TABLE OF CONTENTS The explosion of the space shuttle Challenger (Figure 2.1a) on January 28. 1986, was attributed to a combustible gas leak in the O-ring joint near the bottom of the right solid rocket booster. The solid rocket boosters shown on the shuttle Atlantis, like the Challenger, are assembled using the O-ring joints illustrated in Figure 2.1c. Due to deformation, the gap in the joint was significantly in excess of the allowable design value, causing the combustible gas to escape. Strain is a measure of the intensity of deformation, which is an important variable in the development of formulas used in the design against deformation failures.
The change in the shape of a structure can be described by the displacements of points on the structure. The relationship of strain to displacement is a problem in geometry (kinematics). As depicted in Figure 2.2, this problem represents a link in the logical chain of relating displacements to external forces, which is discussed in greater detail in Section 3.2. Drawing an approximate deformed body shape is the primary analysis tool used to obtain relationships between displacements and strains. The drawing of an approximate deformed shape is analogous to drawing a free-body diagram to obtain forces. Drawing an approximate deformed shape is also important for the development of an intuitive understanding of displacements and strains.
