Fracture Mechanics
Salmi Houda; Hachim Abdeliah; Hanan El Bhilat; Khaled El Had
Abstract
The present work deals with the effect of an external circumferential elliptical crack located at thickness transition on a varied stepped diameter pipe . The purpose is the application of the extended finite element method (XFEM) for the calculation of SIF at the thickness transition region of pipe ...
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The present work deals with the effect of an external circumferential elliptical crack located at thickness transition on a varied stepped diameter pipe . The purpose is the application of the extended finite element method (XFEM) for the calculation of SIF at the thickness transition region of pipe considering internal pressure and compare the effect of the crack between pipes straight and with thickness transition. To model a crack with precision , enrichment functions are used to enrich the displacement approximation, the level set functions are calculated from the crack mesh and definition of the strategy of integration has been performed. A comparative study is made on SIF of crack defect in straight pipe compared to one with thickness transition using XFEM for the crack and pipe geometrical parameters variations. The result shows that the XFEM is an effective and practical tool for elliptic crack modeling in a pipe with thickness transition because a crack is easily modeled through enrichment functions.The comparison of the SIF of a similar defect between pipes shows that a pressurized pipe with thickness transition is more sensitive to the used cracks.
Fracture Mechanics
Alireza Hassani; Amin Hassani; Mojtaba Mahmoudi Monfared
Abstract
Abstract: The solution to problem of an orthotropic long cylinder subjected to torsional loading is first obtained by means of separation valuables. The cylinder is twisted by two lateral shear tractions and the ends of the cylinder surface of the cylinder are stress-free. First, the domain under consideration ...
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Abstract: The solution to problem of an orthotropic long cylinder subjected to torsional loading is first obtained by means of separation valuables. The cylinder is twisted by two lateral shear tractions and the ends of the cylinder surface of the cylinder are stress-free. First, the domain under consideration is weakened by an axisymmetric rotational Somigliana ring dislocation. The dislocation solution is employed to derive a set of Cauchy singular integral equations for the analysis of multiple axisymmetric planner cracks. The numerical solution to these integral equations is used to determine the stress intensity factors (SIFs) for the tips of the concentric planar cracks A preliminary comparison between results of this study and those available in the literature is performed to confirm the validity of the proposed technique. Several examples of multiple concentric planner cracks are solved and displayed graphically. Furthermore, Configuration of the cracks and the interaction between cracks is studied.
Fracture Mechanics
Mahdi Yazdani
Abstract
In fracture mechanics and failure analysis, cracked media energy and consequently stress intensity factors (SIFs) play a crucial and significant role. Based on linear elastic fracture mechanics (LEFM), the SIFs and energy of cracked media may be estimated. This study presents the novel modification of ...
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In fracture mechanics and failure analysis, cracked media energy and consequently stress intensity factors (SIFs) play a crucial and significant role. Based on linear elastic fracture mechanics (LEFM), the SIFs and energy of cracked media may be estimated. This study presents the novel modification of decoupled scaled boundary finite element method (DSBFEM) to model cracked media. In this method, only the boundaries of problems are discretized using specific higher-order sub-parametric elements and higher-order Lagrange polynomials as mapping functions. Implementing the weighted residual method and using Gauss-Lobatto-Legendre numerical integration yield diagonal Euler’s differential equations. The chief modifications among the research conducted and the previous studies concerning DSBFEM is that here in, generation of geometry process of the functional interpolation, integration of the diverse is chosen, and by current technic, the difficulty of the DSBFEM is decreased. Therefore, when the local coordinates origin is located at the crack tip, the geometry of crack problems are implemented directly without further processing. Validity and accuracy of the proposed method are fully illustrated through three benchmark problems, whose results agree very well with those of other numerical and/or analytical solutions existing in the literature.
Fracture Mechanics
Kamal Kolasangiani; Mahmoud Shariati; Khalil Farhangdoost
Abstract
Forming limit curves are used as a parameter in finite element analysis to control the material's level of formability. In this research, forming limit diagram (FLD) of SS304L sheet was obtained by ABAQUSfinite element software. In practice, the experimental determination of a forming limit curve is ...
