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Cure Kinetics and Processing Parameters of Neat and Reinforced High Performance Epoxy Resins: Evaluation of Techniques

Description: Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4’-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC). The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC and temperature-modulated DSC (TMDSC), thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram for rapid determination of processing parameters in the processing of prepregs. Copyright is held by the author, unless otherwise noted. All rights reserved. Files: Thesis.pdf Special Conditions
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: December 1999
Creator: Bilyeu, Bryan
Partner: UNT Libraries

Tobacco Curing

Description: "There are three essentially different ways of carrying out the curing [of tobacco]. These are (1) air curing, in which little or no artificial heat is applied; (2) flue curing, in which the tobacco is entirely cured by artificial heat and in such way as to prevent smoke from coming in contact with the leaf; and (3) fire curing, in which the tobacco is largely cured by artificial heat applied by means of open fires made on the floor of the barn, thus allowing smoke to come in contact with the leaf. It will be necessary to consider separately each of these methods, together with the modifications made in them in curing the various types of tobacco." -- p. 4
Date: 1913
Creator: Garner, W. W. (Wightman Wells), b. 1875
Partner: UNT Libraries Government Documents Department

Haymaking

Description: "Haymaking is an operation that must be done in a certain space of time that is short at best and that is always liable to be made shorter by bad weather. For this reason there is perhaps no farm operation in which system and efficiency count for more than in haymaking; yet throughout the hay-growing area more or less haphazard methods of haymaking are still very common. This bulletin is designed to point out ways in which the more successful hay growers of the country save time and labor in this important field work. It tells how the growing scarcity of farm labor may be met by rearranging crews and changing methods, and by the adoption of up-to-date implements, such as the hay loader, push rake, and stacker. In addition to outlines of methods for various sized crews and acreages the bulletin presents, briefly, a discussion of the theory of curing hay, a thorough understanding of which is a great help in planning an efficient method of haymaking." -- p. 2
Date: 1918
Creator: McClure, H. B. (Harry B.)
Partner: UNT Libraries Government Documents Department

Raspberries

Description: Report discussing the cultivation of both red raspberries and black raspberries, as well as their preparation by curing and drying.
Date: 1905
Creator: Corbett, L. C. (Lee Cleveland), 1867-1940
Partner: UNT Libraries Government Documents Department

Modifications of epoxy resins for improved mechanical and tribological performances and their effects on curing kinetics.

Description: A commercial epoxy, diglycidyl ether of bisphenol-A, was modified by two different routes. One was the addition of silica to produce epoxy composites. Three different silane coupling agents, glycidyloxypropyl trimethoxy silane (GPS), -methacryloxypropyl trimethoxy silane (MAMS) and 3-mercaptopropyltriethoxy silane (MPS), were used as silica-surface modifiers. The effects of silica content, together with the effects of chemical surface treatment of silica, were studied. The results indicate that epoxy composites with silica exhibit mechanical and tribological properties as well as curing kinetics different than the pure epoxy. The optimum silica content for improved mechanical and tribological properties (low friction coefficient and wear rate) was different for each type of silane coupling agent. An unequivocal correlation between good mechanical and improved tribological properties was not found. Activation energy of overall reactions was affected by the addition of silica modified with MAMS and MPS, but not with GPS. The second route was modification by fluorination. A new fluoro-epoxy oligomer was synthesized and incorporated into a commercial epoxy by a conventional blending method. The oligomer functioned as a catalyst in the curing of epoxy and polyamine. Thermal stability of the blends decreased slightly at a high oligomer content. Higher wear resistance, lower friction coefficient and higher toughness were found with increasing oligomer content; thus in this case there was a correlation between good mechanical and improved tribological properties. The results indicated that increasing toughness and formation of a transfer film contribute to improved tribological performances.
Date: May 2008
Creator: Chonkaew, Wunpen
Partner: UNT Libraries

