Leak rate performance of three silicone elastomer compounds after ground-simulated and on-orbit environment exposures

7th AIAA Atmospheric and Space Environments Conference

2015

Surface blending is a typical step in the manufacturing process of molded elastomer seals used to remove surface imperfections. Using O-rings molded from S0383-70 silicone elastomer oriented in a face seal configuration, this study screened for negative effects of docking seal surface blending. The study was separated into two distinct phases. Phase I used twenty-seven different surface treatments applied to a sample set of 130 O-ring specimens to examine the individual and combined effects of surface blending and ultraviolet radiation exposure on air leak rate. Combinations of blend surface area, blend location, and ultraviolet radiation exposure level were screened to determine the most influential factors and to narrow the variables investigated in Phase II. The second phase employed an enhanced leak rate test system and a test sample set comprised of both Phase I specimens and supplementary O-rings to quantitatively examine the impact of blending and ultraviolet radiation exposure on measured leak rate. Statistical analysis of leak rate test data indicated that blending alone did not significantly affect the leak rate of specimens not exposed to ultraviolet radiation. In the absence of surface blending, ultraviolet radiation exposure was shown to increase sample leak rate at statistically significant levels. The largest leak rate increases, however, occurred when O-ring sealing surface blending was coupled with subsequent ultraviolet radiation exposure. In those instances, the ability of the O-rings to create an effective seal was significantly compromised. Nomenclature CV= coefficient of variation x = sample average s = sample standard deviation

Section: Introductionmentioning

confidence: 99%

Investigation of the Impact of Surface Blending and Ultraviolet Radiation Exposure on Elastomer Seal Leak Rate Performance for Space Seal Applications

Taylor

Mather

7th AIAA Atmospheric and Space Environments Conference

2015

“…[2][3][4][7][8] As the United States plans to embark on missions with longer durations, 12 the challenges of utilizing elastomer compound seals become more evident. Destinations such as low-Earth orbit, asteroids, and the lunar and Martian surfaces are harsh environments for materials to survive and require materials to withstand atomic oxygen, 13-17 ultraviolet and particle radiation, [13][14][15]18 micrometeoroids and orbital debris, 14,[18][19][20][21] and dust, 18,[22][23] amongst others.…”

Section: Introductionmentioning

confidence: 99%

Elastomer Seal Performance after Terrestrial Ultraviolet Radiation Exposure

7th AIAA Atmospheric and Space Environments Conference

Oravec

Mather

et al. 2015

Ultraviolet radiation was evaluated to determine its negative effects on the performance of elastomeric gas pressure seals. The leak rates of the silicone elastomer S0383-70 O-ring test articles were used to quantify the degradation of the seals after exposure to vacuumultraviolet and/or middle-to-near-ultraviolet wavelength radiation. Three groups of seals were exposed in terrestrial facilities to 115-165 nm wavelength radiation, 230-500 nm wavelength radiation, or both spectrums, for an orbital spaceflight equivalent of 125 hours. The leak rates of the silicone elastomer S0383-70 seals were quantified and compared to samples that received no radiation. Each lot contained six samples and statistical t-tests were used to determine the separate and combined influences of exposure to the two wavelength ranges. A comparison of the mean leak rates of samples exposed to 115-165 nm wavelength radiation to the control specimens showed no difference, suggesting that spectrum was not damaging. The 230-500 nm wavelength appeared to be damaging, as the mean leak rates of the specimens exposed to that range of wavelengths, and those exposed to the combined 115-165 nm and 230-500 nm spectrums, were significantly different from the leak rates of the control specimens. Most importantly, the test articles exposed to both wavelength spectrums exhibited mean leak rates two orders of magnitude larger than any other exposed specimens, which suggested that both wavelength spectrums are important when simulating the orbital environment. Nomenclaturea 0 = zero-order regression coefficient a 1 = first-order regression coefficient β = bias error i, k = indices m = mass ̇ = mass leak rate N = number of samples p = absolute pressure φ = precision error R = specific gas constant T = temperature t = time

“…2 Unfortunately, silicone seals have a high relative leak rate due to the compound's permeability. [2][3][4] The overall leak rate rises even further when the sealing surface is degraded from on-orbit atomic oxygen impingement, [4][5][6][7] ultraviolet radiation exposure, 4 micrometeoroids and orbital debris impacts, 8,9 and foreign object debris and lunar dust contamination. [10][11][12] As the leak rate performance of the gas pressure seals dictates the quantity and weight of resources required to replenish breathing air, lengthy and costly developmental programs are undertaken for each seal design considered for use in space.…”

Section: Introductionmentioning

confidence: 99%

Leak-Rate-Quantification Method for Gas Pressure Seals with Controlled Pressure Differential

Journal of Spacecraft and Rockets

Braun

Oravec

et al. 2017

An enhancement to the pressure decay leak rate method with mass point analysis solved deficiencies in the standard method. By adding a control system, a constant gas pressure differential across the test article was maintained. As a result, the desired pressure condition was met at the onset of the test, and the mass leak rate and measurement uncertainty were computed in real-time. The data acquisition and control system were programmed to automatically stop when specified criteria were met. Typically, the test was stopped when a specified level of measurement uncertainty was attained. Using silicone O-ring test articles, the new method was compared with the standard method that permitted the downstream pressure to be non-constant atmospheric pressure. The two methods recorded comparable leak rates, but the new method recorded leak rates with significantly lower measurement uncertainty, statistical variance, and test duration. Utilizing this new method in leak rate quantification, projects will reduce cost and schedule, improve test results, and ease interpretation between data sets.