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In this research, stress intensity factor of a small radial crack in a rotating thick cylinder made of viscoelastic materials subjected to internal pressure and radial temperature distribution is investigated. The radial crack is assumed to be located at the outer edge of the cylinder. The Zener model (i.e., standard three parameter solid) is applied to simulate the viscoelastic behavior of the cylinder. To obtain the stress intensity factor of the viscoelastic cylinder, the problem of uncracked viscoelastic cylinder subjected to internal pressure and radial temperature distribution is analyzed with plane strain assumptions. Then, the hoop stress distribution is determined. Finally, by assuming the small crack length and applying the superposition method, the problem of cracked viscoelastic cylinder is replaced by the problem of cracked viscoelastic cylinder subjected to determined average stress in the previous step. By employing the proper geometry factor, the stress intensity factor of the viscoelastic cylinder is determined. A parameter study is performed to investigate the effects of various parameters on the stress intensity factor of the cylinder. To validate the results, the problem of viscoelastic cracked cylinder is simplified to an elastic cracked cylinder by neglecting the viscoelastic terms, and the data obtained in the present work are compared with those given in the literature search. The results show that the proposed method is quite capable of estimating the stress intensity factor of small cracks in structures made of viscoelastic materials. A parameter study is performed to investigate effect of various parameters on stress intensity factor of the cylinder. The parameter study shows that a) the stress intensity factor of the viscoelastic cylinder in early moments of loading is higher than its equivalent elastic cylinder, b) increasing the elastic properties of the viscoelastic material results in higher stress intensity factor, and increasing the viscous properties of the material decreases the stress intensity factor.

The purpose of this paper is to reinforce the pressurized pipe containing a fully circumferential crack (internal and external) using composite patches due to their remarkable properties. In the research procedure, in order to validate the proposed models, firstly, a cylindrical pipe with a circumferential crack subjected to the uniform tension was modeled and the results of stress intensity factors were compared with an existing paper. Then, in order to examine the modeling process of composite patch and adhesive, a damaged plate with a central crack was considered and the results of stress intensity factors were investigated and evaluated. Stress intensity factor at the crack tip was calculated using the J-integral. In this regard, using the 3D finite element method, the stress intensity factors in the crack before and after the pipe repair were evaluated with boron/epoxy, carbon/epoxy and glass/epoxy composite patches. The crack geometries correspond to different relative depths from 0.4 to 0.8. The results showed that the use of composite patches significantly decreased the stress intensity factors, and this reduction in the external circumferential cracks is more than the internal ones. Also, in the research process, the effect of the patch thickness, the angle of the fiber and the adhesive material on the stress intensity factors has been investigated.

In this paper, the effect of composite patch on cylindrical pipe with circumferential through-wall crack has been investigated under internal pressure. For this purpose, using three-dimensional finite element and J-integral, stress intensity factors is determined before and after the repair. In order to ensure the accuracy of modeling, a pipe with circumferential through-wall crack under uniform tension load is simulated and the results are compared with theoretical data. Then, the cracking cylinder is repaired using four composite patches of Boron/Epoxy, Carbon/Epoxy, Kevlar/Epoxy and Glass/Epoxy in a local manner. The results of study are shown the significant effect of composite patches on reducing the stress intensity factor of cracked cylinder. It is observed that the use of composite patches with higher stiffness has a more decreasing effect on stress intensity factor. Also, the effect of composite patch, properties and thickness of adhesive on stress intensity factors along crack front is evaluated.

In this paper, the stress intensity factor (SIF) in the opening mode I is investigated in cracked beams with the I-shaped cross sections under axial loading. In cracked cross sections, a couple is made due to shifting the two centroids, or in the other word due to a misalignment between the axes of the axial force. The analysis is carried out through two analytical and numerical approaches. In analytical approach, a mathematical model for SIF is proposed via the theory of the energy release rate in the region around the crack. This model is adapted by considering the moment of the couple. It is presented in two situations in terms of the crack location including the crack in a part of the flange, and the crack in the flange and a part of the web. In numerical approach, geometric and material characteristics and type of loading are modeled by using Abaqus software; then SIF values of the I-shaped cracked beam are determined. In the presented numerical solution, two methods of C-integral and X-FEM are employed to model the crack. The validity of proposed equations is confirmed by the comparison between the presented results of numerical and analytical approaches.

