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Materials Engineering Research

Conducting materials research within Thayer School's single unified department of engineering creates a seamless environment where students benefit from a wide range of disciplines under one roof. In addition, Dartmouth fosters numerous opportunities for cross-campus projects such as within the Center for Nanomaterials Research at Dartmouth, which resulted from collaboration between Thayer School and other Arts & Sciences Faculty.

Biomaterials, Soft Materials & Tribology

Orthopaedic biomaterials research at Thayer School takes place within the Dartmouth Biomedical Engineering Center for Orthopaedics (DBEC). Since 1976, DBEC has acquired the largest collection of retrieved joint implant specimens in the world and has systematically identified and solved most problems related to the production, design, and materials of joint replacement technology. Debris generation from polyethylene wear is considered the biggest problem facing joint replacement today. Current research on cross-linked polyethylene is targeting this problem which involves an analysis of the trade-offs between wear resistance achieved by cross links, and toughness and contact fatigue resistance of the polymer. Additional topics include:

determination of the rate of oxidation in vivo of polyethylene subjected to new sterilization techniques
wear of new metal-on-metal and ceramic-on-ceramic technologies

(Faculty contacts: Kennedy, Collier, Van Citters)

Tribology research focuses on the measurement and prediction of friction, wear, and surface temperatures during sliding in mechanical components. One area of study is the friction and wear of polymers, such as those used in orthopaedic prostheses, with a focus on their wear, contact fatigue and viscoelastic behavior in oscillatory sliding or rolling/sliding contact.
(Faculty contacts: Kennedy, Van Citters)

Wear of nanocrystalline metals and alloys is being studied to understand the wear mechanisms and to model accurately wear rate as a function of grain size. To this end, bulk nanocrystalline Al, Al-Si and Mg will be produced by equal channel angular extrusion of milled powders. We will also produce bimodal grain structures consisting of nanocrystalline and conventionally-grained material, which we expect will have high hardness yet good ductility. The microstructures will be characterized using a TEM and XRD. Such bulk nanocrystalline materials should not suffer from the difficulties of interpreting wear data that occur for coatings and modified surface layers where the grain size and strain often vary throughout the layers.
(Faculty contact: I. Baker, Kennedy)

Electronic & Optoelectronic Materials

High power density magnetic components for dc-dc power converters are being developed using microfabrication techniques. The small size and fast response time of these high-frequency converters will make them advantageous for power delivery to low-voltage microprocessors and other digital systems.
(Faculty contact: Sullivan)

Thin Films, Nanocomposites & Nanostructures

High Temperature Materials

Alloys for high-temperature power applications that are strong, corrosion resistant and economically viable are critical for the operation of power generation plants at higher temperatures. Operation at high temperature can lead to energy conversion efficiencies of >50%, which will not only reduce running costs, but also extend the lifetime of fossil fuels and/or reduce the carbon footprint of the plants. In this project, iron-based austenitic steels strengthened with Laves phase precipitates, and alloyed with aluminum for improved oxidation resistance, e.g. Fe-20Cr-20Ni-2Nb-5Al (at.%), are being studied. The project aims to generate finer, higher volume fractions of Laves precipitates in the matrix by using enhanced nucleation on dislocations introduced through cold work. These precipitates will increase the strength and also minimize the formation of grain boundary precipitates, thus retarding the growth of the latter and extending the creep life of the alloy. The precipitates are being characterized after both static ageing and creep using transmission electron microscopy (TEM), and TEM hot in-situ straining experiments are being used to examine the deformation mechanisms.
(Faculty contact: I. Baker)

Intermetallic compounds show great promise as structural materials for high-temperature applications because of their high strength and resistance to oxidation and corrosion. However, many intermetallic compounds are brittle at ambient temperatures. Current research aims to understand the causes of brittle fracture and to observe the yield anomaly in these compounds.
(Faculty contact: I. Baker)

