Automatic controls and regulators: A compilation

Devices, methods, and techniques for control and regulation of the mechanical/physical functions involved in implementing the space program are discussed. Section one deals with automatic controls considered to be, essentially, start-stop operations or those holding the activity in a desired constraint. Devices that may be used to regulate activities within desired ranges or subject them to predetermined changes are dealt with in section two

In-Hand Object Stabilization by Independent Finger Control

Grip control during robotic in-hand manipulation is usually modeled as part of a monolithic task, relying on complex controllers specialized for specific situations. Such approaches do not generalize well and are difficult to apply to novel manipulation tasks. Here, we propose a modular object stabilization method based on a proposition that explains how humans achieve grasp stability. In this bio-mimetic approach, independent tactile grip stabilization controllers ensure that slip does not occur locally at the engaged robot fingers. Such local slip is predicted from the tactile signals of each fingertip sensor i.e., BioTac and BioTac SP by Syntouch. We show that stable grasps emerge without any form of central communication when such independent controllers are engaged in the control of multi-digit robotic hands. These grasps are resistant to external perturbations while being capable of stabilizing a large variety of objects.Comment: Submitted to IEEE Transactions on Robotics Journal. arXiv admin note: text overlap with arXiv:1612.0820

Shock Wave Behavior of Particulate Composites

Material heterogeneity at some scale is common in present engineering and structural materials as a means of strength improvement, weight reduction, and performance enhancement in a great many applications such as impact and blast protection, construction, and aerospace. While the benefits of transitioning toward composites in practical applications is obvious, the methods of measurement and optimization required to handle spatial heterogeneity and bridge length scale differences across multiple orders of magnitude are not. This is especially true as loading rates transition into the shock regime. Composite materials, such as concrete, have advantages afforded to them by their microstructure that allow them to dissipate and scatter impact energy. The mechanical mismatch between constituent phases in composites (mortar and cement paste in concrete, crystals and binder in polymer bonded explosives, ceramic powder and epoxy in potting materials, etc.) provides the interfaces required for shock wave reflection. The degree to which a shock is disrupted from its accepted form as a propagating discontinuity in stress and particle velocity is highly dependent upon the size, shape, and density of the interfaces present. The experimental and computer aided simulations in this thesis seek to establish a scaling relationship between composite microstructure and shock front disruption in terms of particulate size and density through the use of multi-point heterodyne velocity interferometry. A model particulate composite has been developed to mimic the wave reflection properties of materials such as Ultra High Performace Composite (UHPC) concrete and polymer bonded explosives, while also being simple to source and manufacture repeatably. Polymethyl Methacrylate (PMMA), a thermoplastic polymer, and silica glass spheres satisfy the manufacturing constraints with a shock impedance mismatch of 4.1, when placed in-between the shock impedance of UHPC concretes (~ 10) and polymer bondedexplosives (~ 2). The flexibility afforded by the model composite allows for the use of mono-disperse bead particle diameter distributions centered at 5 discrete diameters centered in the range associated with high scattering effectiveness (5-50 times the shock thickness in the pure matrix material). Shock front disruption is measured at multiple points on the rear surface of a plate impact target to observe shock spreading and spatial heterogeneity in material response due to random particle placement. Shock rise times are reported for composites of 30% and 40% glass spheres by volume, with glass spheres of 100, 300, 500, 700, and 1000 micron diameter. Composites with single mode as well as bi-modal bead diameter distributions are subjected to plate impact loading at an average pressure of 5 GPa. In single mode composites, a linear dependence of shock wave rise time on particle diameter is observed, with a constant of proportionality equal to the bulk shock speed in the material. Bi-modal bead diameter composites were fabricated in order to achieve higher volume fractions without composite degradation. The addition of a second phase to a base 30% glass by volume composite mix results in significant increases in shock wave rise time for base mixes of 500 micron beads, while a point of maximum scattering effectiveness is observed for base mixes of 1000 micron diameter beads. A comprehensive two dimensional series of CTH hydrocode simulations has been completed in tandem with experiments. An evaluation of the discrepancies in simulation and experimental results is presented. Shock disruption mechanisms and matrix/interface damage effects are discussed as possible sources of error and potential avenues for model improvement. The scaling arguments and model deficiency corrections made in this thesis have the potential to drive the development of new approaches of modeling shock waves in heterogeneous materials as well as optimization of microstructure for maximum shock front disruption.</p

