Experimental investigation of anisotropic viscoelastic properties of glass fiber-reinforced polymeric composite material

The article presents an experimental investigation of anisotropic viscoelastic properties of a glass fiber-reinforced polymeric composite material. The experimental rig consisting of mechanical and heating parts was prepared for running the tests at room and elevated temperatures. Composite specimens, cut in three different directions, enabled evaluating three independent viscoelastic technical parameters. The stress–strain curves obtained at room temperature allowed to derive the elastic–plastic properties of the composite. It was found that the viscoelastic properties were not observed for room temperature, while an increase of the temperature up to 100°C shortens the relaxation time for less than 1 h. The creep curves, determined for the elevated temperature and different values of loads, demonstrate a good consistency for each type of specimens. In addition, strains are directly proportional to stresses for every time moment, which shows an evidence of linear viscoelastic properties of the composite material. A comparison of the creep curves proved an anisotropy of composite’s viscoelastic properties. Approximation of them by exponential Prony series makes the evaluated data applicable to the existing viscoelastic material models.