Joel W. House

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.

HIGH STRAIN‐RATE PROPERTIES OF TANTALUM PROCESSED BY EQUAL CHANNEL ANGULAR PRESSING

Current ingot refinement and solidification techniques used in tantalum processing often result in inconsistent mechanical properties. Subsequent processing by equal channel angular pressing (ECAP) has been shown to reduce or eliminate internal structural variations as well as part‐to‐part variability [2]. This paper presents the effects of ECAP processing on the properties of tantalum. The materials of interest are 2.5‐inch round bar tantalum supplied by H.C. Starck and Cabot Supermetals. Three metallurgical conditions were examined for each material: as worked, fine‐grain annealed, and large‐grain annealed. Prior to annealing, each bar was processed eight times through a 135‐degree ECAP die using route C (billet rotated 180 degrees between passes) and then forged into 0.25‐inch thick plates. Mechanical property specimens were subsequently removed from the plates for low and high‐rate uniaxial compression experiments. Orientation dependence was characterized by orienting specimen load axes through the th...

Dynamic Failure Resistance of Two Tantalum Materials with Different Melt Practice Sequences

The dynamic failure resistance of a Cabot Ta is compared to that of a Starck Ta under nearly identical loading conditions. The two materials have nominally very similar grain sizes, texture, and bulk impurity contents. The two materials do differ in the melt practice used, the Cabot material underwent triple e‐beam re‐melting, while the Starck material underwent a double e‐beam re‐melting followed by a vacuum arc re‐melt (VAR). Melt practice strongly influences the material cleanliness in most materials and hence greatly influences fracture properties such as fatigue resistance and fracture toughness. The samples were tested in a flyer plate experiment with momentum trapping and soft recovery. A VISAR recorded the free surface velocity profile of the samples. The resulting damage in the microstructures was quantified, statistically reduced and used in developing separate parameters for a damage model. Comparisons between simulation predictions and experimental measurements of free surface velocity, porosi...

Damage Characterization in Copper Deformed under Hydrostatic Stress — Experimental Analysis

The results of an experimental investigation designed to determine the effect of damage created by hydrostatic tensile loading on the properties of copper are reported. Three metallurgical conditions of half‐hard OFHC copper were investigated; as worked; annealed 2hr at 400°C (∼40 micron grain diameter); and annealed 2hr at 800°C (∼80 micron grain diameter). Mechanical property characterization included uniaxial compression tests. High rate plasticity and damage was introduced by Taylor and rod‐on‐rod impact tests. The damage from the high rate experiments was characterized using optical and scanning electron microscopy. Quasi‐static compression specimens machined from recovered high rate samples were tested to determine the influence of damage on the mechanical response of the material. The compression test results will be discussed in relationship to the starting microstructure and the extent of damaged introduced into the material.