The effect of meso-structure and surface topography on the indentation variability of viscoelastic composite materials

Most viscoelastic composites such as biomaterial, polymeric materials and silicone rubber consist of the viscoelastic matrix and the elastic inhomogeneities. Mechanical characterization of the viscoelastic composites helps us to better understand their responses under mechanical stimulation, or improve the design and manufacturing of composite products. The indentation test is the main method for measuring the mechanical properties of viscoelastic composites at present. However, the response of indentation test is sensitive to the microstructural of composites. What's more, the surface topography also has great influence on the indentation response that cannot be ignored. In this paper, a semi-analytical method is used to model the indentation test in order to explain and improve the indentation test results. The correlation between matrix and inhomogeneity is built by the equivalent inclusion method. The conjugate gradient method and the fast Fourier transform are used to accelerate the solution of unknown variables. Based on the developed model, the effect of micro structure and surface topography on the indentation creep is investigated. The conclusions obtained from the indentation simulation agree well with the experimental results in literatures and provide solid theoretical explanation for the scatter in experimental results.