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Specially designed sensor is attached to or imbedded in propellant. When sensor is driven into vibration, it moves with a phase lag directly proportional to internal friction or loss coefficent. Resonance frequency of the system is related to Young's modulus. Modulus or internal friction can be monitored over long period of time.
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To evaluate commercially developed solid film lubricants for aerospace bearing applications, we investigated the friction and wear behavior of bonded molybdenum disulfide (MoS2), magnetron-sputtered MoS2 and ion-plated silver films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440 C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Herizian contact pressure of 0.79 GPa maximum 1.19 GPa), and a sliding velocity of 0.2 m/s at room temperature in three environments: ultrahigh vacuum (7x10 (exp -7Pa)), humid air (approx. 20 percent humidity), and dry nitrogen (less than 1 percent humidity). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in friction and wear resulted front the environmental conditions and the film materials. The main criteria for judging the performance were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10 (exp -6mm exp 3/Nm or less), respectively. The bonded MoS2 and magnetron-sputtered MoS2 films met the criteria in all three environments. Also, the wear rates of the counterpart AISI 440 C stainless steel balls met that criterion in all three environments. The ion-plated silver films met the criteria only in ultrahigh vacuum. In ultrahigh vacuum the bonded MoS2 films were superior. In humid air the bonded MoS2 films had higher coefficient of friction and shorter wear life than did the magnetron-sputtered MoS2 films. The ion-plated silver films had a high coefficient of friction in humid air but relatively low coefficients of friction in the nonoxidative environments. Adhesion and plastic deformation played important roles in all three environments. All sliding involved adhesive transfer of materials.
To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of ion-plated lead films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7 x 10(exp -7 Pa), humid air (relative humidity, approx. 20 percent), and dry nitrogen (relative humidity, less then 1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the ion-plated lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated lead films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 1(exp -6) cu mm/N.m or less, respectively. The ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments. Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.
To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DLC) films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of L-2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7x10(exp -7) Pa), humid air (relative humidity, approx.20 percent), and dry nitrogen (relative humidity, <1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the DLC films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10(exp -6) cu mm/N-m or less, respectively. MS DLC films and PACVD DLC films met the criteria in humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding contact with 440C stainless steel balls in all three environments the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.
Elastic properties of amorphous solids remain a topic of intense interest due to their important roles in a wide range of applications. Prior works have focused on short-range, local structural features, such as number density and coordination number, to elucidate the underlying mechanism of elastic moduli in glasses. Here, we report strong correlations among the spatial extension of the interatomic potential, elastic moduli, and the coherence lengths of the medium-range structural order through molecular dynamics simulations for single element glasses. Our findings demonstrate an unconventional design principle to engineer elastic properties by extending the medium-range order and provide insights into the microscopic origin of elastic properties in amorphous solids.
Integral property calculation is an important application for solid modeling systems. Algorithms for computing integral properties for various solid representation schemes are fairly well known. It is important to deigners and users of solid modeling systems to understand the behavior of such algorithms. Specifically the trade-off between execution time and accuracy is critical to effective use of integral property calculation. The average behavior of two algorithms for Constructive Solid Geometry (CSG) representations is investigated. Experimental results from the PADL-2 solid modeling system show that coarse decompositions can be used to predict execution time and error estimates for finer decompositions. Exploiting this predictability allow effective use of the algorithms in a solid modeling system.
