Papers by Keyword: Stress Intensity Factor (SIF)

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Authors: Ke Li, Ying Yi Wang, Xing Chun Huang
Abstract: Structural plane is different from common crack, as it is often under pressure and has non-linear normal and tangential deformation behavior. This paper simulates the propagation of non-linear deformation structural plane by 3D displacement discontinuity method (DDM). Through least square regression of the elements near the tip, the stress intensity factor (SIF) of the tip is obtained. Maximum energy release rate criterion is adopted to be the fracture criterion in this paper, assuming the propagation occurred in the normal plane of the front edge, KI is modified to consider the effect of mode Ⅲ crack. The structural plane model is considered as a hyperbolic non-linear model, the Barton-Bandis model is adopted as the normal deformation model, the Kulhaway model is adopted as the tangential deformation model, and the Mohr-Coulomb criterion is adopted as the shear strength criterion. The result shows that the propagation direction is along the direction of the load, DDM could efficiently trace this process.
Authors: Cristian Sorin Nes, Nicolae Faur, Liviu Marsavina
Abstract: Objectives: Numerical determinations of Stress Intensity Factors (SIFs) for a shaft under mixed-mode load with a crack of different sizes in the connection zone between square and circular cross-sections. Methods: Linear-elastic Fracture Mechanics principles are used. The numerical analysis program used was ABAQUS CAE version 6.9-3. The shaft consists in a circular section and a square section, with a fillet connecting zone. Cracks of different lengths and different depths are modeled. The shaft is subjected to torsion and bending. The SIFs were determined using the contour integral method. Results: The stress distribution was determined and plotted, and the stress concentration effect of the notches was highlighted. Crack propagation was also performed, using the XFEM module of ABAQUS code. The computed SIFs were plotted along the crack front. Conclusions: Crack initiation and propagation matched the pattern obtained in experimental tests, thus validating the model. The results confirmed that the fillet zone between the two sections acts as a stress concentrator. The fillet radius determines the magnitude of stress concentration. Crack geometry has a significant influence on SIFs, as well as on the global stress distribution.
Authors: Yu Zhou Sun, Dong Xia Li, Hui Wang
Abstract: This paper presents a boundary element-free computational method for the fracture analysis of 2-D anisotropic bodies. The study starts from a derived traction boundary integral equation (BIE) in which the boundary conditions of both upper and lower crack surfaces are incorporated into and only the Cauchy singular kernal is involved. The boundary element-free method is achieved by combining this new BIE and the moving least-squares (MLS) approximation. The new BIE introduces two new variables: the displace density and The dislocation density. For each crack, the dislocation density is first expressed as the product of the characteristic term and unknown weight function, and the unknown weight function is approximated with the MLS approximation. The stress intensity factors (SIFs) can be calculated from the the weight function. The examples of the straight and circular-arc cracks are computed, and the convergence and efficiency are discussed.
Authors: Ming Guang Shi, Chong Ming Song, Hong Zhong, Yan Jie Xu, Chu Han Zhang
Abstract: A coupled method between the Scaled Boundary Finite Element Method (SBFEM) and Finite Element Method (FEM) for evaluating the Stress Intensity Factors (SIFs) is presented and achieved on the platform of the commercial finite element software ABAQUS by using Python as the programming language. Automatic transformation of the finite elements around a singular point to a scaled boundary finite element subdomain is realized. This method combines the high accuracy of the SBFEM in computing the SIFs with the ability to handle material nonlinearity as well as powerful mesh generation and post processing ability of commercial FEM software. The validity and accuracy of the method is verified by analysis of several benchmark problems. The coupled algorithm shows a good converging performance, and with minimum additional treatment can be able to handle more problems that cannot be solved by either SBFEM or FEM itself. For fracture problems, it proposes an efficient way to represent stress singularity for problems with complex geometry, loading condition or certain nonlinearity.
