Effect of Shock and Vibration Preloading on the Deformation and Fracture Behavior of 17G1S-U Steel

Abstract

The procedure of evaluating the crack resistance of 17G1S-U sheet steel after shock and vibration loading was advanced and experimentally tested using the method of complete deformation diagrams. The technical potential was employed to provide the growth of a mixed mode (I+III) macrocrack on the specimens with an identical central circular opening, which guaranteed the self-similar macrocrack propagation. The complete deformation diagrams displayed initial almost straight descending portion. In real constructions of gas mains, rather long macrocracks can arise after this fracture mode. The advanced procedure permits of reliable assessment of energy variations spent for a (I+III) mode crack propagation under any complex combined loading. The straight descending branch slope of the deformation diagram is established to be used for evaluating crack resistance variations of pipe steel subject to thermomechanical loading. Shock and vibration loading of a high frequency (1–2 kHz) is shown to essentially influence the crack resistance of pipe steel and plastic strain in the vicinity of a stress raiser. The impact of a power pulse on the material is dependent on its prestrain level through static tension and damage of its initial structure correspondingly. The controlling factor influencing the change in mechanical properties is the intensity of the power pulse. Basic fracture mechanisms of steel were established on the basis of examination of specimen fractures with scanning electron microscopy. The shock and vibration loading is evidently accompanied by energy contribution not only to the existing damages of the material but also to the initiating ones, which causes the localization of deformation and growth of pores in their vicinity. Since the energy accumulation can contribute to the modification of the material in the vicinity of those damages, the shape and sizes of ductile tear dimples are the informative parameters for evaluating the strength and plasticity of examined steel.