Development of Pneumatic Drive Small Disk Bending Fatigue Testing Apparatus and Fatigue Strength Assessment of Epoxy Resin

An applicability of pneumatic drive small disk bending test to fatigue strength assessment of resin materials was examined in this study. The effects of specimen thickness and air pressure on deformation behavior of epoxy resin were investigated using a finite element method to determine specimen geometry and test conditions. Then, the pneumatic drive bending fatigue testing apparatus with small disk-type specimen (8 mm in diameter) was designed. Fatigue test was carried out at a variety of maximum pressures of 0.25-0.73 MPa and frequency of 2 Hz using epoxy resin. The experimental results showed that the stable air pressure was alternately applied to both specimen surfaces. The change in the strain measured at the center of specimen surface using a strain gauge, followed well to the change in pressure. It was found the fatigue life, which was defined as the number of cycles to 10% drop in air pressure, decreased by attaching the strain gauge, because crack was initiated in the vicinity of strain gauge. It was revealed that there was a relatively good correlation between the applied pressure and the fatigue life.