Evaluation of static and fatigue strength of long fiber GRP composite material considering moisture effects

The paper presents results of a partial experimental programme of evaluation of static mechanical and fatigue properties of long glass-fiber reinforced polymer composite material with a multiaxial orientation of glass fibers to be used for a manufacture of the flywheel hub disc, the main component of the storage unit accumulating kinetic energy of a vehicle during braking for further use during acceleration. Though humidity is not supposed to be an issue in operation of the unit, an experimental programme evaluating the material static strength and durability under combination of static load with vibration component was carried out to complete the overall general material characterisation. Study of an effect of absorbed moisture was a part of the experimental work. Water absorption was a long-term process, without saturation even after several months. Degradation of strength and fatigue properties due to the absorbed distilled water was confirmed for this material. The material sensitivity on vibration component of the load, even with quite low amplitude of 10% of the static load was ascertained. Damage accumulation and continuous stiffness reduction during fatigue tests, which rate was connected with final durability, was an important phenomenon.