Authors: José A.S. Cardoso, Virgínia Infante, Bruno A.S. Serrano
Abstract: The stop-drilling technique is a simple and economic way to delay crack propagationby drilling a hole on the crack tip and reducing stress concentration. This paper presents thepropagation of cracks and investigates how the increasing of the stop-drill diameter improvescrack initiation life in specimens of 2024-T3 aluminium alloy of C-130 aircraft skin. A numericalmethod was applied to simulate an automatic crack propagation by interacting ANSYSr andMATLABr, and several experimental fatigue tests were done to support the computationalresults. A Morrow equation was used to predict the fatigue life of the stop-drill. Good agreementof stress intensity factor along crack length was obtained between numerical and experimentalresults. All results show that fatigue life increases when the stop-drill diameter is larger. Whencompared to the 2mm diameter stop-drill, the experimental results show an improvement of189% and 464% to 4mm and 6mm diameter stop-drill fatigue life, and the numerical results of333% and 952%, respectively.
Authors: Z.C. Xuan, J.W. Peng
Abstract: We present a method for computing the stress intensity factors in bimaterials based on the goal oriented finite element error estimate. The goal oriented analysis focuses on computing the bounds on the local quantities of interest, e.g. local stresses, local displacements, stress intensity factors etc, of a structure, and with the bounds obtained on the coarse finite element mesh we can obtain the quantities of interest with nearly the same accuracy as that obtained on the fine finite element mesh. In this paper the stress intensity factors in bimaterials are first formulated as explicit computable linear function of the displacements by means of the two-points extrapolation method. Then the goal oriented finite element method is used to compute the lower and upper bounds on the stress intensity factors, and the average of the bounds is considered as a prediction of the stress intensity factor. At last, the stress intensity factors, 0 K and r K , in bimaterials are computed with the proposed method to show its efficiency.
Authors: Jin Fang Zhao, Qun Zhao
Abstract: This paper introduced compounding method to calculate the SIF of typical MSD configurations. Complex function method was proposed to calculate the modification coefficient of the adjacent holes. Combining the method with compounding method, the SIF calculation of typical MSD configurations was achieved. The calculation process is easy to operate and the results are reliable which can be verified by FEM calculation. By studying the SIF results of typical MSD configurations, a series of conclusions with practical value in engineering can be obtained.
Authors: Xiao Shun Yan, Xiao Ping Huang
Abstract: The calculation of stress intensity factor (SIF) in fracture mechanics-based fatigue life prediction is mainly based on empirical formulas, the poor applicability of which limits the wide application of fatigue assessment based on crack propagation. This paper proposed a SIF calculation method for structures under wave loads. It was proved correct by comparing with the empirical formulas. Then, the method proposed was applied for the surface crack at weld toe of a connection between the column and brace of a semi-submersible platform. The predicted results showed that SIF ranges varied with wave loads, which were subjected to the effects of wave directions and frequencies. In addition, SIF ranges calculated by empirical formulas were very different from those of the proposed method. In order to accurately predict fatigue crack propagation life for ocean engineering structures, it is necessary to take the characters of wave loads into consideration. The proposed method in this paper may provide a reference.
Authors: Takahiro Matsueda
Abstract: Aspect ratio is a key factor to calculate stress intensity factor (SIF) K using fracture mechanics. While cracks are approximated to be semi-circle or semi-ellipse for simply evaluation, their shapes are changed by stress concentration source. In this study, a new method to modify aspect ratio of a crack at a notch root is proposed. Modified aspect ratio in this method succeeded to decrease prediction error of fatigue crack initiation stress, σw1 which was calculated using experimental value.
Authors: Jie Jia, Yuan Yuan Chen, Ling Yu, Ming Bao Li
Abstract: A new interaction integral technique is derived for computation of mixed-mode stress intensity factors (SIFs) in nonhomogeneous materials with continuous or discontinuous properties. This method is based on a conservation integral that relies on two admissible mechanical states (actual and auxiliary fields). In the equivalent domain formulation, the integrand does not involve any derivatives of material properties. Moreover, the formulation is proved to be still valid when the integral domain contains material interfaces. Therefore, its applicable range is greatly enlarged. The method is combined with the extended finite element method (XFEM) to calculate the SIFs for different integral domains. Numerical results show that the interaction integral has excellent convergence for material nonhomogeneity and discontinuity.
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