Paul E. Specht

Configurational effects on shock wave propagation in Ni-Al multilayer composites

The shock compression response of cold-rolled Ni and Al multilayered composites at various angles of inclination are investigated by employing meso-scale simulations. The orientation of the laminate layers in the multilayered composite is varied at 0°, 45°, and 90° to the direction of shock front propagation to determine and understand the resulting changes in the shock compression response. Real, heterogeneous microstructures, obtained from optical micrographs of the multilayered composite cross-section, are incorporated into the Eulerian, finite volume code, CTH. The simulations are performed to establish the role that the orientation of material interfaces plays in the dispersion and dissipation of the shock wave as well as the US-UP relationship for each configuration. Noticeable differences are observed at the meso-scale in the pressure, temperature, and strain response, as a function of the underlying microstructure. Geometric dispersion is seen to alter the shape of the resulting pressure pulse and...

Numerical simulation of shock initiation of Ni/Al multilayered composites

The initiation of chemical reaction in cold-rolled Ni/Al multilayered composites by shock compression is investigated numerically. A simplified approach is adopted that exploits the disparity between the reaction and shock loading timescales. The impact of shock compression is modeled using CTH simulations that yield pressure, strain, and temperature distributions within the composites due to the shock propagation. The resulting temperature distribution is then used as initial condition to simulate the evolution of the subsequent shock-induced mixing and chemical reaction. To this end, a reduced reaction model is used that expresses the local atomic mixing and heat release rates in terms of an evolution equation for a dimensionless time scale reflecting the age of the mixed layer. The computations are used to assess the effect of bilayer thickness on the reaction, as well as the impact of shock velocity and orientation with respect to the layering. Computed results indicate that initiation and evolution o...

Shock compression response of cold-rolled Ni/Al multilayer composites

Uniaxial strain, plate-on-plate impact experiments were performed on cold-rolled Ni/Al multilayer composites and the resulting Hugoniot was determined through time-resolved measurements combined with impedance matching. The experimental Hugoniot agreed with that previously predicted by two dimensional (2D) meso-scale calculations [Specht et al., J. Appl. Phys. 111, 073527 (2012)]. Additional 2D meso-scale simulations were performed using the same computational method as the prior study to reproduce the experimentally measured free surface velocities and stress profiles. These simulations accurately replicated the experimental profiles, providing additional validation for the previous computational work.

Interfacial Effects on the Dispersion and Dissipation of Shock Waves in Ni/Al Multilayer Composites

The influence of interfacial density, structure, and strength in addition to material strengths on the dispersion and dissipation of a shock wave traveling parallel to the layers in a laminar, multilayer composite was investigated using two-dimensional, meso-scale simulations incorporating a real, heterogeneous microstructure. Optimum interfacial densities for maximizing wave dispersion and dissipation were identified. Interfacial structure strongly influenced the dispersion by altering the wave interactions internal to the composite. Interfacial strength effected both the dispersion and dissipation through drastic changes to the interfacial strain generated. Lastly, material strength influenced only the dissipation of the shock wave by altering the compressibility of the constituents. The combined results identified interfacial strain as the driving mechanism influencing the shock compression response of the Ni/Al multilayered composites.

Design of a Multi-Point Microwave Interferometer Using the Electro-Optic Effect.

A multi-point microwave interferometer (MPMI) concept is presented for non-invasively monitoring the internal transit of a shock, detonation, or reaction front in energetic media. The concept utilizes an electro-optic (EO) crystal to impart a time-varying phase lag onto a laser with a microwave signal. Polarization optics convert this phase lag into an amplitude modulation. A heterodyne interferometer compares the modulated laser beam to a constant reference. This enables the detection of changes in the modulating microwave frequency generated by the motion of the measurement surface. The design is scalable and makes use of the established construction and analysis methods employed in photonic Doppler velocimetry (PDV). The technical challenges associated with the concept are the frequency stability of the lasers, the amount of light return after EO modulation, and the frequency uncertainty of fast Fourier transform (FFT) methods.

Development of a Multi-Point Microwave Interferometry (MPMI) Method

A multi-point microwave interferometer (MPMI) concept was developed for non-invasively tracking a shock, reaction, or detonation front in energetic media. Initially, a single-point, heterodyne microwave interferometry capability was established. The design, construction, and verification of the single-point interferometer provided a knowledge base for the creation of the MPMI concept. The MPMI concept uses an electro-optic (EO) crystal to impart a time-varying phase lag onto a laser at the microwave frequency. Polarization optics converts this phase lag into an amplitude modulation, which is analyzed in a heterodyne interfer- ometer to detect Doppler shifts in the microwave frequency. A version of the MPMI was constructed to experimentally measure the frequency of a microwave source through the EO modulation of a laser. The successful extraction of the microwave frequency proved the underlying physical concept of the MPMI design, and highlighted the challenges associated with the longer microwave wavelength. The frequency measurements made with the current equipment contained too much uncertainty for an accurate velocity measurement. Potential alterations to the current construction are presented to improve the quality of the measured signal and enable multiple accurate velocity measurements.

MESO‐SCALE COMPUTATIONAL STUDY OF THE SHOCK‐COMPRESSION OF COLD‐ROLLED Ni‐Al LAMINATES

Meso‐scale computational analysis is used to study the shock‐compression response of cold‐rolled Ni‐Al laminates which represent a fully dense reactive system with continuous interparticle contacts. The laminates were prepared through rolling multiple Ni and Al foils with initial thicknesses of 127 μm and 178 μm, respectively. Simulations of shock wave propagation through the laminates are performed using CTH on heterogeneous, imported microstructures obtained through optical microscopy. Uniaxial strain experiments are utilized to validate the simulated responses in order to draw comparisons to previously obtained results for Ni‐Al powder compacts. The Baer‐Nunziato nonequilibrium multiphase granular mixture model is then used to model the 1D reaction response of the materials during dynamic loading.

Thermal Diffusivity and Specific Heat Measurements of Titanium Potassium Perchlorate Titanium Subhydride Potassium Perchlorate 9013 Glass 7052 Glass SB-14 Glass and C-4000 Muscovite Mica Using the Flash Technique

The flash technique was used to measure the thermal diffusivity and specific heat of titanium potassium perchlorate (TKP) ignition powder (33wt% Ti 67wt% KP) with Ventron supplied titanium particles, TKP ignition powder (33wt% Ti 67wt% KP) with ATK supplied titanium particles, TKP output powder (41wt% Ti 59wt% KP), and titanium subhydride potassium perchlorate (THKP) (33wt% TiH1.65 67wt% KP) at 25 C. The influence of density and temperature on the thermal diffusivity and specific heat of TKP with Ventron supplied titanium particles was also investigated. Lastly, the thermal diffusivity and specific heats of 9013 glass, 7052 glass, SB-14 glass, and C-4000 Muscovite mica are presented as a function of temperature up to 300 C.