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On the Permeability of Porous Materials

Description: Note presenting an investigation of the effects on porous-material permeability characteristics of the absolute pressure level, choking of the flow, bending the material, and other factors. Experiments showed permeability characteristics to be appreciably affected by absolute pressure level, flow choking, and thickness of the material. Results regarding testing with wire cloth and sintered metal are provided.
Date: January 1956
Creator: Yates, E. Carson, Jr.
Partner: UNT Libraries Government Documents Department

Fabrication and Properties of Hot-Pressed Molybdenum Disilicide

Description: Report presenting an investigation of hot-pressed molbdenum disilicide bodies produced by industrial processes at a temperature of 2950 degrees and a pressure of 3000 pounds per square inch. Results regarding the short-time tensile strength, stress-rupture data, compression strength, air-corrosion resistance, hardness, coefficient of linear thermal expansion, thermal conductivity, and density are provided.
Date: May 26, 1950
Creator: Long, Roger A.
Partner: UNT Libraries Government Documents Department

Competencies Required for the Design and Implementation of Manufacturing Systems for Advanced Composite Structures

Description: The problem with which this investigation is concerned is that of identifying and prioritizing the competencies required to design and implement manufacturing systems for advanced composite structures. The classical Delphi procedure is the research method used for the conduct of this study. A five-member advisory board developed a list of seventeen categories under which the competencies would reside. In the first-round questionnaire, the seventeen categories were presented to a Delphi panel of experts who provided up to five competencies required in each category. The first-round returns provided two new categories and 973 competency statements. Duplications were eliminated and 366 competency statements remained in nineteen categories. The second, third, and fourth rounds were a reiterative rating process. The panel was asked to rate the items in the questionnaire based on their relative importance to the intent of the study. The importance rating scale included "very important," "important," "slightly important," and "unimportant." The means and interquartile ranges were calculated for each statement and provided as feedback in the successive round. Kendall's coefficient of concordance W for tied ranks was used to validate the panel consensus. The W was significant at the .01 level for each of the three rounds where rating was performed. The data were presented in rank order within categories by importance level. Eighteen percent of the competency statements were rated "very important," 77 percent "important, and 5 percent "slightly important." No statements were rated "unimportant" by the panel. It was concluded that, as indicated by the 19 categories and 366 competencies, the scope of the requirements for designing and implementing manufacturing systems for advanced composite structures represent a broad range of knowledge and skill requirements. The breadth of the range of the requirements indicated the need for the development of areas of specialization within the subject field to adequately ...
Date: May 1986
Creator: Lange, Robert Douglas
Partner: UNT Libraries

Characterization of three dimensional fiber orientation in short-fiber composites

Description: A mathematical procedure for recovering from image analysis the three dimensional nonsymmetric fiber-orientation distribution in short-fiber composites is proposed. Microphotographs from two orthogonal faces of a composite sample are needed to determine the three dimensional fiber orientation. A simple weighting function is derived to take into account the probability of intercepting fibers at varying inclination angles. The present procedure improves the previous works of other researchers in the following two aspects. First, it can obtain the single-angle fiber-orientation distribution from one micrograph in reference to the normal of the photographed surface. This distribution is often needed in predicting the mechanical and physical properties of short-fiber composites in this direction. Second, no symmetry in fiber-orientation distribution is assumed in the determination of the three dimensional fiber-orientation, which makes the present procedure more practical and versatile.
Date: May 1, 1995
Creator: Zhu, Yuntian T. & Blumenthal, W.R.
Partner: UNT Libraries Government Documents Department

Waste Materials from Tetra Pak Packages as Reinforcement of Polymer Concrete

Description: This article discusses how compressive and flexural strength and modulus of elasticity decrease gradually, when either Tetra Pak particle concentration or particle size is increased.
Date: September 28, 2015
Creator: Martínez-López, Miguel; Martínez-Barrera, Gonzalo; Barrera-Díaz, Carlos; Ureña-Núñez, Fernando & Brostow, Witold, 1934-
Partner: UNT College of Engineering

