Jennifer L. Jordan

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.

Observation of a minimum reaction initiation threshold in ball-milled Ni+Al under high-rate mechanical loading

Two types of microstructurally distinct ball-milled Ni+Al powder compacts are characterized for the investigation of reaction initiation threshold under high-rate mechanical loading using a modified rod-on-anvil Taylor impact-test setup. It is observed that the kinetic energy threshold for reaction decreases to a minimum then increases with milling time. It is also observed that the kinetic energy required for reaction initiation is lower for the 95% theoretical maximum density (TMD) ball-milled powder compacts than for the 65% theoretical maximum density (TMD) compacts. The results are discussed on the basis of competing effects of reactivity enhancement and deformability reduction caused by prior ball-milling of the powder mixtures.

High Strain Rate Mechanics of Polymers: A Review

The mechanical properties of polymers are becoming increasingly important as they are used in structural applications, both on their own and as matrix materials for composites. It has long been known that these mechanical properties are dependent on strain rate, temperature, and pressure. In this paper, the methods for dynamic loading of polymers will be briefly reviewed. The high strain rate mechanical properties of several classes of polymers, i.e. glassy and rubbery amorphous polymers and semi-crystalline polymers will be reviewed. Additionally, time–temperature superposition for rate dependent large strain properties and pressure dependence in polymers will be discussed. Constitutive modeling and shock properties of polymers will not be discussed in this review.

Shock equation of state of multi-constituent epoxy-metal particulate composites

The shock properties of epoxy-based particulate composites have been extensively studied in the literature. Generally, these materials only have a single particulate phase; typically alumina. This paper presents equation of state experiments conducted on five epoxy-based particulate composites. The shock stress and shock velocity states were measured for five different composites: two epoxy-aluminum two-phase composites, with various amounts of aluminum, and three epoxy-aluminum-(metal) composites, where the metal constituent was either copper, nickel, or tungsten. The impact velocities ranged from 300 to 960 m/s. Numerical simulations of the experiments of epoxy-Al are compared with mesoscale simulations of epoxy-Al2O3 composites to investigate the effect of the soft versus hard particulate; additionally, an epoxy-Al–W simulation was conducted to investigate the material properties of the second phase on shock response of these materials. In these epoxy-based particulate composites, the slope of the shoc...

Mechanical Properties of Low Density Polyethylene

The mechanical properties of polymers, particularly as a function of temperature and strain rate, are key for implementation of these materials in design. In this paper, the compressive response of low density polyethylene (LDPE) was investigated across a range of strain rates and temperatures. The mechanical response was found to be temperature and strain rate dependent, showing an increase in stress with increasing strain rate or decreasing temperature. A single linear dependence was observed for flow stress on temperature and log strain rate over the full range of conditions investigated. The temperature and strain rate data were mapped using the method developed by Siviour et al. based on time–temperature superposition using a single mapping parameter indicating that there are no phase transitions over the rates and temperatures investigated. Taylor impact experiments were conducted showing a double deformation zone and yield strength measurements in agreement with compression experiments.

High Strain Rate and Shock Properties of Hydroxyl-Terminated Polybutadiene (HTPB) with Varying Amounts of Plasticizer

Hydroxyl-terminated polybutadiene (HTPB) has long been used as a binder in propellants and explosives. However, cured HTPB polyurethanes have not been characterized in a systematic fashion as a function of plasticizer content. In this study, three isocyanate-cured HTPB variants with different amounts of plasticizer were formulated. The materials were characterized across a range of strain rates from 10−3 to 106 s−1. Group interaction modeling (GIM) was used to predict the material behavior based on the underlying structure of the polymer. Increasing the amount of plasticizer was found to reduce the strength of the material across all strain rates. GIM was found to overpredict the modulus but predicted the shock response very well.

Shock equation of state of a multi-phase epoxy-based composite (Al–MnO2-epoxy)

There are several studies in the literature regarding the equation of state of alumina-epoxy composites. Although these single component systems interact in a complex manner with shock waves, the addition of a second metal or ceramic particulate can result in even more complex interactions. This paper presents the shock equation of state results on a multi-phase composite Al–MnO2-epoxy. Equation of state experiments were conducted using three different loading techniques—single stage light gas gun, two stage light gas gun, and explosive loading—with multiple diagnostic techniques. The Us−up relationship is shown to be linear, with deviations from linearity at low, and possibly high, pressures due to the behavior of the epoxy binder. The experimental equation of state data is compared to volume averaged and mesoscale mixture models.

THE EFFECT OF PARTICLE REINFORCEMENT ON THE DYNAMIC DEFORMATION OF EPOXY‐MATRIX COMPOSITES

Multiphase composite materials consisting of one or more types of particle reinforcement in an epoxy matrix are being studied to determine the effect of reinforcement on the dynamic yield strength and critical impact velocity for plastic deformation. Casting was used to prepare epoxy‐matrix composites with varying particle loading fractions (20–50 Vol%), size (5 and 50 μm), and type (Al or Ni+Al). The cast samples were tested at strain rates in the range of 103 to 104 s−1 using a 7.62 mm gas gun with a rod‐on‐anvil (Taylor) impact experiment setup. The recovered impacted specimens were analyzed to determine the dimensions of their deformed and undeformed regions. The yield strength and critical velocity for plastic deformation were evaluated using Hutching’s analysis and correlated with quantitative characteristics of the size and distribution of the reinforcement phases [1, 2].

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.

SHOCK EQUATION OF STATE OF SINGLE CONSTITUENT AND MULTI‐CONSTITUENT EPOXY‐BASED PARTICULATE COMPOSITES

There are several studies in the literature regarding the equation of state of alumina‐epoxy composites. Although this single component system interacts in a complex manner with shock waves, the addition of a second metal or ceramic particulate can result in even more complex interactions. This paper presents a review of shock loading studies on epoxy‐based particulate composites. The relationship between equation of state parameters and particulate concentration is investigated. The measured shock properties are compared with a mixture model for two and three phases.