Search for: stress-intensity-factor
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    Interacting cracks and ellipsoidal inhomogeneities by the equivalent inclusion method

    , Article Journal of the Mechanics and Physics of Solids ; Volume 51, Issue 5 , 2003 , Pages 945-960 ; 00225096 (ISSN) Shodja, H. M ; Rad, I. Z ; Soheilifard, R ; Sharif University of Technology
    Based on the Eshelby's equivalent inclusion method (EIM) and Hill's theorem on discontinuities of elastic fields across the interfaces, a theory for the determination of the stress intensity factors (SIFs) of arbitrarily oriented interacting cracks under non-uniform far-field applied stress (strain) is developed. As shown in this investigation the EIM proposed by Moschovidis and Mura can be extended for treatment of such problems, but their formulations are quite cumbersome and computationally inefficient. An alternative analytical approach is proposed that is computationally more efficient, and unlike the method of Moschovidis and Mura can easily handle complex problems of interacting... 

    State functions: the milestone of fracture

    , Article Archive of Applied Mechanics ; Volume 86, Issue 7 , 2016 , Pages 1311-1324 ; 09391533 (ISSN) Ranjbaran, A ; Ranjbaran, M ; Sharif University of Technology
    Springer Verlag  2016
    The fracture phenomenon is defined via the change of state of structure (entity) between the intact and the fractured end states as the function of the state variable. The twin state functions are defined for the transition of unit of the entity between its two end states. The state ratio is defined as the ratio of the two state functions. The property of the cracked structure is defined as the product of the structure property and the state ratio. The work is then used to derive the main parameters of the fracture mechanics. The work is verified via five examples. © 2016, Springer-Verlag Berlin Heidelberg  

    Innovative theory for the compliance computation in rotors

    , Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 1779-1788 ; 10263098 (ISSN) Ranjbaran, A ; Ranjbaran, M ; Sharif University of Technology
    The conventional energy release rate approach to the computation of the crack compliance in rotors is critically reviewed and its shortcoming is highlighted. The state functions and the generic compliance are introduced, defined, and verified. The proposed functions are defined based on the end states' conditions and are exact. The crack compliance of the shaft in torsion is explicitly defined as the function of the crack depth ratio and recommended as a good alternative to the classical procedure of the energy release rate method. The accuracy and efficiency of the work are verified by concise mathematical formulation and comparison of the results of the work with the others in four... 

    Investigation of Fatigue Crack Growth in a Landing Gear Support Fitting

    , M.Sc. Thesis Sharif University of Technology Ghodoosi, Hamed (Author) ; Adib Nazari, Saeid (Supervisor)
    In this thesis failure analysis of a critical part in a landing gear of a commercial aircraft was conducted.Fatigue phenomenon was determined as the reason for the failure and fracture of the mentionedcomponent. Fractography investigation of the fracture surface and charasteristicswas conducted.Scanning Electron Microscope was utilized for the study of the fracture surface. In the fracture surface, fatigue striations were observed. An experimental model of the crack growth is presented by using the fracture surface characteristics. By counting the fatigue striations and measuring their distance betwwn them on the fracture surface, the rate of the crack growth and crack growth life were... 

    Effects of loading modes on reliability of cracked structures using FORM and MCS

    , Article International Journal of Precision Engineering and Manufacturing ; Volume 18, Issue 1 , 2017 , Pages 63-76 ; 22347593 (ISSN) Delbariani Nejad, A ; Nazari, S. A ; Sharif University of Technology
    SpringerOpen  2017
    Studying the reliability of cracked structures under different types of failure modes such as a mixture of Mode I and Mode II loadings has been of great importance in many applications. The purpose of this study is to evaluate the effects of different modes of loading, i.e. pure Mode I, pure Mode II and Mixed mode I/II loadings on the reliability of cracked structures via three typical case studies including 1st: through crack in a very wide plate, 2nd: cracked pressurized fuselage and 3rd: cracked fastener holes under actual geometries and loading conditions using the FORM, the fracture toughness and the equivalent SIF for Mixed mode I/II loading which is extracted by the Energy release... 

