Papers by Larry D Stephenson
: Fiber-reinforced polymer (FRP) composites offer cost and performance advantages for patching co... more : Fiber-reinforced polymer (FRP) composites offer cost and performance advantages for patching concrete structures that have corroded reinforcing steel, but the Army largely avoids structural composite repair applications because of the lack of long-term performance data. Established composite patch inspection methods are fast but highly subjective. This report describes the demonstration of acoustic guided wave (AGW) technology as a nondestructive evaluation (NDE) methodology for assessing the condition of FRP composite structural patches. The technology uses a hand-guided rolling probe to collect ultrasonic inspection data that can then be analyzed to determine patch condition. The technology was used to evaluate more than 250 composite seismic upgrade patches installed in 1999 at historic Michie Stadium, U.S. Military Academy. The amplitude difference between the probe s emitted signal and the measured reflection provides data about bond quality and potential material defects. Th...
: The U.S. Army makes worldwide use of high-performance ballistic-resistant fiberglass composite ... more : The U.S. Army makes worldwide use of high-performance ballistic-resistant fiberglass composite panels for force protection and other applications. This widespread use creates a need for an improved panel material that offers better bullet resistance at a lighter weight while still meeting existing ballistic resistance standards. The team s work to solve the Army s need included conceiving, developing, and validating a new nanocomposite material that is made of epoxy resin blended with functionalized carbon nanotubes (CNTs) that exhibits highly improved flexural strength and electrical conductivity for improving ballistic resistance in lighter weight glass fiber reinforced polymer (GFRP) ballistic panels. In addition, the team s work tested various options for adding self-healing, CNT reinforcement, EMI shielding, and self-decontaminating properties for GFRP panels. Results of separate studies included in this report are: loading panels with CNTs by using different mass fractions a...
Microcapsules on the order of 50-150 microns in size have been developed that can contain and rel... more Microcapsules on the order of 50-150 microns in size have been developed that can contain and release a small quantity of selfrepairing compound in liquid form when they are broken. These microcapsules are mixed in commercially available latex paints and used to overcoat lead-based paint. Should the overcoating become damaged, the microcapsules break open and release liquid coating repair and lead dust suppression compounds. In effect, the coating becomes self-healing when damaged. The self-healing coatings were tested in the laboratory and demonstrated on a wooden building at the former Fort Ord, CA. In both cases, when the self-healing coatings were applied to lead based paint, cut, and wipe tested, significant reductions in lead dust were realized compared with the results of applying the same test procedure to plain latex paint overcoatings. 15. SUBJECT TERMS lead-based paint (LBP), hazardous waste, coatings, paint, self-healing coatings, wooden buildings, Fort Ord, CA 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON
This project demonstrated the following cost-effective paint maintenance procedures: utilization ... more This project demonstrated the following cost-effective paint maintenance procedures: utilization of smart coatings containing fluorescing compounds, self-healing microcapsules, and purpose-formulated surface tolerant coatings to overcoat existing paints. Smart coatings incorporate microcapsules, and fluorescing compounds which are mixed into paint at the time of application. Microcapsules instill the coating with selfhealing, corrosion resistance, and passive sensing capabilities. Fluorescing compounds improve the coating service life by faster and better inspections, early identification of problems, and timely repairs. The overcoating process does not require extensive surface preparation, and can be significantly less expensive than other maintenance practices, particularly when the existing coating contains lead or other hazardous materials. The smart coatings were demonstrated on pipes used in a water-handling system for a central vehicle wash facility. The overcoating procedure was demonstrated on two types of structures: steel tanks and corrugated steel hangars. It is recommended that these technologies be implemented as standard practice for coating of steel structures for the Army and DoD.
The objective of this project was to successfully demonstrate and evaluate two technologies for e... more The objective of this project was to successfully demonstrate and evaluate two technologies for extending in place the service life of failed metal roofs on two different buildings at Wheeler Army Airfield, which is located in a severely corrosive marine environment. A polyurea-hybrid coating was applied to a leaking corrugated aluminum-panel roof on a barracks building, and a structural standing-seam metal roofing (SSSMR system) with an innovative sub-purlin framing system was used to recover a severely corroded metal roof over the Bowling Center.
