Boundary Control of Embedded Heaters for Uniform Bondline Temperatures During Composite Joining

This paper investigates an out-of-autoclave (OoA), embedded-resistive heating method to precisely control the bondline temperature when curing high strength adhesives for joining composite adherends. A challenge with OoA methods is that nonuniform heat loss, e.g., due to substructures that act as local heat sinks, can lead to nonuniform temperatures in the bondline, which in turn, can result in uneven curing, residual stresses, and potentially weak joints. The main contribution of this work is to apply a voltage pattern at the boundary of the embedded heater to control the distribution of the electrical power at the interior bondline, and thereby reduce temperature variations. Additionally, this work devises an empirical model (that can be applied when material parameters and models are not readily available) to predict the desired power generation, and to design the embedded heater and voltage pattern that minimizes the bondline temperature variation. The technique is demonstrated experimentally for bonding a single-lap joint, and the maximum temperature variation in the bond area was reduced by five times from 31.6 °C to 6.0 °C.