Session K3: ED-2a: PDV Applications

Study on Dynamic Compression Properties of K9 Glass with Doppler Pins Array Measurements

K9 glass is one of archetypal brittle materials for studies of dynamic fracture, failure wave, and so on. This paper presented the dynamic compression properties of K9 glass under uniaxial strain condition. Experimental sample is K9 glass with internal pre-existed defects, and the shape of pre-existed defects is disc with less than 0.5 mm diameter. All tests were conducted by power gun with 37 mm diameter chamber. Doppler Pins array with high space-time resolutions, which consists of sixteen pins in range of 2 mm line length, were applied to measure the particle velocity histories in different positions at the sample rear surface, and the space-resolution is 127 $\mu $m, Experimental results show failure waves initiate at internal micro-surfaces of the sample under shock loading, and the dynamic stress concentration is likely attributed to be a physical mechanism of the initiation of the failure wave. These defects that by the controlled laser irradiation in advance are some internal micro-surfaces. Meanwhile, the experimental results show that internal micro-surfaces of the sample have influence on the elastic precursor wave decay.   

Improved Bar Impact Tests using a Photonic Doppler Velocimeter

Bar impacts were used to measure the dynamic strength of glasses. The conventional bar technique has been greatly improved through use of a photonic Doppler velocimeter (PDV) to measure free surface motion. The PDV records a compression pulse corresponding to compressive failure of the impact zone and a spall signal corresponding to tensile failure of the distal end. Best results were obtained using polished free surfaces, as opposed to retroreflective tape. Use of a graded density film had little effect on strain rate but reduced the peak transmitted stress. The experiments were interpreted with the aid of EMU (peridynamics) calculations. Indications are that the impact end of the bar fails in compression. The bar separates into two sections when the reflected tensile wave arrives at the zone of impact damage. The rear of the bar fails from an inward propagating failure wave that originates at surface flaws.   

Ultrafast Dynamics of Coherent Acoustic Phonons in the GaMnAs/GaAs Heterostructure System

Pronounced oscillations were found in the reflectivity curves of ferromagnetic GaMnAs/GaAs heterostructure using pump-probe spectroscopy that are caused by coherent acoustic phonons propagating through the sample. The difference in the oscillations period, damping and amplitude as the phonons travel across the GaMnAs/GaAs interface reflect sin electronic structures and optical properties of these materials. Analysis of the oscillation amplitude indicates that this method provides a novel, non-invasive, and non-destructive way to depth profiling.   

Line-imaging ORVIS measurements of interferometric windows under quasi-isentropic compression

A line-imaging optically recording velocity interferometer system (ORVIS) has been implemented on the Veloce pulsed power generator to enable measurement of spatially resolved velocity histories of materials under dynamic compression. Interferometric windows are regularly used to maintain the high-pressure state of shock and ramp (quasi-isentropic) loaded materials. Although imaging through a shock or rapid ramp ($\le $ 10 ns) loaded transparent window material has been reasonably successful, for slower ramp loading ($\sim $ 440 ns) experiments, the elastic-plastic yielding of the window has an adverse effect on return light to the line-imaging ORVIS. The results of quasi-isentropic loading experiments with various interferometric windows such as LiF, NaCl, SiO2, PMMA, and sapphire are presented. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.