The initial crack sizes were relatively large with surface lengths of 30. Modified stress intensity factor equations for semielliptical surface. Ginzton laboratory stanford university stanford, ca 94305 j, c. Improved probabilistic modeling of multisite fatigue cracking. Fractographic methods are routinely used to determine the cause of failure in engineering structures, especially in product failure and the practice of forensic engineering or failure analysis.
This paper presents a new simplified approach for ductile failure analysis of semi elliptical surface cracks under uniform tension by representing the load as a multiplication of two separate functions. These have been derived by finite element analysis of the welded joint ignoring the presence of residual stresses. Fractography is the study of the fracture surfaces of materials. Simplified approach for ductile failure analysis of semi. The rather large scatter of crack growth curves calls for reanalysis of stress intensity factors. The derived weight functions account for both the global weldment geometry and the weld profile characterised by the weld angle. The theoretical model is applied to semielliptic surface cracked al 7075t6 alloy plate under cyclic loading, and five different initial crack shapes are discussed in.
Citeseerx citation query an empirical stressintensity. Stress intensity factors for a semielliptical surface crack. The deepest point a and corner point b of the semi elliptical surface crack are depicted. This paper presents a numerical investigation on semi elliptical surface cracks in round bars subjected to mode iii loadings.
In this current study, semielliptical surface cracks are considered because most surface flaws are represented as semielliptical dong et al. Experimental data of specimens with wide range of crack depth, crack width, and thickness are used in the implementation of this. This paper presents a new simplified approach for ductile failure analysis of semielliptical surface cracks under uniform tension by representing the load as a multiplication of two separate functions. Rapid method of stress intensity factor calculation for semi. A three dimensional finite element model 3d fe is employed in this study to evaluate the stress intensity factors for a crack on a corroded pipe surface. A useful reference solution is that for the similarly aligned and loaded elliptical crack in an in. Pdf stress intensity interaction between dissimilar semi.
A theoretical model of semielliptic surface crack growth. The solutions obtained in the present work can be used in various practical applications, such as cracks in pressure vessels, welded structures and mechanical engineering compo. Stressintensity factors for surface cracks in functionally. A semi elliptical surface crack is assumed at the weld toe perpendicular to the plate surface. Dear all,for fire case calculations for relief valves in the equation. Moulder and j, gerlitz national bureau of standards boulder, co. The validity of the approximations and the results are judged by validation with results from alternative fully 3d cases. Feb, 2017 the sif of a semi elliptical surface crack in a plate subjected to pure bending can also be estimated by the alternating approach. Stress intensity factor distributions at the edge of semicircular and semielliptical surface cracks are obtained for cracks aligned perpendicular to the surface of a semiinfinite solid subject to remote shear parallel to the plane of the crack. A half space with a semielliptical surface crack is shown in fig. Stress intensity factors for axial semielliptical surface. Fatigue crack growth behaviour of semielliptical surface cracks for. For coplanar surface defects, assessment codes typically provide rules for conservatively characterising the defects as semielliptical or rectangular cracks. The effect of corrosion patch geometry on stress intensity.
Tension and bending of a semielliptical surface crack springerlink. The weight function method was applied and appropriate weight functions have been derived using the petroskiachenbach crack opening displacement expression. The sif of a semielliptical surface crack in a plate subjected to pure bending can also be estimated by the alternating approach. Broken crankshaft failed from a surface defect at lower centre. A half space with a semi elliptical surface crack is shown in fig. Lack of information can be found in open literature regarding to the jintegral solution especially the surface crack subjected to mode iii loadings.
At first the applicability of published parametric equations for sif of elliptical cracks in plates is validated. A method for calculating stress intensity factors for edge and surface cracks in weldments has been presented. Mar 01, 2016 the results showed that the sif of the inner crack was lower than a single crack by 16% to 48%, and the outer crack had the highest sif and was most likely to fail. Rapid method of stress intensity factor calculation for. Both semi circular and semi elliptical cracks are examined. Very good agreement is found between trends in stress intensity factor with changes in crack size and applied tractions. Diameter of line, sewer pipe material rcp, mcip, brick, etc. Using the compatibility conditions, these equations are. In this study, sif for axial semielliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel liners are studied by means of the finite element method. In the present note semielliptical surface cracks in long cylinders. In common a thermal shock experiments, the quenching test is used to simulate the thermal shock process. Pdf flaw stability analysis of semielliptical surface. Astm e740 fracture testing with surfacecrack tension. Improved probabilistic remaining useful life estimation in.
