Because of the inhomogeneity, deterioration and defects of the welded metal materials, there are three basic assumptions in materials science; The continuity hypothesis, uniformity hypothesis and isotropy hypothesis are not satisfied, which requires the application of fracture mechanics theory. The task of fracture mechanics is to use linear elastic fracture mechanics and elastic-plastic fracture mechanics to solve the crack problem of components based on the fact that there are macro microcracks in the components. Namely, the crack size, working stress and the ability of materials to resist cracks (that is, the crack tip opening displacement CTOD fracture toughness value) in the component are quantitatively linked, and the safety and life test analysis and evaluation are carried out for the components containing microcracks and joints with poor quality tissue.

Today, let me analyze the development trend of pneumatic butterfly valves in domestic and foreign markets.