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Accurate modeling of combustion systems requires knowledge of the radiative properties of the system. Gas phase properties are well known, but detailed knowledge of surface properties is limited. Recent work has provided spectrally resolved data for some solid fuels, but only for the unburned material at room temperature, and for limited sets of previously burned and quenched samples. Due to lack of knowledge of the spectrally resolved properties at elevated temperatures, as well as processing limitations in the modeling effort, graybody values are typically used for the fuels surface radiative properties. However, the spectrally resolved properties for the fuels at room temperature can be used to give a first-order correction for temperature effects on the graybody values. Figure 1 shows a sample of the spectrally resolved emittance/absorptance for a thin solid fuel of the type commonly used in combustion studies, from approximately 2 to 20 microns. This plot clearly shows a strong spectral dependence across the entire range. By definition, the emittance is the ratio of the emitted energy to that of a blackbody at the same temperature. Therefore, to determine a graybody emittance for this material, the spectrally resolved data must be applied to a blackbody curve. The total area under the resulting curve is ratioed to the total area under the blackbody curve to yield the answer. Due to the asymmetry of the spectrally resolved emittance and the changing shape of the blackbody curve as the temperature increases, the relative importance of the emittance value at any given wavelength will change as a function of temperature. Therefore, the graybody emittance value for a given material will change as a function of temperature even if the spectral dependence of the radiative properties remains unchanged. This is demonstrated in Figures 2 and 3, which are plots of the spectrally resolved emittance for KimWipes (shown in Figure 1) multiplied by the blackbody curves for 300 K (Figure 2) and 800 K (Figure 3). Each figure also shows the blackbody curve for that temperature. Ratioing the areas under the curve for each of these figures give a graybody emittance of 0.64 at 300 K, and 0.46 at 800 K. It is recognized that materials undergoing pyrolysis will change in composition as they heat up, and that the radiative properties of the materials may have inherent temperature dependence. Both of these effects will contribute to changes in the radiative characteristics of a given material, and are not accounted for here. However, this paper demonstrates the temperature dependence of graybody radiative properties, and provides a method for a first-order correction (for temperature) to the graybody values if the spectrally resolved properties are known.
This presentation consists of two parts: comments on the results of measurements on thermophysical properties based on the paper, 'Things Mother Never Taught Me (About Thermophysical Properties of Solids)' and results of thermophysical property measurements on selected solid and molten semiconductors and a proprietary superalloy. The first part may be considered as a tutorial for those involved in using or procuring thermophysical property data. The second part is presented as illustrations of what has been accomplished on molten materials at the Thermophysical Properties Research Laboratory (TPRL). The materials include Ge, PbTe, PbSnTe, HgCdTe and a superalloy.
Lanthanum strontium cobaltite (LSCo) is considered as a good candidate cathode contact material for solid oxide fuel cells, due to high electrical conductivity. However, LSCo has a very large coefficient of thermal expansion (CTE) than the cells and metallic interconnects. As a result, poor mechanical stability is expected during thermal cycling. To minimize the CTE mismatch, we investigate a composite approach involving mixing LSCo with an inert material of low CTE, such as mullite at volume fractions from 0.1 to 0.4. Composite’s CTE shows a decreasing trend with increasing mullite volume fractions, and is consistent with model predictions. X-ray powder diffraction analysis of sintered LSCo/mullite composites exhibits no presence of other phases for samples aged for 500h at 800oC, indicating chemical compatibility. Electrical conductivity by a 4-pt method shows a decreasing trend with increasing mullite content. Contact strength of as-sintered and thermally cycled samples show that only the composite with 0.4 volume fraction has a measurable strength; the other composites have no strength. Overall, the composite approach is demonstrated in the LSCo/mullite system to lower the CTE and hence achieve thermal cycle stability. The addition of the inert phase to the LSCo matrix; however, also reduces the electrical conductivity.
This paper reports synthesis, structure, and properties of novel hybrid solid polymer electrolytes (SPE's) consisting of organically modified aluminosilica (OM-ALSi), formed within a poly(ethylene oxide)-in-salt (Li triflate) phase. To alter the structure and properties we fused functionalized silanes containing poly(ethylene oxide) (PEO) tails or CN groups.
Thermodynamic properties of interstitial solid solutions with fcc metals from atomically discrete model by computer simulation
A comparative study is conducted of the mechanical properties of foam-core and honeycomb-core sandwich panels, using a normalizing procedure based on common properties of cellular solids and related properties of dense solids. Seven different honeycombs and closed-foam cells are discussed; of these, three are commercial Al alloy honeycombs, one is an Al-alloy foam, and two are polymeric foams. It is concluded that ideal, closed-cell foams may furnish compressive strengths which while isotropic can be fully comparable to the compressive strengths of honeycombs in the thickness direction. The shear strength of ideal closed-cell foams may be superior to the shear strength of honeycombs.
