When 10:30 AM - 11:30 AM Sep 23, 2016
Where 1571 G.G. Brown
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Life and Death of Materials in the Fast Lane: Deformation and Fracture Under Dynamic Loading


Todd Hufnagel
Department of Materials Science and Engineering, Johns Hopkins University

The mechanical behavior of materials is commonly studied under low loading rates. But behavior under high-rate loading is important in many situations - automobile crashes and ballistic penetration of armor being two examples. Because macroscopic phenomena such as plastic deformation and fracture reflect underlying time-dependent microscopic processes, it should come as no surprise that the behavior of materials under dynamic loading can be quite different from that under loading at lower rates.

 

Synchrotron x-ray radiation has characteristics that make it ideally suited for in situ, time-resolved studies that have the potential to provide new insights into the microscopic processes that govern deformation and fracture of materials under dynamic loading. We will focus on two classes of experiments: Diffraction studies of plastic deformation of metals, and imaging studies of fracture of ceramics. We will show examples of microsecond and sub-microsecond diffraction from metals under dynamic compression, including deformation twinning in magnesium alloys and stress-assisted martensitic transformations in austenitic steels. Turning to imaging, we will describe how x-ray phase-contrast imaging exploits the coherent nature of synchrotron radiation to provide enhanced sensitivity to cracks and other internal defects. Examples here will include crack nucleation and propagation in boron carbide and quartz. Throughout the talk we will emphasize how the in situ structural observations relate to other data collected in the experiments (such as stress-strain history) and how these can be used to inform computational models of the behavior of materials under dynamic loading.

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