In the different applications of thin plats in engineering industrial, some holes are created in the structure that can have different shapes such as circular, elliptical, and quasi-square. When the plate is subjected to loading, stress concentration around the hole causes the crack initiation in these areas that can results in a catastrophic failure. In this paper, mode II stress intensity factor (SIF) for two unequal aligned cracks emanating from a circle or a quasi-square hole in an infinite plane was investigated. The complex variable theory of Muskhelishvili and conformal mapping method were used. To obtain mapping function, Schwarts Christoffel integral was combined with some simple mapping functions. Accordingly, a new mapping function is presented and approximated to the sum of series expansion. Using this approximate mapping, SIF is calculated with high accuracy. Surfaces of the cracks and hole are traction-free. The plane is subjected to the pure shear at infinity. The analytical results are in good agreement with the literature. The obtained stress intensity factors have good accuracy for small cracks. The equation presented in this paper is applicable to the length of the different cracks and calculates the intensity coefficients of mode II for very small cracks with high accuracy. Results show that the shape of the hole is important only for the small cracks. [ABSTRACT FROM AUTHOR]

The use of numerical methods, particularly finite element methods in solving different problems are used in abundance. Because these methods are approximate, having a real understanding of the extent and distribution of the errors is extremely important. Studies show that the mesh used in the finite element method will be an essential error rate. So many different ways to find the optimal mesh and minimize the error of the proposed method. These methods are mainly aimed at reducing the error in the stress field have been obtained. Although one of the aims of reducing errors tension field finite element method is adaptive, but no guarantee is intended to achieve specific issues. These issues can be Craek to the issues noted in the analysis of the elastic parameters of the stress intensity factor will play a key role in determining the direction and Craek the design. The purpose of this study is to measure the stress intensity factor adaptive analysis on the parameter to be modified to accommodate ancillary parameters such as strain, stress intensity factor able to modify the target parameter

The Griffith crack, a central crack in an infinite plane under uniform loading, is converted to a subsurface one by moving close to a loaded edge of the plane. Subsurface cracks initiate under rolling contact fatigue conditions. In this paper, first, finite element model of the Griffith crack has been developed and validated by calculating stress intensity factors (SIFs) under uniform tension and shear loadings. Then, by moving the crack close to a parallel edge of the plane, mixed mode SIFs of the subsurface crack have been determined for a wide range of the cracks depths. Non-symmetrical geometry with respect to the crack edge causes coupling between fracture modes and so, considerable shear and tension fracture modes under tension and shear loadings, respectively. The ratio of SIF for the coupling mode to the direct mode is creased up to 69% for the length to depth ratio of 20. Also, by fitting third-degree polynomials to the mixed mode SIFs, four geometry correction factors have been obtained for SIFs of subsurface cracks under uniform loadings. These approximate equations can be used easily and efficiently by engineers. Also, the relations can be utilized as a primary estimation for non-uniform loadings, especially when the crack length as well as the load variation along it is small. [ABSTRACT FROM AUTHOR]

