Abstract:

In view of the future application of polymer matrix composites for structural components subjected to impact loads, there is a need for development of experimentally calibrated constitutive models for polymers that include their inherent viscoelastic and viscoplastic behavior. These models could be then incorporated in micromechanical models of composite ply for simulation of composite failure locus as a function of rate of loading.

A preliminary version of the strain rate dependent constitutive model has been developed. In this case, just viscoplasticity has been considered and a power law relation for the compression yield stress with strain rate has been assumed.

Experimental calibration of these models depends on the development of micromechanical test techniques for in-situ characterization of the material that allow high strain rates of testing. A pendulum-based nanoindentation device that is able to perform impact nanoindentation tests is used for this purpose. A methodology is developed for analysis of the data. Several challenges have been encountered during the development of the methodology and solutions are proposed.

Two validations techniques are proposed to assess the technique and analysis methodology. Results suggest that the presented methodology is valid. Then, the technique and analysis method is applied to several rate dependent materials. Although a logical trend was obtained for two of the tested materials, where the material behaves harder for higher rates, the other two show a strong size effect in the impact results. This remains an issue to be analyzed in further research.