Thomas J. Ahrens received his B.S. from the Massachusetts Institute of Technology, his M.S. from Caltech, and his Ph.D. from Rensselaer Polytechnic Institute.
We study the dynamic properties and response of solid, porous, and molten materials to shock waves. We also conduct experimental and computational research on impact processes, especially on ceramics, and geological and planetary materials. We operate a unique laboratory containing some four hypervelocity gun launchers, and conduct experiments utilizing high explosives. We also measure in-situ stress within deep boreholes in the earth's crust and relate these to present-day earthquake and volcanic processes.
We use unique high-speed radiative techniques are being used to measure the temperature of iron and iron compounds under shock compression. The shock temperature data provide information on the melting point of these materials (in the range of 4000 to 6000 K) at pressures in the range of 2 to 3 million atmospheres. Current research is directed toward measuring thermal diffusivity of matter at these ultrahigh pressures and relating them to theories of phonon transport and other thermodynamic properties.
Our research includes the physics of dynamic consolidation of diamond and cubic boron nitride, admixed with whiskers of silicon carbide and boron nitride. A series of very hard and strong composite materials have resulted from this effort. Scanning electron micrographs comparing the starting mixture of cubic boron nitride powder and silicon carbide whisker with the final configuration show clearly that the mixture has been dynamically consolidated into a hard and tough solid material.
We developed a new method for measuring the stresses that are present in the earth's crust and that reflect the forces that give rise to earth movement, including those relating to earthquakes and volcanic eruptions. This technique utilizes a unique laser holographic imaging system which operates within fluid-filled boreholes. At a given station in a borehole, the apparatus images the rock of the borehole wall. A side hole is drilled and a second image is taken in the same location. Interference fringes occur in the double-exposure hologram at a position where the optical path change is an odd number of one-half light wave lengths. By obtaining such interference fringes in different orientation, the stress field in the absence of the borehole is obtained. Measurements are under way in a series of southern California boreholes to measure stresses in the vicinity of the numerous active faults in this region.
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