Research Of Interaction Between Uniform Radial Multiple Cracks Of Thick-Walled Pipes By FEM

The structure safety evaluation methods widely used present are mostly based on the single crack theories and couldn’t considering the interactions between multiple cracks, so it has bring more and more problems in application of engineering. Actually the defections of service equipment are mostly exist in the form of crack groups and the interaction between cracks has important influence on the equipment with cracks, so the multiple crack problems has bring more and more attention of researchers’.In this paper, the abstract expression of stress intensity factor of multiple radial cracks and the influencing factor of multiple crack’ interactions were proposed based on the Fracture mechanics theory and the influence factors of multiple cracks’ stress intensity factors in plate. The thick wall pipes contains radial cracks in different situations (different crack depth ratio, different diameter of thick wall pipes, different angular between cracks and different crack numbers) were analyzed by finite element analysis method and ANSYS software. The stress intensity factor of cracks in different situations is calculated in linear-elasticity. And with the results calculated before, stress intensity factor of the crack tip is studied and the impact of stress intensity factor and influencing factor of multiple crack’ interactions of double radial cracks and multiple cracks were discussed.The main work of this paper includes:(1) According the Fracture mechanics theory and finite element analysis method, the solving methods of stress intensity factor in2-D structures with cracks were analyzed. The software ANSYS was used to establish the2-D model of thick wall cylinder with radial crack and calculate the intensity stress factor of cracks; the accuracy of calculation and reliability of modeling was confirmed by comparing the FEAM results and theory solution, and foundation was built stably for later work.(2) The abstract expression of stress intensity factor of evenly distributed multiple radial cracks and the influencing factors of multiple crack’ interactions were proposed based on the fracture mechanics theory and the influence factors of multiple cracks’ stress intensity factors in plate.(3) Thick wall pipes with double radial cracks in linear-elasticity under inner-pressure has been extensively analyzed and stress intensity factors of double crack’in different situations were calculated. Influences of angular between cracks, crack depth ratio and outer diameter of thick wall cylinder to stress intensity factor and influencing factor of multiple crack’ interactions of double crack were discussed.The analysis result of influencing factors on stress intensity factors show that the affect of different factors are varies and the expression of stress intensity factors of multiple crack proposed in this article is reasonable. The analysis result of cracks’ interactions impact factors show that when tht angular about110°is the turning point of open and close effect and influences by different factors are varies.(4) Thick wall cylinder with multiple radial cracks in linear-elasticity under inner-pressure has been analyzed and stress intensity factor of multiple crack’in different situations were calculated. Influences of crack numbers, crack depth ratio and outer diameter of thick wall cylinder to stress intensity factor and influencing factor between multiple cracks of multiple cracks were discussed. The analysis result of influencing factors on multiple cracks’ stress intensity factors and cracks’ impact factors show that influences by different factors are varies and the turning point of open and close effect of multiple cracks’interaction is N=3.The analysis conclusion of multiple cracks verifies the expressions proposed before again.(5)The combination influences of two factors to stress intensity factor and influencing factor between multiple cracks were discussed by the calculation results before.The results show that the influencing strength by different factors are varies and one may be outstripped another.(6)The FEM model of pipes with uniform multiple cracks and pipes(inner diameter is Rl+a and out diameter is R0)were used to analyzed the varies of maximum σθ.The results show that varies of stress intensity factors along with the increasing of cracks number just show the down of cracks’growth,not the improvement of pipes’ strength.