Doctoral Dissertations
Date of Award
8-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Civil Engineering
Major Professor
Dayakar Penumadu
Committee Members
Dayakar Penumadu, David Harper, Uday Vaidya, Timothy Truster
Abstract
Three commercially available glass fiber sizings for a given sheet molding compound (SMC) formulation using vinyl-ester and unsaturated polyester resin were compared mechanically and thermodynamically through multiple length-scales on the premise that the chemical sizing packages are different and the fiber it’s coated on is the same. Goals of this work include assessing the process-property relationship of SMC and the structural performance related to differences in processing resulting from the different chemical sizing treatments on fiber reinforcement throughout compounding and molding. Spiral flow compression molding indicated no noticeable differences in flow length resulting from sizing. One of the sizing treatments did show signs of incompatibility with the SMC formulation as 1/3rd of the panels contained blister defects. Quantitative comparison of charge wetting and sheet density resulting from sizing treatment indicated blister defects to be the result of entrapped gas during compression molding. A range of mechanical characterizations were performed including single fiber tension, in-situ single fiber interfacial shear strength (IFSS) of the fiber-matrix interface via push-out, and complete quasi-static characterization of macro-mechanical bulk composite panels. Analysis of variance indicated significant differences at the micromechanical fiber-matrix interface, but no significant differences in strength or modulus of composite properties. Post-hoc testing indicated that sources of variances stemming from localized fiber volume and orientation in molded panels of each glass fiber type were much greater than variance induced by the 17 % – 20 % difference in IFSS between sizings. Surface free energy of sized multi-end rovings measured via inverse gas chromatography correlated with IFSS and the presence of blisters suggesting adhesion being important to processing and properties. Meso-scale tow tension tests were performed on unidirectional multi-end rovings infused with resin containing varied amounts of calcium carbonate to determine how thermodynamic adhesion changes for each sizing when varying the SMC formulation. Tensile strength and modulus of the tow samples prepared from each sizing showed difference and the improvement of properties with addition of calcium carbonate was observed and correlated with surface energy. Continuum mechanics and process model material cards were generalized and validated using Moldex3D and micromechanics modeling to describe this material system.
Recommended Citation
Henken, William J., "MULTI-SCALE CHARACTERIZATION OF GLASS SURFACE MODIFICATION IN STRUCTURAL SHEET MOLDING COMPOUNDS. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/12654