Example Summer 2008 REU Projects.
More projects will be available.
Multiscale simulations of mechanical behavior of material (Advisors: S. Dj. Mesarovic and H. M. Zbib)
Current research in the School of MME with collaboration with the Mathematics Department of WSU and the Pacific Northwest National Laboratory involves a number of multiscale models of materials behavior, including:
- (a) Network-continuum models, applicable to granular materials, dense suspensions and atomistic-continuum hybrids and,
- (b) Dislocation plasticity models intended to bridge the gap between the discrete dislocation model and the continuum plasticity. A higher order plasticity theory applicable to small, constrained volumes of plastically deforming crystals is under development.
Modeling and characterization of Scale effects (Advisor: B. Muhunthan):
An understanding of and the development of methods to quantify the phenomenon of size effects in engineering materials is critical in design. This study will focus on the size effects observed in granular materials. Granular microstructure is the underlying cause of nonlinearities and size effects in these materials. In this study, REU students will perform mechanical triaxial tests on specimens made from spherical glass beads, Ottawa sand, and Silica sand. These materials were chosen to provide a wide range in shape and angularity. In addition, the specimens will be prepared using different methods of deposition. The use of different materials with differing methods of preparation will enable the students to perform tests on materials that have a suite of underlying microstructure. The microstructure of each specimen will be characterized using the Computed Aided Tomography equipment with the assistance of the principal investigators and graduate students. The stress-strain behavior of each specimen will be monitored and recorded. The strain gradient constitutive model developed by the PI's and implemented into the commercial code ABAQUS will be used by the REU students to predict the observed stress strain behavior on laboratory specimens. The gradient parameter used in the constitutive model is dependent on the microstructure of the specimens. Graduate students and the PI's will assist them in the evaluation of the gradient parameter and its link in the prediction of scale effects.
Plastic Deformation of Aluminum - Experiments and Characterization (Advisor: D. Field)
Simply stated, plastic deformation of metals occurs by dislocation motion. The specific details of dislocation motion determine the flow behavior of the material. Interactions with other defects including point defects, other line defects, and interfaces control the constitutive response of the material. Interfaces consist of phase boundaries, grain boundaries and free surfaces. As grain sizes shrink the volume fraction of material classified as a grain boundary region increases. Flow in these regions is complicated, and the mechanisms of deformation likely vary with grain size. The relationship between flow properties and structure at various length scales is important to understand in gaining a better comprehension of how processes should be designed to maximize performance of the material.
In this work, REU students will perform deformation experiments on commercial alloys of 5005 aluminum (Al-Mg) and characterize the microstructures. Processing of the metal will be designed to obtain three types of specimens differentiated by grain size. The average grain sizes are on the order of 2 ?m and 200 ?m for two specimen types with a single crystal providing the third type. This difference in grain size will result in different mechanical properties with a slightly higher strength and significantly higher ductility expected in the material with a smaller grain size. Of particular interest in this work is the interaction of dislocations with grain boundaries. The structures will be characterized using electron microscopy to obtain information on dislocation structures and grain boundary character before and after deformation. A relationship will be sought between observed mechanical properties and dislocation pileup near boundaries, scale dependence of the dislocation structures, and grain boundary character. This will be assessed for both grain sizes investigated and compared with single crystal results.
Developing multi-scale modeling techniques for nano mechanics and materials (Advisor: S. N. Medyanik)
As the field of nanotechnology progresses, the role of multi-scale modeling techniques is constantly increasing. Atomistic simulation methods, such as molecular dynamics, are usually applied to study mechanical behavior at the nano scale. However, length and time scales accessible through direct molecular dynamics simulations are very limited and despite the use of super computers remain several orders of magnitude lower than those of the typical nano scale systems studied experimentally. Multi-scale methods have recently become a powerful tool for modeling mechanical processes at the nano scale. The main idea of multi-scale modeling is to decrease the number of degrees of freedom involved in the computer simulation while preserving the level of accuracy necessary to adequately model the original problem. The multi-scale techniques help to reduce the size of the simulation by using more accurate and thus more expensive approaches only in a small part of the original domain - the part where such accuracy is necessary. In this project, REU students will participate in developing novel multi-scale modeling techniques. They will perform testing and validation of several multi-scale methods that are currently being developed in the School of MME at WSU. They will also apply the new methods to model various nano mechanical processes and phenomena. Particular applications will include atomic scale contact and friction, as well as studies of plasticity and fracture at the nano scale.
