A test fixture for fully reversed axial fatigue characterization of composites

Fatigue of fiber-reinforced polymer matrix composites has been studied exhaustedly over the years. However, most fully reversed fatigue testing has concentrated on flexural fatigue. The resulting stress state through the laminate thickness is non-uniform and as such may give rise to unconservative life estimates. Fully reversed (R=-1) axial testing has not been heavily reported due to the difficulties associated with precluding local or global buckling of the axial specimen. The few reported fully reversed axial tests utilize either cylindrical specimens or fixturing that is very large, expensive to fabricate, and difficult to handle. Herein we report on a simple side support fixture that allows the use of standard ASTM tensile test specimens (D3039 or D638, depending on test material), which are readily prepared. The fixture allows fully reversed axial fatigue testing as well as static baseline compression and residual compression strength characterization. Also presented herein are tension-tension (R=0.1) and fully reversed tension-compression (R=-1) S-N diagrams for an E-glass/epoxy composite.