Creep analysis of a GRP cylinder under hydrostatic test

Abstract

The GRP (Glass Reinforced Polymer) has been widely used in several industrial applications mainly due to its low cost, high availability, and easy manufacturing process. The matrix made by a combination of glass fibers and epoxy offers good engineering properties for the composite material. This study aims to investigate the creep behavior of a glass fiber/epoxy composite cylinder when it was subjected to hydrostatic pressure at room temperature, and when heated at 50ºC. The geometrical viscoelastic deformation was identified by processing signal data positioned on the cylinder surface. Then, electronic data processing was performed to obtain the characteristic of the creep phase phenomenon attributed to this polymeric composite. The cylindrical specimen has been manufactured using a 4-axis CNC (Computer Numeric Control) filament winding machine, which is equipment designed to produce cylindrical components in the composite industry. A creep test was performed by submitting the cylinder to a hydrostatic load for 500 hours, with a controlled injection of fluid up to a 50 bar pressure. Moreover, fiber volume fraction and composite density were determined to control de manufacturing parameters. The results showed that the glass transition temperature of the composite was 120°C. This also indicated a high level of reliability in the manufacturing parameters of the composite specimen. In the experiment carried out at 50ºC, the polymer matrix showed a loss of stiffness, which contributed to increased strain levels in the composite material. The structure did not show a significant creep effect after 500 hours, ensuring good dimensional and structural stability from the cylinder. Once the creep test finished, the cylinder was submitted to increase the pressure level to rupture. The microstructure was also evaluated using scanning electron microscopy (SEM). The SEM analyses presented a good agreement with the filament winding manufacturing parameters and showed the excellent quality of impregnation between glass fiber and epoxy resin applied on the cylinder specimen. The images presented evidence of an excellent adhesion of the fiber into the matrix, contributing to a good performance of the composite.