Flow, Mixing and Separation in Multiscale Fluidic Devices (Advisor: P. Dutta)
Miniaturized fluidic devices are in strong demand in medical, pharmaceutical and defense applications, for example in drug discovery, DNA analysis and sequencing and biological/chemical agent detection sensors on micro-chips. The main advantages of these emerging micro/nanofluidic technologies are their low-cost, light-weight, small-size, fast analysis time, and better resolution. The technological needs of micro/nanofluidic devices in biotechnology and life sciences require a better understanding of the micro/nanoscale fluidic transport phenomena, which differ from their larger-scale counterparts mainly due to the size and the surface force effects. For devices smaller than one millimeter in length, the surface forces are more dominant than the body forces, and the nature of flow becomes laminar. In this proposed REU module, undergraduate students would study (a) flow in meso and micro/nanoscale fluidic components, (b) mixing in meso and microscale fluidic chips, or (c) bioseparation in meso and microscale fluidic devices. WSU microscale thermo fluid research group has been developing experimental modules for flow, mixing and separation in microfluidic devices. Undergrads would perform experiments in those microscale setups, and then compare their research findings with corresponding mesoscale components. For instance, undergraduate students will get hands-on experience of laminar and turbulent flow phenomena by performing mixing experiments in micro and macro-scale channels. Moreover, by utilizing the characteristics of laminar flow in microfluidic devices, students will be able to develop membraneless biofuel cell for portable power generation.
Fabrication and characterization of a Thermal Switch (Advisor: C. Richards):
The ability to control heat transfer on small time and length scales would have a significant impact in areas such as, thermoelectric micro-coolers, DNA amplification via PCR, microelectronic cooling and harvesting waste heat for microscale power. In this project a thermal switch is fabricated and characterized. Carbon nanotubes (CNT's) are used as the contacts for the switch due to their high thermal conductivity. The CNT's are used to bridge scales from nanometers to micrometers, and MEMS techniques are used to bridge scales from micrometers to millimeters. Manufacturing across six orders of length scales from nano to meso is made possible by utilizing the mixed-scale architectures of high aspect ratio CNT's (nm diameters to ?m lengths) and two-dimensional lithographic-based low-aspect ratio MEMS fabrication techniques (?m thicknesses to mm planar dimensions). The fabrication of this device begins with the deposition of an iron nitrate sol gel on a silicon wafer followed by a photoresist and then patterning. Vertically aligned CNT growth is accomplished via a chemical vapor deposition (CVD) method. The die is then assembled into a switch by bonding onto a benchtop apparatus for characterization. The thermal resistance of the vertically aligned carbon nanotube turf is then measured. REU students, working with graduate students, will deposit and pattern the catalyst. A study of catalyst and pattern density will be conducted and the results evaluated by measurements of the thermal resistance of the vertically aligned nanotube turf. In this project students will help fabricate a device across six orders of magnitude. They will then perform thermal measurements on the nanotube turf and compare the turf thermal properties to those observed for single nanotubes.
Surface Preparation Effects of Composite Adhesive Joints (Faculty Advisor: L. Smith)
Composite structures often derive part of their weight savings from adhesive bonding. However, bonded joints tend to be more difficult to inspect than traditional mechanical fasteners. Reliable bonding practices are necessary to ensure the structural and economic integrity of composite structures. Inadequate surface preparation is often the cause for poor adhesion between bonded structures. Repeatability, for instance, is usually considered over strength when selecting surface preparation procedures. We propose to examine the effect of surface preparation technique and adherent moisture content on joint strength. We will use lap shear coupons to compare the strength of surfaces produced from peel ply, sanding, and grit blasting. Since moisture content can vary widely in many manufacturing facilities, bonded test coupons will be produced from dry and moisture saturated adherents. Adherents will be produced from unidirectional aerospace grade carbon/epoxy prepreg. The coupon failure surfaces will be microscopically examined to understand how the surface preparation affects the failure mode in the adherent, adhesive, or their interface. The REU student will determine how microscopic topography produced by the surface preparation technique and layer moisture content affect the macroscopic strength and failure mechanism.