Circumferential Semi-elliptical Crack Research Articles

Weight function for an external circumferential semielliptical crack in a cylinder

AbstractIn this paper, the weight function was extracted at the deepest point of a semielliptical circumferential crack. The crack is assumed to exist on the outer surface of the cylinder. For this purpose, the three‐dimensional finite element method was accomplished to specify two reference loads, which are indispensable for determining the weight function. The verification study confirms the accuracy of the derived weight function under prescribed mechanical loading on the crack surfaces. There is consistency among the solution results compared with those in the literature. The second part describes the application of the weight function for the thermal boundary conditions. Steady‐state thermal stress intensity factors are demonstrated using the weight function and presented as a closed‐form solution. The results were compared with the finite element data on the special case of thermal loading, and good agreement is obtained.

Calculation of stress intensity factors for circumferential semi-elliptical cracks with high aspect ratio in pipes

In this paper, stress intensity factors are calculated at the deepest point of an internal circumferential semi-elliptical crack in a pipe subjected to any arbitrary load. Based on the three dimensional finite element analysis, a weight function is proposed for high aspect ratio semi-elliptical cracks in pipes. An effective expression is developed analytically to evaluate the stress intensity factor using the weight function method. For several crack face stress fields and welding residual stress distributions, the weight function is validated against finite element data and those in the literature. Based on the comparison results, it can be concluded that the solution proposed in this paper is effective in engineering applications.

Weight function for circumferential semi-elliptical cracks in cylinders due to residual stress fields induced by welding

A method is developed to evaluate the stress intensity factors (SIFs) for semi-elliptical circumferential cracks located at the inner wall of a pipe under arbitrary welding residual stress distribution. To accomplish this, at first, the three-dimensional finite element analysis (FEA) is performed employing singular elements along the crack front. Next, the weight function (WF) is incorporated in conjunction with the finite element results to predict the SIFs of semi-elliptical circumferential cracks in pipes. Then, the presented WF is extended to estimate the SIFs of fully circumferential cracks in pipes. Moreover, a closed-form formulation of SIFs is presented as a function of arbitrary loading condition and crack geometry. Finally, the closed-form relation has been used to predict the stress intensity factors of circumferential cracks under highly nonlinear residual stress fields. Comparison of the results and those in the literature shows an acceptable agreement.

New study of fatigue crack growth in pipes having a circumferential semi-elliptical crack prone to bending

A peripheral crack in a steel rounded pipe beneath periodic bending loading is studied in this paper. The analysis of the crack is done in accordance with Paris law. The of crack is also analyzed with various initial crack α beneath periodic loading. The weight of the Paris exponent on crack propagation is presented as well. Furthermore, the fatigue crack growth progression of several specimens is evaluated experimentally by an invented setup. Conclusively, the experimentally achieved results are compared with the numerical results. This comparison demonstrates good compliance with the theoretical results.

Experimental Investigation and Finite Element Analysis of Fatigue Crack Growth in Pipes Containing a Circumferential Semi-elliptical Crack Subjected to Bending

In this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered. Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region must be done with great care. This may lead to an increase in the run time which makes it difficult to reach valid results and conclusions. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this method is used. Stress intensity factors in mode I condition are determined using three-dimensional finite element modeling with 20 node iso-parametric brick elements in the ANSYS 9.0 standard code and the singular form of these finite elements at the crack front. In order to estimate the analysis error, the structural parameter error in energy norm criterion was used. Because of the advantages of non-dimensional analysis, this method is employed, and the stress intensity factors are normalized. For the analysis of the fatigue crack growth, the Paris law is used. The propagation path of the surface flaw is obtained from the diagram of aspect ratio versus relative crack depth. The fatigue crack growth analysis (the relative crack depth against loading cycles diagram) of different initial crack aspect ratio under cyclic loading is also considered. Fatigue shape development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending loading tests are compared with the numerical results. The experimental results show good conformity with the finite element results.

Stress intensity factor calculation of steel-lined hoop-wrapped cylinders with internal semi-elliptical circumferential crack

The purpose of this paper is to present mode I stress intensity factor for a circumferential semi-elliptical crack on the inner surface of a hoop-wrapped steel-lined CNG cylinder. The stress intensity factors along the crack front are directly computed by 3D finite element method for a wide range of variations of the crack geometry. Also influence of many parameters such as cylinder internal pressure, composite layer thickness, composite material properties and undertaking Auto-Frettage pressure are studied on the stress intensity factor of the crack and some conclusive results are drawn. For the sake of validation of the results and because of lack of the results for a circumferential semi-elliptical crack in the literature, a semi-elliptical axial crack in a composite hoop-wrapped cylinder has been modeled and the results have been compared with those in the literature showing a good agreement.

Stress intensity factors in a hollow cylinder containing a circumferential semi-elliptical crack subjected to combined loading

The problem of mixed mode fracture induced by a semi-elliptical circumferential crack lying at the outer surface of the cross-section of a hollow cylinder is considered. The cylinder is under the action of axial force, bending moment and torsion. To make the results comprehensive, dimensionless analysis is used, and a large variation limit of parameters that define the crack geometry is considered. Because of the advantages of the sub-modeling technique in problems which need very high mesh density, this method is used. Stress intensity factors in mixed mode condition are determined using three-dimensional finite element modeling with 20 node-isoparametric elements and the singular form of these finite elements at the crack front. The obtained results show to be in good accordance with those cited in the literature for the cases of separate application of axial load and bending moment. However, when torsion is added to tension and bending moment, a non-symmetrical distribution of stress intensity factor along the crack front is observed which can cause non-symmetric fatigue crack propagation.