Characteristics of tensile and compressive deformation: Although the tensile or compressive members have different shapes and different loading methods, their common characteristics are that the lines of resultant force acting on both ends of the members are coincident with the axis of the members, and the deformation of the members is elongated or shortened along the axis. Therefore, if the shapes and forces of these rods are simplified, they can all be simplified into force diagrams.

Force characteristics, in order to express the internal force on the section of tension (compression) bar, along the section? m？ m？ Imagine dividing the pole into two parts. The left and right sections of the rod are in section m? The internal force acting on m is a distributed force system, and its resultant force is? FN？ . From the left half of the equilibrium equation? ∑Fx=0？ . Have to? FN=F .

Because the line of action of the external force F coincides with the axis of the rod, the line of action of the resultant force FN of the internal force must also coincide with the axis of the rod, so the weft is called the axial force. Traditionally, the axial force in tension is defined as positive and the axial force in compression is defined as negative.

Stress-strain relationship between tension and compression-Hooke's law

Longitudinal elongation? δl？ It only reflects the total deformation of the rod, but can not explain the deformation degree of each section along the length direction of the rod. Because the elongation of each section of the tie rod is uniform, its deformation degree can be expressed by the longitudinal elongation per unit length (that is, δ L/L/). The elongation (or shortening) per unit length is called linear strain, which is labeled ε? Express delivery.