Engineering topics

Ray, Asit K.

Publications and source records attributed to Ray, Asit K..

5 records

NASA NTRS1995

Positron annihilation spectroscopic study of high performance semi-interpenetrating network polyimids

Semi-interpenetrating (S-IPN) network polyimids were made from different proportions of LaRC RP46 (a thermosetpolyimid) and LaRC BDTA-ODA (a thermoplastic polyimid). The ultimate goal of this networking is to improve the mechanical properties of the thermoset polyimid. Positron lifetime study was made to calculate lifetime based on second component of the life time spectra and the free volume & microvoid size. All these properties tend to decrease steadily with increasing thermoset content except at the 50 percent thermoset level where these properties show sudden drop. This result contradicts with the initial expectation that the blend properties should change gradually if it were a solid solution of thermoset (TSP) and thermoplastic (TPP) components. Thermal analyses (TMA, DSC, DMA & TGA) were run to complement the positron life time studies. The TMA and DSC studies confirm the contradiction mentioned above. Further experimentation with S-IPN polymers made at TSP/TTP content around 50/50 level are being conducted to explain this anomaly. Scanning electron microscope study of the S-IPN polyimid samples is under way in order to detect morphological differences which might help explain the phenomenon mentioned above.

Ray, Asit K.↗

NASA NTRS1992

Material selection and evaluation of new encapsulation compounds for electric cables for launch support system

Eight urethane compounds were evaluated as possible replacement for the existing encapsulating compoounds for electrical cables for the Launch Support System at Kennedy Space Center (KSC). The existing encapsulating compound, PR-1535, contains the curative MOCA 4-4'-Methylene-BIS (2-chloroaniline), which is a suspect carcinogen and hence may be the subject of further restrictions of its use by the Occupational Safety and Health Administration (OSHA). The samples made in the configuration of cable joints and in the form of disks were evaluated for flammability and hypergolic compatibility. These also underwent accelerated weatherability tests that measured the residual hardness of the exposed samples. Three candidates and the existing compound passed the hardness test. Of these, only one candidate and the existing compound passed the flammability test. The thermal and hydrolytic stability (weatherability) of these samples was studied using thermogravimetric analysis (DSC) techniques. The TMA and DSC data correlated with the residual hardness data; whereas, the TGA data showed no correlation. A hypergolic compatibility test will be conducted on the compound V-356-HE80, which passed both the flammability and accelerated weatherability tests.

Ray, Asit K.↗

NASA NTRS1992

Material selection and evaluation aimed at resolving deficiencies of a space technology material

NASA-Kennedy Space Center propellant handlers' visors are undergoing conversion from Plexiglass G to a Surlyn 8920-based material; various Surlyn compositions are here subjected to a battery of environmental and mechanical-properties tests under the relevant conditions. Specially-molded Surlyn samples have exhibited much higher impact strengths than either Plexiglass G or Lexan, and passed the ANSI weight-drop test. DSC results show that Surlyn and Plexiglass G exhibit strikingly different thermal transitions.

Ray, Asit K.↗

NASA NTRS1991

Evaluation of Surlyn 8920 as PHE Visor Material and Evaluations of New Adhesives for Improving Bonding Between Teflon and Stainless Steel at Cryogenic Temperature

Two studies are presented, and in the first study, Surlyn 8920 (an ionic and amorphous low density polyethylene made by Dupont) was evaluated as a possible replacement of Plexyglass G as PHE visor material. Four formulations of the polymer were made by adding different amounts of UV stabilizer, energy quencher, and antioxident in a Brabender Plasticorder. The formulated polymers were molded in the form of sheets in a compression molder. Cut samples from the molded sheets were exposed in a weatherometer and tested on Instron Tensile Tester for strength and elongation. Specially molded samples of the formulated polymers were subjected to Charpy Impact Tests. In the second study, preliminary evaluations of adhesives for improvement of bonding between Teflon and stainless steel (SS) were performed. Kapton, a high temperature polyimide made by Dupont, and a rubber based adhesive made by Potter Paint Co., were evaluated against industrial quality epoxy, the current material used to bond Teflon and SS. The degreased surfaces of the SS discs were etched mechanically, with a few of these etched chemically. The surfaces of the SS discs were etched mechanically, with a few of these etched chemically. Bonding strengths were evaluated using lap shear tests on the Instron Tensile Tester for the samples bonded by Kapton and industrial quality epoxy. Bond strengths were also evaluated using a pull test on the Instron for the samples bonded by Potter adhesive (CWL-152) and industrial quality epoxy. Based on limited lap shear data, Kapton gave bond strength favorable compared to that of industrial epoxy. Based on limited pull test data, Kapton bonded and CWL-152 bonded samples showed poor strength compared to epoxy bonded sample.

Ray, Asit K.↗

NASA NTRS1990

Fine-tuning of process conditions to improve product uniformity of polystyrene particles used for wind tunnel velocimetry

Monodisperse polymer particles (having uniform diameter) were used for the last two decades in physical, biological, and chemical sciences. In NASA Langley Research Center monodisperse polystyrene particles are used in wind tunnel laser velocimeters. These polystyrene (PS) particles in latex form were formulated at the Engineering Laboratory of FENGD using emulsion-free emulsion polymerization. Monodisperse PS latices particles having different particle diameters were formulated and useful experimental data involving effects of process conditions on particle size were accumulated. However, similar process conditions and chemical recipes for polymerization of styrene monomer have often yielded monodisperse particles having varying diameters. The purpose was to improve the PS latex product uniformity by fine-tuning the process parameters based on the knowledge of suspension and emulsion polymerization.

Ray, Asit K.↗