Process Control for Polymeric Composite Manufacture

Polymeric composite materials (PCM), originally developed for aerospace applications, have since been adapted and used for a wide variety of civil and military applications due to their desirable properties including low weight, high specific strength, fracture toughness, morphological and thermomechanical stability, and in many cases, resistance to corrosion. In the last two decades the usage of advanced PCM interested also other fields, such as automotive, sporting goods, and electrical, to name but a few, which are more oriented toward cost effective productions, beside product performance. Fundamentally, an advanced composite used for such applications consists of any of a variety of high strength and stiffness fibers (e.g., graphite, aramid, or glass) embedded in a matrix material (e.g., organic resin matrices include polyester, epoxy, polyimide, and cyanate esters). Composite plies are laid up in predetermined directions, impregnated (if not pre-impregnated) and cured, through the application of heat and pressure, according to a predefined cure cycle usually determined by trial-and-error or process modeling. The mechanical behavior of the end product (and the ultimate performance of the associated component for which it is used) is determined not only by the lay-up of the composite but also by the parameters and stability of the manufacturing process. Ultimately, the process parameters (i.e.pressure/temperature profiles as a function of time) are chosen to yield the performance and behavior characteristics necessary for the intended applications. The manufacturing process for composites can often be controlled by means of just a reduced number of parameters, such as temperature and pressure. However, changes in the temperature, pressure, and rates of change in temperature and pressure influence numerous cure behavior attributes such as chemical kinetics and cross-linking, exothermic formation, void formation, moisture diffusion, consolidation, resin flow, gelation, and degree of volatization. In essence, the manufacturing process for composite is based on acomplex series of chemical and physical processes that interact together to form the final product.