One material option for the offshore drilling is graphite/epoxy composite. The materials that are used in this industry are exposed to extreme conditions, which can increase the property degradation rate and in turn reduce its life span. So far, graphite/epoxy composites have proven to be quite durable, and can survive degradation in many conditions. Considering these factors, tests will be performed to determine the durability of graphite/epoxy composites under cyclic loading. This study investigates the fatigue behavior of filament wound graphite/epoxy tubes under cyclic loading. The experimental method used for this study is based on two criteria:
One million-cycle specification set by the manufacturer on the tubes being tested.
Point of failure based on the one million-cycle specification. Fatigue tests conducted on seven tubes at the following temperatures: 75° F, 125° F, 150° F, and 175° F. The test results showed that failure occurred in the weakest ply, which is the 90-degree ply in the (03/±25/903) Laminate. Therefore, it is natural that cracks in tensile fatigue also appeared first in the plies with the fiber direction normal to loading. The tensile test recorded a maximum load capacity of 56,347 lbs. with maximum stress of 66,492 psi. The data collected gave a smooth fatigue curve as expected with one exception. The sample loaded in the load range 7,500 to 42,500 lbs. recorded twice the amount of cycles as the sample with a load range between 10,000 to 40,000 lbs.
Composite materials have been of keen interest for the past few decades as a structural material. The offshore drilling industry has been particularly interested in composites, partly, due to their low weight and high strength.