Advanced insulation materials provide resistance to heat flow. Properly insulating shelters can r... more Advanced insulation materials provide resistance to heat flow. Properly insulating shelters can reduce heating and cooling costs, as well as improves comfort. However, the long-term performance of insulation materials is relatively unknown. This research investigated the long-term performance of five commercially available insulation materials including nonwoven insulation liner, aerogel blankets, closed cell spray polyurethane foam (ccSPF), extruded polysterene (XPS), and fiberglass batt. Accelerated aging simulation experiments were conducted in an environmental chamber. All materials were subjected to 5 weeks in the chamber and exposed to various temperature and humidity conditions. Thermal conductivity using a heat flow meter apparatus (HFMA) and corresponding Rvalues of each material were calculated. The results indicate that moisture absorption was a major contributor to changes in the thermal properties of the materials. Additional degradation in R-values in ccSPF was caused by loss of blowing agent over time. The results of this research are expected to help formulate an accelerated aging methodology that allows reliable prediction of long-term advanced insulation materials performance. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.
Energy and Buildings, 2017
Building insulation materials have been subjected to various temperature and humidity conditions ... more Building insulation materials have been subjected to various temperature and humidity conditions and their thermal performance during several weeks of controlled environmental exposure. Several commercially available insulation materials (three aerogel composite blankets, two extruded polystyrene foams (XPS) and one blown polyurethane foam (PUR)) were evaluated. The purpose is to compare performance of newer types (aerogel composites) with established types (foams). Thermal conductivity was measured with a heat flow metering apparatus at one week intervals for five weeks. Insulations were exposed to conditions of 65.6°C and 90% RH, 65.6°C and 60% RH, 65.6°C and 30% RH, and 32.2°C and 90% RH. Results indicate that humidity levels play a significant role in PUR performance, but not a significant role in XPS performance. The three aerogel composites have mixed results: one has little relationship between moisture content and thermal performance, one is strongly affected by moisture and the remaining is moderately affected by moisture. Fourier infrared spectrometry was performed on some of the materials to observe chemical stability. Results indicate that factors other than moisture content, such as hygroscopy and volume expansion, significantly contribute to thermal performance.
The purpose of this Corrosion Prevention and Control (CPC) demonstration was to investigate the l... more The purpose of this Corrosion Prevention and Control (CPC) demonstration was to investigate the life-cycle cost impact of three corrosionresistant roofing technologies that provide several secondary benefits over the outdated roofing systems they replace. Fort Bragg, NC, was selected as the location to demonstrate (1) a heat-resistant metal shingle roofing system with above-sheathing ventilation (ASV), (2) a sloped-roof conversion using standing-seam metal roofing system with heat-shedding coating, and (3) a fiberglass-reinforced plastic (FRP) panel roofing system with ultraviolet (UV) radiation protection. Metrics were established to evaluate improvements in performance, corrosion resistance, and energy efficiency over older conventional roofing. Performance was documented through data collection, observation, and reports by facility users. None of the demonstrated technologies was found to provide sufficient return on investment (ROI) to warrant their selection solely to improve building energy efficiency. The ASV and slope-conversion methods could be modified to reduce first costs to improve their applicability in properly selected cases. The FRP panel roofing provides a modest ROI and provides interior daylighting benefits in applications such as equipment maintenance sheds and workshops without climate control. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
Transformational Science and Technology for the Current and Future Force, 2006
Recent research has examined the feasibility of detecting biological warfare agents by conjugatin... more Recent research has examined the feasibility of detecting biological warfare agents by conjugating their antibodies (receptors) with taggant nanoparticles (also known as "quantum dots"), which subsequently fluoresce upon excitation, when they are bound to a specific biowarfare agent, or its simulant. Furthermore, when they react with their target bacteria, optically excited nanoparticle-receptor conjugates generate spectra in which the intensities of primary emission peaks are diminished, while the secondary emission peaks increase in intensities, i.e., energy is transferred from major peaks to minor peaks. These optical emission spectral signatures, with emission wavelength shifts of 140 nm in some cases, strongly suggest the possibility of homogeneous (one step) assays, leading to positive detection of bacterial agents, without wash steps using nanoparticle-receptor conjugates.
Journal of Nanomaterials, 2013
The dynamic mechanical behavior and high-strain rate response characteristics of a functionally g... more The dynamic mechanical behavior and high-strain rate response characteristics of a functionally graded material (FGM) system consisting of vertically aligned carbon nanotube ensembles grown on silicon wafer substrate (VACNT-Si) are presented. Flexural rigidity (storage modulus) and loss factor (damping) were measured with a dynamic mechanical analyzer in an oscillatory three-point bending mode. It was found that the functionally graded VACNT-Si exhibited significantly higher damping without sacrificing flexural rigidity. A Split-Hopkinson pressure bar (SHPB) was used for determining the system response under high-strain rate compressive loading. Combination of a soft and flexible VACNT forest layer over the hard silicon substrate presented novel challenges for SHPB testing. It was observed that VACNT-Si specimens showed a large increase in the specific energy absorption over a pure Si wafer.
