Effect of non-penetrating impact damages of pre-stressed GRP tubes at low velocities on the burst strength

In this study, failure behavior of pre-stressed Glass Fiber Reinforced Plastic (GRP) tubes subjected to low velocity impact was investigated. Filament wound E-glass/epoxy composite tubes with a winding angle of +/- 55 degrees were used in the experiments. The tubes pre-stressed to 32 bars internal pressure, one of the specified operating pressures according to ANSI/AWWA C950 standards. Both prestressed and non-prestressed GRP tubes were subjected to low velocity impact tests at 5, 10 and 15 J low energy levels. Plots of contact force and internal pressure with respect to time and those of force-displacement were obtained and damages occurred on the specimens were examined by means of reflected and transmitted light photography and light microscope. No marked fiber breakages are observed; however, debonding and some sort of delamination on the layers were observed. The GRP tubes with impact damages were subjected to monotonic burst pressures up to failure based on the ASTM D 1599-99 standards. Burst damages on the tubes were studied and variations of their corresponding burst strengths were spotted. Besides that, diameter changes with internal pressures were determined during the tests. Diameter changes with internal pressures for the impacted and the non-impacted tubes were found to be the same. (C) 2014 Elsevier Ltd. All rights reserved.