Dielectric properties of continuous fiber reinforced polymer composites: Modeling, validation, and application

Abstract

Microwave curing technologies can realize a fast and energy saving curing process with less temperature gradients in the composite thickness compared with traditional autoclave curing techniques. A fundamental understanding and quantitative characterization for the dielectric properties of composites are crucial steps to ensure an effective microwave curing process. Herein, this study aims at providing a practical method to predict the effective complex permittivity of continuous fiber reinforced composites. A stochastic method was used to simulate the real distribution of fibers in the resin matrix. The huge scale factor between the micro architecture and macro structure of composites was balanced by using homogenization methods. Then the dielectric properties of composites in both longitudinal and transverse directions were computed by finite element analysis. The effectiveness of the proposed model was validated by various experimental measurements. Statistical analysis showed that the relative error was only 1.48-3.17% between model calculations and experimental results. Based on curing kinetics, the proposed model was further applied to investigate the permittivity of composites during microwave cure. POLYM. COMPOS., 00:000-000, of composites during microwave cure. POLYM. COMPOS., 39:4646-4655, 2018. FIG. 1. A two-phase model of carbon fiber/epoxy composites. (a) Model generated cross-sectional image of the composite brick; (b) Gray-scale image identified by COMSOL Multiphysics; (c) Resolved function of permittivity and position; (d) Electric displacement modulus and potential distribution within a FRP composite brick. [Color figure can be viewed at wileyonlinelibrary.com]

An Easy Method to Determine the Effective Conductivity of Carbon Fiber Composites Using a Wall Perturbation Approach

“…Zhang et al reported a permittivity of approximately for a cured CFRP sample with parallel polarization [ 2 ], which is similar to the findings of Zhou et al, who measured a permittivity of [ 3 ]. In contrast to that, Jaleel Akhtar et al reported values of up to [ 4 ].…”

“…This is particularly valid in the case of a composite with unidirectional fiber reinforcement. While there is a long history of theoretical considerations on the effective electric parameters of fiber materials, there are only few sources which provide some values of the effective electrical parameters of CFRPs [ 1 , 2 , 3 , 4 ]. Those values are not consistent and differ from each other significantly, which is particularly true for cases for which the electric field is parallel to the reinforcing fibers.…”

“…In contrast to that, Jaleel Akhtar et al reported values of up to [ 4 ]. Moreover, while Zhang et al and Zhou et al observed a significant change in effective material properties during cure for both polarizations [ 2 , 3 ], the measurements of Zhou et al in [ 5 ] show nearly identical reflectivity transmittance or absorptivity between cured and uncured samples for the case of orthogonal polarization. This illustrates that effective parameters of CFRPs always need to be evaluated for the specific material.…”

A multi-pattern compensation method to ensure even temperature in composite materials during microwave curing process

“…During the multi-pattern compensation process, although the dielectric properties of the composite may change with the progress of the curing reaction [28], it will only affect the specific value of heating rate at each point according to Eq.4 and 5, but the heating preference/pattern will almost not change since the composite laminate is uniformly heated (compensation will be triggered when temperature difference exceeds 6°C) from the beginning to the end, thus the dielectric properties of each point is uniformly changed. As for the exothermic heat of cure reaction, it will influence the temperature distribution of the composite during microwave curing, but the temperature distribution is monitored in real-time by temperature sensors, and then a normal compensation process will be carried out.…”

Circular braided glass fiber/epoxy composites with helical architecture (coil spring) fabricated by plaster‐sacrificial compression molding for structural automotive applications

“…Long FRPC have been used due to their high mechanical stiffness and productivity, despite a drawback of anisotropic properties in the case of external multi‐axial load 8–10 . Continuous FRCP have been used for parts carrying high load, such as structural frames, despite their low productivity 11–14 . Short FRCP with high productivity can be utilized for parts undergoing intermediate amount of stress, such as impellers, brackets, and canisters 15–18 …”