A quadtree-polygon-based scaled boundary finite element method for crack propagation modeling in functionally graded materials
- Authors: Chen, Xiaojun , Luo, Tao , Ooi, Ean Tat , Ooi, Ean Hin , Song, Chongmin
- Date: 2018
- Type: Text , Journal article
- Relation: Theoretical and Applied Fracture Mechanics Vol. 94, no. (2018), p. 120-133
- Full Text: false
- Reviewed:
- Description: This paper presents a method to improve the computational efficiency of the scaled boundary finite element formulation for functionally graded materials. Both isotropic and orthotropic functionally graded materials are considered. This is achieved using a combination of quadtree and polygon meshes. This hybrid meshing approach is particularly suitable to be used with the SBFEM for functionally graded materials because of the significant amount of calculations required to compute the stiffness matrices of the polygons/cells in the mesh. When a quadtree structure is adopted, most of the variables required for the numerical simulation can be pre-computed and stored in the memory, retrieved and scaled as required during the computations, leading to an efficient method for crack propagation modeling. The scaled boundary finite element formulation enables accurate computation of the stress intensity factors directly from the stress solutions without any special post-processing techniques or local mesh refinement in the vicinity of the crack tip. Numerical benchmarks demonstrate the efficiency of the proposed method as opposed to using a purely polygon-mesh based approach. © 2018 Elsevier Ltd
Crack propagation modelling in concrete using the scaled boundary finite element method with hybrid polygon-quadtree meshes
- Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Ooi, Ean Hin
- Date: 2017
- Type: Text , Journal article
- Relation: International Journal of Fracture Vol. 203, no. 1-2 (2017), p. 135-157
- Full Text: false
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- Description: This manuscript presents an extension of the recently-developed hybrid polygon-quadtree-based scaled boundary finite element method to model crack propagation in concrete. This hybrid approach combines the use of quadtree cells with arbitrary sided polygons for domain discretization. The scaled boundary finite element formulation does not distinguish between quadtree cells and arbitrary sided polygons in the mesh. A single formulation is applicable to all types of cells and polygons in the mesh. This eliminates the need to develop transitional elements to bridge the cells belonging to different levels in the quadtree hierarchy. Further to this, the use of arbitrary sided polygons facilitate the accurate discretization of curved boundaries that may result during crack propagation. The fracture process zone that is characteristic in concrete fracture is modelled using zero-thickness interface elements that are coupled to the scaled boundary finite element method using a shadow domain procedure. The scaled boundary finite element method can accurately model the asymptotic stress field in the vicinity of the crack tip with cohesive tractions. This leads to the accurate computation of the stress intensity factors, which is used to determine the condition for crack propagation and the resulting direction. Crack growth can be efficiently resolved using an efficient remeshing algorithm that employs a combination of quadtree decomposition functions and simple Booleans operations. The flexibility of the scaled boundary finite element method to be formulated on arbitrary sided polygons also result in a flexible remeshing algorithm for modelling crack propagation. The developed method is validated using three laboratory experiments of notched concrete beams subjected to different loading conditions.
Crack propagation modelling in functionally graded materials using scaled boundary polygons
- Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Tin-Loi, Francis
- Date: 2015
- Type: Text , Journal article
- Relation: International Journal of Fracture Vol. Online first, no. 192 (2015), p. 87-105
- Full Text: false
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- Description: A recently developed scaled boundary finite element formulation that can model the response of functionally graded materials is further developed to model crack propagation in two-dimensions. This formulation can accurately model the stress singularity at the crack tip in heterogeneous materials. The asymptotic behaviour at the crack tip is analytically represented in the scaled boundary shape functions of a cracked polygon. This enables accurate stress intensity factors to be computed directly from their definitions. Neither local mesh refinement nor asymptotic enrichment functions are required. This novel formulation can be implemented on polygons with an arbitrary number of sides. When modelling crack propagation, the remeshing process is more flexible and leads to only minimal changes to the global mesh structure. Six numerical examples involving crack propagation in functionally graded materials are modelled to demonstrate the salient features of the developed method.
