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For naval applications, composite sandwich structures are of significant interest, and are often manufactured using thin (2 to 4 mm) composite facings made from carbon or glass fiber reinforcement, attached to a thick (25 to 50 mm) section of PVC cellular foam or balsa wood-based core materials using a suitable polymeric resin. In the present study, we focus on the hygrothermal effect on the fiber-dominated compression properties of carbon fiber reinforced vinyl ester resin based polymeric composite (CF/VE), used as "skin" for a polymeric composite sandwich material. Hygrothermal conditioning is achieved by saturating samples in simulated seawater at 40°C. Compression properties are evaluated for coupons extracted along warp and fill undergoing- no conditioning, conditioning till saturation (up to 6 months), and long-term conditioning (2 years). Sea-water saturation yields in up to 12% drop in compression strength with a further 3–4% drop resulting from long-term conditioning. No statistically significant modulus degradation is noticed due to short or long-term hygrothermal exposure. The failure mechanism of the warp extracted coupon, which fails in a splitting failure mode originating due to the delamination between the 0/90 interface, or the fill extracted coupon, which fails due to the instability caused by tow micro-buckling, remains unchanged due to combined exposure (short or long-term) of seawater and temperature. The loss in strength is attributed to the degradation of the fiber-matrix interface, which is validated via conducting single fiber push-in tests with a nominal diameter of 7 micron for conditioned and unconditioned coupons. [ABSTRACT FROM AUTHOR]

The production of concrete leads to substantial carbon emissions (~8%) and includes reinforcing steel which is prone to corrosion and durability issues. Carbon-fiber-reinforced concrete is attractive for structural applications due to its light weight, high modulus, high strength, low density, and resistance to environmental degradation. Recycled/repurposed carbon fiber (rCF) is a promising alternative to traditional steel-fiber reinforcement for manufacturing lightweight and high-strength concrete. Additionally, rCF offers a sustainable, economical, and less energy-intensive solution for infrastructure applications. In this paper, structure–process–property relationships between the rheology of mix design, carbon fiber reinforcement type, thermal conductivity, and microstructural properties are investigated targeting strength and lighter weight using three types of concretes, namely, high-strength concrete, structural lightweight concrete, and ultra-lightweight concrete. The concrete mix designs were evaluated non-destructively using high-resolution X-ray computed tomography to investigate the microstructure of the voids and spatially correlate the porosity with the thermal conductivity properties and mechanical performance. Reinforced concrete structures with steel often suffer from durability issues due to corrosion. This paper presents advancements towards realizing concrete structures without steel reinforcement by providing required compression, adequate tension, flexural, and shear properties from recycled/repurposed carbon fibers and substantially reducing the carbon footprint for thermal and/or structural applications. [ABSTRACT FROM AUTHOR]

Traditionally, thermoset resins such as polyesters (PE) and epoxies are used as the polymer matrix for construction of wind turbine blades. However, concern about their end‐of‐life treatment garners interest to use thermoplastics for increased recyclability. However, the high viscosity of molten thermoplastics inhibits their use in manufacturing wind turbine blades with injection or compression molding. A recently developed, infusible, reactive thermoplastic resin overcomes this technological barrier. Toward verifying that this recyclable resin is suitable for use in wind turbine blades, a dataset of R = 0.1 and R = 10 fatigue data for glass fiber–reinforced acrylic composites is provided and equal fatigue life to industry standard epoxy and unsaturated PE resin systems is demonstrated. Specifically, R = 0.1 fatigue data for acrylic composites at room temperature and −30 °C for verification of low‐temperature performance are tabulated. To elucidate failure mechanisms, in situ mechanical testing with X‐ray computed tomography demonstrates that damage accumulation occurs by crack propagation along the fiber–matrix interface under cyclic loading. Infrared (IR) thermography predicts failure points in composites specimens with porosity defects introduced from nonideal manufacturing processes. Furthermore, these manufacturing defects are shown to compromise the fatigue life of the acrylic laminates by an order of magnitude. [ABSTRACT FROM AUTHOR]

Infusible thermoplastic Elium® family of resins from Arkema have garnered much attention in recent years as a possible replacement for thermoset resins in laminate and sandwich composite manufacturing for wind blade applications due to its ease of recyclability and the ability to utilize existing manufacturing processes without imposing complicated variations. However, physical and mechanical properties of the proposed Elium® based thermoplastic composites must be comparable to existing epoxy (thermoset) based composites using manufacturing processes relevant for large wind turbine blades. A 13-meter-long demonstration blade was manufactured for that purpose and sandwich samples were obtained from that project for a detailed study. This paper details three-point flexural properties of unidirectional E-glass fiber reinforced acrylic and epoxy based sandwich panels with identical balsa wood core materials. In addition, to evaluate the relative merit considering debond failure mode, the interfacial critical strain energy release rate, predominantly in mode-1, was compared via single cantilever beam testing. In sandwich composites constructed with balsa wood core material, resin uptake by the balsa core is traditionally impeded via the insertion of a scrim material at the facesheet to core interface. Results revealed that inclusion of scrim mesh layer at the facesheet to core interface reduced flexural properties and strain energy release rates in panels infused with acrylic resin but did not significantly reduce these properties in epoxy infused facesheets. [ABSTRACT FROM AUTHOR]

