Steven H. Goods

Mechanical properties of a particle-strengthened polyurethane foam

Quasi-static compression tests have been performed on polyurethane foam specimens. The modulus of the foam exhibited a power-law dependence with respect to density of the form: E* ∝ (ρ*)n, where n = 1.7. The modulus data are described well by a simple geometric model (based on the work of Gibson and Ashby) for a closed-cell foam in which the stiffness of the foam is governed by the flexure of the cell struts and cell walls. The compressive strength of the foam is also found to follow a power-law behavior with respect to foam density. In this instance, Euler buckling is used to explain the density dependence. The modulus of the foam was modified by addition of gas-atomized, spherical, aluminum powder. Additions of 30 and 50 wt % Al measurably increased the foam modulus, but without a change in the density dependence. However, there was no observable increase in modulus with 5 and 10 wt % additions of the metal powder. Strength was also increased at high loading fractions of powder. The increase in modulus and strength could be predicted by combining the Gibson–Ashby model, referred to above, with a well-known model describing the effect on modulus of a rigid dispersoid in a compliant matrix.

Mechanical properties of CRETE, a polyurethane foam

The room-temperature mechanical properties of a closed-cell, polyurethane encapsulant foam were measured as a function of foam density. Over the range of densities examined, the modulus could be described by a power-law relationship with respect to density. This power-law relationship was the same for both tension and compression testing. The basis for this power-law relationship is explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model put forth by Gibson and Ashby. The elastic collapse stress, a property relevant to compression testing, also is found to exhibit a power-law relationship with respect to density. The density dependence of this property is also found in the work of Gibson and Ashby and is explained in terms of the Euler buckling of the struts that comprise the cellular structure. Energy absorption during deformation is also reported for both tension and compression testing.

Annealing Effects on Mechanical and Transport Properties of Ni and Ni-Alloy Electrodeposits

The effect of annealing at temperatures up to 600 degC on the mechanical properties and the thermal and electrical transport characteristics of nickel and a nickel-manganese electrodeposits are presented. The samples include Ni plated from sulfamate salt with dodecyl sulfate surfactant and from NiSO4 with saccharin additive and a NiMn alloy deposited from a nickel sulfamate bath with added MnCl2. Recrystallization and grain growth, induced by annealing, are shown to strongly affect the mechanical and transport properties. Relatively coarse-grained Ni-sulfamate electrodeposits yielded properties closest to bulk Ni. The incorporation of sulfur (from saccharin additions to the plating electrolyte) or Mn into electrodeposited Ni produces materials with exceptionally fine grain size and with very high yield and ultimate strength. At the same time, the thermal and electrical conductivities are smaller than bulk Ni. Thermal annealing leads to a reduction in strength and an enhancement of the transport properties. The Ni-Mn alloy shows the best temperature stability of the mechanical and transport properties among the tested samples. The observed trends are explained in terms of the influence of microstructure on the mechanical and transport properties

Microstructure and mechanical properties of nickel microparts electroformed in replicated LIGA molds

A novel process for the rapid replication of electroforming plastic micromolds has been developed and is now being used to produce plated nickel test specimens. The process combines hot embossing or injection molding with metallic microscreens to produce sacrificial electroforming molds with conducting bases and insulating sidewalls. The replicated micromolds differ from standard LIGA molds in that the holes in the microscreen act as insulating defects in the electroforming base. The effects of such defects on the materials properties of electroformed microparts will be discussed and it will be shown that when the surface irregularities corresponding to the microscreen holes are removed, mechanical properties are experimentally indistinguishable from those found in conventionally processed LIGA specimens.

Mechanical properties of a structural polyurethane foam and the effect of particulate loading

The room temperature mechanical properties of a closed-cell, polyurethane encapsulant foam have been measured as a function of foam density. Tests were performed on both unfilled and filler reinforced specimens. Over the range of densities examined, the modulus of the unloaded foam could be described by a power-law relationship with respect to density. This power-law relationship could be explained in terms of the elastic compliance of the cellular structure of the foam using a simple geometric model found in the literature. The collapse stress of the foam was also found to exhibit a power-law relationship with respect to density. Additions of an aluminum powder filler increased the modulus relative to the unfilled foam.

Fast neutron environments.

