Louis Ferranti

EQUATION OF STATE OF ALUMINUM-IRON OXIDE - EPOXY COMPOSITE

We report on the measurements of the shock equation of state (Hugoniot) of an Al∕Fe2O3/epoxy composite, prepared by epoxy cast curing of powder mixtures. Explosive loading, with Baratol, trinitrotoluene (TNT), and Octol, was used for performing experiments at higher pressures, in which case shock velocities were measured in the samples and aluminum, copper, or polymethyl methacrylate (PMMA) donor material, using piezoelectric pins. The explosive loading of the metal donors (aluminum and copper) will be discussed. Gas gun experiments provide complementary lower pressure data in which piezoelectric polyvinylidene fluoride (PVDF) stress gauges were used to measure the input and propagated stress wave profiles in the sample and the corresponding shock propagation velocity. The results of the Hugoniot equation of state are compared with mesoscale finite-element simulations, which show good agreement.

Dynamic high-strain-rate mechanical behavior of microstructurally biased two-phase TIB2+AL2O3 ceramics

The dynamic high-strain-rate behavior of two-phase TiB2+Al2O3 ceramics with biased microstructures was investigated in this study. The microstructural bias includes differences in phase (grain) size and phase distribution such that in one case a continuous (interconnected) TiB2 network surrounds the Al2O3 phase (qualitatively termed “T@A”) and in another case the TiB2 and Al2O3 phases are interdispersed and uniformly intertwined with each other (qualitatively termed “TinA”). Quantitative microscopy was used to characterize the phase size and the integral curvature which is taken as a measure of TiB2 phase connectivity around Al2O3. Dynamic compression and tension (spall) properties were measured using plate impact experiments. The measurements used piezoelectric polyvinyldine fluoride stress gauges to obtain the loading profile and to determine the Hugoniot elastic limit. In addition, velocity interferometry system for any reflector interferometry was used to obtain the spall signal and the tensile dynami...

Dynamic Mechanical Behavior Characterization of Epoxy‐Cast Al+Fe2O3 Mixtures

Dynamic mechanical property measurement experiments were conducted on epoxy‐cast Al+Fe2O3 powder mixture specimens using the classic Taylor anvil test at impact velocities up to 200 m/s. Reverse Taylor anvil impact experiments were also conducted at lower velocities using a single stage gas gun by impacting a rigid anvil onto a stationary specimen. Dynamic deformation, fracture, and viscoelastic response of the cast specimens (containing 20–50 and 100% epoxy) were captured in real time utilizing high‐speed photography. Detailed image analysis of transient deformation reveals a significant elastic strain contribution to the total strain, which complicates the calculation of a constant dynamic yield strength value for the composite material.

Equation of State of Aluminum — Iron Oxide (Fe2O3) — Epoxy Composite: Modeling and Experiment

We report on the investigation of the equation of state of an 2Al+Fe2O3+ 50 wt.% epoxy composite in the 2–23 GPa pressure range. An explosive loading technique, with piezoelectric pins to measure the shock velocity in the sample and in a donor material, was used for experiments exceeding 5 GPa. Gas gun experiments were performed on the same composites at lower pressures, using PVDF stress gauges to record the input and propagated stresses and the shock velocity based on the time of travel through the sample thickness. The experimental results are compared to numerical simulations of shock compression in discrete particle models. Model results are in agreement with experimental results.

INCREMENTAL STRESS‐STRAIN RESPONSE OF POLYMERS USING INSTRUMENTED REVERSE TAYLOR ANVIL IMPACTS

Instrumented reverse Taylor impact experiments were conducted on pure epoxy and epoxy‐cast Al+Fe2O3 composites to determine the incremental stress‐strain response under dynamic loading. High‐speed camera images were used to measure transient (axial and areal) deformations, and velocity interferometry was used to record complex elastic and plastic wave interactions. For polymeric materials, elastic strains are generally not negligible compared to plastic strains and the rigid‐plastic material behavior assumed in typical Taylor tests for metallic materials cannot be applied. Hence, in this work, a one‐dimensional elastic‐plastic wave propagation analysis, developed by Hutchings [J. Mech. Phys. Solids 26, 1979] to account for the appreciable elastic strains that develop before the material yields, was used to obtain stress‐strain behavior for each polymer composition. The relative strengths between each composition are compared to ascertain the influence that particle reinforcement has on material properties...

