Creep of concentrically loaded circular plates

Using a strain-energy approach and the Rayleigh-Ritz procedure, a nonlinear compressible theory was developed to predict the creep deflections of circular plates laterally loaded by a point force acting at the center of the plates. Both clamped and simply supported boundary conditions were considered. The theory applies to transient as well as to steady-state creep. The stress-strain-time relations for the material were represented by a family of isochronous stress-strain curves. For analytical purpose, each curve was approximated by an arc hyperbolic sine function. Experimental data were obtained from eight plates made of high-density polyethylene tested in a controlled-atmosphere room. Material properties were obtained from tension and compression specimens. All test members were subjected to the same load history. An initial load was held constant for a specified time and then increased by 10 percent of its initial value at four equal intervals of time. Good agreement was found between theory and experiment.