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CAMP Annual Report: Page 11

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Mechanical Behavior of Porous Aluminum Foams




Figure 7.  (A) Cellular structure of Alporas aluminum foam (Shinko Wire Co.) overlaid with a contour plot of surface axial strain (%) after 33,000 cycles.  Dark red zone corresponds to the crack region (crack is enclosed by the dashed line box).  (B) Enlarged image of the dashed line box, clearly showing the crack propagated across the cell wall.

Professors Kathleen Issen and David Morrison and their research group are investigating the mechanical behavior of porous aluminum foams.  Due to the cellular structure of aluminum foams (Figure 7A), these lightweight materials have good strength and stiffness to weight ratios, suitable for use in air, space, marine and ground vehicles.  Recent low cycle tension-compression fatigue tests provided several significant results.  For example, although the strain amplitudes used in this work were significantly below those for failure under monotonic loading, damage began to accumulate during the first few cycles.  Under continued cycling, these initial damage zones intensify, leading to formation and propagation of a through-going crack.  The onset and evolution of damage were examined using digital image correlation.  Figure 7A shows surface axial strain after crack formation; the dark red zone represents intense local tensile deformation, corresponding to the crack region.  An enlarged image of the crack region (Figure 7B) shows a crack propagated across a cell wall.  Current work involves monotonic tension and compression testing and low cycle tension-compression fatigue of open cell metal foams.

Monitoring and Modeling of Composite and Smart Structures 

Professor Ratan Jha, of Clarkson's Department of Mechanical and Aeronautical Engineering, has conducted research in structural health monitoring, modeling of composite and smart structures, adaptive control of structural vibrations, intelligent flight controls, and multidisciplinary design optimization. He has established the Smart Structures Laboratory at Clarkson University which is well equipped for vibration measurement and control experiments, including a scanning laser vibrometer. Dr. Jha's contributions include both theoretical and experimental research which have resulted in over 60 publications in international archival journals and refereed conferences. He was awarded the Graham Faculty Research Award by Clarkson University in 2005. Dr. Jha is an Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA) and a member of ASME and ASEE. He is a member of the AIAA Adaptive Structures Technical Committee and has served as Session Chair/Co-Chair for Adaptive Structures Conferences. Dr. Jha has received research grants from the National Science Foundation, NASA, the US Army, the New York State Energy Research and Development Authority, Pratt & Whitney, and other industries. Prior to joining Clarkson, he worked in the aerospace industry from 1983 to 1995 where he led a team of engineers working on conceptual and preliminary designs of combat aircraft. 

Development of Higher-Order Spectra for Structural Health Monitoring of Composite Structures

Higher order spectral analysis techniques are often used to identify nonlinear interactions in modes of complex dynamical systems. The bi-spectrum and tri-spectrum have proven to be useful tools in testing for the presence of quadratic and cubic nonlinearities based on a system's stationary response. See Figure 8.  Professor Pier Marzocca is carrying out structural health monitoring research in collaboration with the Naval Research Laboratory in Washington DC. This collaboration started when Marzocca spent two summers at NRL under the support of the ASEE and ONR Summer Fellowship Program. His studies involved numerical and experimental investigations to identify the presence and extent of nonlinear interactions between frequency components and to understand how modes interact nonlinearly producing intermodulation components at the sum and/or difference frequency of the fundamental modes of oscillation. New identification tools have been proposed. They can be used as a benchmark for validation of nonlinear analysis methods associated with structural health monitoring techniques and to reduce the burden of these methods.









Figure 8.  (A) Numerical High Order Spectra and (B) Estimated High Order Spectra, both for the experiment carried out in 8D.  (C) Probability function for damage detection. (D) Experimental investigation of damage in a bolted composite beam.

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Incorporating Sensor Networks for In-Service Monitoring of Civil and Industrial Systems

Professor Kerop Janoyan and his research team in the Civil and Environmental Engineering Department at Clarkson continue to work on developing and deploying novel wireless sensors and sensor networks for applications in industrial process monitoring, quality control, in civil infrastructure structural health monitoring, and in environmental monitoring and tracking.  See Figure 9.  Professor Janoyan also leads the Laboratory for Intelligent Infrastructure and Transportation Technologies (LIITT) at Clarkson University, whose core focus is the design and integration of advanced sensing tools, measurements, and quantitative databases to enable event response, in-service condition assessment, and long-term decision making in infrastructure management systems.

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