Material propertiesEffect of thermo-oxidation on the failure properties of an epoxy resin

This experimental work aims at characterizing the effect of thermo-oxidation on the failure properties of a thermoset polymer used as matrix in an aeronautical composite for applications at intermediate temperatures. PR520 resin specimens were aged at 120 °C under different oxidative conditions. Thermo-oxidation leads to the occurrence of a surface layer, in which a gradient of mechanical properties (stiffness, strength, toughness …) can be measured. A multi instrumented 4-point bending test was used to evaluate the decrease of the polymer failure stress as a function of its oxidation state. According to the oxidation conditions, the embrittlement of the resin results either in an abrupt failure of the sample or in multicracking of the oxidized layer, quantified by means of strain measures and acoustic emission technique. A methodology is proposed in order to analyse the experimental data taking into account the gradient of elastic properties and residual stresses present in the oxidized layer of the specimen. In this way, the failure stress of the oxidized material is determined as function of the oxidation conditions: ageing time and oxygen partial pressure.