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Inspection of and around joints, beams, and other three-dimensional structures is integral to practical nondestructive evaluation of large structures. Non-contact, scanning laser ultrasound techniques offer an automated means of physically accessing these regions. However, to realize the benefits of laser-scanning techniques, simultaneous inspection of multiple surfaces at different orientations to the scanner must not significantly degrade the signal level nor diminish the ability to distinguish defects from healthy geometric features. In this study, we evaluated the implementation of acoustic wavenumber spectroscopy for inspecting metal joints and crossbeams from interior angles. With this technique, we used a single-tone, steady-state, ultrasonic excitation to excite the joints via a single transducer attached to one surface. We then measured the full-field velocity responses using a scanning Laser Doppler vibrometer and produced maps of local wavenumber estimates. With the high signal level associated with steady-state excitation, scans could be performed at surface orientations of up to 45 degrees. We applied camera perspective projection transformations to remove the distortion in the scans due to a known projection angle, leading to a significant improvement in the local estimates of wavenumber. Projection leads to asymmetrical distortion in the wavenumber in one direction, making it possible to estimate view angle even when neither it nor the nominal wavenumber is known. Since plate thinning produces a purely symmetric increase in wavenumber, it also possible to independently estimate the degree of hidden corrosion. With a two-surface joint, using the wavenumber estimate maps, we were able to automatically calculate the orthographic projection component of each angled surface in the scan area. [ABSTRACT FROM AUTHOR]

This paper presents results on the dynamics of damage in copper under incipient spall conditions for multicrystalline specimens. Specimens were annealed from polycrystalline material to reduce the number of grain boundaries the shock wave traverses in passing through the specimen. The specimens incorporated unique fiducials that permit accurate correlation of pre-shot characterization of the grain orientations, grain size etc. with the location of the dynamic diagnostics and with post-shot metallography. The dynamic diagnostics—Transient Imaging Displacement Interferometry (TIDI), point VISAR, line VISAR—were all precisely aligned on the specimen surface to view regions of interest revealed in the pre-shot characterization. Initial analyses demonstrate the wealth of information obtained from this experimental approach. Examples include observation that regions in the surface microstructure most likely to be damaged based on pre-shot characterization show some of the largest displacements during the shock-loading. Post-shot microscopy shows damage in the same places. Another observation is there appears to be localized plastic deformation that occurs during the first compression wave which then remains and evolves through several cycles of compression and release from the spall plane. [ABSTRACT FROM AUTHOR]

We have applied Transient Imaging Displacement Interferometry (TIDI) to copper targets loaded by laser-launched flyers. TIDI captures the full-field out-of-plane surface displacement map single-shot with the time resolution of the illumination pulses (180 ps). Displacement sensitivity of ∼10 nm with lateral spatial resolution of ∼5 microns is achieved over our ∼1 mm2 field-of-view. A framing camera allows capture of up to eight displacement maps for a single loading event, allowing the evolution of the surface motion to be tracked. Point and line VISARs are used as complementary diagnostics that provide a temporally continuous record of the velocity history of the sample, and also provide time stamps for the TIDI displacement maps. The rich heterogeneity in the surface displacement due to the grain structure of the sample is readily measured. [ABSTRACT FROM AUTHOR]

The TRIDENT laser at Los Alamos has been used to drive small plate impact experiments. Flyers are typically 8 mm in diameter and 0.1 to 1.0 mm thick, while the targets are 10 mm in diameters and 0.2 to 2.0 mm thick. One of the sample materials is copper composed of large columnar grains. These samples can reveal information about damage in single crystals and bi-crystals. This work will focus on simulating these experiments to reveal the stress loading histories. A phenomenological single crystal plasticity model in the FLAG hyrdocode will be used. At the time of first negative pressure, calculated stress and strain concentrations occur at regions of high damage seen by metallurgical examination of a recovered sample. These calculated concentrations help to reveal the driving conditions that cause damage formation. [ABSTRACT FROM AUTHOR]

We are investigating interactions between shocks and grain boundaries in the anisotropic alloy NiAl; as part of this work, we need to know the shock response of single crystals. The equation of state (EOS) and elasticity were predicted using ab initio quantum mechanics. NiAl crystals were obtained from GE, and also prepared locally, and cut to thickesses between about 100 and 500 microns. Laser-driven flyer impact experiments were used to verify the EOS and to measure the elastic precursor wave as a function of crystal orientation. Shocks induced by direct laser irradiation were used to investigate the elastic precursor and to demonstrate that the imaging VISAR system had a temporal resolution adequate to distinguish between different orientations. A single-crystal plasticity model is under development to design and interpret experiments on bicrystals. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have used a full-field displacement interferometry technique known as Transient Interferometric Microscopy (TIM) to generate displacement maps of surface motion at several delay times for single dynamic loading events. The high lateral resolution and out-of-plane displacement sensitivity allow the rich details of the motion of a single grain relative to the surrounding material to be quantitatively measured. Simultaneous line VISAR measurements allow detailed understanding of the complex surface motion. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]