Aeronautical engineering: A special bibliography with indexes, supplement 80

This bibliography lists 277 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1977

Scale-dependent fracture in gradient elastic materials

Micro-electromechanical systems (MEMS) and Nano-electromechanical systems (NEMS) have a wide range of applications in aerospace, power industry, automation & robotics, chemical & medical treatment analysis, information technology and in the infrastructure health monitoring equipments. To ensure the reliability of such small devices, the mechanical and hence fracture behaviour of their common building blocks such as beams, tubes, and plates should be carefully evaluated. However, on a smaller scale, the microstructural effects such as size effects, load-induced and geometrically prompted stress singularities are more noticeable, particularly at the micro/nano scale. Classical continuum elasticity theories are inadequate to accurately describe the situations controlled by the microstructure effects since the influence of these effects are not properly accounted for. On the other hand, the higher order gradient theories such as strain gradient theory may effectively describe the effects of microstructure through the solution of properly formulated boundary value problems. Moreover, when dealing with piezoelectric micro/nano materials, due to the presence of massive strain gradient, the electric field-strain gradient coupling (flexoelectricity) should also be considered. The objective of this research is to evaluate the scale-dependent fracture behaviour of gradient elastic materials using strain gradient theory. In particular, two most widely studied geometrical configurations i.e. double cantilever beam (DCB) and centrally cracked material layer are employed in this work. The findings presented in this thesis are expected to give useful insights to those working in the structural integrity analysis at the micro/nano scale. They are anticipated to help in the design of micro/nano structural components and serve as a benchmark for future theoretical and empirical studies

Monitoring of long steel pipes using acoustic emission

This thesis relates to the condition monitoring of long steel pipes using acoustic emission (AE). A number of experiments were carried out on pipes with a range of internal and external environments using a linear axial array of sensors with the ultimate aim of locating and reconstituting the time-domain and frequency-domain signatures of AE sources. The AE waves were generated from simulated, discontinuous, continuous, and semi-continuous sources and from real sources generated by impacts and crack propagation. The simulated source work in different internal and external environments was carried out to develop a generic empirical approach to AE propagation in long steel pipes which acknowledges the distortion of a source disturbance in the time and frequency domains. Generally, the acquired signals have two identifiable components and methods are developed for separating these components automatically and determining their group velocities. A simple model for attenuation is also developed which includes effects brought about by burial of the pipe and /or the nature of the fluid transported (liquid or gas). In the impact and crack extension tests a variety of intensities were simulated and the effect of type and intensity on time- and frequency-domain characteristics of the source was determined. The overall outcome is the demonstration of the potential of AE for identifying the nature, intensity and location of damaging events, such as crack growth and denting, and for the location and intensity assessment of leaks

Advanced Composites

Engineering practice has revealed that innovative technologies’ structural applications require new design concepts related to developing materials with mechanical properties tailored for construction purposes. This would allow the efficient use of engineering materials. The efficiency can be understood in a simplified and heuristic manner as the optimization of performance and the proper combination of structural components, leading to the consumption of the least amount of natural resources. The solution to the eco-optimization problem, based on the adequate characterization of the materials, will enable implementing environmentally friendly engineering principles when the efficient use of advanced materials guarantees the required structural safety. Identifying fundamental relationships between the structure of advanced composites and their physical properties is the focus of this book. The collected articles explore the development of sustainable composites with valorized manufacturability corresponding to Industrial Revolution 4.0 ideology. The publications, amongst others, reveal that the application of nano-particles improves the mechanical performance of composite materials; heat-resistant aluminium composites ensure the safety of overhead power transmission lines; chemical additives can detect the impact of temperature on concrete structures. This book demonstrates that construction materials’ choice has considerable room for improvement from a scientific viewpoint, following heuristic approaches

Aeronautical Engineering: A special bibliography with indexes, supplement 75, October 1976

This bibliography lists 300 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1976

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully