Towards understanding stress corrosion cracking of austenitic stainless steels exposed to realistic sea salt brines
Not Available
36 MATERIALS SCIENCE↗
Engineering topics
Taylor, J. M.
Publications and source records attributed to Taylor, J. M..
Influence of Realistic, Cyclic Atmospheric Cycles on the Pitting Corrosion of Austenitic Stainless Steels
Pitting corrosion was evaluated on stainless steels 304H, 304, and 316L the surfaces of which had ASTM seawater printed on them as a function of surface roughness after exposure to an exemplar realistic atmospheric diurnal cycle for up to one year. Methods to evaluate pitting damage included optical imaging, scanning electron microscopy imaging, profilometry analysis, and polarization scans. The developed cyclic exposure environment did not significantly influence pitting morphology nor depth in comparison to prior static exposure environments. Cross-hatching was observed in a majority of pits for all material compositions with the roughest surface finish (#4 finish) and in all surface finishes for the 304H composition. Evidence is provided that cross-hatched pit morphologies are caused by slip bands produced during the grinding process for the #4 finish or by material processing. Additionally, micro-cracking was observed in pits formed on samples with the #4 surface finish and was greatly reduced or absent for pits formed on samples with smooth surface finishes. This suggests that both a low RH leading to an MgCl 2 -dominated environment and a rough surface containing significant residual stress are necessary for micro-cracking. Finally, the use of various characterization techniques and cross sectioning was employed to both qualitatively and quantitatively assess pitting damage across all SS compositions and surface finishes.
36 MATERIALS SCIENCE↗
Long-Term Effects of Humidity on Stainless Steel Pitting in Sea Salt Exposures
Ground 304 stainless steel (SS) samples were exposed to sea salt particles at 35 °C and two relative humidity (RH) levels for durations ranging from 1 week to 2 years. For all exposure times, pit number density and total pit volume at 40% RH were observed to be considerably greater than those at 76% RH. Statistical analysis of distributions of pit populations for both RH conditions showed that pit number density and total pit volume increased rapidly at first but slowed as exposure time increased. Cross-hatched features were observed in the 40% RH pits while ellipsoidal, faceted pits were observed at 76% RH. Optical profilometry indicated that most pits were not hemispherical. X-ray tomography provided evidence of undercutting and fissures. Piecewise curve fitting modeled the 40% RH data closely, predicting that corrosion damage would eventually plateau. However, a similar treatment of the 76% RH data suggested that corrosion damage would continuously increase, which implied that the piecewise power-law fit was limited in its ability to model atmospheric corrosion generally. Based on these observations, the operative mechanisms determining long-term corrosion behavior were hypothesized to be different depending on the RH of exposure.
36 MATERIALS SCIENCE↗
Mechanical quantum sensing in the search for dark matter
Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Here, searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.
79 ASTRONOMY AND ASTROPHYSICS↗
The use of precession modulation for nutation control in spin-stabilized spacecraft
The relations which determine the nutation effects induced in a spinning spacecraft by periodic precession thrust pulses are derived analytically. By utilizing the idea that nutation need only be observed just before each precession thrust pulse, a difficult continuous-time derivation is replaced by a simple discrete-time derivation using z-transforms. The analytic results obtained are used to develop two types of modulated precession control laws which use the precession maneuver to concurrently control nutation. Results are illustrated by digital simulation of an actual spacecraft configuration.
Taylor, J. M.↗
Nutation control during precession of a spin-stabilized spacecraft
The effects of precession thrust pulses and energy dissipation upon nutation of a spin-stabilized spacecraft are studied. Methods for controlling nutation during a precession maneuver are proposed and examined. A precession modulation control law is developed which uses precession thrust pulses to control nutation. Digital simulations show that precession control with separate nutation control is the fastest precessing system; however, the precession modulation method is only fractionally slower while not requiring a separate nutation control system.
Taylor, J. M.↗
The SAS-D nutation control system
A control law is developed for the SAS-D nutation control system. Nutation is removed in a sub-optimal manner with respect to fuel consumed, but attitude errors are minimized. The research performed consist of an investigation of nutation theory and nutation due to energy dissipation, nutation detection analysis, nutation control analysis, and error analysis. The resulting nutation control system uses an accelerometer or rate gyro to sense the nutation angle theta which varies sinusoidally at the nutation frequency omega. The sensed nutation angle is compared with a threshold theta sub tau. If the sensed nutation is greater, a thrust pulse of duration equal to the period of one spin cycle is initiated. Since the threshold theta sub tau is set equal to the amount of nutation that can be removed by one thrust pulse of duration equal to one spin cycle, the spacecraft nutation is reduced to near zero. Error analysis indicates that the nutation sensed, the threshold, the amount of nutation that can be removed during one thrust pulse, and the time duration of one thrust pulse are all sensitive to the spacecraft spin frequency imparted by the Delta rocket. Thus, the nutation control system was designed to be adaptive to the possible variations in imparted spin frequency.
Taylor, J. M.↗