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The Combined Influence of Molecular Weight and Temperature on the Aging and Viscoelastic Response of a Glassy Thermoplastic PolyimideThe effect of molecular weight on the viscoelastic performance of an advanced polymer (LaRC-SI) was investigated through the use of creep compliance tests. Testing consisted of short-term isothermal creep and recovery with the creep segments performed under constant load. The tests were conducted at three temperatures below the glass transition temperature of five materials of different molecular weight. Through the use of time-aging-time superposition procedures, the material constants, material master curves and aging-related parameters were evaluated at each temperature for a given molecular weight. The time-temperature superposition technique helped to describe the effect of temperature on the timescale of the viscoelastic response of each molecular weight. It was shown that the low molecular weight materials have higher creep compliance and creep rate, and are more sensitive to temperature than the high molecular weight materials. Furthermore, a critical molecular weight transition was observed to occur at a weight-average molecular weight of M (bar) (sub w) 25000 g/mol below which, the temperature sensitivity of the time-temperature superposition shift factor increases rapidly. The short-term creep compliance data were used in association with Struik's effective time theory to predict the long-term creep compliance behavior for the different molecular weights. At long timescales, physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested.
Document ID
20000096391
Acquisition Source
Langley Research Center
Document Type
Technical Memorandum (TM)
Authors
Nicholson, Lee M. (National Academy of Sciences - National Research Council Hampton, VA United States)
Whitley, Karen S. (NASA Langley Research Center Hampton, VA United States)
Gates, Thomas S. (NASA Langley Research Center Hampton, VA United States)
Date Acquired
September 7, 2013
Publication Date
September 1, 2000
Subject Category
Nonmetallic Materials
Report/Patent Number
NASA/TM-2000-210312
NAS 1.15:210312
L-18005
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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