SHOCK HUGONIOT BEHAVIOR OF PARTICLE REINFORCED POLYMER COMPOSITES

The shock Hugoniot of polymers is known to exhibit a non‐linear US‐UP relationship at relatively low pressures and commonly displays a concave curvature with an initially rapid shock velocity. However, the experimentally measured shock Hugoniot of particle reinforced composites shows an opposite effect displaying a convex curvature with an initially rapid change in particle velocity. Transformation to pressure‐volume space shows an initial expansion that is not related to a low‐pressure phase change or reaction. In contrast, the volume expansion is connected to decohesion of solid particles from the polymer matrix. Equation of state experiments conducted for epoxy‐cast Al+Fe2O3 composites show deviation from ideal Hugoniot behavior as a result of damage evolving at a critical impact stress. Two compositions prepared with significantly different volume fractions of the binder phase show damage occurring at approximately the same critical impact stress. The Burch‐Murnaghan equation of state (BM‐EOS) is used to characterize the composites compressibility and identify the magnitude of the critical damage stress.The shock Hugoniot of polymers is known to exhibit a non‐linear US‐UP relationship at relatively low pressures and commonly displays a concave curvature with an initially rapid shock velocity. However, the experimentally measured shock Hugoniot of particle reinforced composites shows an opposite effect displaying a convex curvature with an initially rapid change in particle velocity. Transformation to pressure‐volume space shows an initial expansion that is not related to a low‐pressure phase change or reaction. In contrast, the volume expansion is connected to decohesion of solid particles from the polymer matrix. Equation of state experiments conducted for epoxy‐cast Al+Fe2O3 composites show deviation from ideal Hugoniot behavior as a result of damage evolving at a critical impact stress. Two compositions prepared with significantly different volume fractions of the binder phase show damage occurring at approximately the same critical impact stress. The Burch‐Murnaghan equation of state (BM‐EOS) is used...

Ultrafast dynamic response of single crystal β-HMX

We report results from ultrafast compression experiments conducted on β-HMX single crystals. Results consist of nominally 12 picosecond time-resolved wave profile data, (ultrafast time domain interferometry –TDI measurements), that were analyzed to determine high-velocity wave speeds as a function of piston velocity. TDI results are used to validate calculations of anisotropic stress-strain behavior of shocked loaded energetic materials. Our previous results derived using a 350 ps duration compression drive revealed anisotropic elastic wave response in single crystal β-HMX from (110) and (010) impact planes. Here we present results using a 1.05 ns duration compression drive with a 950 ps interferometry window to extend knowledge of the anisotropic dynamic response of β-HMX within eight microns of the initial impact plane. We observe two distinct wave profiles from (010) and three wave profiles from (010) impact planes. The (110) impact plane wave speeds typically exceed (010) impact plane wave speeds at t...

Effect of Processing Induced Microstructural Bias of Phase Distribution on Spall Strength of Two‐Phase TiB2‐Al2O3 Ceramics

The influence of microstructural bias on the spall strength of two‐phase TiB2+Al2O3 ceramics was investigated in this study. The microstructural bias generated by varying the extent of ball‐milling time prior to hot pressing of combustion synthesized or mechanically‐mixed pre‐alloyed powders, includes differences in connectivity of TiB2 around Al2O3 and grain size of respective phases. Tensile spall properties were measured using plate‐impact gas‐gun experiments, with velocity interferometry. The results of these tests correlated with quantitative microscopy analysis of the microstructural bias illustrate that increase in connectivity of TiB2 around Al2O3 lowers the spall strength due to tensile residual stresses developing during processing of the two‐phase ceramics.

Influence of Microstructural Bias on the Hugoniot Elastic Limit and Spall Strength of Two‐Phase TiB2+Al2O3 Ceramics

The influence of microstructural bias on the Hugoniot Elastic Limit and spall strength of two‐phase TiB2+Al2O3 ceramics was investigated in this study. The microstructural bias includes differences in phase (grain) size and phase distribution such that in one case a continuous (interconnected) TiB2 network surrounds the Al2O3 phase, and in another case the TiB2 and Al2O3 phases are interdispersed and uniformly inter‐twined with each other. Dynamic compression and tension (spall) properties were measured using plate‐impact gas‐gun experiments. The measurements used piezoelectric PVDF stress gauges to obtain the loading profile and determine the Hugoniot Elastic Limit, and VISAR interferometry to obtain the spall signal and determine tensile properties. The experimental results reveal that while the strength under dynamic compression (HEL) is more dominantly dependent on the phase size, the tensile spall strength scales with the connectivity of the TiB2 phase.