Stress intensity factors for semielliptical surface cracks. In this study, sif for axial semi elliptical surface cracks and embedded elliptical cracks at longitudinal butt welded joints of steel liners are studied by means of the finite element method. Stressintensity factors for semielliptical surface. The results for the semielliptical surface cracks agreed quite well with the eac initiation criterion, and provide confirmation of the applicability of the criterion. Department of energy by westinghouse electric corporation. This behavior is compared with the life of the line pipe in an inert environment e. Astm e740 testing covers design, preparation, and testing of a metal sample containing a surfacecrack. Semielliptical surface crack an overview sciencedirect topics. Evolution and interaction of surface cracks under thermal. A numerical solution to the threedimensional equations of elasticity is presented for the problem of a semielliptical surface crack in the surface of a f. Semielliptical surface cracks at the centre of a hole in a finite plate subjected to uniform uniaxial tension. The semielliptical surface cracka solution by the alternating. However, a standard practices is to characterize a surface crack by projecting it onto the plane normal to the principal stress and assume the crack to be semi elliptical in shape.
Then some structural characteristics of the surfacecracked t and ljoints are studied by mixed mode linespring finite element. Mixed mode conditions along the crack edge are characterized. It was also observed that, the maximum modei stress intensity factors of semi elliptical cracks with high aspect ratios for different inclination angles all appear near the free surface, which is different from the semielliptical cracks with low aspect ratio. Improved formula for the stress intensity factor of semi. This method has proved to be extremely accurate for the cracking along the weld toe.
Influence of the interaction on stress intensity factor of. The crack surface is covered by the penetrant material and a higher magnification view identifies the transition of the penetrant material out of the fatigue region that has different microscopic features, so it can be recognized as the final fracture zone. Kamaya 7, 8 evaluated the growth behaviour and the sif of interacted coplanar and parallel semielliptical surface cracks through finite element analysis quantitatively. In common a thermal shock experiments, the quenching test.
Consider the tension and the bending of a finite thickness plate with a semi elliptical surface crack. The interaction between multiple surface cracks is an important consideration in the cracking behavior due to thermal fatigue and stress corrosion cracking. Stress intensity factors for elliptical and semielliptical. Fracture analysis of generator fan blades intechopen. A magnification factor is commonly used to multiply the sif of semielliptical surface cracks to account for the stress concentration effect in welded connections. Transient thermal cracking of a brittle half space medium. This procedure is used to calculate the loadcarrying capacity of structural components that have a possible type of flaw. Department of energy contract deac1 1 93pn38195 proposed for submittal to the 1997 asme pressure vessel and pidina conference beltis atomic power laboratory pittsburgh, pennsylvania 151220079 operated for the u. Semielliptical surface flaw ec interaction and inversion. This revised cefm accurately predicted the dependence of crack growth rates on the stress intensity factor and offers an alternative explanation for the development of semielliptical cracks to those suggested by fracture mechanics alone. Based on the semi elliptical assumption, yang et al.
Here, the elastic interaction between coplanar semi elliptical surface cracks is examined in detail by considering a large number of dissimilar crack pairs with different depths and aspect ratios. Constraint of semielliptical surface cracks in t and l. For coplanar surface defects, assessment codes typically provide rules for conservatively characterising the defects as semi elliptical or rectangular cracks. The paper is presenting the fatigue crack growth fcg behavior of semi elliptical surface cracks for api x65 gas pipeline using sversion fem. Hachures are the lines on fracture surface that can be traced back to the origin of the fracture.
Use of wood forms impeded cooling at the pvc surface resulting in excessive temperature differential across the grout thickness that resulted in cracking of the grout high cement content produced high heat of hydration. The formula can be divided into the following two parts. Pdf a crack compliance analysis approach was used to calculate stress intensity factors for surface cracks in flat plates with builtin ends. Stress intensity interaction between dissimilar semi. Astm e740 fracture testing with surfacecrack tension specimens. Then some structural characteristics of the surface cracked t and ljoints are studied by mixed mode linespring finite element. So the nodes of the top face can penetrate the bottom face or vice versa. It is a theoretical construct usually applied to a homogeneous, linear elastic. The discrepancies obtained by early methods were sometimes 250%. Semielliptical external surface crack in a pipe this paper aims to investigate the effect of corrosion geometry on the stress intensity factors for external surface cracks in cast iron pipes. Recently, a critical evaluation of numerical solutions to the benchmark surface flaw problem has been made in ref.
