Engineering topics

Slemp, Wayne S.

Publications and source records attributed to Slemp, Wayne S..

At least 19 records

NASA NTRS1995

LDEF polymeric materials: A summary of Langley characterization

The NASA Long Duration Exposure Facility (LDEF) enabled the exposure of a wide variety of materials to the low earth orbit (LEO) environment. This paper provides a summary of research conducted at the Langley Research Center into the response of selected LDEF polymers to this environment. Materials examined include graphite fiber reinforced epoxy, polysulfone, and additional polyimide matrix composites, films of FEP Teflon, Kapton, several experimental high performance polyimides, and films of more traditional polymers such as poly(vinyl toluene) and polystyrene. Exposure duration was either 10 months or 5.8 years. Flight and control specimens were characterized by a number of analytical techniques including ultraviolet-visible and infrared spectroscopy, thermal analysis, scanning electron and scanning tunneling microscopy, x-ray photoelectron spectroscopy, and, in some instances, selected solution property measurements. Characterized effects were found to be primarily surface phenomena. These effects included atomic oxygen-induced erosion of unprotected surfaces and ultraviolet-induced discoloration and changes in selected molecular level parameters. No gross changes in molecular structure or glass transition temperature were noted. The intent of this characterization is to increase our fundamental knowledge of space environmental effects as an aid in developing new and improved polymers for space application. A secondary objective is to develop benchmarks to enhance our methodology for the ground-based simulation of environmental effects so that polymer performance in space can be more reliably predicted.

Young, Philip R.↗

NASA NTRS1995

Surface characterization of LDEF carbon fiber/polymer matrix composites

XPS (x-ray photoelectron spectroscopy) and SEM (scanning electron microscopy) analysis of both carbon fiber/epoxy matrix and carbon fiber/polysulfone matrix composites revealed significant changes in the surface composition as a result of exposure to low-earth orbit. The carbon 1s curve fit XPS analysis in conjunction with the SEM photomicrographs revealed significant erosion of the polymer matrix resins by atomic oxygen to expose the carbon fibers of the composite samples. This erosion effect on the composites was seen after 10 months in orbit and was even more obvious after 69 months.

Grammer, Holly L.↗

NASA NTRS1995

A Materials Exposure Facility

The objective of the Materials Exposure Facility (MEF) is to provide a test bed in space for conducting long-term (greater than one year) materials experiments which require exposure to the low Earth orbit (LEO) space environment. The proposed MEF is planned to be an integral part of the agency's Space Environments and Effects Research Program. The facility will provide experiment trays similar to the Long Duration Exposure Facility (LDEF). Each tray location is planned to have a power and data interface and robotic installation and removal provisions. Space environmental monitoring for each side of the MEF will also be provided. Since routine access to MEF for specimen retrieval is extremely important to the materials research, Space Station Freedom has been chosen as the preferred MEF carrier.

Slemp, Wayne S.↗

NASA NTRS1993

Thermal-Control Coatings Evaluated

Report describes tests of variety of thermal-control coating materials, including white paints, second-surface-metalized fluorinated ethylene propylene, aluminum anodized in sulfuric acid, and plasma-sprayed alumina.

Dever, Joyce A.↗

NASA NTRS1993

Performance of selected polymeric materials on LDEF

The NASA Long Duration Exposure Facility (LDEF) provided a unique environmental exposure of a wide variety of materials for potential advanced spacecraft application. This paper examines the molecular level response of selected polymeric materials which flew onboard this vehicle. Polymers include epolyimide, polysulfone, and polystyrene film and polyimide, polysulfone, and epoxy matrix resin/graphite fiber reinforced composites. Several promising experimental films were also studied. Most specimens received 5.8 years of low Earth orbital (LEO) exposure on LDEF. Several samples received on 10 months of exposure. Chemical characterization techniques included ultraviolet-visible and infrared spectroscopy, thermal analysis, x-ray photoelectron spectroscopy, and selected solution property measurements. Results suggest that many molecular level effects present during the first 10 months of exposure were not present after 5.8 years of exposure for specimens on or near Row 9. Increased AO fluence near the end of the mission likely eroded away much environmentally induced surface phenomena. The objective of this work is to provide fundamental information for use in improving the performance of polymeric materials for LEO application. A secondary objective is to gain an appreciation for the constraints and limitations of results from LDEF polymeric materials experiments.