New, higher-order, elasticity-based micromechanics model

Description: The formulation for a new homogenization theory is presented. The theory utilizes a higher-order, elasticity-based cell analysis of a periodic array of unit cells. The unit cell is discretized into subregions or subcells. The displacement field within each subcell is approximated by an (truncated) eigenfunction function expansion of up to fifth order. The governing equations are developed by satisfying the pointwise governing equations of geometrically linear continuum mechanics exactly up through the given order of the subcell displacement fields. The specified governing equations are valid for any type of constitutive model used to describe the behavior of the material in a subcell. The fifth order theory is subsequently reduced to a third order theory. The appropriate reduction of the fifth and third order theories to the first order theory (which corresponds to a variant of the original method of cells (MOC) (Aboudi, 1991) theory) is outlined. The 3D ECM theory correctly reduces to the 2D ECM theory microstructures and the exact 1D theory for bilaminated structures. Comparison of the predicted bulk and local responses with published results indicates that the theory accurately predicts both types of responses. Furthermore, it is shown that the higher order fields introduced coupling effects between the local fields that can result in substantial changes in the predicted bulk inelastic response of a composite.
Date: January 1, 2003
Creator: Williams, T. O. (Todd O.)
Partner: UNT Libraries Government Documents Department

Anisotropic fiber alignment in composite structures

Description: High strength material composite structures are formed with oriented fibers to provide controlled anisotropic fibers. Fibers suspended in non-dilute concentrations (e.g., up to 20 volume percent for fibers having an aspect ratio of 20) in a selected medium are oriented by moving an axially spaced array of elements in the direction of desired fiber alignment. The array elements are generally perpendicular to the desired orientation. The suspension medium may also include sphere-like particles where the resulting material is a ceramic.
Date: December 31, 1992
Creator: Graham, A.L.; Mondy, L.A. & Guell, D.C.
Partner: UNT Libraries Government Documents Department

CRADA Final Report for NFE-08-01826: Development and application of processing and processcontrol for nano-composite materials for lithium ion batteries

Description: Oak Ridge National Laboratory and A123 Systems, Inc. collaborated on this project to develop a better understanding, quality control procedures, and safety testing for A123 System’s nanocomposite separator (NCS) technology which is a cell based patented technology and separator. NCS demonstrated excellent performance. x3450 prismatic cells were shown to survive >8000 cycles (1C/2C rate) at room temperature with greater than 80% capacity retention with only NCS present as an alternative to conventional polyolefin. However, for a successful commercialization, the coating conditions required to provide consistent and reliable product had not been optimized and QC techniques for being able to remove defective material before incorporation into a cell had not been developed. The work outlined in this report addresses these latter two points. First, experiments were conducted to understand temperature profiles during the different drying stages of the NCS coating when applied to both anode and cathode. One of the more interesting discoveries of this study was the observation of the large temperature decrease experienced by the wet coating between the end of the infrared (IR) drying stage and the beginning of the exposure to the convection drying oven. This is not a desirable situation as the temperature gradient could have a deleterious effect on coating quality. Based on this and other experimental data a radiative transfer model was developed for IR heating that also included a mass transfer module for drying. This will prove invaluable for battery coating optimization especially where IR drying is being employed. A stress model was also developed that predicts that under certain drying conditions tensile stresses are formed in the coating which could lead to cracking that is sometimes observed after drying is complete. Prediction of under what conditions these stresses form is vital to improving coating quality. In addition to understanding the drying process ...
Date: December 15, 2012
Creator: Daniel, C.; Armstrong, B.; Maxey, C.; Sabau, A.; Wang, H.; Hagans, P. (A123 Systems, Inc.) et al.
Partner: UNT Libraries Government Documents Department

Field-structured composite studies.

Description: Field-structured composites (FSCs) were produced by hosting micron-sized gold-coated nickel particles in a pre-polymer and allowing the mixture to cure in a magnetic field environment. The feasibility of controlling a composite's electrical conductivity using feedback control applied to the field coils was investigated. It was discovered that conductivity in FSCs is primarily determined by stresses in the polymer host matrix due to cure shrinkage. Thus, in cases where the structuring field was uniform and unidirectional so as to produce chainlike structures in the composite, no electrical conductivity was measured until well after the structuring field was turned off at the gel point. In situations where complex, rotating fields were used to generate complex, three-dimensional structures in a composite, very small, but measurable, conductivity was observed prior to the gel point. Responsive, sensitive prototype chemical sensors were developed based on this technology with initial tests showing very promising results.
Date: April 1, 2004
Creator: Martin, James Ellis & Williamson, Rodney L.
Partner: UNT Libraries Government Documents Department