    A transversely isotropic medium containing a penny-shaped crack subjected to a non-uniform axisymmetric loading via an anchored smooth rigid disk

    , Article Applied Mathematical Modelling ; Volume 45 , 2017 , Pages 491-504 ; 0307904X (ISSN) Ordookhani, A ; Kamali, M. T ; Shodja, H. M ; Sharif University of Technology
    A smooth rigid circular anchor disk encapsulated by a penny-shaped crack is embedded in and unbounded transversely isotropic medium. The lamellar rigid disk exerts a nonuniform axisymmetric loading to the upper face of the crack. With the aid of an appropriate stress function and Hankel transform, the governing equations are converted to a set of triple integral equations which in turn are reduced to a Fredholm integral equation of the second kind. For some transversely isotropic materials the normalized stiffness of the system falls well outside of the envelope pertinent to isotropic media. It is shown that mode I stress intensity factor is independent of the material properties and solely... 

    A study of nanovoid, Griffith-Inglis crack, cohesive crack, and some associated interaction problems in fcc materials via the many body atomic scale FEM

    , Article Computational Materials Science ; Volume 45, Issue 2 , 2009 , Pages 275-284 ; 09270256 (ISSN) Shodja, H. M ; Kamalzare, M ; Sharif University of Technology
    Due to inadequacy of the classical continuum theories at the nano-scale when dealing with defects, stress concentrators, and relevant deformation phenomena in solids, a refined approach that can capture the discrete atomic features of solids is essential. The inability to detect the size effect, giving unrealistically high values for some components of the stress field right on the edge of the stress concentrators, and infirmity to address the complex interaction between small inhomogeneities, cracks and as such when they are only a few nanometers apart, are among some of the drawbacks of the classical approach. An atomistic study which employs atomic finite element method in conjunction... 

    Modeling crack in orthotropic media using a coupled finite element and partition of unity methods

    , Article Finite Elements in Analysis and Design ; Volume 42, Issue 13 , 2006 , Pages 1165-1175 ; 0168874X (ISSN) Asadpoure, A ; Mohammadi, S ; Vafai, A ; Sharif University of Technology
    The problem of crack modeling in 2D orthotropic media is considered. The extended finite element method has been adopted for modeling and analyzing a crack and its domain numerically. In this method, first the finite element model without any discontinuities is created and then the two-dimensional asymptotic crack-tip displacement fields with a discontinuous function are added to enrich the finite element approximation using the framework of partition of unity. The main advantage is the ability of the method in taking into consideration a crack without any explicit meshing of the crack surfaces, and the growth of crack can readily be applied without any remeshing. Mixed-mode stress intensity... 

    The Effect of Stress Due to Repair of a Heat Exchanger on Crack

    , M.Sc. Thesis Sharif University of Technology Shishegar, Mehdi (Author) ; Farrahi, Gholamhossein (Supervisor) ; Selk Ghafari, Ali (Co-Advisor)
    A heat exchanger is a piece of equipment is built for efficient heat transfer from one medium to another. They are widely used in air conditioning, chemical plants and petrochemical plants, so studying the different failures and problems of them is important.
    One of the common problems is fracturing of the tubes. This will allow the hot water to enters them and then hit the refractory of the tubesheet. This coating slowly washing away and that will lead to direct contact between the hot fluid and the tubesheet. Tubesheet is not designed for such a hot thermal load so cracks will initiate on it due to this new situation. They will shut the fractured tube by shut it down and welding a... 

    A general unified treatment of lamellar inhomogeneities

    , Article Engineering Fracture Mechanics ; Volume 74, Issue 9 , 2007 , Pages 1499-1510 ; 00137944 (ISSN) Shodja, H. M ; Ojaghnezhad, F ; Sharif University of Technology
    Consider a lamellar inhomogeneity embedded in an unbounded isotropic elastic medium. When the elastic moduli of the lamellar inhomogeneity are zero it is a crack, if its elastic moduli are infinite it is an anticrack, and when its elastic moduli are finite it is called a quasicrack. Based on the Eshelby's equivalent inclusion method (EIM), the present paper develops a unified approach for determination of the exact closed-form expressions for modes I, II, and III stress intensity factors (SIFs) at the tips of lamellar inhomogeneities under a remote applied polynomial loading. © 2006 Elsevier Ltd. All rights reserved  