Young, Philip R.↗

NASA NTRS1993

LDEF polymeric materials: 10 months versus 5.8 years of exposure

The chemical characterization of several polymeric materials which received 10 months of exposure and 5.8 years of exposure on a Row 9 Long Duration Exposure Facility (LDEF) experiment (A0134) is reported. Specimens include fluorinated ethylene propylene (FEP) teflon film, polysulfone film, and graphite fiber reinforced epoxy amd polysulfone matrix composites. The responses of these materials to the two LEO exposures are compared. The results of infrared, thermal, x-ray photoelectron, and scanning electron microscope analyses are reported. Solution property measurements of various molecular weight parameters are presented for the thermoplastic polysulfone materials. Molecular level effects attributable to exposure that were present in 10-month exposed specimens were not found in 5.8-year exposed specimens. This result suggests that increased atomic oxygen fluence toward the end of the LDEF mission may have eroded away selected environmentally induced changes in surface chemistry for 5.8-year exposure specimens.

Young, Philip R.↗

NASA NTRS1993

Surface characterization of selected LDEF tray clamps

The surface characterization of chromic acid anodized 6061-T6 aluminum alloy tray clamps has shown differences in surface chemistry depending upon the position on the Long Duration Exposure Facility (LDEF). Water contact angle results showed no changes in wettability of the tray clamps. The overall surface topography of the control, trailing edge(E3) and leading edge(D9) samples was similar. The thickness of the aluminum oxide layer for all samples determined by Auger depth profiling was less than one micron. X-ray photoelectron spectroscopy (XPS) analysis of the tray clamps showed significant differences in the surface composition. Carbon and silicon containing compounds were the primary contaminants detected.

Cromer, T. F.↗

NASA NTRS1993

LDEF thermal control coatings post-flight analysis

The NASA Long Duration Exposure Facility (LDEF) provided a unique flight opportunity for conducting experiments in space and return of these experiments to Earth for laboratory evaluation. The results of one of these experiments, S0010, Exposure of Spacecraft Coatings, in which selected spacecraft thermal control coatings were exposed to the low-Earth orbital (LEO) environment on LDEF are reported. The objective of the experiment is to evaluate the response of thermal control coatings to LEO exposure, which includes atomic oxygen, ultraviolet and particulate radiation, meteoroid and debris, vacuum, and temperature cycling.

Slemp, Wayne S.↗

NASA NTRS1992

Characterization of selected LDEF: Exposed polymer films and resins

The Long Duration Exposure Facility (LDEF) provided a unique environmental exposure of a wide variety of materials. The effects of 5 years and 10 months of Low-Earth Orbit (LEO) exposure of these materials to atomic oxygen, ultraviolet and particulate radiation, meteoroid and debris, vacuum, contamination, and thermal cycling is providing a data base unparalleled in the history of space environment research. Working though the Environmental Effects on Materials Special Investigation Group (MSIG), a number of polymeric materials in various processed forms have been assembled from LDEF investigators for analysis at the NASA Langley Research Center. This paper reports the status of on-going chemical characterization of these materials.

Young, Philip R.↗

NASA NTRS1992

LDEF thermal control coatings post-flight analysis

The optical, physical, and chemical properties of selected spacecraft thermal control coatings, exposed for 10 months and 5.8 years on the leading edge (Row 9) of the LDEF, are reported. The following coatings were used: quartz/silver optical solar reflector; silvered FEP Teflon; S-13GLO, YB-71, and A-276 white paints; black paint; and sputter deposited coatings over graphite-epoxy composite substrates. The solar absorptance, total normal emittance, scanning electron and X-ray photoelectron microscopy, and X-ray diffraction analyses will be compared for the control, the 10 month exposed, and the 5.8 year exposed specimens. Data suggests that the high atomic flux over the last 6 months of the LDEF mission may have influenced the results from from this coatings experiment.

Slemp, Wayne S.↗

NASA NTRS1992

LDEF polymeric materials: 10 months versus 5.8 years of exposure

The chemical characterization of several polymeric materials which received both 10 months and 5.8 years of exposure on a Row 9 experiment (A0134) is reported. Specimens include polysulfone film, polysulfone matrix/graphite-fiber reinforced composites, and coated and uncoated epoxy matrix/graphite fiber reinforced composites. The effect of 10 months of exposure on an experimental silicon-containing polyimide copolymer film is also reported. The results of infrared, thermal, x-ray photoelectron, and scanning electron microscope analyses will be compared for the two exposures. Solution property measurements on the thermoplastic polysulfone resin will also be presented. Molecular level effects attributable to exposure and present in 10-month specimens are not present in 5.8-year specimens. This suggests that increased atomic oxygen fluence toward the end of the mission may have eroded selected environmentally-induced changes in surface chemistry for 5.8-year specimens.

