Aeronautical engineering: A continuing bibliography with indexes (supplement 267)

This bibliography lists 661 reports, articles, and other documents introduced into the NASA scientific and technical information system in June, 1991. Subject coverage includes design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; theoretical and applied aspects of aerodynamics and general fluid dynamics; electrical engineering; aircraft control; remote sensing; computer sciences; nuclear physics; and social sciences

Interfacial degradation mechanisms with applications to polymer-matrix composites and intergranular stress corrosion cracking of steels

Structural interface property controls a wide spectrum of applications, ranging from the hybrid integration of dissimilar structural materials, to the enhanced physical properties of high performance engineering alloys. Practically, interfaces can be perceived as the weakest part of a heterogonous material or a structure. They are the most prone to environmental disturbances such as chemical or thermal, with significant deterioration of the structural integrity. Despite the large volume of literature on the topic, there remains a lack of proper understanding of degradation mechanisms of these interfaces. The challenge remains in the early detection of interfacial damage, and assessment of the remaining safe service life. This work is an attempt to provide some physical and mechanical understanding of these interfacial degradation mechanisms in two problem sets; (1) contamination-induced interfacial degradation in polymer matrix composites, and (2) early stage degradation of microstructure and mechanical properties in pipeline steels. The ultimate goal is to provide metrics for the physical and mechanical changes associated with these degradation mechanisms, and provide the bases for further development of new nondestructive evaluation techniques. For the first topic, the contamination-induced degradation mechanisms in polymer-matrix interfaces were examined experimentally and the observed trends were rationalized analytically and numerically. Two complementary frameworks were developed for the prediction of residual interfacial fracture energy, based on the changes in the adhesive hardness, and the level of the surface contaminants. Both of these quantities can be measured nondestructively by nanoindentation and IR-spectroscopy, respectively. Additionally, role of bond line contamination on mode-I failure and fracture surface evolution is quantified by performing statistical fracture surface analysis. With additional examination of other material systems, the proposed correlations may provide the basis for nondestructive evaluation of bond line integrity. For the second topic, initial microstructure surface evolution was examined in high strength steel under corrosive environment. The environmentally occurring corrosion process is mimicked by laboratory scale electrochemical experiments. Nanoindentation technique was utilized to locally characterize the mechanical property degradation in the sub-surface layer of a pipeline steel undergoing intergranular corrosion at active dissolution potentials at pH 8.2. Additionally, atomistic computational analysis was conducted to rationalize the experimentally observed trends. The present study reports two key observations: (1) mechanically degraded grains in the subsurface layer with 10% reduction in hardness, (2) 1 μm-thick mechanically degraded layers adjacent to corroded grain boundaries with 25% lower hardness relative to the grain interior. The observed degradation is attributed to weakening of lattice resistance arising from the clusters of non-equilibrium atomic vacancies generated by the preferential dissolution of silicon atoms by intergranular corrosion activity. The findings might provide a new insight for the corrosion process and might suggest a mitigation strategy

The Fifth National Technology Transfer Conference and Exposition

No abstract availabl

Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

Aeronautical engineering: A cumulative index to a continuing bibliography

This bibliography is a cumulative index to the abstracts contained in NASA SP-7037 (197) through NASA SP-7037 (208) of Aeronautical Engineering: A Continuing Bibliography. NASA SP-7037 and its supplements have been compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). This cumulative index includes subject, personal author, corporate source, foreign technology, contract, report number, and accession number indexes

Wood Properties and Processing

Wood-based materials are CO2-neutral, renewable, and considered to be environmentally friendly. The huge variety of wood species and wood-based composites allows a wide scope of creative and esthetic alternatives to materials with higher environmental impacts during production, use and disposal. Quality of wood is influenced by the genetic and environmental factors. One of the emerging uses of wood are building and construction applications. Modern building and construction practices would not be possible without use of wood or wood-based composites. The use of composites enables using wood of lower quality for the production of materials with engineered properties for specific target applications. Even more, the utilization of such reinforcing particles as carbon nanotubes and nanocellulose enables development of a new generation of composites with even better properties. The positive aspect of decomposability of waste wood can turn into the opposite when wood or wood-based materials are exposed to weathering, moisture oscillations, different discolorations, and degrading organisms. Protective measures are therefore unavoidable for many outdoor applications. Resistance of wood against different aging factors is always a combined effect of toxic or inhibiting ingredients on the one hand, and of structural, anatomical, or chemical ways of excluding moisture on the other