Advanced composites technology

Description: The development of fiber composite components in next-generation munitions, such as sabots for kinetic energy penetrators and lightweight cases for advanced artillery projectiles, relies on design trade-off studies using validated computer code simulations. We are developing capabilities to determine the failure of advanced fiber composites under multiaxial stresses to critically evaluate three-dimensional failure models and develop new ones if necessary. The effects of superimposed hydrostatic pressure on failure of composites are being investigated using a high-pressure testing system that incorporates several unique features. Several improvements were made to the system this year, and we report on the first tests of both isotropic and fiber composite materials. The preliminary results indicate that pressure has little effect on longitudinal compression strength of unidirectional composites, but issues with obtaining reliable failures in these materials still remain to be resolved. The transverse compression strength was found to be significantly enhanced by pressure, and the trends observed for this property and the longitudinal strength are in agreement with recent models for failure of fiber composites.
Date: October 1, 1998
Creator: DeTeresa, S J; Groves, S E & Sanchez, R J
Partner: UNT Libraries Government Documents Department

Characterization of SiC fibers by soft x-ray photoelectron and photoabsorption spectroscopies and scanning Auger microscopy

Description: Synchrotron radiation soft x-ray photoelectron and photoabsorption spectroscopy was used to characterize commercially obtained SiC fibers produced by CVD on a W core and followed by a C passivating layer. Depth profiling of the fiber through the C/SiC interface was done by making Si 2p and C 1s core level PES and PAS, as well as scanning Auger microscopy, measurements following Ar{sup +} sputtering. No significant changes in either photoemission or absorption or Auger line shapes were observed versus depth, indicating no significant interfacial reaction. The line shapes of the carbonaceous coatings are predominantely graphite-like and those of the CVD SiC coatings are microcrystalline, with disorder present to some extent in both cases.
Date: August 1996
Creator: Ma, Qing; McDowell, M. W. & Rosenberg, R. A.
Partner: UNT Libraries Government Documents Department

Development of a new class of satellites: a composite lightweight affordable spacecraft structure

Description: The Los Alamos National Laboratory (LANL) in partnership with Composite Optics Incorporated (COI) has successfully designed and tested a Composite Lightweight Affordable Structure (CLASS). The use of advanced composites in space applications is well developed, but the application of an all-composite satellite structure has not been achieved until now. The development of this low-cost, lightweight, composite technology for use in small satellite structures, in this case, for the Fast On-Orbit Recording of Transient Events (FORT{acute E}) satellite mission will make a considerable contribution to the advanced spacecraft community. A common practice for constructing small spacecraft structures is to use an all-aluminum spacecraft bus. Compared to a composite structure, this reduces the payload capacity significantly; however, the cost of the aluminum structure has historically been lower than one of that uses lightweight components. LANL mission requirements dictate the need for a long term solution that substantially increased the ratio of payload to structural mass while maintaining a low-risk low-cost approach. LANL intends to use the concept developed for FORT{acute E} on future missions requiring similar enhanced payload capacities. 1 fig.
Date: June 1, 1996
Creator: Thompson, T.C. & Parietti, L.
Partner: UNT Libraries Government Documents Department

Measurement of gas transport properties for chemical vapor infiltration

Description: In the chemical vapor infiltration (CVI) process for fabricating ceramic matrix composites (CMCs), transport of gas phase reactant into the fiber preform is a critical step. The transport can be driven by pressure or by concentration. This report describes methods for measuring this for CVI preforms and partially infiltrated composites. Results are presented for Nicalon fiber cloth layup preforms and composites, Nextel fiber braid preforms and composites, and a Nicalon fiber 3-D weave composite. The results are consistent with a percolating network model for gas transport in CVI preforms and composites. This model predicts inherent variability in local pore characteristics and transport properties, and therefore, in local densification during processing; this may lead to production of gastight composites.
Date: December 1, 1996
Creator: Starr, T.L. & Hablutzel, N.
Partner: UNT Libraries Government Documents Department

Characterization and Process Development of Cyanate Ester Resin Composites

Description: Cyanate ester resins offer advantages as composite matrices because of their high thermal stability, low outgassing, low water absorption, and radiation resistance. This paper describes the results of a processing study to develop a high-strength hoop-wound composite by the wet-filament winding method using Toray TI 000G carbon fiber and YLA RS- 14A cyanate ester resin as the constituent materials. The study shows that the cyanate ester resin has a broad process envelope but that an inert-atmosphere cure is essential for obtaining optimum resin and composite properties. Minimizing moisture exposure prior to and during cure is also crucial as it affects the glass transition temperature of the resin and composite. Composite cylinders wound and cured with these methods yielded excellent ring tensile strengths both at room and elevated temperature. A summary of the measured mechanical and thermal property data for these composites is presented. Potential applications for these materials include flywheeI energy storage systems for space and satellite structures.
Date: May 23, 1999
Creator: Frame, B.J.
Partner: UNT Libraries Government Documents Department