    Computational modeling of strong and weak discontinuities using the extended finite element method

    , Article Mechanics of Advanced Materials and Structures ; Volume 23, Issue 5 , 2016 , Pages 578-585 ; 15376494 (ISSN) Moradi, A ; Adib Nazari, S ; Sharif University of Technology
    Taylor and Francis Inc  2016
    In this article, the extended finite element method is employed to solve problems, including weak and strong discontinuities. To this end, a level set framework is used to represent the discontinuities location, and the Heaviside and Branch function are included in the standard finite element method. The case of two arbitrary curved cracks is solved numerically and stress intensity factor (SIF) values at the crack tips are calculated based on the evaluation of the crack tip opening displacement. Afterwards, J-integral methodology is adopted to evaluate the SIFs for isotropic and anisotropic bi-material interface crack problems. Numerical results are verified with those presented in the... 

    Experimental and numerical investigation of the center-cracked horseshoe disk method for determining the mode I fracture toughness of rock-like material

    , Article Rock Mechanics and Rock Engineering ; Volume 51, Issue 1 , 2018 , Pages 173-185 ; 07232632 (ISSN) Haeri, H ; Sarfarazi, V ; Yazdani, M ; Bagher Shemirani, A ; Hedayat, A ; Sharif University of Technology
    This paper presents a new procedure for determining the fracture toughness of rock-like specimens using the diametric compression test with the center-cracked horseshoe disk (CCHD) method. Using finite element analysis, a dimensionless stress intensity factor was obtained and a formula was rendered for determining mode I fracture toughness. To evaluate the accuracy of the measurement results produced by the CCHD method, fracture toughness experiments were conducted on the same rock-like material using the notched Brazilian disk (NBD) method. The CCHD tests were simulated using a two-dimensional particle flow code for validation of the experimental results, and a great agreement between the... 

    Experimental and numerical simulation of the microcrack coalescence mechanism in rock-like materials

    , Article Strength of Materials ; Volume 47, Issue 5 , September , 2015 , Pages 740-754 ; 00392316 (ISSN) Haeri, H ; Khaloo, A ; Marji, M. F ; Sharif University of Technology
    Springer New York LLC  2015
    Rocks and rock-like materials frequently fail under compression due to the initiation, propagation and coalescence of the pre-existing microcracks. The mechanism of microcrack coalescence process in rock-like materials is experimentally and numerically investigated. The experimental study involves some uniaxial compression tests on rock-like specimens specially prepared from portland pozzolana cement, mica sheets and water. The microcrack coalescence is studied by scanning electron microscopy on some of the prepared thin specimens. It is assumed that the mica sheets play the role of microcracks within the specimens. Some analytical and numerical studies are also carried out to simulate the... 

    Evaluation of Stress Intensity Factor of a Bi-material Interfacial Crack Using Extended Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Veisi, Hossein (Author) ; Adib Nazari, Saeed (Supervisor)
    In this study, Interfacial crack is modeled by the extended finite element method (XFRM) in order to evaluate the stress intensity factors for interface crack problems. These problems have crack edge discontinuity, material interfaces and singularity at the crack tip, which is inappropriate to finite element (FEM) mesh. Furthermore, around crack tips and interface edge, extremely fine discretization is required to achieve reasonable accuracy. All these factors increase the time and cost of the FEM solution. Recently the extended finite element method is developed and applied to interface fracture problems. In the XFEM, special enrichment functions are added to the finite element displacement... 

    Numerical and Experimental Study on Optimization of Overload arameters for Fatigue Life Increase

    , M.Sc. Thesis Sharif University of Technology Sarkheil, Saeed (Author) ; Saadat Foumani, Mahmoud (Supervisor)
    Fatigue life and crack growth retardation due to periodic tensile overload that superposed on constant amplitude cycles has been investigated. The tests were performed using C(T) specimens made of 7075 aluminium. All periodic overload tests were carried out at the same spacing between overloads and the effect of overload ratio on fatigue life has been investigated. Results of experiments revealed that the at low and high overload ratios, crack growth rate is relatively high and there is an optimum OLR that maximize interaction and thus minimize FCGR. Whit OCR-1=50, overload ratio of 1.85 led to maximum interaction and resulted in 219% increase in specimen's life relative to CA loading. Also... 

