ABSTRACT
In Chapter 1, we focused on the analysis of members subjected to axial loads and learned how to determine the stresses and deformations produced by such loads. In this chapter, we will discuss members subjected to torsional loads, namely, moments (couples) about the centroidal axes of such members. These types of moments or couples are generally referred to as torques and the members subjected to torques are generally known as shafts. Shafts are encountered often in practice in such engineering applications where it is necessary to transmit power from one location to another. We encounter such applications, for example, in the propeller shafts of ships and aircraft as well as in the drive shafts of automobiles and power tools and other equipment. As an example of such applications, consider the case of an electric motor driving a power tool as shown in Figure 2.1. The connecting shaft AB serves to transmit the power from the electric motor to the power tool. Thus, shaft AB is subjected to couples (torques Q) about its centroidal x axis that may be represented by curved arrows as shown Figure 2.2a. However, in dealing with three-dimensional drawings, it is more convenient, less ambiguous, and easier to interpret if these torques are represented by doubleheaded vectors along the x axis as shown in Figure 2.2b. In constructing and interpreting these vectors, use is made of the right-hand rule. Thus, for example, in the case of the double-headed vector at A, placing the thumb of the right hand along the vector, the curved four fingers point in the direction of rotation that the torque Q would produce. Therefore, in most instances when dealing with three-dimensional drawings, the vector approach, along with the right-hand rule, is used in this text. There are exceptions, of course, especially in certain two-dimensional drawings, where the use of the curved arrow is advantageous.