Sandwich structured (SS) composites demonstrate considerable flexural stiffness and high strength-to-weight ratios and can be tailored as functional materials. Historically they have been constrained to specific material types and geometry due to limitations in manufacturing methods. However, employing additive manufacturing (AM), specifically direct ink writing (DIW), can provide an alternative method for making SS composites with complex and controllable micro and mesostructures with multifunctionality targeted at desired mechanical, thermal, and electrical properties. DIW, an extrusion-based AM technique, uses a viscous and thixotropic ink with desired components that, once printed, is cured to obtain the final complex net shape parts. In this paper, a novel hybrid AM technique is employed to manufacture SS composite materials containing bisphenol A-based epoxy core and carbon fiber reinforced polymer (CFRP) face sheets that are fabricated via DIW and vacuum infusion process (VIP), respectfully. We demonstrate that the fabrication of these SS composites can be tailored from a thermosetting material, from which additives and/or various lattice structures can be manufactured to achieve enhanced and desirable mechanical integrity with functional properties. Surface topology and mechanical testing techniques are used to characterize the fabricated hybrid SS composites to study and assess mechanical stability. A rheo-kinetic cure model was developed for the core material to allow for additive manufacturing process requirements while ensuring complete cross-linking for the thermoset-based core material. Because of the ability to obtain relatively small core-thickness and controlled architecture, this method now allows for fabricating layered micro-sandwich structures for realizing further light-weighting in relevant applications. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced concrete as a structural material is attractive for civil infrastructure because of its light weight, high strength, and resistance to corrosion. Ultra-high performance concrete, possessing excellent mechanical properties, utilizes randomly oriented one-inch long steel fibers that are 200 microns in diameter, increasing the concrete's strength and durability, where steel fibers carry the tensile stress within the concrete similar to traditional rebar reinforcement and provide ductility. Virgin carbon fiber remains a market entry barrier for the high-volume production of fiber-reinforced concrete mix designs. In this research, the use of recycled carbon fiber to produce ultra-high-performance concrete is demonstrated for the first time. Recycled carbon fibers are a promising solution to mitigate costs and increase sustainability while retaining attractive mechanical properties as a reinforcement for concrete. A comprehensive study of process structure–properties relationships is conducted in this study for the use of recycled carbon fibers in ultra-high performance concrete. Factors such as pore formation and poor fiber distribution that can significantly affect its mechanical properties are evaluated. A mix design consisting of recycled carbon fiber and ultra-high-performance concrete was evaluated for mechanical properties and compared to an aerospace-grade and low-cost commercial carbon fiber with the same mix design. Additionally, the microstructure of concrete samples is evaluated non-destructively using high-resolution micro X-ray computed tomography to obtain 3D quantitative spatial pore size distribution information and fiber clumping. This study examines the compression, tension, and flexural properties of recycled carbon fibers reinforced concrete considering the microstructure of the concrete resulting from fiber dispersion. [ABSTRACT FROM AUTHOR]

