a specific cylindrical volume defined by its radius and height, are calculated and compared with analytical ones. In addition, several different types of MR valves are optimized in the same specific volume and results are presented. </P>