Semielliptical surface crack an overview sciencedirect. Here, the elastic interaction between coplanar semielliptical surface cracks is examined in detail by considering a large number of dissimilar crack pairs with different depths. However, a standard practices is to characterize a surface crack by projecting it onto the plane normal to the principal stress and assume the crack to be semielliptical in shape. The semielliptical and semispherical defects included have a depth equal to onehalf the pipe thickness.
The stress intensity factor solution given by isida et al. The stress intensity factor, is used in fracture mechanics to predict the stress state stress intensity near the tip of a crack or notch caused by a remote load or residual stresses. Both semicircular and semielliptical cracks are examined. The paper concludes with a parametric study that provides a set of stressintensity factors for semielliptical surface. Pdf semielliptical surface cracks in finitethickness plates with. The test is performed by creating a small semi elliptical crack in a sample, applying tremendous amounts of increasing pressure to the top of that sample until fracture, and recording the maximum pressure it could withstand before cracking.
Stress intensity factors for semielliptical surface. The crack top and bottom face nodes are not connected through any constraint equation. The results showed that the sif of the inner crack was lower than a single crack by 16% to 48%, and the outer crack had the highest sif and was most likely to fail. Therefore, this work investigates and analyzes crack behavior using jintegral approach. In addition, in one specimen, the surface crack penetrated welddeposited cladding into the highsulfur steel. A full 3dmesh generating program for semi elliptical surface cracks is employed to provide such reference 3d solutions. The present paper expands upon the work of wire and u by presenting results for significantly deeper initial semielliptical surface cracks. Fatigue crack growth behaviour of semielliptical surface. A method known as globallocal overlay technique was used in this study to predict the fatigue behavior that involve of two separate meshes each specifically for global geometry and local crack. In this figure the semielliptical fatigue region is obvious. Defects are treated as equivalent surface semielliptical cracks figure 3. The initiation of environmentally assisted cracking in semi. The membrane and bending stresses acting in the base plate correspond to the structural stresses perpendicular to the weld seam measured or calculated at the weld toe of the tubular joint. Finite element study on semielliptical surface cracks in a cylinder kit.
The results for the semi elliptical surface cracks agreed quite well with the eac initiation criterion, and provide confirmation of the applicability of the criterion to crack configurations with more restricted access to water. The initiation of environmentallyassisted cracking in. Moreover, crack growth and interaction was investigated using a simulation technique that incorporates the stress intensity factor of a single crack with an existing. A full 3dmesh generating program for semielliptical surface cracks is employed to provide such reference 3d solutions.
The semi elliptical beachmarks near the origin, indicate crack growth from fatigue. Corrosion fatigue crack growth in clad lowalloy steels. Fracture testing with surfacecrack tension specimens trl. The depth of surface crack a, the halfwidth of the cracked plate b, the halflength of surface crack c, the plate thickness t, and the parametric angle of the ellipse 3 are indicated in figure5. Denote the coordinate axes and the geometrical parameters. The initiation of environmentally assisted cracking in. Kamaya 7, 8 evaluated the growth behaviour and the sif of interacted coplanar and parallel semi elliptical surface cracks through finite element analysis quantitatively. Experimental data of specimens with wide range of crack depth, crack width, and thickness are used in the implementation. Interaction criteria based solely on the defect geometry have been. The deepest point a and corner point b of the semielliptical surface crack are depicted. Stress intensity factors for a semielliptical surface.
The specimens featured semielliptical surface cracks penetrating approximately 6. Thermoplastic j integral calculation for a semielliptical. Based on the semielliptical assumption, yang et al. It is a theoretical construct usually applied to a homogeneous, linear elastic material and is useful for providing a failure criterion for brittle materials.
This paper presents a numerical investigation on semielliptical surface cracks in round bars subjected to mode iii loadings. The importance of axle load, speed, plasticity and braking thermal load effects on growing of a surface crake situated on a thread of wheels are demonstrated in this paper. The specimens featured semi elliptical surface cracks penetrating approximately 6. The initiation of environmentallyassisted cracking in semi. Fatigue crack growth behaviour of semielliptical surface cracks for an api 5l x65 gas pipeline under tension. Initially, the mathematical model representing tapered rotating disc is solved and the equations for radial stress are obtained. Stress intensity factors for inclined external surface. The paper is presenting the fatigue crack growth fcg behavior of semielliptical surface cracks for api x65 gas pipeline using sversion fem. The crack object only supports semielliptical surface cracks. Stressintensity factors for semielliptical surface cracks. Jintegral prediction for semielliptical surface cracks in.
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