Patch Repair Analysis of Impact Damaged Glass Fiber / Epoxy Composite Tubes Operating Under Internal Pressure

Application of composite patches is a useful technique to repair damaged structures such as wind turbines, air vehicles, pressure tanks because of lightweight, flexible design, and low price, and have found a widespread application area in many more industries. To avoid excessive weight of the repaired region as well as unnecessary material consumption composite patches need to be optimized according to shape, size and material specifications. This paper introduces a numerical assessment of size and material effect in composite-to-composite patches having specific shape and material properties. Adhesively bonded round-tipped composite patch pieces are utilized to repair a quadrilateral puncture damaged cylindrical thin-walled hollow composite tubes loaded by internal pressure. Glass fiber / epoxy patches with five different kinds of stacking sequence and ten different sizes are numerically investigated to achieve the best composite patch solutions. Although the safety factor of repaired tubes enhances by increasing tip radiuses and hence their sticking area, it is found to be not sufficient to ensure that the patching process is completely safe because of the fiber orientation playing an important role on the factor of safety. The patches having [0˚]4, [0˚, -45˚,45˚,90˚], and [0 ˚,90 ˚]2 stacking sequences and having adequate patch areas are found to be able to provide the safety value of “1.15” which is defined for normal safety class and below 5% coefficients of variation (COV) value in DNV’s Offshore Standard (DNV-OS-C501).