Herein, lattice‐specific elastic stiffnesses of a structural alloy with commercial, medical, and military aircraft applications are investigated by neutron diffraction. Macroscopic mechanical properties are characterized by conventional techniques and response to thermally induced strains is probed by X‐ray diffraction (XRD); these findings are compared to data given by neutron diffraction tools. The material used in this study is the forged Ti64 titanium alloy (6% aluminum and 4% vanadium). Diffraction elastic constants are found to range from 114 GPa to 138 GPa. Macroscopic moduli of 118 GPa and 116 GPa are found from extensometry and digital imaging correlation, respectively. The (101) reflection is the reflection that best matches the macroscopic material behavior with a modulus of 117 GPa for the studied material. The effect of mechanical and thermal strains on the axial ratio of the crystal structure is investigated. Texture is an important consideration when comparing micro‐ and macro‐scale behavior; texture from electron backscatter diffraction (EBSD) maps reveals minimal preferred orientation for the material under study thus indicating (101) planes suitably reflect overall material behavior. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer composites are an excellent choice for bridge decks due to high strength, lightweight, resistance to corrosion, and long-term durability with a 100-year design life. Structural health monitoring is useful for the long-term assessment of the condition of the bridge structure and obtaining a response to complex loads considering environmental conditions. Bridge structures have been studied primarily using distributed fiber optic sensing, such as Brillouin scattering; however, critical events, including damage detection, can be missed due to low spatial resolution. There is also a critical need to conduct a comprehensive study of static and dynamic loading simultaneously for fiber-reinforced composite bridge structures. In this study, a novel approach was implemented using two sensor technologies, optical frequency domain reflectometry and fiber Bragg grating-based sensors, embedded in a glass-fiber-reinforced composite bridge deck to simultaneously monitor the deformation response of the bridge structure. The optical frequency domain reflectometry sensor utilizing Rayleigh scattering provides high spatial strain resolution were positioned strategically based on expected stress distributions to measure strain in the longitudinal, transverse, and diagonal directions along the span of the composite bridge. Furthermore, fiber Bragg grating based sensors are used to monitor the response to dynamic vehicular loading and deformations from an automotive-crash-type event on the bridge structure. To monitor environmental variables such as temperature, a custom wireless configured sensor package was developed for the study and integrated with a composite bridge located in Morgan County, Tennessee. Additionally, a triaxial accelerometer was used to monitor the vehicular dynamic loading of the composite bridge deck in parallel with fiber Bragg grating sensors. When appropriate, mid-point displacements were compared with strain-distribution measurements from the fiber optic sensor-based data. [ABSTRACT FROM AUTHOR]

Sheet molding compounds (SMCs) are increasingly used in high-volume automotive applications for lightweighting and as a cost-neutral or low-cost solution to incumbent metal parts. Only a limited number of studies exist on SMC-based structural automotive parts. In this work, the SMCs formulated with vinyl ester resin were considered as they represent cost-efficient and durable automotive composite materials. The concept of manufacturing process with overmolding of continuous fiber at select areas enhancing local strength and stiffness with the bulk SMC domain is also introduced. The studies were extended from the coupon level to the production of an automotive SMC composite seat backrest. Both test coupons and seat backrest parts were compression molded using structural SMCs. These were also evaluated with continuous glass fiber-overmolded SMCs for enhanced performance and damage tolerance. Flexural, interlaminar shear, and Izod impact tests were conducted for SMC and SMC-overmolded (OM) specimens to evaluate their structural integrity. Scanning electron microscopy was conducted to analyze failure modes, fiber wet-out, and interfacial bonds. Mechanical evaluation of SMC-OM across and along the flow direction of the seat was conducted. The flexure, impact, and interlaminar shear strength of SMC-OM was 6% to 27% higher than SMCs. High-resolution X-ray computed tomography was used to study the microstructure and the effect of SMCs on local fiber orientations of continuous glass fiber format after compression molding and the interface of two formats of fiber reinforcement. Vibration-based nondestructive evaluation showed distinct frequency shifts to higher values, indicating higher local stiffness of the overmolded SMC component. [ABSTRACT FROM AUTHOR]

There is global interest in reducing weight and energy efficiency of structures ranging from automobiles, bridges, wind blades, aircraft wing and other industrial components. Carbon fiber is a promising reinforcement due to its superior specific strength and stiffness. Conventional polyacrylonitrile (PAN) based carbon fiber of 12k, 24k, 50k tow size has excellent properties, but its wide-spread use in non-aerospace applications is cost-prohibitive. Oak Ridge National Laboratory (ORNL) Carbon Fiber Technology Facility (CFTF) is pursuing technologies to reduce the cost of carbon fiber via textile grade precursors. The Institute for Advanced Manufacturing Innovation (IACMI)-The Composites Institute is extending the low-cost carbon fibers into composites for use in non-aerospace, automotive, wind, gas storage and industrial sectors. The cost of manufacturing textile grade PAN carbon fiber, referred to as TCF is approximately 50% that of conventional aerospace PAN with estimated reduced embodied energy of -60%. The tow size of TCF is 300-450k (very wide) and hence the processing, processability, intermediate forms and performance (properties) bounds is not well-known. This paper provides representative processing pathways and performance of TCF on studies conducted in the period 2016-2021. The information presented is of value to composite designers, end-users and fabricators considering carbon fiber in applications. [ABSTRACT FROM AUTHOR]

The role of partial saturation in penetration resistance of projectiles in granular materials is not clear due to experimental constraints imposed by high cost and special considerations in equipment design. In this work, granular material near the tip and far-field of the projectile is numerically simulated based on 1D compression and triaxial stress paths, respectively, using the finite discrete element method. The crushing of grains in 1D compression simulations is implemented by pre-inserting cohesive interface elements in regular finite element mesh. The capillary suction is numerically predicted by extracting the deformed granular assembly microstructure at different loading steps as an input to the pore morphology method. The results demonstrate the development of high capillary suction in 1D compression loading due to the significant crushing of grains. The evolution of capillary suction is negligible during triaxial loading compared to the 1D compression loading. This suggests that future simulations related to projectile penetration in partially saturated granular materials should account for coupled hydromechanical effects near the tip whereas the far-field can be approximated as a dry material. Finally, the capillary suction corresponding to extreme comminution near the projectile tip is estimated from a 3D assembly of spherical grains with a mean grain size of 1 µm. [ABSTRACT FROM AUTHOR]

