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Peter AndersonProfessorPh.D., Harvard University, 1986 Tel. (614) 292-0176 Office: 345 Fontana Laboratories
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Dr. Anderson's research interests center on understanding how the microstructural features of materials affect macroscopic mechanical properties such as yield strength, time-dependent creep, and fracture resistance of various materials. Most of his research effort is to simulate critical fracture and deformation events on computer, but a significant amount of work involves tensile testing, electron microscopy, x-ray diffraction, and nanoindentation. Some of the latter work is done in collaboration with investigators at other institutions such as the National Institute of Standards and Technology, the Air Force Research Labs at Wright-Patterson Air Force Base, the Cleveland Clinic Foundation, and University of Minnesota.
Composites
One research focus is on an exciting class of materials consisting of alternating layers of phases with individual layer thicknesses as small as one or two nanometers. Shown below is a nanolayered composite produced by sputtering approximately fifty layers each of Ni and Ni3 Al. The individual layer thicknesses are about 120nm here. Such a material is being explored for beneficial properties during elevated temperature use in an aircraft engine, for example. Our preliminary findings are that this material, like many other metallic/intermetallic nanolayered composites, displays increasing strength with decreasing layer thickness. Even Ag/Ni nanolayered composites that we have tested have failed in tension at approximately 1GPa. However, there often is a critical layer thickness below which the strength does not increase any further. One of our current efforts is to understand just how far one can strengthen materials by using a nanolayered morphology. See the first publication by Anderson, Foecke, and Hazzledine for more information.
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Nanolayered sample with alternating layers of Ni and Ni3Al produced by sputtering. |
One of the fascinating features of nanolayered metallic/intermetallic composites is that crystal slip, or dislocation movement, is often limited to very small volumes of material. It is the interfaces which often confine dislocations to propagate within layers during the early stages of deformation of a nanolayered composite. The transmission electron micrograph image of a Cu/Ni nanolayered composite (below, right) by Tim Foecke at NIST shows evidence of a dislocation loop (denoted by the larger white arrow, bottom center) that has begun to bow into a Ni layer from the interface and the several loops (see smaller arrows, upper left) in that same layer that were formed earlier and are now propagating within the layer. The schematic to the left shows the interpretation of events that leads to "bow-out" of a loop and subsequent propagation along a layer. Based on dislocation theory analyses, we have produced quantitative estimates of the resistance of nanolayered materials to this kind of deformation.
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The fracture surface morphology of nanolayered composites varies remarkably with the thickness and crystallographic texturing of the layers. On the left is the fracture surface of a 20nm/20nm Ni/Ni3Al sample with a (001) crystallographic texture and on the right is a sample with 120nm/120nm layer thickness and a (111) crystallographic texture. One of our current efforts is to understand the change in fracture surface appearance with layer thickness and layer orientation.
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20 nm/20 nm |
120 nm/120 nm |
Biomaterials
A quite different research effort is to understand the mechanical properties of healthy and diseased arterial tissue. We have developed a nonlinear viscoelastic model for healthy tissue based on tests conducted with Geoff Vince, Fred Cornhill, and Jim Thomas at the Cleveland Clinic in which an artery is subjected to various inflation histories and the corresponding deformation of the artery is monitored with Intravascular Ultrasound (IVUS). Our results reveal that healthy tissue has a very nonlinear, time dependent behavior with a relaxation time constant of less than one second. With more accurate measurements of the mechanical properties of tissue, we plan to use finite element analysis of the artery to study how the stress in diseased arteries such as the one shown below (courtesy of Geoff Vince, Cleveland Clinic Foundation) differs from the stress state in healthy arteries.
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Dr. Anderson obtained a Ph.D. in Engineering Sciences from Harvard University in 1986. He was a Postdoctoral Research Assistant at Cambridge University, England, from 1986 to 1988, when he joined the Materials Science and Engineering Department at The Ohio State University.
