Mechanical response of isotropic graphite due to oxidation induced degradation

Durable thermal protection materials for hypersonic environments remain an important research path for atmospheric propulsion systems such as scramjets. Carbon materials are promising candidates; however, these materials have degradative interactions in oxidizing environments. This work investigates the relationship between oxidation and the material properties as exposure times are varied in a reactive environment to inform predictive models. Graphite specimens were prepared in a flow tube furnace to measure mass loss due to oxidation, change in material strength in tension and three-point bending configurations, and measurements of elastic constants using ultrasonic evaluation. Significant reductions in strength, Young’s modulus, and shear modulus occurred due to oxidation, with an increase in Poisson’s ratio being found. Numerical experiments using a cohesive zone model informed by the physical results are also explored for potential use in scramjet combustion simulations.