Monitoring of the plastic state by changing of a deformation sign

Abstract

When a body element is proportionally loaded, its differently oriented material fibers can stretch, compress or not change their length. The direction of material fibers that do not change their length is neutral. Neutral direction divides compressed and stretched directions of the fibers. Within the limits of elasticity, the neutral direction does not change its orientation, and beyond the limit of elasticity, it rotates relative to the material fibers. Some material fibers, the slope of which is close to neutral, can change their deformation sign, and this change indicates that the element of the body has reached the plastic state.The proposed technique of the plastic state monitoring is demonstrated on a uniaxial stress state. The non-monotonicity of the close to the neutral direction material fiber deformation that oriented is confirmed by calculations and in an experiment on the tension of cylindrical specimen.The proposed technique allows fix plastic state of the material at proportional loading without value deformations or stresses measuring but by changing the sign of the deformation of the material fibers, the slope of which is close to the neutral direction.