On the Characterization of Engineered Elastomers At High Strain Rates

The main objective of this research was to develop a methodology for the characterization and modelling of elastomers that were subject to high-strain rate. Four aspects of the problem were accordingly examined. The first aspect of the study was dedicated to the comparison of constitutive equations to numerically model elastomers. The second aspect revolved around the testing of elastomers under dynamic loading. For this purpose, a Kolsky Bar was designed and constructed to test soft, flexible materials. The third aspect of the work dealt with the numerical modelling of the developed testing apparatus. Finite element methodology was used to optimize the testing parameters and validate the modified Kolsky Bar apparatus. Finally, the methodology developed to characterize the response of elastomers under high-strain rate loadings was employed to study two unique engineering materials. The developed approach should help engineers and designers in developing new systems in dynamic application with elastomer

Geomechanical and Hydraulic Behavior of Maryland Graded Aggregate Base Materials

Maryland State Highway Administration (SHA) is in need for evaluation of stiffness and drainage characteristics of graded aggregate base (GAB) stone delivered at highly variable gradations to the construction sites. To fulfill the current need, the mechanical and drainage properties of several Maryland GAB materials were evaluated in the laboratory and field. The resilient modulus (RM) and hydraulic conductivity (HC) test results obtained in the laboratory were compared to the field RM and HC. The effect of moisture content on RM was also evaluated. Summary RM values at Optimum Moisture Content (OMC) minus 2% were higher than those at OMC, with few exceptions; however, the permanent deformations were increased with addition of moisture content. An addition of 4-6% fines over the SHA specification limit of 8% resulted in 2-5 times decrease in the laboratory-based GAB's HC and an increase in time for 50% completion of the drainage

Magnetic Forming Coil Design and Development Final Summary Report, 17 Jun. 1963 - 31 Mar. 1964

Magnetic forming coils for corrective forming of weld-induced distortions in stiffened panel

Laser Shock Peening Pressure Impulse Determination via Empirical Data-Matching with Optimization Software

Laser shock peening (LSP) is a form of work hardening by means of laser induced pressure impulse. LSP imparts compressive residual stresses which can improve fatigue life of metallic alloys for structural use. The finite element modeling (FEM) of LSP is typically done by applying an assumed pressure impulse, as useful experimental measurement of this pressure impulse has not been adequately accomplished. This shortfall in the field is a current limitation to the accuracy of FE modeling, and was addressed in the current work. A novel method was tested to determine the pressure impulse shape in time and space by optimization driven data-matching. FE model development and material model verification was completed in Abaqus. A 2D and 3D model type study was conducted. A proof of concept data-matching optimization tool was developed and verified. This data-matching optimization tool, using the Hooke-Jeeves optimization algorithm, was then applied to match experimentally collected residual stress measurements from single LSP treated spots in 2024-T351 aluminum specimens. Validation of this “best-fit” pressure impulse was attempted in a 6Al-4V titanium material model for the same LSP treatment process. A combination Johnson-Cook viscoplasticity and Mie-Grüneisen equation of state (EOS) material model was shown to be amply sufficient for modeling the highly dynamic LSP event. A 2D axisymmetric FE model was shown to adequately represent a square LSP treatment process, in terms of residual stress field results with the use of a linear adjustment factor. The Hooke-Jeeves optimization algorithm proved highly successful at working through a FE model “black box” to match a target residual stress outcome. Further, this method was successful in matching the residual stress field of experimentally collected data. The validation of the best-fit pressure impulse in titanium was not a perfect match, but exhibited enough accuracy to be useful to design engineers in certain cases, and further shows potential for improvement and implementation toward this impulse matching goal