Crack propagation modelling in functionally graded materials using scaled boundary polygons
- Authors: Ooi, Ean Tat , Natarajan, Sundararajan , Song, Chongmin , Tin-Loi, Francis
- Date: 2015
- Type: Text , Journal article
- Relation: International Journal of Fracture Vol. 192, no. 1 (2015), p. 87-105
- Full Text: false
- Reviewed:
- Description: A recently developed scaled boundary finite element formulation that can model the response of functionally graded materials is further developed to model crack propagation in two-dimensions. This formulation can accurately model the stress singularity at the crack tip in heterogeneous materials. The asymptotic behaviour at the crack tip is analytically represented in the scaled boundary shape functions of a cracked polygon. This enables accurate stress intensity factors to be computed directly from their definitions. Neither local mesh refinement nor asymptotic enrichment functions are required. This novel formulation can be implemented on polygons with an arbitrary number of sides. When modelling crack propagation, the remeshing process is more flexible and leads to only minimal changes to the global mesh structure. Six numerical examples involving crack propagation in functionally graded materials are modelled to demonstrate the salient features of the developed method. © 2015, Springer Science+Business Media Dordrecht.
Dynamic cohesive crack propagation modelling using the scaled boundary finite element method
- Authors: Ooi, Ean Tat , Yang, Zhenjun , Guo, Zaoyang
- Date: 2012
- Type: Text , Journal article
- Relation: Fatigue and Fracture of Engineering Materials and Structures Vol. 35, no. 8 (2012), p. 786-800
- Full Text: false
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- Description: This study develops a scaled boundary finite element method (SBFEM)-based approach for modelling fast cohesive crack propagation in quasi-brittle materials subjected to transient dynamic loadings. In this approach, the elastic bulk material is modelled by SBFEM subdomains and the cracks by nonlinear cohesive interface finite elements that are automatically inserted by a remeshing procedure. The global equation system is solved using an implicit time integration algorithm. Because all the solutions (displacements, stresses, velocities, accelerations) are semi-analytical in an SBFEM subdomain, this approach offers a few advantages over other methods, such as accurate calculation of dynamic stress intensity factors and T-stress without using fine crack-tip meshes, simpler remeshing, more accurate and efficient mesh mapping, and the need of much fewer degrees of freedom for the same accuracy. The approach is validated by modelling two concrete beams under impact, subjected to mode-I and mixed-mode fracture, respectively. © 2012 Blackwell Publishing Ltd.
Failure analysis of articulated paddings at crossing interface between crossing cable and crossed pipeline
- Authors: Reda, Ahmed , Elgazzar, Mohamed , Sultan, Ibrahim , Shahin, Mohamed , McKee, Kristoffer
- Date: 2021
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 115, no. (2021), p.
- Full Text: false
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- Description: While subsea crossings are undesirable for many reasons, they are unavoidable due to the sheer density of subsea assets. The use of articulated paddings is a cost-effective and practical method to achieve the required vertical separation between the crossing and the crossed pipelines or cables, though, not without limitations. In this paper, the failure of articulated padding at several points along a subsea cable in operation was investigated. The articulated padding has experienced partial fractures at numerous crossing locations and in some places has fallen off the cable completely. A complete failure mode analysis was conducted where several possible modes of failure were considered in detail. In-place finite element (FE) analyses of the articulated padding components and the corresponding environment were also performed. The FE modelling concluded that the original design loads were significantly lower than the expected worst-case load scenarios. To replicate the failure mode, two abrasion tests were also conducted and the results of which were studied. It was concluded that the predominant failure mode (partial fracture to the articulated padding discs) was likely a combination of the increased dynamic loads, excessive lateral movement causing unexpected levels of fretting, unbalanced free span causing unexpected stress concentration factors and reduction in material mechanical properties. All above factors have contributed to the root cause of the system failure and instigated the predominant mode of failure “partial fracture”. © 2021