Search Results

Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Description: Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag and Ni particles causes an increase in the wear loss volume while Al can reduce the wear for both polymeric matrices.
Date: December 2007
Creator: Olea Mejia, Oscar Fernando
Partner: UNT Libraries

Aliens and atheists: The Plurality of Worlds and Natural Theology in Seventeenth-Century England.

Description: The plurality of worlds has had a long history in England, which has not gone unnoticed by scholars. Historians have tended to view this English pluralist tradition as similar to those found on the continent, and in doing so have failed to fully understand the religious significance that the plurality of worlds had on English thought and society. This religious significance is discovered through a thorough investigation of plurality as presented by English natural philosophers and theologians, and in so doing reveals much about England in the seventeenth century. As natural philosophers incorporated plurality within the larger framework of natural theology, it became a weapon of science and reason to be used against the unreasonable atheists of late seventeenth-century England.
Date: December 2007
Creator: Oliver, Ryan
Partner: UNT Libraries

Behavior of Concrete Panels Reinforced with Synthetic Fibers, Mild Steel, and GFRP Composites Subjected to Blasts

Description: The paper presents experimental data generated for calibrating finite element models to predict the performance of reinforced concrete panels with a wide range of construction details under blast loading. The specimens were 1.2 m square panels constructed using Normal Weight Concrete (NWC) or Fiber Reinforced Concrete (FRC). FRC consisted of macro-synthetic fibers dispersed in NWC. Five types of panels were tested: NWC panels with steel bars; FRC panels without additional reinforcement; FRC panels with steel bars; NWC panels with glass fiber reinforced polymer (GFRP) bars; and NWC panels reinforced with steel bars and external GFRP laminates on both faces. Each panel type was constructed with three thicknesses: 152 mm, 254 mm, and 356 mm. FRC panels with steel bars had the best performance for new construction. NWC panels reinforced with steel bars and external GFRP laminates on both faces had the best performance for strengthening or rehabilitation of existing structures. The performance of NWC panels with GFRP bars was strongly influenced by the bar spacing. The behavior of the panels is classified in terms of damage using immediate occupancy, life safety, and near collapse performance levels. Preliminary dynamic simulations are compared to the experimental results.
Date: March 1, 2012
Creator: Pantelides, C. P.; Garfield, T. T.; Richins, W. D.; Larson, T. K. & Blakeley, J. E.
Item Type: Article
Partner: UNT Libraries Government Documents Department

Roadmap to NRC Approval of Ceramic Matrix Composites in Generation IV Reactors

Description: This report provides an initial roadmap to obtain Nuclear Regulatory Commission (NRC) approval for using these material systems in a nuclear application. The possible paths taken to achieving NRC approval are necessarily subject to change as this is an on-going process that shifts as more data and a clearer understanding of the nuclear regulations are gathered.
Date: May 1, 2006
Creator: Jenkins, M. G.; Lara-Curzio, E. & Windes, W.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Status of geometry effects on structural nuclear composite properties

Description: structural ceramic composites being considered for control rod applications within the VHTR design. While standard sized (i.e. 150-mm long or longer) test specimens can be used for baseline non-irradiated thermal creep studies, very small, compact, tensile specimens will be required for the irradiated creep studies. Traditionally, it is standard practice to use small, representative test samples in place of full-size components for an irradiated study. However, a real problem exists for scale-up of composite materials. Unlike monolithic materials, these composites are engineered from two distinct materials using complicated infiltration techniques to provide full density and maximum mechanical properties. The material properties may be significantly affected when the component geometry or size is changed. It must be demonstrated that the smaller test samples used in an irradiated study will adequately represent larger composite tubes used for control rod applications. To accomplish this, two different test programs are being implemented to establish that small, flat test specimens are representative of the mechanical response for large, cylindrical composite tubes: a size effect study and a geometry effect study.
Date: September 1, 2005
Creator: Windes, Will; Katoh, Y.; Snead, L.L.; Lara-Curzio, E. & C. Henagar, Jr.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Creep of Structural Nuclear Composites

Description: A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600ยบ C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.
Date: September 1, 2005
Creator: Windes, Will & Lloyd, R.W.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Developing an Innovative Field Expedient Fracture Toughness Testing Protocol for Concrete Materials

Description: The Spiral Notch Torsion Fracture Toughness Test (SNTT) was developed recently to determine the intrinsic fracture toughness (KIC) of structural materials. The SNTT system operates by applying pure torsion to uniform cylindrical specimens with a notch line that spirals around the specimen at a 45 pitch. KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is uniquely suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments. Application of the method to metallic, ceramic, and graphite materials has been demonstrated. One important characteristic of SNTT is that neither a fatigue precrack or a deep notch are required for the evaluation of brittle materials, which significantly reduces the sample size requirement. In this paper we report results for a Portland cement-based mortar to demonstrate applicability of the SNTT method to cementitious materials. The estimated KIC of the tested mortar samples with compressive strength of 34.45 MPa was found to be 0.19 MPa m.
Date: September 1, 2008
Creator: Wang, Jy-An John; Liu, Ken C & Naus, Dan J
Item Type: Report
Partner: UNT Libraries Government Documents Department

Failure analysis and surety design of composite patching systems.

