A local theory of heating in cross‐ply carbon fiber thermoplastic composites by magnetic induction

Abstract

For joining and repair of continuous fiber thermoplastic composites, induction heating has been viewed a strong candidate. Induction heating employs an applied alternating magnetic field, which induces a rotational emf in a grid of conductive carbon fibers, which are then used to carry resulting currents. In continuous carbon fiber crossply composites the available paths for “eddy current” loops are along the network of conductive carbon fibers. For this to occur, an electrical transfer must take place between crossing fibers in adjacent plies. Tests involving variable thicknesses of interply neat film layers have been performed to provide insight into the mechanisms taking place. These tests indicate that the primary mechanism for heating in such laminates is dielectric losses in the polymeric region between fibers in adjacent planes that form the conductive loop. Therefore, heating is not uniform in such composites despite a uniform magnetic flux. Heating patterns were viewed using liquid crystal materials and E‐type thermocouples. Several factors leading to nonhomogeneous thermal distributions have been considered, including current density effects, internal emf cancellation, and rotational field effects. Global and local considerations are addressed, a localized model is proposed, and the corresponding theory is developed qualifying the early results. Additional testing has supported the theory.

A study on the induction heating of carbon fiber reinforced thermoplastic composites

“…For small time scales, the measured rate of temperature change is a good approximation of the heating intensity of each element shown in equation (8). The heat loss due to heat dissipation into air and the laminate is assumed to be negligible in short time scale in the experiment of present study.…”

“…Fink et al [8,9] proposed that the dominant heating mechanism is dielectric polymer heating at the regions (junctions) where bers of adjacent plies overlap. The contention was that the bers of adjacent plies are not in complete contact, but separated by a small polymer gap.…”

Modeling and experimental investigation of induction welding of thermoplastic composites and comparison with other welding processes

“…8 The first numerical works about induction heating of composites were dedicated to the identification of the dominant heating mechanisms. Many authors claimed that Joule heating within the carbon fibers is mainly responsible for the temperature increase, [9][10][11][12][13][14][15][16][17][18][19] while others [20][21][22][23] believed that heating occurs at the fiber junctions. This last heating mechanism relies on dielectric heating or Joule losses caused by contact resistance at fiber junctions.…”

Experimental and numerical approach to identify major heating mechanism in induction thermography of carbon fiber reinforced plastic components

“…According to them, the dominant heating mechanism was joule losses in the carbon fibres when the current pass through the conductive loops. Later, Fink et al proposed a new theory of dielectric losses in the polymer at the junctions of fiber layers [4]. They developed various models based on this mechanism [5], [6].…”