Document DOI: 10.1209/epl/i2001-00305-x
Europhys. Lett., 54 (2) , pp. 269-274 (2001)
Defect-mediated creep of structured materials
R. H. Colby1, L. M. Nentwich2, S. R. Clingman3 and C. K. Ober31 Materials Science and Engineering, Pennsylvania State University University Park, PA 16802, USA
2 James Franck Institute, University of Chicago - Chicago, IL 60637, USA
3 Materials Science and Engineering, Cornell University - Ithaca, NY 14853, USA
(Received 28 July 2000; accepted in final form 13 February 2001)
Abstract
Low-stress creep measurements on a nematic liquid crystal polymer indicate
that it is a viscoelastic solid, with a modulus of
100 dynes/cm2 and a
yield stress of
50 dynes/cm2. Both smectics and nematics are
viscoelastic solids at very low stress levels, with a modulus that is
related to their defect texture. At stress levels somewhat above the yield
stress, there is a yielding regime where the deformation rate and defect
spacing are power laws in the applied stress. We understand these power laws
using the ideas developed long ago by Orowan for the motion of line defects
in crystalline solids. The exponents of these power laws are different for
nematics and smectics, but the nematic universality class also appears to
apply to superplastic metals and ceramics.
83.80.Xz - Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
61.30.Jf - Defects in liquid crystals.
62.20.Fe - Deformation and plasticity (including yield, ductility, and superplasticity).
© EDP Sciences 2001