Description: This work presents an experimental evaluation of patch repair of solid laminated composites. The study was focused on destructive and nondestructive tests of full-scale repaired panels under static tension loading conditions. The testing program consisted of ten panels: three pristine, three damaged, three repaired and one repaired with mismatched fiber orientation patch. The evaluated panels were (300 mm x 675 mm) in size and consisted of 6-ply ((-60 /60/0){sub s}) quasi-isotropic laminates. The destructive tests were performed by North Carolina A&T State University and the nondestructive tests were performed by Iowa State University using Pulse-echo C-scan, Air coupled TTU and Auto-Tap. Sandia National Laboratories validated the NDT tests by implementing NDE field methods. Based on the evaluation performed in this study, it appears that the patch repair is an effective means in retrofitting damaged solid composite laminates.
Date: August 1, 2004
Creator: Hamoush, Sameer (North Carolina A&T State University, Greensboro, NC)
Item Type: Report
Partner: UNT Libraries Government Documents Department

Microstructural evolution in elastically stressed systems. Final report

Description: The results, which have been compared to numerical simulations and found to be in very good agreement, predict that diviations in composition on the order of several atomic percent (measured with respect to equilibrium compositions) are possible at the interface. Interfacial compositions are strongly time dependent and are also influenced by the stress state.
Date: September 14, 1997
Creator: Johnson, W.C.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Subcritical Crack Growth in Ceramic Composites at High Temperature Measured Using Digital Image Correlation

Description: An in situ experimental technique is described that allows high resolution, high sensitivity determination of displacements and full-field strains during high temperature mechanical testing. The technique is used to investigate elevated temperature crack growth in SiC/Nicalon sub f composites. At 1150 degrees C, the reinforcing fibers have a higher creep susceptibility than the matrix. Fiber creep leads to relaxation of crack bridging tractions, resulting in subcritical crack growth. Differential image analysis is used to measure the crack opening displacement profile u(x) of an advancing, bridged crack. With appropriate modeling, such data can be used to determine the traction law, from which the mechanics of cracking and failure may be determined.
Date: January 11, 1996
Creator: Mumm, D.R.; Morris, W.L.; Dadkhah, M.S. & Cox, B.N.
Item Type: Book
Partner: UNT Libraries Government Documents Department

Fiber-Matrix Interface Studies on Electron Beam Cured Composites

Description: The recently completed Department of Energy (DOE) and industry sponsored Cooperative Research and Development Agreement (CRADA) entitled, ''Electron Beam Curing of Polymer Matrix Composites,'' determined that the interlaminar shear strength properties of the best electron beam cured IM7/epoxy composites were 19-28% lower than autoclave cured IM7/epoxy composites (i.e. IM7/977-2 and IM7/977-3). Low interlaminar shear strength is widely acknowledged as the key barrier to the successful acceptance and implementation of electron beam cured composites in the aircraft/aerospace industry. The objective of this work was to improve the interlaminar shear strength properties of electron beam cured composites by formulating and evaluating several different fiber sizings or coating materials. The researchers have recently achieved some promising results by having discovered that the application of epoxy-based, electron beam compatible sizings or coatings onto surface-treated, unsized IM7 carbon fibers improved the composite interlaminar shear strength properties by as much as 55% versus composites fabricated from surface-treated, unsized IM7 fibers. In addition, by applying these same epoxy-based sizings or coatings onto surface-treated, unsized IM7 fibers it was possible to achieve an 11% increase in the composite interlaminar shear strength compared to composites made from surface-treated, GP-sized IM7 fibers. Work is continuing in this area of research to further improve these properties.
Date: May 23, 1999
Creator: Drazel, L.T.; Janke, C.J. & Yarborough, K.D.
Item Type: Article
Partner: UNT Libraries Government Documents Department

Intermediate Temperature Carbon - Carbon Composite Structures. CRADA Final Report

Description: The objective of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC (the "Contractor") and Synterials, Inc. (the "Participant") was to demonstrate promising processing methods, which can lead to producing Carbon-Carbon Composites (CCC), with tensile and interlaminar properties comparable to those of organic matrix composites and environmental stability at 1200 F for long periods of time. The participant synthesized carbon-carbon composites with two different fiber coatings and three different matrices. Both parties evaluated the tensile and interlaminar properties of these materials and characterized the microstructure of the matrices and interfaces. It was found that fiber coatings of carbon and boron carbide provided the best environmental protection and resulted in composites with high tensile strength.
Date: June 1, 2007
Creator: Lara-Curzio, Edgar
Item Type: Report
Partner: UNT Libraries Government Documents Department