Chapter 14 - Engineering case studies

Abstract

This chapter presents case studies on pipes for natural gas distribution, bicycle helmets, and data storage on polycarbonate discs. The three case studies illustrate different areas of product design. The case study on gas pipes involves mechanical properties such as creep, yield and fracture, and the process technology of welding. Unlike the bicycle helmet case study, the mechanical design loads are well known where the type of impact is unpredictable, and the impact tolerance of the brain and skull is variable. Bicycle helmets can be designed for impacts of up to 100 J kinetic energy, their mass can be as low as 200 g, and they are comfortable to wear. Helmets designed for much higher impact energy levels would be unacceptably large, so it is impossible to protect riders from the most extreme impacts. Compromises are necessary when designing to protect people who have variable—and unknown—tolerances to impact acceleration, from crashes with variable circumstances. The last case study on digital data storage illustrates the optical properties of the glassy polymers and the injection-molding technology required to make compact discs. The compact disc surface detail requirements and optical birefringence limits could only be satisfied by development of the polymer and the process technology. The discs are mass-produced at a low cost using the established technology of injection molding. Significant advances are required in process cleanliness and excluding bubbles from the molding.