Research Of Interference Between Multiple Cracks In The Inner Surface Of Piping Based On FEM

At present, it has practical significance that the theory of fracture mechanics is used in the Fracture Analysis of pipes which in service. Not only the single crack but also multiple cracks may exist in the piping structure. The problem of multiple cracks is more complex than that of single crack because of the interference of cracks.In this paper, based on fracture mechanics, the straight pipe which contained all kinds of multiple inner surface cracks are analyzed by the finite element analysis (FEA) method and ANSYS software. Finite element models are established for straight pipe which contain Circumferential inner surface crack in different situations(different crack size、different load conditions).They are analyzed and calculated. The stress intensity factor(KI)which contained the Circumferential inner surface crack in different situations in linear-elasticity is calculated, and is transformed to correction coefficient F of stress intensity factor. And with radial cracks, circumferential cracks and circumferential and axial cracks in the pipe, stress intensity factor of the crack tip is studied and the impact of interference factors between cracks is discussed.The main contents in this paper include:(1) According to the theory of fracture mechanics, the way for solution of2D/3D crack tip’s stress intensity factor is analyzed and studied; the ANSYS software of finite element analysis is applied to set up2D/3D crack finite element model; the accuracy and the reliability of modeling as well as the application of the selected unit is confirmed in this paper, and foundation is built stably for later work.(2) Pipeline with2-dimensional radial multiple cracks in linear-elasticity under inner-pressure has been extensive analyzed. Stress intensity factor’ value of double radial cracks is given, and with the impact of different factors, summarized the variation; the effect of the crack length, crack angle, inner and outer diameter on interference on the multiple cracks is discussed.(3) Models for Circumferential inner surface crack of straight pipeline in different situations are established by FEA; K, in linear-elasticity under inner-pressure is calculated. The result of the finite element is picked up, charts of K, changing along with the different influence factors are plotted, and rule of change is analyzed and discussed.The stress intensity factor shape correction coefficient F is solved further, graphs are drawn up,its change rules are summarized and discussed. (4) Under pressure load, analyze the Circumferential multiple cracks stress intensity factor of the mutual influence of pipeline wall thickness. Discuss impact of stress intensity factor under the thickness of pipeline、the depth of crack and the distance between the crack.(5) When the pipeline contains two different types of cracks, circumferential and axial elliptical cracks, analyze and discuss the effect of two cracks’their stress intensity factor by their distance, parameters changes.