Characterization of nanoscale property Variations in polymer composite systems: 2. Numerical modeling

In Part 1 (the companion paper) a technique utilizing the indenting capabilities of the atomic force microscope (AFM) was used to evaluate the local changes in material response of polymer composite systems near the fiber-matrix interface. Responses for two model composite systems at both room temperature and elevated temperatures were studied. In this paper (Part 2), we compare the AFM indentation results with finite element model predictions to gain a fundamental understanding of the influence that the interphase properties have on the measured responses. Good agreement between the finite element model predictions and the AFM measured results was found for all cases studied. The finite element results confirmed that the interphase region for an unsized graphite fiber is too small (relative to the physical size of the indentation probe) to conduct realistic characterization. It was shown, however, that the sized fiber case has an interphase region sufficiently large to obtain useful measurements. The finite element model was then used to identify the effects of interphase region size on the potential usefulness of the AFM as a viable interphase characterization method. (C) 1998 Published by Elsevier Science B.V. All rights reserved.