    An Atomistic Study of the Interacting Crack and Coated Inhomogeneity

    , M.Sc. Thesis Sharif University of Technology Ghassemi, Mohsen (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    Classical continuum mechanics fails to give an accurate solution near the crack tip, moreover, it implies that a solid is able to sustain an infinite stress at the Griffith-Inglis crack tips. Among other critical issues is the inability of classical approach to sense the size effect. For these reasons, for more in-depth understanding and accurate behavioral predictions, it is essential to develop some atomistic methods which properly accounts, not only for the structure but also the long and short range atomic interactions effectively. In this work the interaction of coated inhomogeneity and crack under polynomial loading is simulated by using the many body Rafii-Tabar and Sutton potential... 

    Elastic Field of an Anticrack Via Reproducing Kernel Particle Method

    , M.Sc. Thesis Sharif University of Technology Sohrabpour, Amir Hossein (Author) ; Mohammadi Shodja, Hossein (Supervisor)
    Meshless Methods using kernel approximation like Reproducing Kernel Particle Method (RKPM) are methods for solving partial differential equations that require only nodal data and a description of the geometry without requiring element connectivity data and mesh producing. An innovative method of nonplanar material partitioning method (NMPM) with implementation of RKPM is employed to calculate the stress intensity factor (SIF) at the tip of an anticrack sited in an isotropic plate under a remote applied loading. Numerical examples in comparison with the exact closed form expressions show that accurate SIF for mode I can be obtained.


    Application of Isogeometric Analysis in Determining Stress Distribution at the Tip of a Crack

    , M.Sc. Thesis Sharif University of Technology Zandinia, Meysam (Author) ; Jahanshahi, Mohsen (Supervisor)
    Isogeometric Analysis is one of the new methods for solving partial differential Equations which has special advantages compared to conventional methods such as the finite Element method. Some of these benefits can be used to approximate the geometry and solving the Equations governing the behavior of materials. Calculating the stress intensity factor at the tip of the Crack using classical method such as finite element method is done as well as IGA and gives Acceptable Results in linear range. Studying how to calculate these coefficients in combination with Isogeometric analysis method and comparing results with FEM due to novelty of the approach can have considerable importance for... 

    Developing new enrichment functions for crack simulation in orthotropic media by the extended finite element method

    , Article International Journal for Numerical Methods in Engineering ; Volume 69, Issue 10 , 2007 , Pages 2150-2172 ; 00295981 (ISSN) Asadpoure, A ; Mohammadi, S ; Sharif University of Technology
    New enrichment functions are proposed for crack modelling in orthotropic media using the extended finite element method (XFEM). In this method, Heaviside and near-tip functions are utilized in the framework of the partition of unity method for modelling discontinuities in the classical finite element method. In this procedure, by using meshless based ideas, elements containing a crack are not required to conform to crack edges. Therefore, mesh generation is directly performed ignoring the existence of any crack while the method remains capable of extending the crack without any remeshing requirement. Furthermore, the type of elements around the crack-tip remains the same as other parts of... 

    Effect of residual stress on stress intensity factors of fretting fatigue cracks

    , Article International Journal of Microstructure and Materials Properties ; Volume 2, Issue 2 , 2007 , Pages 164-177 ; 17418410 (ISSN) Farrahi, G. H ; Mohajerani, A ; Sharif University of Technology
    Inderscience Publishers  2007
    The effect of compressive Residual Stress (RS) on the Stress Intensity Factors (SIFs) of fretting fatigue cracks was studied using semi-analytical methods. The fretting fatigue of a half-plane in contact with a flat rounded pad was taken into consideration, and RS such as those created by shot-peening were added to the model. Studies of several RS profiles were accomplished to consider the effect of changes in RS caused by stress relaxation during service or pretreatment and manufacturing discrepancies regarding parameters. The distribution of dislocations method was applied to the calculation of the SIFs of these cracks and was shown to be capable of dealing with these kinds of problems. It...