Usability of dielectric properties for evaluation and research of deconsolidation of endless fiber-reinforced thermoplastics

Abstract

Abstract Understanding the deconsolidation behavior of endless fiber-reinforced thermoplastics is essential for reliable predictions of parts behavior and advancements in the corresponding processing technologies. Deconsolidation is usually described by an increasing void ratio of the part volume arising due to fiber relaxation effects, which can strongly affect the mechanical performance. Most methods for measuring the degree of deconsolidation are destructive and require long testing or preparation times. As the dielectric permittivity of a material is usually proportional to its porosity, often reported in foam-related research, dielectric measurements are evaluated as a nondestructive alternative to identify the degree of deconsolidation of endless fiber-reinforced thermoplastics. Polypropylene and glass-woven–based organo-sheets are deconsolidated and density measurements are compared with dielectric measurements for their effect strength and measurement deviations. A relative permittivity in the range of 5–20 MHz was found to allow for a proper differentiation of different degrees of deconsolidation with a ratio of measurement deviation to sample deviation of 26.31% for a single-layer composite (42.96% for a four-layer composite). Additional research is required to identify all relevant influences and to further qualify the method for the research of the deconsolidation behavior or quality control.