Michael W. Darlington’s scientific contributions

The shear and tensile creep behaviour of polypropylene and low-density polyethylene has been determined for a range of stress levels and creep times from 5 to 105 seconds. The data at finite strains have been correlated using the concept of shear on octahedral planes. When the experimental 100 second shear strains were matched to those predicted from the tensile tests, the experimental and calculated shear creep curves remained coincident, even in tests where the shear strains reached 8% and the materials were highly non-linear viscoelastic. Manipulation of data in the literature for two amorphous polymers suggests a different pattern of behaviour and this is related to differences in the affect of the hydrostatic component of stress in the tensile tests on the creep response of the four polymers.