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Forming limit curves are used as a parameter in finite element analysis to control the material's level of formability. In this research, forming limit diagram (FLD) of SS304L sheet was obtained by ABAQUSfinite element software. In practice, the experimental determination of a forming limit curve is a very time-consuming procedure which requires special and expensive equipment. Forming limit diagram (FLD) is derived by the simulation of Erichsen test (out-of-plane stretching test) using hemispherical punch. There are few studies on the prediction of necking time, which is obtained by the application of Pepelnjak algorithm and ductile fracture criterion. In order for the validation, the numerical result of forming limit diagram (FLD) was compared with the experimental and analytical results and a good correlation was observed. Forming limit stress diagram (FLSD) and MSFLD were determined by plotting the principal in-plane stress and FLD corresponding to the onset of necking localization, respectively. Effect of the thickness of the sheet on forming limit curves was investigated and the results showed that increased thickness of the sheet led to raised level of the FLD and MSFLD; but, FLSD did not change considerably.
Fracture Mechanics
A. R. Shahani; H. Moayeri Kashani
Abstract
In this paper, three-dimensional modeling of the fatigue crack growth profiles was performed in a simple riveted lap joint. Simulation results showed that mode I was dominated on the one side of the plates and the crack straightly grew on this side, while the other side of the plates was in a mixed-mode ...
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In this paper, three-dimensional modeling of the fatigue crack growth profiles was performed in a simple riveted lap joint. Simulation results showed that mode I was dominated on the one side of the plates and the crack straightly grew on this side, while the other side of the plates was in a mixed-mode condition and the crack propagation path was not straight on this side. Afterward, the fracture mechanics-based life prediction of the riveted lap joint was considered using EIFS concept. Back extrapolation method was used for estimating EIFS. Results demonstrated that EIFS would depend on loading amplitude if ΔK had been implemented in EIFS estimation using Paris equation. In contrast EIFS dependency on loading amplitude significantly reduced when using ΔJ in EIFS estimation. Finally, fatigue life of the riveted lap joint was predicted based on safe life method using Brown-Miller critical plane criterion. Results represented that the predicted life using fracture mechanics concept was much closer to the experimental results.
Fracture Mechanics
M. Shariati; A. M. Majd Sabeti; H. Gharooni
Abstract
Existence of cracks in industrial structures is one of the important causes of their failure, especially when they are subjected to important axial compressive forces that might lead to buckling. Therefore, it must be considered in stress analysis and designing and loading of such structures. In this ...
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Existence of cracks in industrial structures is one of the important causes of their failure, especially when they are subjected to important axial compressive forces that might lead to buckling. Therefore, it must be considered in stress analysis and designing and loading of such structures. In this paper, the buckling and post-buckling behaviors of stainless-steel cracked plates under axial compression load were investigated both experimentally and numerically and effects of the geometrical and mechanical parameters, such as crack length, crack angle, crack position, plate imperfection, load band, and plate thickness on the critical buckling load were studied. In the experimental study, mechanical properties and plastic behavior of stainless steel plates were determined for the subsequent numerical study. Numerical modeling was carried out by ABAQUS finite element software. Numerical predictions were compared with the experimental results and the reliability of the numerical solution was proven. Results demonstrated the considerable effects of the mentioned parameters on the critical buckling load of plate.
Fracture Mechanics
Abstract
In sheet metal forming processes with complex strain paths, a part is subjected to large plastic deformation. This severe plastic deformation leads to high plastic strain localization zones and subsequent accumulation of those strains. Then internal and superficial micro-defects and in other words ductile ...
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In sheet metal forming processes with complex strain paths, a part is subjected to large plastic deformation. This severe plastic deformation leads to high plastic strain localization zones and subsequent accumulation of those strains. Then internal and superficial micro-defects and in other words ductile damage is created. This damage causes quality problems such as fracture. Therefore, design engineers need to accurately estimate the damage initiation and its growth. In this paper, initiation and evolution of damage has been predicted using Lemaitre’s damage and forming limit diagram (FLD) damage models for automotive panel forming, because of its nonlinear strain paths. Lemaitre’s damage criterion has been implemented as a subroutine for an elastic-plastic material and plane stress and finite strain theories. Using this subroutine in explicit finite element code, damage initiation and evolution is predicted for the above mentioned process and the results obtained by FLD and Lemaitre models are compared. In this paper, FLD and Lemaitre damage models results show the fact that the damage localization zones are corresponding to the equivalent plastic strain distributions. Comparison of the FLD damage and Lemaitre damage results show that in an automotive panel forming process, both models predict initiation of cracks in the edges of a sheet. Hence, it is concluded that finite element method combined with continuum damage mechanics can be used as a reliable and rapid tool to predict damage evolution in sheet metal forming processes with nonlinear and complex strain paths such as automotive panel forming.
