An investigation of bending fatigue behavior for glass-fiber reinforced polyester composite materials

To investigate bending fatigue behaviors for glass-fiber reinforced polyester composite material, 800 g/m2, 500 g/m2, 300 g/m2, and 200 g/m2 glass-fiber woven and 225 g/m2, 450 g/m2, and 600 g/m2 randomly distributed glass-fiber mat samples with polyester resin have been used. The samples have been produced by the RTM (Resin Transfer Molding) method and the samples have been cut down with directions of 0/90°, ±45°. As results of the combinations from the samples, nine different structures has been obtained. Furthermore, a new mold have been designed for the RTM method. To provide a full infiltration (wetting) of fibers, a simple method has been applied in this new mold system. A new computer aided and multiple-specimen test apparatus have been designed and constructed to simulate load and stress behavior of axial fan blades on the wind tribunes. This multiple specimen apparatus has a big advantage to shorten test time and to test 16 specimens at the same time. Firstly, composite specimens have been applied to the three-point bending test. Later, fatigue tests have been carried out. For the bending fatigue test, “fixed stress” fatigue type has been used. To determine the fatigue limit of all the specimens, S–N diagrams (Wöhler plots) have been derived from experimental results.According to the test results, the highest fatigue life has been obtained from 800 g/m2 fiber glass woven specimens with 0/90° (group E). The property of anisotropy of the GFRP (Glass Fiber Reinforced Plastic) material is dominant on the fatigue strength which has been clearly observed from the experiments. In the test results, the effective parameters are density of fiber distribution on the area, fiber angle, resin permeability of woven fiber, full infiltration (wetting) or without infiltration of fibers.