Microindentation into an epoxy composition to assess the influence of aging on mechanical properties

This work aims to apply the microindentation technique for assessing the influence of two aging factors—long‐term weathering and long‐term laboratory aging—on the time‐dependent mechanical properties of an epoxy composition. The linear theory of viscoelasticity was taken as a background for the problem, and the time‐independent Poisson ratio value was assumed to simplify the assessment. Two nano/microindenters were used (Hysitron Triboscan and Nano XP Indenter) at two different laboratories. Four special time‐dependent loading histories were applied: indentation under a step load, indentation under a constant load rate, indentation with a fixed depth of penetration, and indentation under a constant rate of penetration. The short‐term histories of the viscoelastic compliance of a common epoxy composition, affected by 5‐year weathering or laboratory aging, measured using a microindentation technique were compared to the data derived from standard macro measurements. The findings suggest that a qualitative assessment of the influence of the investigated aging effects on mechanical properties can be handled using short‐term microindentation data, but the data has to be freed of possible attendant factors, especially of the influence of polishing procedures accompanying the microindentation techniques, before comparing it with standard measurement data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012