Development and Characterization of Inorganic Materials with Energy Sector Applications

Four classes of materials with energy sector applications have been developed or characterized herein. Processing requirements that lead to a toughened carbon fiber reinforced silicon carbide ceramic matrix composite with a compliant and oxidation resistance boron nitride interface coating were developed. Preliminary experiments resulted in highly brittle composites when BN was applied by CVD to as-received fiber. This led to a requirement of heat treating the carbon fiber to favorably modify the fiber surface prior to BN deposition. The compound ammonia borane was investigated as a potential chemical hydrogen storage material for hydrogen fuel cell applications. Two known thermal decomposition steps which yield hydrogen gas, borazine impurities, and residual B-N inorganic polymers were corroborated by several techniques. A high temperature decomposition step leading to boron nitride, and an unreported gaseous impurity from the two known decomposition steps were identified. The reactivity of a γ-alumina supported, fcc cobalt (Co/Al2O3) catalyst was evaluated in a CO2/H2 feedstock for activity towards CO, methane, C2+ hydrocarbons and methanol. Comparable methane selectivites were obtained at low and high pressures. At low pressures the balance was composed mostly of CO while at high pressures the balance was composed mostly of C2+ hydrocarbons. This suggest CO2* is preferentially hydrogenated at higher pressures instead of dissociating to CO* and O*. The evolution of the catalyst composition and structure during fabrication was tracked by a several techniques. The acid/base character of CO2(g) specifically towards exterior framework surfaces (to the exclusion of tunnel sites) on the manganese oxide octahedral molecular sieve OMS-2, was measured using synchrotron based soft X-Ray photoelectron spectroscopy. In addition to fundamental interest, the adsorption of CO2 on OMS-2 has direct relevance to several energy sector applications. CO2 is often considered to be a Lewis acid probe for surface basicity, but may also exhibit basic character towards acidic surface sites. Measurements of surface acidity and basicity aid in the determination of how these properties dictate the activity and selectivity of a heterogenous catalyst towards any given reaction

Testing of Materials and Elements in Civil Engineering

This book was proposed and organized as a means to present recent developments in the field of testing of materials and elements in civil engineering. For this reason, the articles highlighted in this editorial relate to different aspects of testing of different materials and elements in civil engineering, from building materials to building structures. The current trend in the development of testing of materials and elements in civil engineering is mainly concerned with the detection of flaws and defects in concrete elements and structures, and acoustic methods predominate in this field. As in medicine, the trend is towards designing test equipment that allows one to obtain a picture of the inside of the tested element and materials. Interesting results with significance for building practices were obtained

SynerCrete’18: interdisciplinary approaches for cement-based materials and structural concrete: synergizing expertise and bridging scales of space and time, vol. 2

info:eu-repo/semantics/publishedVersio

Stress-Crack Separation Relationship for Macrosynthetic, Steel and Hybrid Fiber Reinforced Concrete

An experimental evaluation of the crack propaga tion and post-cracking response of macro fiber reinforced concrete in flexure is c onducted. Two types of structur al fibers, hooked end steel fibers and continuousl y embossed macro-synthetic fibers are used in this study. A fiber blend of the two fibers is evaluated for spec ific improvements in the post peak residual load carrying response. At 0.5% volume fraction, both steel and macrosynthetic fiber reinforced concrete exhibits load recovery at large crack opening. The blend of 0.2% macrosynthetic fibers and 0.3% steel fibers shows a significa nt improvement in the immediate post peak load response with a significantly smaller load drop and a constant residual load carrying capacity equal to 80% of the peak load. An analytical formulation to predict fle xure load-displacement behaviour considering a multi-linear stress- crack separation (σ -w) relationship is developed. An inverse analysis is developed for obtaining the multi- linear σ -w relation, from the experimental response. The � -w curves of the steel and macrosynthetic fiber reinforced concrete exhibit a stress recovery after a significant drop with increa sing crack opening. Significant residual load carrying capacity is attained only at large crack separation. The fiber blend exhibits a constant residual stress with increasing crack sepa ration following an initial decrease. The constant residual stress is attained at a small crack separation

Behavior of Metallic and Composite Structures (Second Volume)

Various types of metallic and composite structures are used in modern engineering practice. For aerospace, car industry, and civil engineering applications, the most important are thin-walled structures made of di erent types of metallic alloys, brous composites, laminates, and multifunctional materials with a more complicated geometry of reinforcement including nanoparticles or nano bres. The current applications in modern engineering require analysis of structures of various properties, shapes, and sizes (e.g., aircraft wings) including structural hybrid joints, subjected to di erent types of loadings, including quasi-static, dynamic, cyclic, thermal, impact, penetration, etc.The advanced metallic and composite structures should satisfy multiple structural functions during operating conditions. Structural functions include mechanical properties such as strength, sti ness, damage resistance, fracture toughness, and damping. Non-structural functions include electrical and thermal conductivities, sensing, actuation, energy harvesting, self-healing capability, electromagnetic shielding, etc.The aim of this SI is to understand the basic principles of damage growth and fracture processes in advanced metallic and composite structures that also include structural joints. Presently, it is widely recognized that important macroscopic properties, such as macroscopic sti ness and strength, are governed by processes that occur at one to several scales below the level of observation. A thorough understanding of how these processes influence the reduction of sti ffness and strength forms the key to the design of improved innovative structural elements and the analysis of existing ones

