Basic Equations: Differential Form

The fundamental equations for describing the behavior of a solid can be classified into the three categories:

• The conditions of equilibrium • The material law • The conditions of geometric fit (strain-displacement relations). As will be shown in this chapter, these relationships are often expressed as local differen-

tial equations. They can also be written in global or integral form, corresponding to work or variational principles, which are treated in Chapter 2. Both the local and global forms of these relationships are used throughout this text.