جستجوی مقالات مرتبط با کلیدواژه "stress intensity factor" در نشریات گروه "مکانیک"

In this research, an analysis of the stress and stress intensity factor in a cracked plate under thermal and mechanical loading is done. For this purpose, using MATLAB coding, a plate with a center crack was modeled by the isogeometric method (IGA) based on the Bezier extraction operator. In this method, NURBS basis functions are generated as a linear combination of Bernstein polynomials using the Bezier extraction operator. Using this operator Bezier elements with Co continuity (similar to elements of the finite element method) were produced and Bernstein polynomials are defined on these elements. In order to model the crack, the extended isogeometric method (XIGA) was used. In this method, the control points that exist along the crack and at the tip of the crack are identified and extracted using the proper level set functions. Therefore, there is no need to re-meshing or modify the elements. By enriching the extracted control points with appropriate enrichment functions and applying boundary conditions, the analysis process was carried out and the strains and stresses were calculated. Finally, the value of the first mode stress intensity factor was obtained based on the interaction integral method. To check the accuracy of the obtained results, a similar analysis was performed using the finite element method and the results obtained from both methods were compared. These studies showed that the considered isogeometric method provides more accurate solutions with a much smaller number of elements and computational costs.

The aim of this study was to investigate the source of leaks in the natural gas pipeline network. According to the results obtained from the Failure Mode and Effects Analysis (FMEA), the three defects including lack of proper scraping, the presence of oil and existing of moisture at the welding zone in the installation and execution phase had the highest risk. These defect types studied further using experimental methods. The fracture mechanics analysis for the defects with the highest risk in Abaqus software was performed by XFEM method in three dimensions. According to the results, cracks with initial length of 4mm will grow at pressures higher than 1.4 MPa. To obtain results equivalent stress intensity factor has been used. The results imply the application of suitable nondestructive methods for determination of cracks with lengths higher than 4mm. The results of this research can be employed by inspection engineering of natural gas companies.

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.