Uniaxial ratchetting of polymer and polymer matrix composites: Time-dependent experimental observations

The uniaxial time-dependent ratchetting of polyester resin and glass fiber reinforced polyester resin matrix composites was observed by the stress-controlled cyclic tension–compression with non-zero tensile mean stress and tension–tension tests at room temperature. After the ratchetting of the polyester resin had been observed by the cyclic tests with different loading conditions including some time-related factors, such as stress rate and peak stress hold, the ratchetting evolutions of the continuous and short glass fiber reinforced resin matrix composites were also investigated by the stress-controlled cyclic tests, respectively. It is concluded that: both the polyester resin and its composites present apparent ratchetting deformation, i.e., the ratchetting strain accumulates progressively in the tensile direction during the cyclic tension–compression with non-zero tensile mean stress and tension–tension tests; the ratchetting depends on the applied stress amplitude, mean stress, stress rate and peak stress hold, and the time-dependent ratchetting is obvious even for the continuous glass fiber reinforced resin matrix composites with high fiber volume fraction (such as 40% and 50%); the time-dependent ratchetting of the polyester resin and its composites mainly stems from the viscosity of the polyester resin, while the addition of glass fiber into the resin matrix improves the resistance of the composites to the ratchetting deformation and lowers the time-dependence of the ratchetting simultaneously.