STUDY OF YIELDING PHENOMENA
Abstract
In yielding under constant tensile load, glassy polymethyl methacrylate (PMMA) and glassy polystyrene (PS) exhibit work softening at small strains, followed by strain hardening at higher strains. In this work the initial softening was of most interest. In the constant load experiment, the yield point shows up as a minimum of the deformation velocity vs elongation curve. Measurements were made of the variation of delay time (the time for accelerated elongation to occur under load) with stress and temperature (measured on PS and PMMA) with preorientation birefringence (PS), and with thermal history and water absorption (PMMA). The stress influence on strain rate under constant load is expressible as a stress shift factor. The same stress shift factor governs the stress influence on delay time and deformation rate changes associated with incremental stress changes. The influence of stress on strain rate is reversible. The important contribution to the increase in strain rate under constant load is caused by a true strain softening. The conclusion is drawn that it is a consequence of the disturbance of the annealed positions of the polymer segments. In this picture strain causes the breaking up of the relative order that is brought about in annealing; thus leaving the polymer in a far-from-equilibrium state.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1967
- Accession Number
- AD0664804
Entities
People
- D. H. Ender
Organizations
- Massachusetts Institute of Technology