ANALYSIS AND CHARACTERIZATION OF PREPREG TACK

As part of an engineering analysis and experimental methodology to characterize prepreg tack, a compression-to-tension test was optimized to enhance reproducibility and generate intrinsic property data. With the resulting stress-strain compression and tension data, a theoretical model was developed to describe tack as a bulk viscoelastic property of a prepreg laminate stack. Using the viscoelastic analysis, four intrinsic material parameters to characterize prepreg tack could be defined. These were 1) relaxed modulus, 2) unrelaxed modulus, 3) relaxation time, and 4) initial void content of the prepreg stack. Relaxed and unrelaxed moduli of the prepreg stack were independent of temperature, while the relaxation time was highly dependent on temperature and matrix viscosity. In addition, the relaxation time was found to be influenced by resin/fiber content and prepreg surface characteristics, which also influenced the void content of the prepreg stack. Using these measured parameters, good agreement was observed between theory and experimental data for both the stress-strain curve of the tack test and the simplified compression tack index (CTI*), defined as the ratio of output energy of the prepreg stack during tensile unloading to input energy during compressive loading.