Fractographic diagnostics of technical objects fractured when operating in the North

Abstract

Fractographic diagnostics of accidental damage provides data of expert importance which can be used in developing recommendations regarding of accident prevention, improving the reliability and performance of mechanical engineering products and structures in various operating conditions. The goal of the study is fractographic diagnostics of the nature and causes of premature destruction of technical devices and facilities operating in climatic conditions of the North and being the sources of increased technogenic danger, i.e., an automobile gas cylinder and a wind power plant. Using the basic principles of metal science, metal physics, strength and fracture mechanics, the localization of initial cracks we revealed the micromechanisms of crack formation, localization and development and restored the general picture of the fracture. It is shown that the main physical and mechanical causes of the gas cylinder damage are associated with the coarsening and inhomogeneity of the intermetallide phase distribution in the material of the inner metal shell («liner») and with the increased roughness of the internal surface which formed a system of stress microconcentrators. The reason for the collapse of a wind generator was lack of penetration in welded joints of the support structure being the place of origin of the initial cracks. The main fracture mechanism in both cases is time-evolving process of the metal fatigue initiated by technological micro-and macro-defects. The stage of the final destruction of a gas cylinder exhibited a dynamic character realized through the formation of a system of viscous cracks in the liner with their subsequent merging and fragmentation of the liner. The attained critical level of the fatigue crack development caused the onset of the ultimate state of the structure of a wind generator tower resulted in subsequent brittle fracture. The described destructions relate to gradual failures as they are caused by inherent technological defects rather than by external impacts. The results of the study can be used to improve the performance of the considered objects, ensure their operational safety and promote developing of compensating measures.