Magnetorheological elastomers (MREs) are smart materials whose mechanical behavior can be tailored by external
magnetic fields, showing promises for wide use in on-demand stiffness control applications. However, conventional
MREs have comparatively inferior mechanical properties due to matrix materials. Meanwhile carbon nanotubes (CNTs)
have proved to be excellent reinforcing fillers with increased stiffness, strain at failure, and damping performance for
nanocomposites. In this project, synthesis and dynamic mechanical analysis are conducted for silicone-rubber-based
magnetorheological nanocomposites embedded with multi-walled carbon nanotubes.
Smart dampers with on-demand controllable damping curves are key components for semi-active vibration control of structures. Smart dampers utilize friction or viscosity to dissipate mechanical energy by heat. The potential thermal problems are their major drawbacks. Novel colloidal dampers are recently developed with low-heat generation and high damping efficient, they are, however, passive and with no on-demand controllable damping capability. In this paper, we propose a smart colloidal damper by employing water-based ferrofluids in damping media. We find that the corresponding damping hysteresis loops can be affected by applied magnetic fields significantly and rapidly. We further retrieve the instant stiffness and damping coefficient of the smart colloidal dampers from the measured hysteresis loops. It is shown that the negative stiffness and the negative damping coefficient may occur during the operation of the smart colloidal dampers.
Dampers are the key devices for vibration control of structures. The mechanisms of current dampers are internal friction
or viscous flow to dissipate external mechanical energies by heat. The high-heat generation potentially causes thermal
problems to decrease the durability of dampers. Owing to the surface-tension dominated nanoflow on the porous
particles, colloidal dampers have been recently developed with low-heat generation and high damping efficiency. In this
paper, a new type of colloidal dampers are designed and fabricated. Its heat generation and hysteresis loops are tested. It
is found that the heat generation of the colloidal dampers is below 4% of that of hydraulic dampers with the same energy
dissipation capacity. Meanwhile, the hysteresis loops reveal that the colloidal dampers are highly nonlinear devices. We
introduce an efficient algorithm to retrieve its instant stiffness and damping coefficients from measured hysteresis loops
under cyclic excitations at different frequencies. The retrieved stiffness and damping coefficients are plotted against
damping forces or inner pressures. We find that, at low frequencies, the colloidal dampers exhibit the states with
negative stiffness and negative damping coefficients; nevertheless, at the frequencies above 6Hz, both the stiffness and
the damping coefficients are positive. Frequency is one of the key parameters dominating the damping mechanism of the
colloidal dampers.
Research and development related to homeland security has emerged as one of the most challenging topics nationwide in the recent few years. Effective structural health monitoring, diagnosis, and prognosis are of great importance for the safety and reliability analysis for civil infrastructural systems. While the technologies of sensor-arrays embedded in host structures are widely employed for structural health monitoring, the key issue is how to set-up a physics-based model framework and its corresponding efficient algorithm to evaluate the quality of the host structures through the output of the sensors. It is a frontal interdisciplinary topic bridging the microstructural damage mechanics and signal estimation theory. By employing a multi-scale constitutive model of solids with damage, this paper conducts an exploratory research on the modeling and algorithm of estimating the mean value of crack density and the distribution of crack orientation of a cracked plate subjected to unidirectional tension. Simulation results reveal that the framework and algorithm provide a reasonable performance in recovering crack orientation.
We study the magnetomechanical behavior of two-phase composites containing randomly dispersed ferromagnetic particles and nonmagnetic matrix. Starting from Green's functions we investigate the magnetic and elastic fields for two particles embedded in the infinite domain and define pair-wise interaction between particles. Macroscopically, we derive the averaged stress and strain fields over the composite and two phases. We then present effective magnetostriction and elasticity of composites and simulate the magnetomechanical coupling behavior during combined magnetomechanical loading conditions. Simulations are compared with other methods and experimental data to demonstrate the capability of the proposed method.
Conference Committee Involvement (11)
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
9 March 2015 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
10 March 2014 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
10 March 2013 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
12 March 2012 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
7 March 2011 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
8 March 2010 | San Diego, California, United States
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security IV
8 March 2010 | San Diego, California, United States
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security III
9 March 2009 | San Diego, California, United States
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems
9 March 2009 | San Diego, California, United States
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security II
11 March 2008 | San Diego, California, United States
Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security
20 March 2007 | San Diego, California, United States
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