The present paper addresses the influence of shape, size, and frictional characteristics of granular materials by utilizing X-ray computed tomography (CT) imaging and FEM. High-fidelity triaxial shearing simulations are conducted on a realistic assembly of sand grains. Applicable boundary conditions are represented, including the latex membrane for applying confining pressure. For this research, two poorly graded clean sands (SP) with distinct grain morphologies of round and angular particle shapes are considered. The effect of the particle size is naturally embedded in two materials with a difference of small size fraction grains present in angular sand. The deviatoric stress and volume change response increase up to the value of friction coefficient (μ) equal to 0.5 for rounded sand, and the strength-deformation response is unaffected by a further increase in friction. The axial strain, corresponding to peak deviatoric stress, did not depend on the friction value for identical initial microstructure and boundary conditions. The microscale investigation suggests a similar mean coordination number and percentage of grains with a coordination number less than two for friction values producing similar responses. The angular sand resulted in higher strength and low dilation compared to the rounded sand for friction value that best reproduces experimental results. The strength increase due to the particle shape effect becomes less pronounced for smooth grains. The grain-scale analysis indicates angular sand exhibits less dilation in contrast to the general observation in the literature due to smaller grain fractions absent in rounded sand, highlighting the need to introduce additional subclassifiers in classifying SP sands. The localized deformation pattern remains unchanged with friction and varies with grain shape. An attempt is made to link micromechanical insights to the macroscale response. [ABSTRACT FROM AUTHOR]

The integration of repurposed and recycled carbon fibers into high-performance composites is essential to the adoption of composites for automotive structures due to their low-cost, high formability, and reduced environmental impact. When high areal density nonwovens of these fibers are infused with a semi-crystalline thermoplastic resin, organosheets offering competitive mechanical properties can be produced. This study examined the optimization of such composites through multiscale material characterization and post-process annealing. Single fiber tensile tests were used to characterize repurposed and recycled fiber formats. The thermomechanical properties of the polyphenylene sulfide matrix and resulting composites subjected to different post-process annealing conditions were characterized using differential scanning calorimetry, dynamic mechanical analysis, and nano-indentation. Single fiber push-in testing was conducted to evaluate the fiber–matrix interface as a function of annealing. It was shown that statistical methods based on the bootstrap principle successfully identify the effects of post-process annealing, which are otherwise masked by material inhomogeneity. Post-process annealing was shown to be an effective method of improving the resulting mechanical properties of repurposed and recycled carbon fiber organosheet composites, thereby optimizing their properties for use as a high-performance automotive structural material. [ABSTRACT FROM AUTHOR]

The multiphase flow transport properties find ubiquitous applications in partially saturated granular media, particularly in the vadose zone due to alternate drying and wetting cycles. The spatial heterogeneity in the degree of saturation at the pore scale has a significant impact on the transport properties of the porous materials. In the present work, three-dimensional (3D) computed tomography (CT) images of the two-phase flow experiments are used to visualize and investigate the pore space and fluid phase microstructure of sands with rounded and angular grain morphology. The dual image modality utilizing X-rays and neutrons is used to obtain 3D information on the arrangement of solids and water in a sand sample. Advanced analysis of the experimental data is carried out using a mathematical framework known as persistent homology. This approach allows quantification of geometry as well as connectivity of pore space and fluid phase directly from the CT images with powerful implications in exploring pore-scale physics of multiphase granular materials. Persistent homology predicted percolation length of 52.5 µm and 41.86 µm consistent with the hydraulic conductivity measurements for rounded sand and angular sand, whereas the value of global void ratio equal to 0.512 and 0.69, respectively, suggests the contrasting response. The fluid distributions obtained from numerical predictions using the pore morphology method (PMM) are compared with results from experiments utilizing persistent homology. These results demonstrate the need for incorporating pore-scale physics in boundary value problems related to multiphase flow in granular materials. [ABSTRACT FROM AUTHOR]

