A methodology to reduce thermal gradients due to the exothermic reactions in composites processing Vincenza Antonucci a , Michele Giordano b , Kuang-Ting Hsiao c , Suresh G. Advani c, * a Department of Materials and Production Engineering, University of Naples, Federico II, Italy b Institute for Composite Materials Technology CNR, P. le Tecchio 80, 80125 Napoli, Italy c Department of Mechanical Engineering, Center for Composite Materials, University of Delaware, Newark DE 19716, USA Received 18 February 2001; received in revised form 15 August 2001 Abstract In resin transfer molding (RTM) process, a polymer composite part is fabricated by injecting a thermoset resin into a fiber preform placed in a closed mold cavity. After the infiltration of the resin into the empty spaces in the mold, the manufacturing process is characterized by a curing reaction, which is an exothermic resin polymerization phenomenon that cross-links the resin and results in a solid structure. In most cases, the resin cure is initiated by heating the mold. The heat released during the reaction can cause temperature gradients in the composite, which leads to residual stresses in the part. Residual stresses are undesirable as they can cause shrinkage and warpage. By controlling the temperature of the mold walls, one can control the cure reaction and reduce the thermal gradients through the composite part. In this paper, we present a methodology based on scaling analysis of the energy balance equation to manage the heat generated by the cure reaction that minimizes the temperature gradients before the resin solidifies. The method ca- pability is demonstrated with a highly reactive polyester resin infiltrated into different types of glass fiber preforms in a rectangular mold. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Cure; Control; RTM; Thermal gradients; Heat transfer in a mold 1. Introduction Resin transfer molding (RTM) is one of the most efficient and attractive processes for high performance composite materials with low cost manufacturing. During the process, a thermoset resin is injected into a mold cavity containing a pre-placed fiber preform or a stack of fiber mats of reinforcing material in the shape of the desired part. The resin impregnates the mold cavity to occupy the empty spaces between the fibers. The mold is usually heated to initiate a curing reaction, which is an exothermic resin polymerization phenome- non that cross-links the resin and results in a composite structure. For a composite part to meets the quality control requirements and have the desired properties and di- mensions, several manufacturing hurdles need to be overcome during the mold filling stage and the curing stage. First, during the mold filling stage, the resin should occupy all available space between the fibers. Any space uncovered by the resin is known as voids or dry spots and will be detrimental to the mechanical properties of the composite [1]. In the last decade, modeling and simulation tools for the mold filling stage have helped significantly to design the complete filling of the mold by optimizing the injection location for the resin and manipulating the flow rates or the pressure of the resin [1–11]. The curing stage requires invoking the initiation of the cure reaction and then managing the heat evolved from the part to avoid large thermal gradients and consequently residual stresses that could lead to shrinkage and warpage and lack of dimensional tolerance. Models for resin cure * Corresponding author. Tel.: +1-302-831-8975; fax: +1-302- 831-3619. E-mail address: advani@me.udel.edu (S.G. Advani). International Journal of Heat and Mass Transfer 45 (2002) 1675–1684 www.elsevier.com/locate/ijhmt 0017-9310/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0017-9310(01)00266-6