Young, Philip R.↗

NASA NTRS1992

Evaluation of selected thermal control coatings for long-life space structures

Graphite-reinforced resin matrix composites are being considered for spacecraft structural applications because of their light weight, high stiffness, and lower thermal expansion. Thin protective coatings with stable optical properties and the proper ratio of solar absorption (alpha sub s) to thermal emittance (epsilon) minimize orbital thermal extremes and protect these materials against space environment degradation. Sputtered coatings applied directly to graphite/epoxy composite surfaces and anodized coatings applied to thin aluminum foil were studied for use both as an atomic oxygen barrier and as thermal control coatings. Additional effort was made to develop nickel-based coatings which could be applied directly to composites. These coating systems were selected because their inherent tenacity made them potentially more reliable than commercial white paints for long-life space missions. Results indicate that anodized aluminum foil coatings are suitable for tubular and flat composite structures on large platforms in low Earth orbit. Anodized foil provides protection against some elements of the natural space environment (atomic oxygen, ultraviolet, and particulate radiation) and offers a broad range of tailored alpha sub s/epsilon. The foil is readily available and can be produced in large quantities, while the anodizing process is a routine commercial technique.

Teichman, Louis A.↗

NASA NTRS1992

Chemical characterization of selected LDEF polymeric materials

The chemical characterization of selected polymeric materials which received exposure on the LDEF is reported. The specimens examined include silvered fluorinated ethylene propylene (FEP) teflon thermal blanket material, polysulfone matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations and, thus, received different environmental exposures. The results of infrared, thermal, x ray photoelectron, and various solution property analyses have shown no significant change at the molecular level in the polymer that survived exposure. However, scanning electron and scanning tunneling microscopies show resin loss and a texturing of the surface of some specimens which resulted in a change in optical properties. The potential effect of a silicon containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Young, Philip R.↗

NASA NTRS1992

Effects of LDEF flight exposure on selected polymer matrix resin composite materials

The characterization of selected graphite fiber reinforced epoxy (934 and 5208) and polysulfone (P1700) matrix resin composites materials which received over five years and nine months of exposure to the low earth orbit (LEO) environment in experiment AO134 on the Long Duration Exposure Facility is reported. The changes in mechanical properties of ultimate tensile strength and tensile modulus for exposed flight specimens are compared to the three sets of control specimens. Marked changes in surface appearance are discussed, and resin loss is reported. The chemical characterization including infrared, thermal, and selected solution property measurements showed that the molecular structure of the polymetric matrix had not changed significantly in response to this exposure.

Slemp, Wayne S.↗

NASA NTRS1992

Spacecraft materials and coatings experiments

The 5.8-year exposure data from the Long Duration Experiment Facility (LDEF) has demonstrated the benefits of long-term exposure in low Earth orbit (LEO) for understanding the behavior of spacecraft materials and coatings for use in extended space missions. The Space Station Freedom represents the next large area spacecraft available in NASA planned missions for obtaining this long term space exposure data. The advantages of using the Space Station Freedom for these studies are presented. Discrepancies between short-term flight exposure result from Shuttle Orbiter experiments and the long-term LDEF results are shown. The major objectives and benefits of conducting materials and coatings experiments on Space Station Freedom are emphasized.

Slemp, Wayne S.↗

NASA NTRS1992

Characterization of selected LDEF-exposed polymeric films

The characterization of selected experimental and commercially available thin polymeric films which received 10 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. The visual appearance of most specimens changed due to exposure. However, except for a silicon-containing copolymer film, chemical characterization including infrared, thermal, and X-ray photoelectron analyses showed that the molecular structure of the surviving material had not changed significantly in response to exposure. Surface texturing due to atomic oxygen erosion was documented using various microscopic analyses. The possibility of continued post-exposure degradation of some polymeric materials is proposed.

Young, Philip R.↗

NASA NTRS1992

Analysis of a space-exposed thermoplastic resin

The chemical characterization of a thermoplastic resin exposed to the low Earth orbit (LEO) environment for 10 months and for 5.8 years is reported. The resin, processed as a thick film and as a matrix for a graphite fiber reinforced composite, few exposed in the RAM direction on the NASA Long Duration Exposure Facility (LDEF). Differences attributable to environmental exposure were detected in infrared spectra and in various molecular weight parameters of film after 10 months in LEO. Those effects were not as apparent in composites after 5.8 years in LEO. Increased exposure to atomic oxygen toward the end of the LDEF mission probably scrubbed these effects from specimens exposed for 5.8 years. The intent of this study is to increase our fundamental understanding of space environmental effects on polymeric materials and to develop a benchmark for enhancing our methodology for and understanding of the ground-based simulation of space environmental effects.

Young, Philip R.↗

NASA NTRS1991

An analysis of LDEF-exposed silvered FEP teflon thermal blanket material

The characterization of selected silvered fluorinated ethylene propylene (FEP) teflon thermal blanket material which received 5 years and 9 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. X-ray photoelectron spectroscopy, infrared, and thermal analyses did not detect a significant change at the molecular level as the result of this exposure. However, various microscopic analyses revealed a roughening of the coating surface due to atomic oxygen erosion which resulted in some materials changing from specular reflectors of visible radiation to diffuse reflectors. The potential effect of silicon-containing molecular contamination on these materials is addressed.

Young, Philip R.↗