Extensive particle fracture has been noticed in projectile penetration tests. However current models for predicting projectile penetration depths do not consider particle fracture. Therefore, in order to understand the role of particle shape on single grain strength and the subsequent comminution process, single grain crushing tests on sand grains of different shapes and sizes were performed. High-resolution, three dimensional images of grain surface, were created using confocal microscope and fracture of the grains were captured with high-speed imaging. Acoustic emissions during single grain crushing was used to estimate the energy released during grain fracture. It was found that local stress fields influence particle strength and in natural granular material surface flaws maybe the critical flaw causing fracture. The estimated critical flaw size causing fracture were submicron in size. The mass specific fracture energy increased with increasing failure stress and decreasing particle size and is significantly greater than that computed from pure diametrical breaking. Except for large angular grains, mass specific energies for different shapes were similar. Angular sands required multiple events to break. The outcome of this work can be utilized in geomechanics to understand the comminution process and in power industry to estimate the energy required for comminution. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced vinyl ester composite facings are being considered by the US Navy for sandwich structures with either low-density polyvinyl chloride foam or balsa wood as the core materials manufactured using Vacuum-Assisted Resin Transfer Molding process. In this paper, experimental techniques are developed to evaluate the variation of surface strain spatially using three-dimensional Digital Image Correlation technique and internal damage evolution using radiation-based tomography. Both X-ray and neutron radiation was utilized to evaluate the microstructure of composite laminate facings in three dimensions at high resolution. Since naval structures are exposed to harsh sea environment, samples were soaked in simulated sea water at 40℃ for long duration, well beyond saturation stage of Fickian diffusion ascertained using weight gain measurements. Results for a series of mechanical tests on fiber dominated samples of [0/90]2S and matrix dominated samples of [±45]2S orientation are reported. Variable specimen sizes (12.5 mm wide by 100 mm long, 25 mm by 200 mm, and 25 mm by 300 mm, all with an average uniform thickness of 2.8 mm) for laboratory tests are utilized in order to evaluate the applicability of results for large ship structures. Different carbon fiber-reinforced vinyl ester failure mechanisms of matrix crack interactions, such as matrix dominated transverse tension, tension along fibers, and fiber delamination were observed. Digital Image Correlation technique was useful to track the existence of localized damage for both fiber and matrix dominated carbon fiber-reinforced vinyl ester laminates. High resolution X-ray and neutron tomography under in-situ mechanical loading were used to investigate interior microstructure evolution and damage at chosen stress levels. The new techniques presented in this paper can enable a comparison between interior specimen damage and surface damage (readily observable using Digital Image Correlation). Use of different modality of radiation (neutrons versus X-rays) was very useful to probe damage resulting from moisture diffused in the matrix resin and fiber interface/interphase and shows a lot of promise for studying the failure modes and damage evolution in polymeric composites and sandwich structures. [ABSTRACT FROM AUTHOR]

Reactive thermoplastics are advantageous for wind turbine blades because they are recyclable at end of life, have reduced manufacturing costs, and enable thermal joining and shaping. However, there are challenges with manufacturing wind components from these new materials. This work outlines the development of manufacturing processes for a thick glass fiber–reinforced acrylic thermoplastic resin wind turbine blade spar cap, with consideration given to effects of the exothermic curing reaction on thick composite parts. Comparative elastic properties of these infusible thermoplastic materials with epoxy thermoset materials, as well as thermoplastic coupon components, are also included. Based on the results of this study it is concluded that the thermoplastic resin system is a viable candidate for the manufacturing of wind turbine blades using vacuum-assisted resin transfer molding. Significant gains in energy savings are realized avoiding heated molds, ability for recycling, and providing an opportunity for utilizing thermal welding. [ABSTRACT FROM AUTHOR]

This paper presents a simple and inexpensive technique for damage identification of bridges using drop weight vibration data of bridges recorded by an array of geophones, highly sensitive sensors to record vibration, and time series analysis. The dynamic response of bridges obtained using drop weight as an excitation source is convolved with white noise to create suitable input for autoregressive (AR) models. A two-stage prediction model, combined AR and autoregressive with exogenous input (ARX), is employed to obtain a damage-sensitive feature. An outlier analysis method is developed based on the Monte Carlo simulation to identify the existence of damage. The proposed technique is verified using unique vibration data of two full-scale steel-girder bridges located on I-40 through downtown Knoxville, Tennessee, and subjected to progressive damage scenarios induced to steel girders. The results of the analysis for the vertical vibration data of the test bridges indicate that the proposed technique is able to detect the damage induced on the real bridge girders consistently even when the damage level is small and damage is located near a support; however, damage is not well localized or quantified in these two highly redundant bridges. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A constitutive model is proposed for clays based on the experimental observations from a series of flexible boundary true triaxial shear tests on cubical specimens of light to heavily overconsolidated kaolin clay. The proposed model adequately captures the combined effect of overconsolidation and intermediate principal stress. Overconsolidated clays often exhibit nonlinear stress-strain response at much lower stress levels than what is predicted by the existing constitutive theories/models. Experimental results for kaolin clay demonstrated sudden failure response before reaching the critical state, which became more prominent for higher relative magnitudes of intermediate principal stress. The observed stress state at failure is governed by the third invariant of stress tensor and the pre-failure yielding of the material by the second invariant of deviatoric stress tensor. The proposed constitutive model considers these issues with a few simplifying assumptions. The assumed yield surface has a droplet shape in q- p′ stress space with hardening based on both plastic volumetric and shear deformations. A dynamic failure criterion is employed in the current formulation that grows in size as a function of consolidation history. Pre-failure yielding is governed by a reference surface, which is different from the failure surface. [ABSTRACT FROM AUTHOR]