Developing the Manufacturing Process for Hylene MP Curing Agent

Description: This report details efforts to scale-up and re-establish the manufacturing process for the curing agent known as Hylene MP. First, small scale reactions were completed with varying conditions to determine key drivers for yielding high quality product. Once the optimum conditions were determined on the small scale, the scaled-up process conditions were determined. New equipment was incorporated into the manufacturing process to create a closed production system and improve chemical exposure controls and improve worker safety. A safe, efficient manufacturing process was developed to manufacture high quality Hylene MP in large quantities.
Date: February 16, 2009
Creator: Eastwood, Eric
Partner: UNT Libraries Government Documents Department

Quantitative prediction of stresses during thermoset cure

Description: Two thin-walled Al tubes were filled with epoxy which were cured isothermally; one tube was instrumented with strain gauges, and the other with thermocouples. Finite element codes were used. Predicted and measured centerline hoop strains are shown; predictions and measurements agree. This is being applied to encapsulated components.
Date: July 1, 1996
Creator: Adolf, D.; Chambers, B. & Burchett, S.
Partner: UNT Libraries Government Documents Department

Measurement techniques for evaluating encapsulant thermophysical properties during cure

Description: Sandia now has the capability to evaluate stresses during cure of epoxies with finite element codes. Numerous material parameters are needed as input to these codes. I present a relatively quick set of tests which enable evaluation of the required thermophysical properties. Ease and accuracy of the tests improve as the reaction rate of the thermoset slows. Material parameters for common encapsulants at Sandia are presented in tables.
Date: June 1, 1996
Creator: Adolf, D.
Partner: UNT Libraries Government Documents Department

Spiral track oven

Description: Final report on development of a continuously operating oven system in which the parts are progressing automatically on a spiral track for in-line service installation for the production of electronic and/or other components to be heat cured or dried.
Date: December 20, 1998
Creator: Drobilisch, Sandor
Partner: UNT Libraries Government Documents Department

Microwave processing of materials. Final report

Description: A Cooperative Research and Development Agreement (CRADA) between Lockheed Martin Energy Systems, Inc. (LMES) and Lambda Technologies, Inc. (Lambda) of Raleigh, N.C., was initiated in May 1995. [Lockheed Martin Energy Research, Corp. (LMER) has replaced LMES]. The completion data for the Agreement was December 31, 1996. The purpose of this work is to explore the feasibility of several advanced microwave processing concepts to develop new energy-efficient materials and processes. The project includes two tasks: (1) commercialization of the variable-frequency microwave furnace (VFMF); and (2) microwave curing of polymer composites. The VFMF, whose initial conception and design was funded by the Advanced Industrial Concepts (AIC) Materials Program, will allow us, for the first time, to conduct microwave processing studies over a wide frequency range. This novel design uses a high-power traveling wave tube (TWT) originally developed for electronic warfare. By using this microwave source, one can not only select individual microwave frequencies for particular experiments, but also achieve uniform power densities over a large area by the superposition of many different frequencies.
Date: November 1, 1997
Creator: McMillan, A.D.; Lauf, R.J. & Garard, R.S.
Partner: UNT Libraries Government Documents Department

In-situ property measurements on laser-drawn strands of SL 5170 epoxy and SL 5149 acrylate

Description: Material behavior plays a significant role in the mechanics leading to internal stresses and, potentially, to distortion (curling) of parts as they are built by stereolithography processes that utilize photocuring resins. A study is underway to generate material properties that can be used to develop phenomenological material models of epoxy and acrylate resins. Strand tests are performed in situ in a 3D System`s SLA-250 machine; strands are drawn by either single or multiple exposures of the resin to a laser beam. Linear shrinkage, cross-sectional areas, cure shrinkage forces and stress-strain data are presented. Also, the curl in cantilever beam specimens, built with different draw patterns, are compared.
Date: August 1, 1995
Creator: Guess, T.R. & Chambers, R.S.
Partner: UNT Libraries Government Documents Department

