Effect of Thermo-oxidation on the local mechanical behaviour of epoxy polymer materials for high temperature applications

• Coupled experimental/numerical approach for the characterization of the effects of thermo-oxidation on the local mechanical behaviour of aged polymer materials.
• Experimental approach based on ultra-micro indentation (UMI) and interferometric microscopy (IM) tests.
• Numerical approach based on an ageing dependent nonlinear viscoelastic/softening constitutive law developed within the framework of the Thermodynamics of Irreversible Processes (TIP) with Internal Variables (TIV).
• The elastic parameters of the constitutive law have the tendency to increase monotonically and linearly with ageing
• The material exhibits less softening behavior with ageing, and, with respect to the virgin state, ageing tends to enhance the short-term viscoelastic response of the material.

This paper presents an original coupled experimental/numerical approach for the characterization of the effects of thermo-oxidation on the local mechanical behaviour of aged polymer materials. The experimental approach is based on ultra-micro indentation (UMI) and interferometric microscopy (IM) tests. The UMI load vs. displacement curve is exploited to gain some information about the material behaviour at the short-range timescales, the IM measurement of the three-dimensional indentation print and of its evolution with time allows characterizing the material behaviour at the long-range timescales. The numerical approach is based on an ageing dependent nonlinear viscoelastic/softening constitutive law developed within the framework of the Thermodynamics of Irreversible Processes (TIP) with Internal Variables (TIV). The constitutive law is integrated within a 3D ABAQUS® finite element model of the test setup and the parameters of the law are identified for different ageing conditions.