Research On Crack Arrest Of Stiffened-strip And Calculation To Limit Load Of Pipe Fittings

It has been proved that the repaired method using stiffened-strip can be used to reinforce cracked components to prevent or delay the extension of cracks. Quantitative studies in this regard have very important significance on increase the operational life of defected structures. In addition, the limit analysis is playing more and more importance part in safety estimation of defected pipe and intensity design of structures due to the nature reflection of structure state, and it's a big problem for engineers to gain limit load. The pipe and panel containing through-wall cracks, which use stiffened-strip to arrest crack are studied by the use of fracture mechanics theory and finite element method. The plastic limit load of typical structure is calculated by using the elastic-plastic theory and three-dimensional finite element method.The following contents are included in this paper:(1) The method of building the finite element model of structure containing cracks with stiffened-strip is discussed. Comparison has been made with the results of example in the existing literature, and the results show that the model method is accuracy. The three-dimensional linear elastic models of pipe and panel with stiffened-strip containing through-wall cracks are established. Then the macro programs including physical model, load and solution have been made by APDL.(2) The crack arrest coefficient f is introduced to measure the effect of crack arrest. The results show that: Parameters which affect crack arrest coefficient of panel with through-wall crack are position, width and thickness, the effect of length is ignored. Parameters which affect crack arrest coefficient of pipe with through-wall crack are position, width, thickness and length. The relationship curves between f and parameters are given. For panel with stiffened-strip, the estimation method of f is given. The advice with which stiffened-strip can reach a good effect in pipe is also given.(3) With the proper estimation rule of limit load, the finite element models of pipe without defects and pipe with axial inside surface crack are built. Comparison has been made with the finite element results and EPRI values of limit load, and the results show that the finite element model and estimation rule of limit load are correct. The limit loads of these structures are calculated: Pipe containing through-wall cracks with stiffened-strip, 90°elbow, oblique nozzle, oblique nozzle with chamfer. The non-dimensional plastic limit load is defined as follows: the ratio of the structure's limit load and the pipe's limit load (main pipe's) in the same dimension. Factors which affected the non-dimension plastic limit load p are discussed. The non-dimension plastic limit load of the structures above is calculated under the different parameters. The relationship of p and factors is gained. Tables of non-dimension plastic limit load p are done.