Due to the large natural variability of its microphysical properties, the characterization of solid precipitation is a longstanding problem. Since in situ observations are unavailable in severe convective systems, innovative remote sensing retrievals are needed to extend our understanding of such systems. This study presents a novel technique able to retrieve the density, mass, and effective diameter of graupel and hail in severe convection through the combination of airborne microwave remote sensing instruments. The retrieval is applied to measure solid precipitation properties within two convective cells observed on 2324 May 2014 over North Carolina during the IPHEx campaign by the NASA ER-2 instrument suite. Between 30 and 40 degrees of freedom of signal are associated with the measurements, which is insufficient to provide full microphysics profiling. The measurements have the largest impact on the retrieval of ice particle sizes, followed by ice water contents. Ice densities are mainly driven by a priori assumptions, though low relative errors in ice densities suggest that in extensive regions of the convective system, only particles with densities larger than 0.4 gcm3 are compatible with the observations. This is in agreement with reports of large hail on the ground and with hydrometeor classification derived from ground-based polarimetric radars observations. This work confirms that multiple scattering generated by large ice hydrometeors in deep convection is relevant for airborne radar systems already at Ku band. A fortiori, multiple scattering will play a pivotal role in such conditions also for Ku band spaceborne radars (e.g., the GPM Dual Precipitation Radar).
I worked for the United Space Alliance, LLC (USA) with the Solid Rocket Booster (SRB) Materials and Process engineers (M&P). I was assigned a project in which I needed to research and collect chemical and physical properties information, material safety data sheets (MSDS), and other product information from the vendor's websites and existing "inhouse" files for a select group of materials used in building and refurbishing the SRBs. This information was then compiled in a report that summarized the information collected. My work site was at the Kennedy Space Center (KSC). This allowed for many opportunities to visit and tour sites operated by NASA, by USA, and by the Air Force. This included the vehicle assembly building (VAB), orbital processing facilities (OPF), the crawler with the mobile launch pad (MLP), and the SRB assembly and refurbishment facility (ARF), to name a few. In addition, the launch, of STS- 117 took place within the first week of employment allowing a day by day following of that mission including post flight operations for the SRBs. Two Delta II rockets were also launched during these 7 weeks. The sights were incredible and the operations witnessed were amazing. I learned so many things I never knew about the entire program and the shuttle itself. The entire experience, especially my work with the SRB materials, inspired my plan for implementation into the classroom.
Finite-element computer program solves for nodal point displacements in an axisymmetric solid. The options in the program include plane stress analysis, axisymmetric solids analysis, nonlinear /plastic/ analysis, and equivalent stress and strain.
Properties of solid–liquid interfaces and surface charge characteristics mediate ionic and molecular transport through porous systems, affecting many processes such as separations. Herein, we report experiments designed to probe the electrochemical properties of solid–liquid interfaces using a model system of a single polyethylene terephthalate (PET) pore in contact with aqueous and propylene carbonate solutions of LiClO 4 . First, the existence and polarity of surface charges were inferred from current–voltage curves recorded when a pore was placed in contact with a LiClO4 concentration gradient. Second, the electro-osmotic transport of uncharged polystyrene particles through the PET pore provided information on the polarity and the magnitude of the pore walls’ zeta potential. Our experiments show that the PET pores become effectively positively charged when in contact with LiClO 4 solutions in propylene carbonate, even though in aqueous LiClO 4 , the same pores are negatively charged. Additionally, the electro-osmotic velocity of the particles revealed a significantly higher magnitude of the positive zeta potential of the pores in propylene carbonate compared to the magnitude of the negative zeta potential in water. The presented methods of probing the properties of solid–liquid interfaces are expected to be applicable to a wide variety of solid and liquid systems.