Stress intensity factors for surface semielliptical crack. The effect of the weld toes in welded joints is considered using a weld toe magnification factor mk, and the scf equations are taken into account for misalignment. The stress intensity factor, k \displaystyle k, is used in fracture mechanics to predict the stress state near the tip of a crack or notch caused by a remote load or residual stresses. Mixedmode stress intensity factors at the surface and deepest points of quarter elliptical corner cracks in mechanical joints such as bolted or riveted joints are analyzed by weight function method. There are various stress intensity factor solutions, particularly for flat plates and pressure vessels with various cracked geometries. These cracks then grow into semielliptical shapes while extending into the shaft. A stress intensity factor sif which includes this effect increases the accuracy of fatigue lives prediction. Stress intensity factor of a wide range of semielliptical. Conclusions the stress intensity factor solution for an elliptical crack. This high stress concentration reduces fatigue lives of welded structures. In these equations, the newman and raju equation 15for a semielliptical surface crack in a plain plate is chosen as the base stress intensity equation. Determination of fracture mechanics parameters j and c by. The crack opening displacement for the reference problem is calculated with a.
Estimation of stress intensity factors for semielliptical. Calculation of stress intensity factors for elliptical. Materials 2017, 10, 166 3 of 19 determination of the sif under bending stress 35. Stressintensity factors for semielliptical surface. By definition the stress concentration factor, k t, is the ratio of the maximum stress at the hole to the nominal stress at the same point. For plates with semielliptical surface crack, newman, raju and kou have reported the stress intensity factor. The solution technique for multiple cracks in an infinite body has recently been developed by. The observation in the third semielliptical region showed that the fracture surface has completely transformed into a plasticized structure and the stress intensity factor was estimated to be 0. Stress intensity factor for a semielliptical rail head crack under traction to cite this article. Stress intensity factor of semielliptical surface crack in internally. The knowledge of this crucial parameter enables the prediction of crack growth rate and residual strength of damaged structure. Stress intensity factors for semielliptical surface.
In this report, we emplo the domain integy ral method to obtain the mode i stressintensity factor distributions for elliptical and straight cracks emanating from a centrall located countersunk y rivet hole in a. The behavior of semielliptical surface flaws in cylinders is of interest in the technology of pressure vessels. Approximate determination of stress intensity factor for. Stress intensity factor determination plays a central role in linearly elastic fracture mechanics lefm problems. Stressintensity factors for semielliptical surface cracks under. Stress intensity factor for a semielliptical crack subjected to an.
Some of these solutions are based on the use of thinshell theory18, which does not take into account the three dimensional nature. The ki values are calculated for each of the individual terms. The stress intensity factor sif is the basic parameter used in fracture mechanics for stress field determination in the crack tip region. Their studies showed formulations of stress intensity factor sif to predict the behaviour of semielliptical surface cracks 16. The stress intensity factor of a semi elliptical crack in a tshaped welded joint. Stress intensity factor analysis of elliptical corner. Variation stress intensity factor for crack size with ac0.
Pdf stress intensity factor for a semielliptical crack subjected to. For a semicircular surface crack in a semiinfinite solid and a semielliptical surface crack in a plate of finite thickness, smith, emery, and kobayashi 6, and kobayashi 7, respectively, used the alternating method to obtain stressintensity factors along the crack front. Stress intensity factors for semielliptical surface cracks in. Fracture mechanics is the field of mechanics concerned with the study of the propagation of cracks in materials. The weight function represents the sif induced by a unit concentrated load. The most effective method of evaluating the stress intensity factor induced by an applied stress field is by using the weight function for a given cracked body. Stress intensity factors for elliptical and semielliptical cracks subjected to an arbitrary mode i loading.
That is, since the nominal stresses and the peak stress at the edge of the hole, are all uniaxial, the strain and stress are proportional. The concept can also be applied to materials that exhibit smallscale yielding at a cra. The weight function method is an efficient technique to calculate the. Albert and yamada 1977 defined a factor fg similar to mk. The most e ective method of evaluating the stress intensity factor induced by an applied stress eld is by using the weight function for a given cracked body. Stress intensity factors for semielliptical surface cracks in pressurised cylinders using the boundary integral equation method. The object of this study is to determine the stress intensity factor distribution around the crack front under arbitrary loading conditions for a longitudinal semielliptical flaw with ac and rit 10. Improved formula for the stress intensity factor of semi. The aim of this article is to calculate stress intensity factors ki, kii and kiii along the semielliptical crack front using the ansys code. A zareei 2 calculated the stress intensity factor at the deepest point of the semielliptic crack and proposed the weighting function of the high aspect ratio semielliptical crack on the basis.
