The potential for composites in structural automotive applications

Abstract

The primary use of fiber-reinforced composites in automobiles, with the exception of a few specialized low volume vehicles, has been in semi-structural or decorative parts. Use of composites in primary structural areas of the vehicle, such as body structures, has been very limited to date. Such applications offer a tremendous opportunity for future expansion of composites in the automotive industry. In addition to materials cost, there are two over-riding criteria for significant application of FRP materials in automotive structures: (1) proof of structural functionality/durability; and (2) development of rapid, reproducible fabrication procedures to optimize manufacturing economics. From a structural viewpoint, there are two major categories of material response which are critical to the application of composites to automobiles: fatigue (durability) and energy absorption. An abundance of evidence is accumulating relating the functional properties of these materials in simple structures. It is clear that the fundamental requirements of energy absorption and fatigue resistance are satisfied by composites and the main challenge is to translate these capabilities into complex structures with less well-defined load inputs. The less quantifiable, but equally important, functional requirement of ride quality (usually defined in terms of noise, vibration and ride harsness, NVH) also appears to be attainable through the utilization of composites. Even though this factor has been historically related to vehicle stiffness, and composite materials are less stiff than steel, all the indications are that the effective stiffness of composite structures meet NVH requirements—the elimination of joints through part integration plays a critical role in achieving such synergistic effects. Many of the properties of composite structures depend on the control of fiber location and part integration which in turn are a direct fucntion of the fabrication process. Current high production rate fabrication processes such as compression molding of sheet molding compound (SMC) type materials go only part way to optimizing the properties and economics. Optimum automotive composite structures will probably require a combination of processes, some of which will need significant development, to realize the enormous potential for composites in the automotive industry. Full-scale structures may involve SMC type molding, thermoplastic stamping and the developing preform molding (HSRTM) process which hasm perhaps, the greatest potential of all the processes of revolutionizing the use of composite structures. Technological breakthroughs in fabrication technology do not appear to be necessary, the main requirement is the development of existing assorted techniques combined with a concerted effort by all aspects of the composite and automotive industry.