Influence of load type and stress gradient on flexural strength of epoxy resin polymeric material

Abstract A piecewise-linear parametric uniaxial stress-strain approach has been used to obtain the nonlinear moment curvature response based on strain compatibility in bending for epoxy resin materials. It has been shown that the direct use of tension and compression stress-strain models underestimates the flexural strength of epoxy resin materials in a three-point bending (3PB) setup. An analytical and experimental investigation is conducted to better evaluate the degree of flexural overstrength for epoxy resin material. Four-point bending (4PB) and a round plate (RP) supported on three symmetrically arranged pivot points on a circle are chosen. An algorithm is developed to obtain the load-deflection response of the 4PB and RP samples from the nonlinear moment curvature curve. Small-sized 3PB tests are conducted to examine the size effects on the flexural response. The experimental nonlinear load-deflection responses obtained in the various load arrangements are satisfactorily simulated through the developed algorithm. The simulations and experiments reveal that the ratio of the experimental flexural strength to that obtained through simulation (flexural overstrength factor) in 4PB is higher than the corresponding values in 3PB and the round panel. The conservative value of 1.14 could be used as the flexural overstrength factor for epoxy resin materials in analysis and design.