Stress intensity factors for elliptical cracks dtic. Shallow crack means that the crack depth is less than half of the plate. Stress intensity factor sif of the crack is evaluated for. Higherorder terms depend on the geometry, but the main term depends only on. Stress intensity factors for elliptical and semielliptical cracks subjected to an arbitrary mode l. Stress intensity factor for semielliptical surface cracks. Stress intensity factor for a semielliptical rail head crack under traction article pdf available in iop conference series materials science and engineering 4021. The stress intensity factor at the deepest point of a semielliptical surface crack is calculated for stress gradients in direction of depth. Modified stress intensity factor equations for semi. Coordinate systems associated with a surface semielliptical crack in a semi in. This page provides stress intensity factor solutions for common cases. Stress intensity factors for elliptical and semielliptical cracks.
He suggested that this must be effectively one half of the elliptical embedded crack case divided on a plane of symmetry, but with a free surface correction factor. Semielliptical surface cracks in welded joints under. The paper presents numerical estimation of stress intensity factor sif of such cracks in circular solid shaft when subjected to bending and twisting loads in elastic conditions. Fracture propagation is controlled by the stress field near the crack tip. Sub model of semi elliptical surface crack at inside73 figure 73. Dotfaaar95111 stressintensity factors for elliptical. Crack tip stress dependence on the stress intensity factor k s y x w xy v yy v xx m u y r a s s s 3 yy 2 k x v s 2 yy 2 k x v s k 1 definition thumbnail crack, dictionary englishenglish online.
Engineering methods for deformation, fracture, and fatigue, 3rd edition elliptical surface crack in plate. Stress state and polar coordinates system defined at crack front. So, many different methods have been developed for sifs determination. Stress intensity factor sif, first introduced by irwin, is a physical quantity used as a control parameter to evaluate the critical state of a crack. Calculating stress intensity factors for a semielliptical surface crack. Since many rock types show brittle elastic behaviour under hydrocarbon reservoir.
Brief note on the stress intensity factor of elliptical cracks. Variation of normalized stress intensity factor for different. Because this stress field is asymptotic dominant or singular, it is characterized by the stress intensity factor sif. Fatigue cracks nucleate at the surface of the shaft operating under cyclic load. A wellknown procedure for the estimation of stress intensity factors for arbitrary stresses is the evaluation of an upper and a. Solutions are known for pure tension and bending as proposed by newman and raju. Improved formula for the stress intensity factor of. In addition, a recent threedimensional fe study on the sif of a tshaped welded joint was reported in reference. The only exact analytical weight function for a planar crack was obtained for a circular one.
Here, we consider a semielliptical crack located in such a way that its major axis is perpendicular to the rail axis and minor axis is in the depth direction. Stress intensity factors for semielliptical surface cracks under arbitrary stress distributions are hardly available for surface cracks with aspect ratios of ac1. The sif results in reference were used to further validate the accuracy of the modified formula. A threedimensional elastic finite element analysis of an observed thumbnail shaped crack indicated that the stress intensity factor was. Improved formula for the stress intensity factor of semielliptical. Coordinate systems associated with a surface semielliptical crack in a semiin. However, for plates with partly throughwall cracks, namely an semielliptical crack with an imaginary crack depth a which is greater than the thickness t of the plate, the stress intensity factor was not reported. Modified stress intensity factor equations for semielliptical surface. Pdf stress intensity factor for a semielliptical rail. Irwin applied similar arguments to derive the stress intensity factor for semielliptical surface cracks in a semiinfinite body with remote tension stress s as shown in figure 4. Paper open access stress intensity factor for a semi. Further researchers also confirmed that calculating the sif is essential to indicate the distribution of crack growth along semielliptical surface cracks 1721. Semielliptical definition of semielliptical by the free.
It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the materials resistance to fracture in modern materials science, fracture mechanics is an important tool used to improve the. Stressintensity factors for semielliptical surface cracks under tension or bending. Assuming an isotropic material with linear elastic behavior, the stress field on any linear elastic body that holds a crack can be determined, according to irwin 1, as follows. This paper presents stress intensityfactor influence coefficients sifics for axially and circumferentially oriented. Stress intensity factor, surface crack, crack propagation, fatigue, fracture. The problem is solved for a semicircular crack front and various crack inclination angles. Generally occurring surface crack is of semielliptical shape. An empirical stress intensity factor equation for a surface crack.