Page 29 - Mechanical Behavior of Materials

28 Chapter 1 Introduction

Figure 1.10 Main mast region of a helicopter, showing inboard ends of blades, their
attachment, and the linkages and mechanism that control the pitch angles of the rotating
blades. The cylinder above the rotors is not ordinarily present, but is part of instrumentation
used to monitor strains in the rotor blades for experimental purposes. (Photo courtesy of
Bell Helicopter Textron, Inc., Ft. Worth, TX.)

could occur where a gear is fastened on a shaft by shrink fitting or press fitting. Similarly, corrosion
fatigue is the combination of cyclic loading and corrosion. It is often a problem in cyclically loaded
components of steel that must operate in seawater, such as the structural members of offshore oil
well platforms.
Material properties may degrade with time due to various environmental effects. For example,
the ultraviolet content of sunlight causes some plastics to become brittle, and wood decreases in
strength with time, especially if exposed to moisture. As a further example, steels become brittle if
exposed to neutron radiation over long periods of time, and this affects the retirement life of nuclear
reactors.

1.3 DESIGN AND MATERIALS SELECTION

Design is the process of choosing the geometric shape, materials, manufacturing method, and other
details needed to completely describe a machine, vehicle, structure, or other engineered item. This