ABSTRACT
This chapter will deal with two-dimensional elastic problems in the plane stress condition or the plane strain condition. The three-dimensional stress condition at a single point is said to be plane if the stress vector belongs to the same plane, independently of the cross section chosen. Likewise, the strain condition is said to be plane if the displacement vector belongs to the same plane, regardless of the direction chosen. A necessary and sufficient condition for a state of stress or strain to be defined as plane at a point is that one of the three principal values (of stress on the one hand and of strain on the other) should be equal to zero.