Behavior of Hybrid NSM Reinforced and Externally Confined Reinforced Concrete Columns under Eccentric Compression –Experimental and Numerical Studies

The effectiveness of hybrid combination of ne ar surface mounted (NSM) and externally confined (EC) FRP strengthenin g on the performance of RC column elements under uniaxial eccentric compression is investigated. In total, ten short RC column elements were cast. Carbon FRP is used for strengthening due to its inherent stiffness and strength properties on par with other FRP materials. The columns were strengthened using NSM CFRP laminates, EC using CFRP fabrics and their hybrid combi nations. A non-linear finite element model is developed using ABAQUS and the numerical model is calibrated using the experimental results to improve the accuracy of the predict ions. Experimental results revealed that hybrid strengthening of RC columns was able to show a better performance in terms of stiffness, strength, ultimate displacement ductility when compared to other FRP strengthening techniques. The numerical predictions obtained were able to better capture the initial stiffness, peak load and post-peak behavior. Thus, the proposed hybrid strengthening technique for RC columns possess the capability of restoring the loss in stiffness, strength and ductility due to additional bending moment induced by the eccentric compression loading

Role of Steel Fibers in Shear Resistance of Beams in Arch Action

Reinforced concrete beams with discrete hooked-end steel fibe rs were tested with a shear span to depth ratio equal to 1.8. Digital im age correlation (DIC) technique was used to obtain the full-field displacements from the beam during the load response. The formation and propagation of a shear crack which directly influences the load response and peak load in the load response of the beam is moni tored using the displacement fr om the DIC measurements. There is a continuous slip across the crack face s of the shear crack with increasing load carrying capacity up to the peak load. The shear crack exhibits a dilatant behavior with increasing slip. Failure in control beams is brittle which was by the opening of dominant shear crack in shear span at a small value of crack opening. At the peak load, the shear crack pattern in fiber reinforced conc rete was identical to the crack pattern in the control beam. The dilatant behavior from the measured crack opening a nd crack slip displacements obtained from the control and the SFRC beams is identical. The fiber reinforced concrete beams exhibit a ductile response with a post peak load car rying capacity even after the continued opening of the dominant shear crack

Role of Reactive Alumina and Reactive Oxide Ratios on Strength Development in Alakaline Activation of Low-Calcium Fly Ash

The role of reactive alumina and process varia bles such as sodium content and molarity on alkaline activation of different low calcium fly ashes are explored. Reactive alumina content of a fly ash is the key parameter which dete rmines the maximum compressive strength achieved from the alkaline activati on. The oxide ratios in the activated system, based on the total silica in the system consisting of the re active silica contributed by fly ash and the reactive alumina in fly ash are shown to provide consistent results for achieving the highest strength. A method called XRD-based direct decomposition is used to determine the unreacted glassy content and amorphous reaction product in the system. The strength gain in the system is directly related to a decrease in the unreacted fly ash glassy content and an increase in the reaction product content in the system

Aeronautical engineering: A continuing bibliography with indexes (supplement 289)

This bibliography lists 792 reports, articles, and other documents introduced into the NASA scientific and technical information system in Mar. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Micro-mechanical testing of afvanced ceramics: tools, procedures and first results

Micro-mechanical testing has lately become a more accessible tool for understanding deformation, strengthening and failure mechanisms at small scales. It has been found that the often considered intrinsic or “intensive” properties of materials, i.e. not size dependent, start to exhibit an extrinsic behaviour if the volume of material tested is reduced down to the level of the micro- or nano-scale. This is true at least for metals, where diverse experimental approaches have shown that the ultimate strength strongly increases in enough small material volumes in the micro-nano range. In ceramics, the small scale testing approach has received much less attention probably because of the absence of dislocation-controlled deformation mechanisms. Even though, it is the only direct method for the study of the mechanical behaviour of ceramics in thin coatings, superficial layers induced by surface degradation processes as in wear, corrosion, etc. Besides, in ceramics with a grain size dependent transformation toughening mechanism, such as zirconia-based ceramics, a clear effect is expected when testing at the micro-scale. In this work the methodology of micro-mechanical testing is presented and is applied to yttria-stabilized zirconia. Advantages and limitations of the technique are discussed and details about the combination of FIB-machining and nanoindentation testing are illustrated. At the same time, first results of the strength in compression of zirconia micropillars are presented and the failure mechanism is discussed.Postprint (published version