Experimental study of micro-deformation of structural steel under simulation of operating conditions

Abstract

Diagnostics of the load bearing capacity of machines and structures, service properties of structural materials are carried out by destructive and non-destructive methods. In the system of non-destructive methods of diagnosing and monitoring of the service properties of materials and products, radiation technologies are of particular importance, since they have instrumental capabilities for diagnosing and controlling changes in the soundness of a solid body at different structural levels. The X-ray diffractometry method provided determination of the stability of the stress-strain state of structural steel samples subjected to prolonged (over 5 years) static loads not exceeding the yield strength of the material. The purpose of the study is to determine experimentally the effect of continuous (since 2013) elastic stress and climatic factors on the change in the half-width of the diffraction line profile. It is shown that the straight-line dependence of the half-width of the diffraction line profile is maintained in the range of elastic stresses not exceeding 0.5σt. The results of changes in the microstructural state (micro-strains) identified by the characteristics of the diffraction lines profile are presented and discussed. The results of the experimental study of the effect of small steady elastic stresses reveal that periodic annual fluctuation of temperatures (2013 – 2018) does not cause a significant change in the properties of the diffraction line profile of the 08ps structural steel samples. On the contrary, low climatic temperatures contributed to the elimination of individual instrumental errors attributed to design conditions of the experiment. A sharp change in the true half-width of the diffraction line profile at the stress values σ > 0.5σt, probably indicates the minimum margin of safety of 08ps structural steel when setting the permissible stress value (σ). The revealed changes in microplastic deformation observed in structural steels in the range of elastic stresses corresponding to real operational loads require further study and analysis.