Static and fatigue failure of aerospace grade epoxy resins

Polymer composites are becoming increasingly prevalent in structural engineering and especially aircrafts manufacture. Highly-crosslinked epoxy resins are used as matrix because of their good properties for reduced weight. However the use of such materials leads to complicated fracture mechanisms which are not fully understood. In this work the fracture behavior of the HexFlow RTM6 epoxy resin is studied. A mechanical testing campaign is performed on dog-bone cylindrical samples and on CT specimens under both static and cycling loadings. This campaign is associated with finite elements analyses to confirm the results and predict the stress state at the crack tip. A fracture toughness of 0.9 MPa √m is found and a stiffness degradation is observed when the material undergoes cycling loading at a sufficient level. An endurance limit of 38 MPa is also found for unnotched specimens and the crack propagation rate curve is obtained. This curve has a threshold of amplitude of stress intensity factor of 0.28 MPa √m, where the crack start to slowly propagate and a critical amplitude of stress intensity factor of 0.4MPa √m where final failure occurs. A stable growth is observed between those two behaviors, where a Paris coefficient of 12.3 is found.