Growing and Curing Hops

Description: "In keeping with the great progress made in agriculture within recent years the methods employed in hop production have not remained unchanged. Nevertheless certain practical principles of great importance to successful hop growing merit a much wider consideration and use than they now enjoy. These will be discussed in the following pages in which is also presented a brief general outline of hop culture." -- p. 7. Hops culture is discussed with regard to climate and soil requirements, propagation, planting, trellises and training, picking, and curing.
Date: 1907
Creator: Stockberger, W. W. (Warner Webster)
Partner: UNT Libraries Government Documents Department

Characterization of polyurethane systems which contain low levels of free TDI

Description: EN-7, EN-8, and EN-9 are polyurethane systems that are used in numerous applications in the Department of Energy complex. These systems contain high levels of toluene diisocyanate (TDI). Currently, TDI is being treated as a suspect human carcinogen within the Department of Energy complex. This report documents the results of a material characterization study of three polyurethane systems that contain low levels of free (potentially airborne) TDI. The characterization has been accomplished by performing a set of statistically designed experiments. The purpose of these experiments is to explore the effects of formulation and cure schedule on various material properties. In general, the material properties (pot life, glass transition temperature, hardness, and tear strength) were relatively insensitive to variation in the cure schedule. On the other hand, variation in curative level had measurable effects on material properties for the polyurethane systems studied. Furthermore, the material properties of the three low-free-TDI polyurethane systems were found to be comparable or superior (for certain curative levels) to commonly-used polyurethane systems. Thus, these low-free-TDI systems appear to be viable candidates for applications where a polyurethane is needed.
Date: April 1, 1995
Creator: Myers, R.L. & Thomas, E.V.
Partner: UNT Libraries Government Documents Department

Effects of Temperature and Humidity on Wilethane 44 Cure

Description: Wilethane 44 is a polyurethane adhesive developed by the Materials Team within ESA-MEE at Los Alamos National Laboratory as a replacement for Hexcel Corporation Urethane 7200. Urethane 7200 is used in numerous weapon systems, but it was withdrawn from the market in 1989. The weapons complex requires a replacement material for use in the W76-1 LEP and the W88, as well as for assembly of JTAs for other warheads. All polyurethane systems are susceptible to moisture reacting with unreacted isocyanate groups. This side reaction competes with the curing reaction and results in CO{sub 2} formation. Therefore, a polyurethane adhesive can exhibit foaming if appropriate environmental controls are not in place while it cures. A designed experiment has been conducted at TA-16-304 to determine the effects of ambient conditions on the properties of cured Wilethane 44. Temperature was varied from 15 C to 30 C and relative humidity from 15% to 40%. The density, hardness at 24 hours, and butt tensile strength on aluminum substrates were measured and fitted to quadratic equations over the experimental space. Additionally, the loss and storage moduli during cure were monitored as a function of cure temperature. These experiments provide a stronger basis for establishing appropriate environmental conditions and cure times when using Wilethane 44. The current guidelines are a working time of 90 minutes, a cure time of 18 hours, and a relative humidity of less than 25%, regardless of ambient temperature. Viscosity measurements revealed that the working time is a strong function of temperature and can be as long as 130 minutes at 15 C or as short as 90 minutes at 30 C. The experiments also showed that the gel time is much longer than originally thought, as long as 13 hours at 15 C. Consequently, it may be necessary to extend the ...
Date: October 1, 2006
Creator: Weigle, John C.
Partner: UNT Libraries Government Documents Department

Packaging strategies for printed circuit board components. Volume I, materials & thermal stresses.