Recently, the concept of X-ray diffraction contrast tomography (DCT) has been extended to the case of more widely available laboratory source CT systems. Using well known concepts from geometrical ray optics, an exact formulation is derived for the forward and backward projection geometry encountered under polychromatic cone beam illumination, and it is shown how this projection model can be efficiently implemented in practice. The new projection model is subsequently used for iterative tomographic reconstruction of the three-dimensional shape of a grain from a set of experimentally observed cone beam projections and shows a clear improvement compared to the simplified projection model used previously. [ABSTRACT FROM AUTHOR]

Evaluating the state of residual strain or stress is critically important for structural materials and for reliable design of complex shape components that need to function in extreme environment subjected to large thermo-mechanical loading. When residual stress state is superposed to external loads, it can lead to reduction or increase in failure strength. Past diffraction studies for evaluating the residual strain state involved measuring lattice spacings in three orthogonal directions and do not often correspond to principal directions. To completely resolve the state of strain at a given location, a full strain tensor must be determined. This is especially important when characterizing materials or metallic components exposed to biaxial or complex loading. Neutron diffraction at the second Generation Neutron Residual Stress Facility (NRSF2) at Oak Ridge National Laboratory is used in this study to measure strain tensors associated with different modes of stress path. Hollow cylinder steel samples with 2 mm wall thickness are subjected to either pure axial extension or pure torsion to simulate multi-axial loading conditions. A virgin sample that is not subjected to any deformation, but subjected to identical manufacturing conditions and machining steps involved to obtain hollow cylinder geometry is used for obtaining reference d-spacing for given hkl planes at target spatial location(s). The two samples which are subjected to either pure tension or torsion are loaded to a deformation state that corresponded to equal amount of octahedral shear strain which is an invariant. This procedure is used so that a basis for comparison between the two samples can be made to isolate the stress path effects. A 2-circle Huber orienteer is used to obtain strain measurements on identical gauge volume at a series of φ and ψ values. The residual state of stress tensor corresponding to ex situ (upon unloading) conditions is presented for three lattice planes (211, 110, 200) for a bcc ferritic system exposed to tension and pure torsion. [ABSTRACT FROM AUTHOR]

Three-dimensional neutron and X-ray tomography reveals the textural and spatial relationship of diamonds and associated mineralsin situ, in a unique suite of 17 diamondiferous eclogites. We emphasize the reporting of X-ray imaging on mantle xenoliths, which in combination with neutron imaging enables the clear identification of diamonds and interstitial metasomatic secondary minerals. In particular, neutrons are highly sensitive to hydrogen (H), allowing for the identification of OH- and H2O-bearing metasomatic minerals. The identification of metasomatic minerals allows for the delineation of distinct metasomatic pathways through the eclogite xenoliths. Diamonds are readily identified as the darkest greyscales due to their low attenuation, and are typically surrounded by secondary minerals, never in contact with primary minerals, and always confined within metasomatic pathways. The ubiquitous occurrence of diamonds in association with pathways suggests a potential genetic link. Both octahedral and dodecahedral diamonds are observed within individual xenoliths, suggesting multiple heterogeneous growth and dissolution processes at small scales. The distinct age dichotomy between eclogite xenoliths and metasomatic mineral assemblages implies that the observed textural relationship of diamonds and late-stage metasomatic pathways for this suite of 17 eclogites casts doubt on the theory that eclogitic diamonds formed billions of years ago. Diamonds are interpreted to have formed from multiple growth episodes, with the last of these episodes represented by the metasomatic assemblages observed in this study. This further indicates that eclogitic diamond inclusions may span large time scales from ancient ages (>2 Ga) all the way to the last growth event, perhaps even close to the time of kimberlite emplacement (~360 Ma), which has significant implications for age-dating of diamonds and the study of diamonds as a whole. [ABSTRACT FROM AUTHOR]

Thin polymeric films are evaluated in this research as a potential replacement technology for radiation portal monitors where specific attention is given to the physical basis for neutron-photon discrimination.  It is shown that the difference in the energy deposition mechanics from charged particle reaction products and from the Compton scattered electrons allows for the effective discrimination between neutrons and gammas. One goal of this study was to establish optimal thickness for polymeric films that maximize the neutron interactions and simultaneously minimize the measured interaction of photons. Polymeric films ranging from 15~\mu\m to 600~\mu\m containing ^6LiF were fabricated and tested for their capability to satisfy criteria established by the Department of Homeland Security.  Results from Monte Carlo simulations with the GEANT4 code and data from measurements confirm the technical basis for our proposed understanding of neutron-photon discrimination characteristics for thin films. [ABSTRACT FROM AUTHOR]