Abstract: This project demonstrated innovative remote sensors (LPR sensors) the size of postage s... more Abstract: This project demonstrated innovative remote sensors (LPR sensors) the size of postage stamps which can provide instantaneous corrosion rate data from under a coating. These sensors were installed beneath a coating on a mission-critical metal structure roof ...
The corrosion of steel rebar in reinforced concrete structures is a pervasive and expensive probl... more The corrosion of steel rebar in reinforced concrete structures is a pervasive and expensive problem for the Department of Defense. The maintenance and repair costs for affected structures and equipment amounts to hundreds of millions of dollars each year, and the degradation negatively impacts military readiness and infrastructure safety. This report documents a demonstration of a concrete rebar corrosion inhibitor system and a liquid galvanic coating that provides cathodic protection for steelreinforced concrete. These treatments were applied to critical infrastructure in a highly corrosive environment located at U.S. military facilities in Okinawa, specifically, two portions of a wall ring girder in a warehouse at Naha Military Port and two culvert bridges at the Kadena Air Force Base fuel storage depot. The data obtained in this demonstration show quantitatively that the corrosion inhibitor application significantly reduced the corrosion rate of the rebar on the tested structures. The galvanic coating appears to be providing protection to the rebar, but quantifying the extent of protection or positive impact on service life would require further monitoring and evaluation. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
The objective of this research was to demonstrate and implement cost-effective paint maintenance ... more The objective of this research was to demonstrate and implement cost-effective paint maintenance procedures for steel structures, including overcoating existing coatings with surface tolerant, self-healing, and extremely durable coatings. Maintenance painting of this type does not require extensive surface preparation, and can be significantly less expensive than other maintenance practices, particularly when the existing coating contains lead or other hazardous materials. Candidate steel and galvanized steel structures requiring maintenance painting at Fort Campbell were assessed to determine the suitability of various paint maintenance procedures, prior to overcoating. Air dry fluoropolymer coatings, implemented for the flight control tower, have emerged as a premium recoat product for factory installed polyvinylidene fluoride coatings as well as for use in coating other weathered coatings. Moisture cured polyurethanes (MCU), which are tolerant of relatively poor application conditions and generally can be applied at very high humidity and low temperatures, were successfully implemented as overcoatings for deluge tanks and aircraft hangars. Self-healing smart coatings, which incorporate microcapsules mixed into paint as a dry powder at the time of application, were also implemented for critical areas of deluge tanks. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
A study is presented to quantify the effects of oxygen on the plasma arc vitrification of Fe, Ni,... more A study is presented to quantify the effects of oxygen on the plasma arc vitrification of Fe, Ni, and Cr spiked clay. The experimental system consists of a highly instrumented plasma arc furnace equipped with a 75-kW transferred-arc plasma torch running with Ar. Specimens are composed of 10 wt.% metal powder, dispersed uniformly through a SiO{sub 2}/Al{sub 2}O{sub 3} clay body, which is extruded into bars of square cross-section and dried. Each experiment yields real-time process data, particulate samples and a corresponding slag specimen. The real-time data are used to help identify physical and chemical processes taking place during thermal plasma processing, including the volatilization and oxidation of metals, and the production of particulate and gases. Experiments are performed as a function of furnace oxygen concentration (0, 8.5, and 17 vol.% O{sub 2} in Ar). UV emission spectroscopy of the luminous plasma column is used to identify species escaping from the melt by evaporat...
Ceramic Engineering and Science Proceedings, 2008
Plasma Chemistry and Plasma Processing, 1996
Atomic emission spectroscopy (A ES) is used to monitor volatilization during waste vitrification ... more Atomic emission spectroscopy (A ES) is used to monitor volatilization during waste vitrification with thermal plasmas. Model waste spechnens consist of an ahmTh~osilicate clay spiked with 10 wt. % Fe. Ni, or Cr Spechnens are vitr([ied hi processing atmospheres with O, 8.5, and 17 voL % ox),gen/argon concentrations. Particulate generated from condensation of the volatilized materials is collected follow#lg each specimen run and analyzed by energy dispersive X-ray analysis to determhw composition. Spectra are collected.front the ultraviolet range 240-380 mn where the presence ¢?f metal vapor L~ readill' detected Correlation between Ihw emission hltensities and volatilization rates allows the establishnwnt of provisional detection Ionits for the volatilization of Ni, Cr, Si, and Fe, of I × 10 • g/s, 4 × 10 ~ g/s, 2 x 10 ~ g/s, and 5 × I0 s g/s. respectively. The results of thL~ investigation support the concept of using A ES as an i n-sit u process monitor for feedback to optimize plasma processing of hazardous metal-contah#ng waste.
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Papers by Larry D Stephenson