Fatigue damage in composite cylinders

In this study, optimal angle-ply orientations of symmetric shells designed for fatigue burst pressure were investigated. Burst pressure of filament wound composite pressure vessels under alternating pure internal pressure has been investigated. The cylindrical section of composite pressure vessels is conducted. Experimental approaches are studied to verify optimum winding angles. Glass reinforced plastic (GRP) pipes are made of E-glass/epoxy applied internal fatigue pressure test close ended condition. For this study, a PLC controlled hydraulic pressure testing machine has been established. Study deals with the influences of winding angle on filament wound composite pressure vessels. The layers were oriented symmetrically [± 75°]2 , [ ]2 ± 60° , [ ]2 ± 55° , [ ]2 ± 45° and [ ]2 ± 88° orientations. Specimen?s static burst pressure values were known from before studies. Fatigue test applied %70, %60 and %50 stress levels of burst pressure. Damage propagation on these stress levels are observed as whitening, leakage and final failure and these cycle?s noted. When [ ]2 ± 75° angle-ply orientations composite?s damage propagation observed, these are determined: whitening and leakage do not occurred and final failure occurred suddenly. Stress and final failure cycle values which are known %70, %60 and %50 stress levels of burst pressure on fatigue pressure test utilized to obtain S-N (stresscycle) curves. A relation between %70, %60 and %50 stress levels? final failure cycles and chancing winding angles investigated and final failure versus winding angle diagrams obtained. The optimum winding angle for the composite pressure vessel analysis with the internal fatigue pressure loading case was obtained as [45 °]. Key words: Composite pressure vessels, fatigue life, internal pressure, damage propagation.