Process conditions and volumetric composition in composites

The obtainable volumetric composition in composites is linked to the gravimetric composition, and it is influenced by the conditions of the manufacturing process. A model for the volumetric composition is presented, where the volume fractions of fibers, matrix and porosity are calculated as a function of the fiber weight fraction, and where parameters are included for the composite microstructure, and the fiber assembly compaction behavior. Based on experimental data of composites manufactured with different process conditions, together with model predictions, different types of process related effects are analyzed. The applied consolidation pressure is found to have a marked effect on the volumetric composition. A power-law relationship is found to well describe the found relations between the maximum obtainable fiber volume fraction and the consolidation pressure. The degree of fiber/matrix compatibility and the related amount of interface porosity is found to have a negligible effect on the volumetric composition. Only for the extreme case where an interface gap of 250 nm is considered to exist along the entire fiber perimeter, the porosity of the composites is noticeable above zero, but still the fiber and matrix volume fractions are only slightly changed. Air entrapment in the matrix due to non-ideal process conditions is found to have a marked effect on the volumetric composition. For composites with such type of matrix porosity, the porosity content is decreased when the fiber content is increased. Altogether, the model is demonstrated to be a valuable tool for a quantitative analysis of the effect of process conditions. Based on the presented findings and considerations, examples of future work are mentioned for the further improvement of the model.