The goal of this LDRD project is to develop a rapid first-order experimental procedure for the testing of advanced cladding materials that may be considered for generation IV nuclear reactors. In order to investigate this, a technique was developed to expose the coupons of potential materials to high displacement damage at elevated temperatures to simulate the neutron environment expected in Generation IV reactors. This was completed through a high temperature high-energy heavy-ion implantation. The mechanical properties of the ion irradiated region were tested by either micropillar compression or nanoindentation to determine the local properties, as a function of the implantation dose and exposure temperature. In order to directly compare the microstructural evolution and property degradation from the accelerated testing and classical neutron testing, 316L, 409, and 420 stainless steels were tested. In addition, two sets of diffusion couples from 316L and HT9 stainless steels with various refractory metals. This study has shown that if the ion irradiation size scale is taken into consideration when developing and analyzing the mechanical property data, significant insight into the structural properties of the potential cladding materials can be gained in about a week.

X-ray Lithography Techniques, LIGA-Based Microsystem Manufacturing: The Electrochemistry of Through-Mold Deposition and Material Properties

Certain microsystem fabrication techniques are critically dependent on the electrochemistry of metal deposition into lithographically defined features that are developed in insulating molding materials. One such technique, developed originally at the Forschungzentrum Karlsruhe, Germany, is known as LIGA, the German acronym for lithography, electroplating, and replication (Lithographie, Galvanoformung, and Abformung) [1–3]. An example of typical miniature structures formed by plating through thick photoresist (the insulating molding materials) is shown in Fig. 1. Since its inception in Germany in the 1980s, LIGA research activities have expanded throughout Europe, as well as in Asia and North America.

Thermomechanical Fatigue Evaluation of Haynes® 230® for Solar Receiver Applications

Haynes® 230® is a Ni–Cr–W–Mo alloy commonly used in aerospace and chemical process industries because of its excellent oxidation resistance, fatigue and creep performance at very high temperatures. In this study, the alloy was evaluated as a candidate for its use as tubing material in solar receivers, where coupled thermal-mechanical cycling is imposed in-use by heating imposed during diurnal cycles. The effect of temperature, 425 and 677 °C, and hold times on isothermal fatigue was evaluated and fatigue-life curves were developed for the alloy in its as-received condition and after aging at 677 °C for 3 months. Experimental apparatus and techniques were developed to apply thermomechanical cycles, between 425 and 677 °C, in an expedited manner to determine fatigue life at low strain ranges, again for both material conditions. The influence of stress ratio, R = −1 and R = ∞, was also assessed. The experimental techniques developed and resulting data and findings will be presented.

FLASHFOAM: A Triboluminescent Polymer Foam for Mechanical Sensing

The formulation and processing of a brittle polyurethane foam containing triboluminescent powder additives is described. Two powder additives, known to exhibit triboluminescence, were individually examined: triethylammonium tetrakis (dibenzoylmethanato) europate [NEt3H][Eu(DBM)4] and ordinary table sugar (sucrose, C12H22O11). In each instance, the powders were mixed into the polyol component of the foam. When combined with the isocyanate component, the resulting foams had these powders incorporated into their cellular structure so as to induce a triboluminescent response upon crushing during impact testing. The triboluminescent response of foam specimens containing each of these powder additives was characterized by measuring: the time rate of change in the optical output (measured as Watts), the peak optical output, the total integrated output (Watt-seconds), during the impact event. Foams containing the europate compound were found to yield several orders of magnitude higher output when compared to the sugar-containing foam. Strain rate and concentration of the powder (in the foam) were important variables with respect to optical output. Both the peak and total triboluminescent output increased with increasing powder concentration. Peak output was also found to increase with increasing strain rate. However, the total output was found to be roughly constant for a given concentration regardless of strain rate (over the strain rate range: 20 sec-1< e& < 150 sec-1). At very low strain rates, no triboluminescent response was measured.

The Structure and Properties of Boundaries in Bicrystals of Boron-Doped Ni 3 (Al,l at% Ta)

The effect of boron on the structure and macroscopic properties of an isolated grain boundary in bicrystals of a non-stoichiometric Ni 3 Al alloy (76 at% Ni, 23 at% Al, 1 at%Ta) has been studied. The room temperature tensile ductility and fracture mode of the bicrystals varies dramatically with the rate of cooling after elevated temperature heat treatment. In the absence of significant segregation of boron to the boundary, the bicrystals fail via brittle interfacial fracture with little or no ductility. When the segregation of boron to the boundary is maximized, the bicrystals are highly ductile. High resolution transmission electron microscopy reveals that this ductile state is achieved without the formation of a detectable region of compositional disorder at the boundary. Atomistic calculations using a Monte Carlo scheme predict that only partial disordering of the planes immediately adjacent to the boundary should occur for Ni-rich alloys both with and without boron. These results suggest that the presence of boron causes an increase in the cohesive energy of the boundaries rather than a change in the local compositional ordering.