Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

The use of moire fringes in analysing strains around mine openings

Imperial Users onl

Enabling hybrid process metrology in roll-to-roll nanomanufacturing: design of a tip-based tool for topographic sampling on flexible substrates

This work seeks to demonstrate the efficacy of a novel approach for topography measurement of nano-scale structures fabricated on a flexible substrate in a roll-to-roll (R2R) fashion. R2R manufactured products can be extremely cost competitive compared to more traditional, silicon wafer or glass panel based nanofabrication solutions, in addition to the unique and often desirable mechanical properties inherent to flexible substrates. As such, flexible nanomanufacturing is an area of immense research interest. However, despite the significant potential of these products for a variety of applications, developing manufacturing systems from lab-scale prototypes to pilot- or high volume manufacturing (HVM) has often proven both difficult and infeasibly expensive as research investment and achievable process yield limit advancement. One of the most significant capability gaps in current art, and roadblocks on the path towards adoption of R2R nanomanufacturing, is the lack of high-throughput, nanometer-scale metrology for process development, real-time control, and yield enhancement. This dissertation presents the design of a tip-based measurement tool implementing atomic force microscope (AFM) probes manufactured with a micro-electro-mechanical system (MEMS) approach to the challenge of sub-micron topography measurement which is also compatible with R2R manufacturing on flexible substrates. A proof-of-concept prototype tool with subsystems to regulate a flexible web, isolate and position the atomic force microscope probe, and measure features on the substrate, all coordinated by a real-time embedded control system, was designed and fabricated. The positioning subsystem was evaluated dynamically to ensure initial design requirements were met, and stationery, step-and-scan results were presented. However, to wholly meet this extent need for in-line R2R metrology, a system capable of atomic force microscope scanning despite a continuous, non-zero substrate velocity is required - any regular stoppage of the web in a R2R process all but dooms economically viable production throughput. Refinement and redesign of the proof-of-concept tool was driven by new system requirements to meet this goal, in addition to lessons learned from the initial prototype. Improvements focused on upgrading the web handling spindle design and mechatronics, tool power electronics, moving structures, and control algorithms used for high-speed synchronous positioning of the atomic force microscope and web. The culmination of this work will serve to introduce a new measurement framework which may be used to accelerate and enable future research in R2R manufacturing of nanofeatured products.Mechanical Engineerin

Doctor of Philosophy

dissertationTactile sensors are a group of sensors that are widely being developed for transduction of touch, force and pressure in the field of robotics, contact sensing and gait analysis. These sensors are employed to measure and register interactions between contact surfaces and the surrounding environment. Since these sensors have gained usage in the field of robotics and gait analysis, there is a need for these sensors to be ultra flexible, highly reliable and capable of measuring pressure and two-axial shear simultaneously. The sensors that are currently available are not capable of achieving all the aforementioned qualities. The goal of this work is to design and develop such a flexible tactile sensor array based on a capacitive sensing scheme and we call it the flexible tactile imager (FTI). The developed design can be easily multiplexed into a high-density array of 676 multi-fingered capacitors that are capable of measuring pressure and two-axial shear simultaneously while maintaining sensor flexibility and reliability. The sensitivity of normal and shear stress for the FTI are 0.74/MPa and 79.5/GPa, respectively, and the resolvable displacement and velocity are as low as 60 µm and 100 µm/s, respectively. The developed FTI demonstrates the ability to detect pressure and shear contours of objects rolling on top of it and capability to measure microdisplacement and microvelocities that are desirable during gait analysis

Atom-Based Geometrical Fingerprinting of Conformal Two-Dimensional Materials

The shape of two-dimensional materials plays a significant role on their chemical and physical properties. Two-dimensional materials are basic meshes that are formed by mesh points (vertices) given by atomic positions, and connecting lines (edges) between points given by chemical bonds. Therefore the study of local shape and geometry of two-dimensional materials is a fundamental prerequisite to investigate physical and chemical properties. Hereby the use of discrete geometry to discuss the shape of two-dimensional materials is initiated. The local geometry of a surface embodied in 3D space is determined using four invariant numbers from the metric and curvature tensors which indicates how much the surface is stretched and curved under a deformation as compared to a reference pre-deformed conformation. Many different disciplines advance theories on conformal two-dimensional materials by relying on continuum mechanics and fitting continuum surfaces to the shape of conformal two-dimensional materials. However two-dimensional materials are inherently discrete. The continuum models are only applicable when the size of two-dimensional materials is significantly large and the deformation is less than a few percent. In this research, the knowledge of discrete differential geometry was used to tell the local shape of conformal two-dimensional materials. Three kind of two-dimensional materials are discussed: 1) one atom thickness structures such as graphene and hexagonal boron nitride; 2) high and low buckled 2D meshes like stanene, leadene, aluminum phosphate; and, 3) multi layer 2D materials such as Bi2Se3 and WSe2. The lattice structures of these materials were created by designing a mechanical model - the mechanical model was devised in the form of a Gaussian bump and density-functional theory was used to inform the local height; and, the local geometries are also discussed

Modeling, Analysis, and Optimization Issues for Large Space Structures

Topics concerning the modeling, analysis, and optimization of large space structures are discussed including structure-control interaction, structural and structural dynamics modeling, thermal analysis, testing, and design

Experimental and Theoretical Investigations of Lube Oil Performance and Engine Friction

The feasibility of using a motored small, single-cylinder 517 cc Hatz 1D50 diesel engine to evaluate lube oil performance and engine friction at conditions typical for a fired engine is investigated in the present study. In addition a commercial engine modeling software, AVL Excite Power Unit, is used to predict the effects of lube oil formulations on the engine friction of the same engine. The motored engine can be operated with and without compression and with and without the engine oil pump. Lube oil performance is evaluated for 19 different lube oils by using either instantaneous motoring torque (motoring torque over an engine cycle) or friction mean effective pressure (fmep). For the latter, lube oil performance is evaluated by plotting fmep as a function of lube oil dynamic viscosity calculated using the Vogel’s equation with the mid-stroke cylinder liner temperature. Furthermore, the contribution of engine components such as piston/rings/liner assembly, connecting rod, journal bearings, valve train, and oil pump to the total engine friction is determined by removing components from the engine. For the model, the engine friction is estimated only for two different lube oil formulations via a friction coefficients measured with a line contact friction rig. Lube oil performance is examined for several different base oils, commercial oils with additives, and commercial oils without additives by comparing the motoring torque over a range of viscosities. Engine friction represented by either peak instantaneous torque or fmep is found to decrease with decreasing viscosity; whereas the effect of additives is to increase friction observed as an increase in peak instantaneous torque or fmep. The contribution of several engine components to the total engine friction is also examined by comparing the fmep obtained for different engine configurations. The piston, piston rings, and journal bearings are found to contribute the most to total engine friction, followed by the valve train, and finally the oil pump. The fmeps for two different oils, a 15W40 base oil and a commercial 15W40 oil, predicted by the simulation are generally lower than those for the motored Hatz engine and highly dependent on the modified Stribeck curve