Biaxially stretched composite polyethylene naphthalate (PEN) films (BSCPF) embedded with submicron lithium fluoride (6LiF) particles and luminescent molecules were fabricated to make large area scintillation films (≈1 m × 1 m) for thermal neutron detection. BSCPF had 20.2% higher neutron light yield as compared to unstretched composite film (UCPF), and were 2.46 ± 1.47 times more efficient for detecting thermal neutrons than lithiated glass GS20 above lower level discriminator corresponding to an intrinsic efficiency for gamma <10−6. MCNPX simulations for a layered BSCPF detector resulted 6.1 cps for 1 ng 252Cf, thus meeting the Pacific Northwest National Laboratory criteria for absolute neutron detection efficiency and intrinsic gamma-neutron discrimination. BSCPF have alpha to beta ratio of 0.25, which is higher than that for UCPF (0.11), and also for GS20 (0.22), which offers the possibility of excellent neutron/gamma discrimination. [ABSTRACT FROM AUTHOR]

Thermal neutron imaging is a powerful non-invasive diagnostic technique to study water management within a proton exchange membrane (PEM) fuel cell. To isolate the hydration behavior of membrane, significant increase in detecting thin water films is needed. A humidity cell is developed to study hydration of a PEM using cold neutron imaging. Spatial and temporal changes of PEM water uptake are quantified. Water film as small as 1 μm thick and corresponding to a volume containing 10 ng of liquid water at high spatial resolution is detected. This represents an order of magnitude improvement in water detection efficiency achievable at thermal neutron imaging facilities. [ABSTRACT FROM AUTHOR]

Foamed warm-mix asphalt (WMA) has been widely accepted and used in the United States and many other countries around the world. However, several key concerns about WMA technology still need to be answered, including the major issue of moisture-induced damage. Because of the reduced production temperatures and the foaming process with water, moisture may be entrapped in pavements after compaction. The trapped moisture decreases the adhesion between asphalt binder and aggregates and the cohesion among asphalt binder, resulting in stripping and other forms of pavement distress. The neutron scattering technique provides a unique tool for the determination of the microscopic structure of asphalt and for the detection of the presence of moisture and its spatial distributions in asphalt. In particular, small-angle neutron scattering (SANS) in the wave vector transfer range from is suitable to probe the spatial density fluctuations in the real space from , which has a resolution several orders of magnitude higher than direct imaging techniques. In this study, the SANS technique was utilized to characterize the microstructure of asphalt and to detect the water spatial distributions in foamed asphalt. Two types of asphalt binder and ordinary and heavy water were used to make samples at 150°C using a laboratory foaming device. The samples were then measured using the SANS instrument at the National Institute of Standard and Technology (NIST) Center for Neutron Research (NCNR). The results show that there is no water entity less than 0.1 μm present in the foamed asphalt. Even if moisture does exist in foamed asphalt, it does not cause any structural changes to the asphalt within 0.1 μm. [ABSTRACT FROM AUTHOR]

High spatial resolution () neutron tomography was performed on partially water-saturated compacted silica sand specimens with two different grain morphologies (round and angular) at Helmholtz Zentrum Berlin using cold neutrons at the cold neutron radiography and tomography beam line. A specimen mixed with heavy water was imaged for contrast comparison purposes. Microfocus X-ray imaging was also performed on these specimens with slightly higher resolution () using geometric magnification to locate the solid phase (silica particle boundaries) more precisely. Image processing was performed to remove unwanted gammas detected because of the gadox scintillator used for the high-resolution neutron imaging system. The visualization of solid, gas, and liquid phases for different grain morphologies is presented at the grain level. Using dual-modal contrast possible from simultaneous use of neutrons and X-rays, the authors introduce, for the first time, an improved ability to distinguish solid silica, liquid water, and gas phases. Quantitative analysis using three-dimensional tomography data is demonstrated for obtaining void ratio, void percentage variation over the height, and particle size distribution. [ABSTRACT FROM AUTHOR]

Zircaloy-702 (Zr-702 or UNS R60702) cylindrical tubes are commonly used for applications requiring mechanical stability in extreme environments. Owing to its crystal structure and processing techniques, significant texture and anisotropic mechanical properties are possible. In the current study, combined axial-torsional testing is employed to probe macroscopic stress-strain behavior in three dimensions, and corresponding yield surface in octahedral plane is obtained. Zr-702 tube samples are characterized under pure tension, torsion, and combined (tension and torsion) loading. Three-dimensional digital image correlation using VIC-3D system was implemented to determine surface deformation patterns for identification of strain localizations. Neutron diffraction-based texture analysis is performed to obtain an understanding of the effect of loading path on the material texture compared with the as-received, initial grain orientation. Pole figures for Zr-702 tubes are obtained for each loading path. [ABSTRACT FROM AUTHOR]

Novel ^6Li-loaded polyester scintillation films have been designed and fabricated to detect thermal neutrons. Lithium fluoride crystals containing enriched ^6Li were synthesized and integrated into polyethylene naphthalate polyester matrix containing appropriate luminescent molecules. Thermal neutron capture by ^6Li ions produces charged particles with kinetic energy sufficient to ionize and subsequently excite the components of the polymeric matrix. This energy is transferred to secondary luminescent molecules, which produce net radioluminescence responses detectable by a photomultiplier tube. Design, production and characterization of these scintillation films are discussed herein. The films due to their thinness (<220\ \mum) and low atomic number components have low susceptibility to gamma induced scintillation and thus are effective discriminators for thermal neutrons. [ABSTRACT FROM AUTHOR]

The use of neutron imaging is demonstrated for visualizing and quantifying water distribution in partially saturated granular porous media. Because of the unique difference in the total neutron cross sections of water, sand, and air, a significant contrast for the three phases is observed in a neutron transmission image, and a quantitative analysis provides detailed information on the arrangement and distribution of particles, voids, and water. The experiments in this study are performed at the Neutron Imaging Facility (NIF) at the National Institute of Standard and Technology (NIST). An amorphous silicon flat panel detector was used in this research with a spatial resolution of approximately 250 μm (127 μm/pixel). The effect of particle morphology on water distribution in compacted granular columns is investigated by using round and angular silica sand. Silica sand specimens with different bulk gravimetric water contents (0%, 6%, 9%, and 12%) are studied for evaluating the water phase-distribution spatially for compacted sand specimens in an aluminum cylinder. [ABSTRACT FROM AUTHOR]

Finite element modeling is commonly used to simulate the effect of damage on in-service bridges to facilitate the study of vibration-based damage detection techniques. This study describes the field testing and finite element modeling of an in situ, full-scale, five-girder bridge that is subjected to controlled levels of known damage. The focus of the study is finite element (FE) model calibration to enable the study of damage scenarios including those not imposed during the field tests. Modal parameters are extracted from triaxial vibration records obtained over a relatively dense measurement grid using inexpensive geophones and are used to calibrate a three-dimensional FE model of the bridge. The calibration process and considerations that should be made during field tests for proper model calibration are discussed. Various vibration-based damage detection techniques are evaluated based on their ability to locate the simulated damage. Results show that most of the damage detection techniques evaluated are capable of successfully locating the induced damage on a global level. It is observed from the present study that the horizontal vibration response of the bridge is particularly sensitive to the simulated damage. It is recommended that efforts be made to measure a bridge’s horizontal vibration response (in addition to vertical vibration records) during field tests and this information be included in the FE model calibration processes. [ABSTRACT FROM AUTHOR]

A series of novel ^6Li-loaded plastic scintillation films have been designed and fabricated to detect thermal neutrons. Organolithium salts containing enriched ^6Li were synthesized and interspersed in a series of matrices comprising a polymer doped with an antenna fluor. Thermal neutron capture by ^6Li produces charged particles with kinetic energy which is sufficient to ionize and excite the polymeric matrix. This energy is collected by the antenna fluor, which produces a photonic response detectable by a photomultiplier tube. Design and optimization of these scintillation films is discussed herein. A current problem in the design and fabrication of polymeric composite materials is phase separation. The matrix is a low-dielectric aromatic polymer; hence, ionic molecules in the composite tend to phase-separate from the matrix and produce agglomerates which decrease the quantum efficiency by scattering and/or quenching the photonic response to thermal neutrons. Based on the experimental results, the importance of synthesizing polymers with high quantum yield and efficiency in energy migration and transport for making effective composite neutron scintillators is emphasized. [ABSTRACT FROM AUTHOR]

A novel method for obtaining polystyrene foam, which uses microwave as the source of energy for expansion process, is developed. In this article, a method to disperse target expansion agent using two-stage bulk polymerization and free radical suspension polymerization of styrene is described. Current and proposed research uses environmentally friendly and potentially recyclable expansion agents and highly efficient volumetric heating systems. Spherical polystyrene beads containing 2-propanol as expansion agent are successfully prepared which are then expanded using microwave energy. Microwave processing conditions developed by trial experiments are reported. A brief discussion on the theory of microwave heating in the context of current research is presented for direct reference and convenience to the reader. [ABSTRACT FROM PUBLISHER]