There is no doubt about the increased popularity of composite materials in almost all the most important industrial fields, especially those with the highest innovation rate. The ever increasing demand of lightness, efficiency, reduced energy consumption together with performances and heavier service conditions lead material scientists toward the definition of new materials characterized by a favourable ratio between mechanical properties and weight and engineers toward design solutions able to get advantage from these new materials. Polymer matrix composites are among the materials successfully used with this aim both in high-tech applications and in more conventional fields. For instance, expensive carbon fibre composites are widely used in aerospace, race cars, and bicycle frames, where performances are a key design factor, while cheaper glass fibre composites (obtain by pultrusion or some other technological process) are used in pipelines, civil structures and in many other fields where great quantities of material are needed and used and where the unit cost is a primary factor in any design decision. Besides, polymer matrix composites do not need painting, are not corrosion susceptible, and do not need to be electrically insulated.
All this means that metal alloys are going to become less used and less popular than in the past,  and that surface treatments usually done to enhance the strength of metal alloy could be less used.
The data are clear; about 25% of the Airbus A380 is built with composite materials, and in the A350, XWB composites are used more than metals.
In the automotive industry, even if the trend is still not so clear, composites are gaining positions and their wider utilization is expected in the next generation cars, since they would allow reduction in fuel consumption and related environmental pollution.
Shot peening is one of the most widely used treatments to improve the behaviour of metals with respect to fatigue, stress corrosion, fretting, contact fatigue,…. and an increased use of composites in the automobile risks negatively affecting this traditional and very important market of shot peening.
But is the development of composites only a threat for shot peening, or could it result in a chance for opening new opportunities for its utilization?
Indeed, the development of composite materials could be a threat, but also opens new possible applications for shot peening. In fact the diffusion of composites is forcing the development of new metal alloys with improved properties: aluminium alloys, titanium nuova nota, and high-strength steels are serious competitors of composites for building parts of new cars. And these materials need shot peening to become more high-performance. But even if composites themselves are considered, new application fields for shot peening could be generated: the design of composite components is under evolution and still not matured and may lead to incorporating some form of grit blasting or shot peening into the manufacturing process.
At any rate, perhaps, the most interesting and promising potential new application of shot peening related to the advance of composites in the automotive production system is related to the development of the so-called "hybrid materials"; that is to say, made of metals and composites joined by means of glues, some kind of welding, or other system. These "hybrid" connections could open new and unexplored applications of shot peening, aimed at obtaining different surface states with respect to what is of interest in present applications.
But, whatever the possible new application of shot peening in the construction of new cars is, one thing seems to be clear: the way shot peening is traditionally performed is probably not the best way for these new applications. The different peculiarities of these latter require an in-depth knowledge of the effect of the peening parameters on the induced surface modification and, as a consequence, on the behaviour of the treated parts.
This means that there is a need to deeply investigate the real potential benefit that can be achieved by shot peening. New important and unexpected applications with a high added-value could result from this research effort.

Shot Peening in the Automotive Industry
by Mario Guagliano
Contributing Editor MFN and
Associate Professor of Technical University of Milan
20156 Milan, Italy
E-mail: mario@mfn.li

Author: Mario Guagliano