Description: Decisions on material selections for electronics packaging can be quite complicated by the need to balance the criteria to withstand severe impacts yet survive deep thermal cycles intact. Many times, material choices are based on historical precedence perhaps ignorant of whether those initial choices were carefully investigated or whether the requirements on the new component match those of previous units. The goal of this program focuses on developing both increased intuition for generic packaging guidelines and computational methodologies for optimizing packaging in specific components. Initial efforts centered on characterization of classes of materials common to packaging strategies and computational analyses of stresses generated during thermal cycling to identify strengths and weaknesses of various material choices. Future studies will analyze the same example problems incorporating the effects of curing stresses as needed and analyzing dynamic loadings to compare trends with the quasi-static conclusions.
Date: September 1, 2011
Creator: Neilsen, Michael K. (Kansas City Plant, Kansas City, MO); Austin, Kevin N.; Adolf, Douglas Brian; Spangler, Scott W.; Neidigk, Matthew Aaron & Chambers, Robert S.
Partner: UNT Libraries Government Documents Department

Drying forage by forced ventilation.

Description: Discusses different systems of forced-air ventilation as a means of harvesting and drying forage crops.
Date: August 1951
Creator: Davis, Roy B. (Roy Benjamin), 1919-; Schoenleber, Leonard G. & Campbell, Lowell Eugene, 1920-
Partner: UNT Libraries Government Documents Department

Autonomic Healing of Epoxy Using Micro-Encapsulated Dicyclopentadiene

Description: The autonomic healing ability of an epoxy adhesive containing micro-encapsulated dicyclopentadiene (DCPD) was evaluated. The epoxy resin used was Epon 828 cured with either Versamid 140 or diethylenetriamine (DETA). Variables included total weight percent of microcapsules (MCs) and catalyst, as well as the catalyst to DCPD ratio. The degree of healing was determined by the fracture toughness before and after ''healing'' using double-cantilever beam analysis. It was found that the degree of self-healing was most directly related to the contact area (i.e. crack width) during healing. Temperature also played a significant role. Observed differences between the results of this study and those in literature are discussed.
Date: May 1, 2003
Creator: THOMA, STEVEN G.; GIUNTA, RACHEL K.; STAVIG, MARK E.; EMERSON, JOHN A. & MORALES, ALFREDO M.
Partner: UNT Libraries Government Documents Department

Epoxy and acrylate stereolithography resins: In-situ measurements of cure shrinkage and stress relaxation

Description: Cross-sections of resin strands. Techniques were developed to make in situ measurements of gelled resin to determine linear shrinkage, stress-strain response and stress relaxation of single strands of SL 5170 epoxy and SL 5149 photocurable resins. Epoxy strands shrank approximately 1.4% and the acrylate strands about 1.0% after a single exposure. No forces were measured during cure shrinkage of strands following the first laser exposure. In multiple laser exposures, the acrylate continues to shrink; whereas (University of Dayton data) no additional shrinkage is observed in epoxy strands on a second hit. In force relaxation tests, a strand is drawn and then a 0.5% step strain is applied after different elapsed times. The epoxy initial modulus evolves (increases) with elapsed time following draw of the strand, and this evolution in modulus occurs after linear shrinkage has stopped. On the other hand, acrylates show no evolution of modulus with elapsed time following a single laser draw; i.e., once shrinkage stops after one laser hit, the initial modulus remains stable with elapsed time. Finally, relaxation response times of epoxy strands get larger with increasing elapsed time after laser draw. In acrylate strands there was no evolution in initial modulus with elapsed time after a single draw so relaxation times are not a function of elapsed time after a single hit with the laser.
Date: March 1, 1995
Creator: Guess, T.R.; Chambers, R.S.; Hinnerichs, T.D.; McCarty, G.D. & Shagam, R.N.
Partner: UNT Libraries Government Documents Department

UV Curable Materials Development

Description: Adhesives, coatings, and inks were selected for evaluation based on literature search and possible production applications. A differential photocalorimeter was used to measure degree of cure and allow prediction of optimum processing conditions. UV cure equipment were characterized and the ability to size equipment to specific materials cure needs established. Adhesion tests procedures were developed for the adhesives and solvent resistance testing procedures developed for the coatings and inks.
Date: December 1, 1996
Creator: Parker, B. G.
Partner: UNT Libraries Government Documents Department