Fracture Toughness of Ignalina Npp Steam

Flaws in material, appearing because of imperfections, manufacturing faults or severe service conditions, can easily threaten the structural integrity of engineering components. This is particularly dangerous when concerning equipment whose purpose is to protect larger systems, e.g. pressure safety valves (PSV) that protect pressure vessels and equipment of overpressure. Catastrophic consequences can occur [1] if a weakened pressure safety valve fails to function properly, especially if some its components are susceptible to crack growth. Therefore, it is crucial to assess design of such components according to fracture mechanics principles. Assuming isotropic linear elastic material behavior or dealing with materials that exhibit small-scale yielding at the crack tip, linear elastic fracture mechanics parameters can be used to assess mentioned fracture behavior [2]. One of such parameters is stress intensity factor (SIF), a parameter that completely defines crack tip conditions, i.e. stress, strain and displacement values. Among the first efforts in that direction were pioneer works of Irwin [3] and Williams [4] that deal with stress and strain analysis around the crack. Closed-form solutions for SIF have been derived for a number of simple configurations [5, 6], but the research of the topic is ongoing, especially for the applied solutions. Latest efforts include SIF calculation for a tension plate and study on potential transferability on bended pipe [7]. Least-square method was used to analytically find SIFs of finite elastic disk in polar coordinates [8], while the similar approach used the Hamiltonian formulation to analyze edge cracked cylinder in 3D domain [9]. Weight functions found use in analyzing edge cracked semicircular disk under compressive loading [10], while same authors studied possible use of mentioned disk as a specimen for fracture toughness assessment of brittle materials using compressive loading [11]. As for the crack occurrence in safety valves, only few works have been reported, dealing with a semi-elliptic crack appearing in valve body [12], or intergranular corrosion and fracture of a steel stud used in safety valve assembly [13]. Regarding all mentioned here, it is easy to understand the need for the research of pressure safety valve behavior when a crucial part, disc, is through or partially cracked. This paper is a step in that direction combining experimental investigation of functionality and numerical determination of stress intensity factors.