A discussion is presented regarding interferometer experiments conducted on free surfaces which are impulsively loaded with high amplitude shock waves. It is shown that material ejection from sbooked surfaces can significantly degrade interferometer experiments. In particular, loss of both light intensity and contrast of interferometer signals can result from various scattering and absorption processes occurring in a cloud of ejected material. An experimental technique is presented which allows determination of the mass and velocity of material ejected from free surfaces during shock loading. The technique has been applied to a study of mass ejection occurring naturally from shocked Hurfaces of two aluminum alloys and from lead. These results show that the total ejected mass ranges from a few [ig/cm. in the aluminT«a alloys studied to a few me/car in lead, for shock pressures ranging from about 10 to 50 GPa (100-500 kbar). Surface defects, such as pits and scratches, are thought to strongly influence mass ejection in alumlnumj whereas in lead, localized shock-induced melting and vaporization are thought to be the dominant mechanisms at the higher shock pressures. Experimental results are also presented for aluminum surfaces which contain artificial defects in the form of wedge-shaped cavities. These results show that the maximum ejects velocities of approximately two to four times the free surface volndt^ wlifrli are ohaTVfd In thesp pypprlmrnt n ran be correlated with predictions of steady jetting theory.
A statistical model is presented for estimating the effects of surface roughness on mass ejection from shocked surfaces. In the model, roughness is characterized by the total volume of defects, such as pits, scratches and machine marks, on a surface. The amount of material ejected from these defects during shock loading can be estimated by assuming that jetting from surface depressions is the primary mode of ejection and by making simplifying assumptions about jetting processes. Techniques are discussed for estimating the effects of distribution in defect size and shape, and results are presented for several different geometries of defects. The model Is used to compare predicted and measured ejecta masses from six different materials. Surface defects in these materials range from pits and scratches on polished surfaces to prepared defects such as machined or porous surfaces. Good agreement is achieved between predicted and measured results, which suggests general applicability of the model.
The Sandia National Laboratories Shock Thermodynamics Applied Research (STAR) Facility has recently consolidated three different guns and a variety of instrumentation capabilities into a single location. The guns available at the facility consist of a single-stage light gas gun, a single-stage propellant gun and a two-stage light gas gun, which cover a velocity range from 15 m/s to 8 km/s • Instrumentation available at the facility includes optical and microwave interferometry, time-resolved holography, fast x-radiography, framing and streak photography, fast multi-wavelength pyrometry, piezoelectric and piezoresistive gauges and computer data reduction. This report discusses the guns and instrumentation available at the facility and selected recent applications • J
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