Graduate Thesis Or Dissertation
 

Carbon fiber as a resistive heat generator to accelerate adhesive cure in reinforced wood laminates

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  • As a result of its atomic structure, carbon fiber produced from mesophase pitch has a high electrical conductivity and high tensile strength. Others have used carbon fiber as a resistive heating unit to accelerate matrix solidification in carbon fiber-polymer matrix composites. In this study, a unidirectional carbon fiber reinforced polymer (CFRP) strip, which is usually used as a reinforcement material, was used to generate heat by the application of direct current (DC) power. A CFRP strip measuring 955 x 50 x 1 mm was successfully used to form a reinforced wood laminate using the CFRP resistive heating method. The CFRP strip was a pitch-based unidirectional composite of carbon fibers (9- [micro] m diameter) in a 60 percent carbon fiber volume fraction. The polymer matrix was an epoxy. Due to the carbon fiber alignment and its molecular structure, the thermal-electrical properties of the CFRP strips were orthotropic. To connect the electrical circuit to the CFRP strip, the ends of strip were first electroplated with copper. It was found that a tapered end-geometry and low plating power density combined with a long period for electroplating resulted in an advantageously porous copper deposit. The CFRP strip was subsequently connected to the electrical circuit with solder. It was found that the circuit could produce approximately 34 percent energy conversion efficiency. Measurements showed that the CFRP strip heated quite uniformly over its length. The bonding compatibility of CFRP to wood was explored with phenol resorcinol formaldehyde (PRF) and phenol formaldehyde (PF) adhesives. For this purpose, the effects of temperature on isothermal strength development rates were explored using an Automated Bonding Evaluation System (ABES). These studies were conducted to anticipate the strength development with time of resistively heated bonds. The responsiveness of adhesive-adherend combinations in relation to temperature has been tested under a range of time and temperature conditions in miniature adhesive test bonds. The bonding strength of CFRP-to-wood after three minutes pressing at 100°C using PRF adhesive were around 3 MPa. At this bonding strength, some of the carbon fiber was pulled out from the CFRP strip. Additional bond strength up to 150 percent (up to 4.5 MPa.) was gained when the glueline has cooled to room temperature. However, PF adhesive had weaker bonding strength and very little strength development at the same temperature. PF adhesive was therefore considered not to be viable at this stage. A numerical prediction technique has been established that could give information on how much energy and pressing time are needed to reach optimum bond strength to make a reinforced glulam using resistive heating. The CFRP is concluded to have potential for wood laminate products, since it can be used to accelerate the adhesive cure and act as a reinforcement.
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