Combined Experimental and FEA Based Investigation of Near Fiber Effect of UV Exposure in Carbon Fiber Reinforced Composites.

Abstract

Characterization of the interphase region in carbon fiber reinforced polymer (CFRP) is challenging because of the length scale involved and the lack of analytical solutions that account for the fiber constraint effect. An integrated approach involving Atomic Force Microscope (AFM)-based indentation and Finite Element (FE) modeling is use to determine the extent fiber constraint effect on the properties determined in the interphase region. A gradient was observed in the elastic modulus of the interphase evaluated along a radial line from the fiber, based on which the width of interphase is determined to be 250 nm The 3D FE simulations indicate that fiber constraint impacts interphase modulus only within 40 nm of radial distance from the fiber while using AFM tip. Nonetheless, the apparent increase in interphase modulus is significantly less as compared to the overall gradient in the modulus value of the region, as determined by AFM indentation. Hence, these results confirm that the behavior of interphase is distinct compared to the bulk material. Similar results very observed for viscoelastic response of the interphase region. This approach is further utilized to evaluate the impact of Ultra-Violet (UV) irradiation on the modulus value of the interphase region as a function of exposed time and radial distance from the fiber. This study demonstrates that the response of epoxy t