Deformation steel rods periodic profile with operational damages

Abstract

Introduction. In the transverse and longitudinal sections of the rods with a periodic profile, there are layers with different structural and phase states, physical and mechanical characteristics, stress state and resistance to external influences. The appearance of plastic deformations in the bases of the depressions and other defects of a periodic profile during stre­tching of the rods leads to a decrease in the resistance to corrosion damage due to the occurrence of galvanic pairs between inhomogeneous sections of the rod. This makes the computational and experimental studies of the deformed state of such rods under tension urgent.
 
 Materials and methods. The finite element modeling of the deformation process during the elastic-plastic work of steel was carried out using the ANSYS software complex and solid models of the rods under study. Experimental tests of the samples were carried out using an R-50 tensile testing machine with the recording of a load-elongation diagram in accordance with the requirements of GOST 1497. The process of deformation of the samples was displayed by photographic recording. After the destruction of the samples, the geometric dimensions (lengths, changes in cross-sections) were measured, the typical types of samples and their fragments, and fractures were photographed.
 
 Results. On experimental and finite-element models, it was found that during elastic-plastic deformation of steel rods in dangerous sections, a change in the angle of inclination of the banks of periodic protrusions (undercuts) affects the volume of plastically deformable material at the base of the undercuts. Such an analysis of the models in the limiting state has shown that the volume of the plastically deformed material is significantly reduced at the angles of the protrusions at their bases with the axis of the rod close to 900. The calculation established that the plastically deformed area at the base of sharp undercuts is more than a hundred times smaller than the corresponding volume at the base of the gently sloping undercuts. In samples with a group of protrusions, constraint of plastic deformations at the base occurs only for protrusions, the width of which is comparable to the diameter of the rod in weakened sections. The greatest development of equivalent plastic deformations is observed at the base between narrow projections. Damage to the outer layers of quasi-composite rods with a periodic profile causes significant changes in the stress-strain state of the rods under tension.
 
 Conclusions. The finite element modeling of the tensile work of steel rods with a periodic profile with a quasi-composite structure is a complex multifactorial problem. Plastic deformations develop in the depressions of the periodic profile. At the same time, undeformed areas remain in the metal of the protrusions. These zones have different potentials and between them the occurrence of internal galvanic currents is possible, leading to the acceleration of corrosion processes.