• Advances in materials Research
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• v.12 no.4
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• pp.273-286
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• 2023

The fracture mechanics make it possible to characterize the behavior with cracking of structures using parameters quantifiable in the sense of the engineer, in particular the stress field, the size of the crack, and the resistance to cracking of the material. Any structure contains defects, whether they were introduced during the production of the part (machining or molding defects for example). The aim of this work is to determine numerically by the finite element method the stress concentration factor Kt of a plate subjected to a tensile loading containing a lateral form defect with different sizes: a semicircle of different radii, a notch with different opening angles and a crack of different lengths. The crack propagation is then determined using the extended finite element technique (X-FEM). The modeling was carried out using the ABAQUS calculation code.

• Structural Engineering and Mechanics
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• v.28 no.4
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• pp.461-477
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• 2008

An adaptive finite element method for analyzing two-dimensional and axisymmetric nonlinear elastic fracture mechanics problems with cracks is presented. The J-integral is used as a parameter to characterize the severity of stresses and deformation near crack tips. The domain integral technique, for which all relevant quantities are integrated over any arbitrary element areas around the crack tips, is utilized as the J-integral solution scheme with 9-node degenerated crack tip elements. The solution accuracy is further improved by incorporating an error estimation procedure onto a remeshing algorithm with a solution mapping scheme to resume the analysis at a particular load level after the adaptive remeshing technique has been applied. Several benchmark problems are analyzed to evaluate the efficiency of the combined domain integral technique and the adaptive finite element method.

• Structural Engineering and Mechanics
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• v.18 no.6
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• pp.731-744
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• 2004

Modified virtual crack closure integral (MVCCI) technique has become very popular for computation of strain energy release rate (SERR) and stress intensity factor (SIF) for 2-D crack problems. The objective of this paper is to propose a numerical integration procedure for MVCCI so as to generalize the technique and make its application much wider. This new procedure called as numerically integrated MVCCI (NI-MVCCI) will remove the dependence of MVCCI equations on the type of finite element employed in the basic stress analysis. Numerical studies on fracture analysis of 2-D crack (mode I and II) problems have been conducted by employing 4-noded, 8-noded (regular & quarter-point), 9-noded and 12-noded finite elements. For non-singular (regular) elements at crack tip, NI-MVCCI technique generates the same results as MVCCI, but the advantage for higher order regular and singular elements is that complex equations for MVCCI need not be derived. Gauss numerical integration rule to be employed for 8-noded singular (quarter-point) element for accurate computation of SERR and SIF has been recommended based on the numerical studies.

• Structural Engineering and Mechanics
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• v.35 no.3
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• pp.283-299
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• 2010

This paper addresses the numerical simulation of fatigue crack growth in arbitrary 2D geometries under constant amplitude loading by the using a new finite element software. The purpose of this software is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of fatigue crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement extrapolation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history must be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.191-198
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• 2006

The objective of this study is to examine fracture characteristics of concrete at early ages, i.g. critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of effective-elastic crack model and cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By experimenting with various strengths and ages, load-crack mouth opening curves were obtained, and the results were analyzed by linear elastic fracture mechanics and FEM(finite element method). The results from the test and analysis showed that critical stress intensity factor and facture energy increased while critical crack-tip opening displacement decreased with concrete aging from 1 day to 28 days. Four parameters of bilinear softening curve from 1 day to 28 days were obtained from a numerical analysis. The obtained fracture parameters and bilinear softening curves at early ages from this study are to be used as a fracture criterion and an input data for the finite element analysis of concrete at early ages.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.225-233
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• 1999

This paper describes a versatile finite element technique which has been used to investigate of wide range of structural defects of practical importance. The procedure automatically remeshes the three-dimensional finite element model during the stages of crack growth. Problems analyzed to date include the surface cracks in leak-before-break situations, the development of quarter-elliptical corner defects, planar semi-elliptical surface defects and the fatigue growth of defects.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.133-141
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• 2002

This paper describes a versatile finite element technique which has been used to investigate wide range of structural defects of practical importance. The procedure automatically remeshes the three-dimensional finite element model during the stages of crack growth. Problems include the surface cracks in leak-before-break situations, the shape development of multiple surface defects.

• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.1-8
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• 2023

Power transmission shafts in rotary wing aircraft use a hollow shaft to reduce weight. We can apply linear elastic fracture mechanics to predict crack propagation behavior. This paper predicted crack growth life of a hollow shaft with a circumferential through-type crack by finite element analysis. A 2D finite element model was created by applying a torsion and forming elements considering cracks. We defined the initial crack length and performed the finite element analysis by increasing the crack length to derive stress intensity factor at crack tips. We defined the length just prior to the stress intensity factor exceeding the fracture toughness as the crack limit length. We calculated the crack limit length using a handbook and numerically integrated the crack growth rate equation to derive growth life of each crack. The growth life of each crack was compared to verify the proposed finite element analysis method.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.19-29
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• 1988

This paper reports on the elatic-plastic analysis and fracture behavior of cylinder with outer surface crack which is under external or internal pressure. For the studuty of crack length effects in cylinder, ratios of crack lengths to finite thickness (a/t) are dertermined 0.3, 0.4, 0.5. For the study of curvature effects in cylinders, ratios of mean diameter to finite thicknees (Rm/t) are determined 10.0, 15.0, 20.0. Analysis is conduceted using the theory of fracture mechanics and two dimensional finite element solution assuming the axi-symmetrical plane strain conditon. Main results of this study are as follows. 1) It is known from this paper that elastic-plastic strain is initiated near crack tip and enlarged between crack tip and inner side of cylinder. 2) $K_{1}$ of cylinder under external or internal pressure is evaluated memebrane stress .root..pi.* crack length. The results of this study are inclined to Lomacky's results and Kobayshi's result. 3) Distribution of stress near crack tip is looked higher than of other zone, as crack length of equal model is longer, and as diameter of cylinder is longer. 4) When other conditions are equal, displacemenet near crack tip is looked duller, as length is longer.

• Computational Structural Engineering
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• v.8 no.4
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• pp.107-115
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• 1995

The long term behavior of the Waste Isolation Pilot Plant(WIPP), a nuclear waste repository currently under construction near Carlsbad at New Mexico, depends upon the fracture and deformation behavior of bedded rock salt. Although many numerical analyses of the WIPP have been conducted, to our knowledge none have included the ability to simultaneously predict the effects of fracture and nonlinear deformation of the salt continuum. We are in the process of developing a finite element program to simulate the effects of nonlinear fracture mechanics and nonlinear continuum behavior of rock salt simultaneously.