Molding of Structural Composites. Theorical Aspects

Polymer matrix composites don't exist in their natural state, so they have to be manufactured. Behind this simple statement lies a complex reality with far-reaching consequences for these materials. Indeed, thanks to the wide variety of resins, reinforcements and additives used, and the great freedom of shape and size offered, these materials prove to be extremely versatile, since they can be shaped by adjusting their properties to the specific requirements of an application. This flexibility does, however, have a downside. More than any other material, composites require a close integration of knowledge of the constituent materials, the manufacturing processes and the performance of the resulting parts. Although the properties of composites are mainly determined by those of their constituents, experience has shown that the way they are manufactured has a significant influence on their performance, in at least two ways:

• by the generation of molding imperfections, more commonly referred to as defects, which impair part performance (porosities, fiber misalignment, resin underpolymerization, internal stresses, etc.);

• by modifying the parameters defined during the design phase of the composite part (fiber orientation and distribution).

Manufacturing technology is therefore an essential link in the design-manufacturing chain for composite parts. It plays a major role in the growth of composites, due to the costs it generates, its ability to transform technical parts of varying sizes, its flexibility of use, the production rates it allows and its reproducibility. The choice of a manufacturing process is also guided by its environmental impact and its suitability for technical requirements.

A key factor in the development of technologies, and therefore composites, is the ability to develop processes that meet the requirements of the target market. Over the past three decades, numerous technologies have been developed to meet the needs of high-volume, high-performance markets. Although empiricism has often accompanied the first steps of these technologies, the most important advances have come from efforts to understand and model the physical phenomena associated with these processes. More or less sophisticated models have been developed on the basis of knowledge that is still partial, but nevertheless sufficient to help engineers and technicians implement robust technologies. They enable us to understand how process parameters and component characteristics affect the final properties of composite parts. Historically, design and calculation departments were the first to make use of industry-specific software to compare manufacturing strategies and material choices, and thus support...