| While Fiber Reinforced Composite material is gaining a reputation as a future bridge and civil structure material due to its special advantages, its long-term fatigue property is still an important issue which needs to be known. When designing with composites, life prediction and durability must be understood. Practical and accurate models demonstrating the lifetime of these materials would enable engineers to predict the damage, the residual life and the final stiffness of the structure at failure. This study focuses on experimental characterization of flexure performance under static and fatigue testing of pultruded GFRP beams with unidirectional glass fibers. As a measurable mechanical property of material, effective stiffness is used as an indicator of the deterioration of materials during fatigue. Flexural fatigue tests were performed on beams at different frequencies and load levels. I constructed the fatigue test database, and found the relationship between stiffness degradation and residual life. Material stiffness degradation property is characterized. Composite coupons and box-beams are tested for quasi-static strength, stiffness and fatigue properties, and their fatigue properties are also compared with their original properties. Curves of stiffness versus the fatigue cycles are determined experimentally. Specifically an effort to predict the flexure damage and residual life of composite material is made by monitoring the material stiffness. These tests evaluate how stress level and frequency have effects on the damage accumulation, and affect the composite life; stiffness degradation and damage modes were characterized. Models to predict the stiffness and lifetime are constructed. Life predictions were found to correlate well with simple or complex cyclic loading tests. |
