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Recoverable shear measurements in a parallel plate rheometerz
Author(s) -
Fruh S. M.,
Rodriguez Ferdinand
Publication year - 1970
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690160609
Subject(s) - rheometer , shear modulus , materials science , shear stress , modulus , composite material , shear (geology) , newtonian fluid , shear flow , young's modulus , mechanics , rheology , physics
A parallel plate rheometer has been devised which permits measurements of shear stresses of 10 2 to 10 5 dynes/sq.cm. and shear rates of 10 −5 to 1 sec. −1 . A linear, air lubricated bearing is used to align the apparatus, and a linear variable differential transformer is used to sense changes in position. With a sample of polyisobutylene and with several samples of poly(dimethyl siloxane), it has been established that a Hookean range exists for each sample at low stresses. Hooke's law in shear states that the modulus is independent of stress, where the modulus is defined as the ratio of the shear stress in steady, creeping flow to the strain which can be recovered after the stress is removed. Other conclusions supported by the present work are that the Hookean range does not extend to stresses which are high enough to cause non‐Newtonian flow, that the modulus decreases with increasing molecular weight although not in direct proportion, and that a sample with a broad molecular weight distribution has a lower modulus than one with a narrow distribution.