A family of rotating disks used in Iranian turbine and compressor industry is investigated. Mechanical and thermal loads due to working condition would lead to the crack initiation in the inner surface of the disk. The aim of this paper is the development of the two-dimensional weight function for the rotating disks containing semi-elliptical longitudinal cracks. The general form of the two-dimensional weight function is related to the proposed weight functions for embedded cracked domain in literature. In order to determine the unknown coefficient of the weight function, the reference stress intensity factors for cracked geometry subjected to reference loads are calculated. The analysis indicated that the results are independent of the number of terms in proposed weight function expansion. Extracting the weight function for disks with from 90 to 420 mm thickness enables one to predict the stress intensity factor for cracks in the structure subjected to arbitrary loading. The stress intensity factor for each point on the crack front subjecting to one or two dimensional loads would be calculated using the derived weight function. The results reveal that the increasing of the height to thickness ratio in rotating disks leads to the increase of the stress intensity factor for high depth ratio crack ones. Results show that the configuration of the disk sections affects the stress intensity factors of the same aspect ratio cracks in the structures. The comparison of the results obtained from the weight function method and those obtained with FEM are in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, the effect of nonhomogeneous parameter in orthotropic Functionally Graded Material(FGM) in a cracked layer is investigated. It is assumed that the mechanical and thermal properties of material are dependent on x-coordinate (collinear with crack surfaces) in exponential form. The problem is solved for internal and edge crack in two way, integral equations and generalized differential quadrature method. Thermal loading is in a way that temperature distribution in the layer is uniform. Because of variation in mechanical and thermal properties, stress distribution due to this loading is not uniform. In the solution of problem with integral equations method, first, thermo-elasticity problem with no cracks and then isothermal crack problem are separately solved. Afterward with these solutions, the main problem will be solved. In order to solve isothermal crack problem, after conversion and simplifying the equations in orthotropic material, Navier's equations will be solved with the Fourier. Numerical solution of the problem is the generalized differential quadrature element method that is being presented for verification of the results of the integral equations for a specific state in the diagram format. Also the effect of temperature on intensity factor with various values of nonhomogeneous parameter is investigated. [ABSTRACT FROM AUTHOR]

Human bones experience different modes of loading including tension, compression, bending, and torsion. The modes of loading depend on the activities performed by the body. Regarding the crack shape and loading modes, by the time only the first mode of fracture has been studied in order to analyze the fracture toughness. However, it is necessary to analyze different modes of fracture in order to achieve more reliable results. In this research, finite element analysis and calculations for geometric coefficients were done to obtain the toughness of bone. Hence, first, second, and combined modes of fracture in cortical samples having cracks were studied numerically and experimentally. To this end, bovine tibia was used to make standard tensile samples for implementation in Arcan's device. Some optimizations were made on the Arcan's device. These were included of bone fixation in the device and ability of performing tests in different angels. Stress intensity factor (Kc) was obtained for different fracture modes. Results showed a decrease in K1c with respect to change in loading angle while KIIC acted vice versa. Performing some extra optimizations, the device can be used for torsional fracture mode in a torsion test device. [ABSTRACT FROM AUTHOR]

The use of stop drill holes is one of the most convenient methods for reducing the stress intensity factors and crack growth rate. The efficiency of stop drill holes on the crack growth retardation depends on the amount of reduction in stress intensity factors. The curved plates are frequently used in engineering structures. Therefore, in this paper, by using the finite element method, the effects of configurations and diameters of crack flank holes on the variations of stress intensity factor are studied for a curved plate. The numerical results indicate that the location and the size of stop drill holes affect the stress intensity factors which is mainly due to their interaction with the crack tip stresses. Closer distances to the crack tip and larger diameters of the flank holes provide more reduction in the stress intensity factors. Also, the finite element results show that the use of stop drill hole method for the curved plates has the same efficiency as that of the flat plates. [ABSTRACT FROM AUTHOR]

In this study, the first mode of stress intensity factor of semi-elliptical circumferential crack in the outer surface of a cylinder with radius to thickness ratio of 30, is investigated. The cylinder is applied in semi-submersible drilling platforms. First, the stress field of the cylinder under thermal and mechanical loads is extracted based on semi couple thermo-elastic equations. Then, the weight functions are derived for deepest and surface points using three reference loads results. Explicit expressions of stress intensity factors for surface and deepest points are presented using thermo-elastic stress field and the weight functions of the cracked cylinder. The results obtained by proposed weight functions and those obtained by finite element method and those presented in the literatures have a good accuracy. The interaction effects of thermal and mechanical loads on the stress intensity factors are studied. The results show that with increasing load ratio, the dimensionless stress intensity factors of deepest and surface points, decrease and increase, respectively. [ABSTRACT FROM AUTHOR]