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Research
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We are involved in a broad range of studies of structural materials, mainly in the areas of deformation and fatigue behavior. Our current work in the area of deformation mechanisms involves studies of the processes that control the high-temperature mechanical behavior of dispersion- strengthened metals and metal matrix composites, and development of methods to characterize the mechanical state of a deformed material. Our fatigue studies include examinations of cyclic plasticity in particle-strengthened metals and metal matrix composites, fatigue crack growth behavior of metal matrix composites and laminated composites, and mechanisms of fatigue damage accumulation in polymer matrix composites. In collaboration with colleagues in Orthopaedics and Veterinary Orthopaedics, we are developing techniques to measure and model the mechanical properties of bone. We are presently studying the mechanisms of fatigue damage accumulation in cortical bone, and have developed numerical models of the damage accumulation processes. We are also developing the techniques to measure the fracture properties of bone, with special attention to R-curve behavior.
A substantial part of our work involves the close coupling of mechanical properties measurements with phenomenological models of material behavior, with the goal of understanding deformation mechanisms and the fundamental influence of microstructure on mechanical properties. We have developed a variety of new experimental techniques to probe deformation mechanisms, primarily through the use of experiments in which the external loading parameters (stress, strain rate or stress rate) are perturbed and the resulting material response is monitored. Experiments of this kind require that the mechanical response be measured with extremely high resolution. This need has motivated us to develop both advanced experimental methods to conduct the measurements as well as material models that can be used to validate the results through simulation of the experiments. Our modeling efforts involve both first- principles theoretical treatments as well as finite element modeling of microstructural deformation and failure processes. |
Laboratories
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Our laboratories are equipped with a broad range of instruments for mechanical testing of materials. The primary systems include three computer-controlled servohydraulic testing machines equipped for the study of fatigue crack propagation and cyclic and monotonic deformation at ambient temperatures. One system is equipped with a very high temperature (1500°C) vacuum furnace. These three instruments provide a flexible testing capability that is enhanced by advanced data acquisition and control techniques.
Three constant-stress creep testing machines are used to investigate the time-dependent deformation of materials at elevated temperatures. Two of these systems include the capability of testing in vacuum and one provides a controlled gaseous atmosphere environment. One of these systems is designed for high-resolution strain measurements in conjunction with the stress change experiments used to study basic creep mechanisms. |
Support
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National Science Foundation
National Institutes of Health
Sandia National Laboratories
Industry
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