High-strength quaternary alloys with ultrafine microstructures result from a combination of spinodal decomposition and atomic ordering transformations. Research aims to relate the progression of these transformations to bulk properties such as strength, hardness, and ferromagnetism. Such high-strength low-density alloys would have many industrial and aerospace applications. Some of this work is performed in collaboration with Oak Ridge National Laboratory and also the University of Sydney.
(Faculty contact: I. Baker)

Microstructure and mechanical behavior of FeNiMnAl eutectic alloys is being studied to understand the deformation mechanisms controlling the strength and ductility of a recently-discovered, high-strength, ductile, eutectic FeNiMnAl alloy, Fe₃₀Ni₂₀Mn₃₅Al₁₅, that consists of f.c.c. and B2 (ordered b.c.c.) phases and to model the yield strength and ductility either by using existing models or by developing new models. The work involves mechanical testing and microstructural characterization using a combination of state-of-the-art techniques including transmission electron microscopy (TEM) including convergent beam electron diffraction and energy dispersive x-ray spectroscopy; a high resolution TEM; and atom probe tomography. These will provide information on the lamellar spacing and morphology, microchemistry, lattice parameters, orientation relationships between the f.c.c. and B2 phases, interface strains and interface structure.
(Faculty contact: I. Baker)

Ice Physics & Engineering

Ice plays a significant role in a number of issues such as global climate and oil and gas recovery operations, as well as having a major effect on transportation, infrastructure, and industry. Thayer School's Ice Research Laboratory offers extensive facilities to study this complex and pervasive material. Some projects collaborate with nearby USACE Cold Regions Research and Engineering Laboratory.

Ice mechanics research is conducted to determine physical processes that underlie brittle failure on scales large (Arctic) and small (laboratory). The current goal is to relate failure of the arctic sea ice cover and fracture during ice interaction with off-shore engineered structures to processes such as wing-crack and comb-crack formation and the development of shear faults. The underlying hypothesis is that brittle compressive failure is a scale-independent process driven by intermittent frictional sliding and stable crack growth. The hypothesis is applicable to other brittle materials as well, such as ceramics, rock, and minerals.
(Faculty contact: Schulson)

Dry snow metamorphism is the process whereby the structure of a snowpack changes due both to diffusion, leading to sintering of adjacent crystals, and to vapor pressure gradients, which produce vapor flow and the growth of large crystals. A series of laboratory experiments are being performed using both natural snow and laboratory-grown ice spheres under carefully-controlled conditions to elucidate the underlying physics of the effects of temperature, temperature gradients, impurities and overburden on the mechanisms of dry snow metamorphism. The microstructure of the snow as it undergoes metamorphism is also being related to its mechanical properties. The icrostructural characterization invloves the use of both a cold stage equipped scanning electron microscope and a cold adapted micro X-ray computed tomography unit.
(Faculty contact: I. Baker)

Microstructural characterization of snow and ice cores is crucial to understanding the effects of microstructure and impurities in ice. Researchers here pioneered a way to use the scanning electron microscope (SEM) to study the impurities in uncoated ice and have recently developed a way to gather precise orientation information from ice using electron back scatter patterns (EBSP). Dartmouth engineers are also investigating the type and location of impurities in polar ice cores using a confocal Raman microscope. These efforts will further scientists' understanding of the effect of microstructural properties of ice on the mechanical behavior of ice sheets and glaciers and help paleoclimatologists better interpret the ice core record.
(Faculty contact: I. Baker)

Ice adhesion—causing the icing of airplanes, ships, roofs, and power lines, as well as icy roads and bridges—is a costly and dangerous problem. Because ice strongly adheres to just about everything, including hydrophobic material, several prior empirical attempts to develop durable ice-phobic coatings have failed. A solution requires a fundamental understanding of the physical mechanisms of bonding between ice and other solids, the structure and properties of ice/solid interfaces, and the nature of ice adhesion. Thayer School researchers are studying the fundamental interactions that contribute to ice adhesion strength, and are developing active de-icing techniques including the low-power method of pulse electro-thermal de-icing (PETD).
(Faculty contact: Petrenko)

Victor Petrenko's Ice Engineering (summary)

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