Sharif Digital Repository

In this paper, an automated adaptive remeshing procedure is presented for simulation of arbitrary shape crack growth in multiple cracked bodies. The Zienkiewicz-Zhu error estimator is employed in conjunction with the modified superconvergent patch recovery (SPR) technique to obtain more accurate estimation of error. A stability analysis is performed to determine active cracks from a set of competitive cracks. Various crack growth criteria together with the respective crack trajectory prediction are compared. Several numerical examples are illustrated to demonstrate the efficiency, robustness and accuracy of computational algorithm in the simulation of multiple crack growth  

In this paper, the crack propagation in ductile materials is simulated under cyclic and dynamic loading. The adaptive finite element method is used to model the discontinuity due to crack propagation. The ductile fracture assumptions and continuum damage mechanics are utilized to model the material rupture behavior. Moreover both the rate-independent and rate-dependent constitutive equations are elaborated and the crack closure effect and combined hardening model are discussed in addition to some aspects of finite element implementation. Finally, a comparison is performed between the numerical simulation results and those of experiments to illustrate the robustness of proposed computational... 

In this research, a coupled numerical-experimental analysis of crack propagation, crack coalescence, and breaking process of jointed rock slopes is performed by studying the mechanical behavior of pre-cracked brittle substances considering the specially prepared rock-like specimens (rock-like specimens are specially prepared by a proper mixing of Portland Pozzolana Cement (PPC), fine sand, and water in a rock mechanics laboratory) and natural rock slopes, simultaneously. The numerical analyses are accomplished using a numerical code based on the higher-order displacement discontinuity method (HODDM). A cubic displacement discontinuity variation along each boundary element is assumed to... 

In this paper, a fully coupled numerical model is developed for the modeling of the hydraulic fracture propagation in porous media using the extended finite element method in conjunction with the cohesive crack model. The governing equations, which account for the coupling between various physical phenomena, are derived within the framework of the generalized Biot theory. The fluid flow within the fracture is modeled using the Darcy law, in which the fracture permeability is assumed according to the well-known cubic law. By taking the advantage of the cohesive crack model, the nonlinear fracture processes developing along the fracture process zone are simulated. The spatial discretization... 

A coupled experimental-numerical study on shear fracture in concrete specimens with different geometries is carried out. The crack initiation, propagation and final breakage of concrete specimens are experimentally studied under compression loading. The load-strain and the strength of the specimens are experimentally measured, indicating decreasing effects of the shear behavior on the failure load of the specimen. The effects of specimen geometries on the shear fracturing path in the concrete specimens are also investigate. Numerical models using an indirect boundary element method are made to evaluate the crack propagation paths of concrete specimens. These numerical results are compared... 

In this paper, a numerical model is developed for the fully coupled hydro-mechanical analysis of deformable, progressively fracturing porous media interacting with the flow of two immiscible, compressible wetting and non-wetting pore fluids, in which the coupling between various processes is taken into account. The governing equations involving the coupled solid skeleton deformation and two-phase fluid flow in partially saturated porous media including cohesive cracks are derived within the framework of the generalized Biot theory. The fluid flow within the crack is simulated using the Darcy law in which the permeability variation with porosity because of the cracking of the solid skeleton... 

The objective of this work was to gain a quantitative and qualitative understanding of the degree to which porosity influences thermal-fatigue performance and other mechanical properties of A319 aluminum casting alloy over ranges of commercial interest. The number of cycles to failure for each test was recorded. An increase in porosity content caused degradation in thermal-fatigue life and other mechanical properties. The fractographic examinations identified the pores and some intermetallics as the key microstructural features which promote damage and thermal-fatigue crack initiation sites in the specimens. Crack initiation and propagation is expected to occur sooner in regions of higher... 

Molecular dynamics simulation method was employed to model mode I crack propagation in plates containing nanoscale clusters of impurities located in the vicinity of the crack tip. The plates and the clusters were considered to have an fcc structure. The interactions between the dissimilar atoms in the plates and clusters were modeled via the many-body Sutton-Chen inter-atomic potentials [Sutton, A.P., Chen, J., 1990. Long-range Finnis-Sinclair potentials. Philos. Mag. Lett. 61, 139-164], and their extended versions developed for fcc alloys by [Rafii-Tabar, H., Sutton, A.P., 1991. Long-range Finnis-Sinclair potentials for fcc metallic alloys. Philos. Mag. Lett. 63, 217-224]. In this paper,... 

Not only should dams be evaluated for seismic shaking, but their capability to survive potential fault displacement in their foundations should also be assessed. Safety reviews of existing dams suggest that geological-seismic evaluation of some dam sites has failed to recognize the existence of possibly active faults. In this study, the nonlinear seismic behavior of concrete gravity dams, due to relative fault dislocation occurring in foundations, has been investigated. Two types of fault movement, including normal-slip and reverse-slip, have been considered. These two types, combined with the location of fault lines, with respect to the toe, middle, and heel of the dam base, angle of fault,... 

A novel approach for mesoscale modelling of concrete composites is proposed by combining enriched scaled boundary finite element methods with quad-tree mesh. The concrete meso-structures are comprised of randomly distributed aggregates, mortar matrix, and interface transition zone. An improved random aggregate generation technique is developed to construct digital images of mesoscale concrete models. Based on the quadtree decomposition algorithm, meshes can be generated automatically from the digital images of concrete mesostructure. The whole mesh generation process is highly efficient without any artificial interference and eliminates the issue of hanging nodes faced by standard finite... 

Fatigue life and crack growth retardation due to periodic tensile overloads, which are superposed on constant amplitude cycles, have been investigated in the present study. In the numerical analyses, the Walker equation with the generalized Willenborg model has been used. The analyses and experiments have been performed on C(T) specimens made of 7075 aluminium. The periodic overloads have been induced at two different periodicities and the effect of overload ratio and overload periodicity on the fatigue life has been studied. The results of the experiments and analyses reveal that the normalized fatigue life versus overload ratio curve has a maximum point, which indicates that there are... 

Modeling the water flow in cohesive fracture is a fundamental issue in the crack growth simulation of cracked concrete gravity dams and hydraulic fracture problems. In this paper, a mathematical model is presented for the analysis of fracture propagation in the semi-saturated porous media. The solid behavior incorporates a discrete cohesive fracture model, coupled with the flow in porous media through the fracture network. The double-nodded zero-thickness cohesive interface element is employed for the mixed mode fracture behavior in tension and contact behavior in compression. The modified crack permeability is applied in fracture propagation based on the data obtained from experimental... 

The phase field approach (PFA) for the interaction of fracture and martensitic phase transformation (PT) is developed, which includes the change in surface energy during PT and the effect of unexplored scale parameters proportional to the ratio of the widths of the crack surface and the phase interface, both at the nanometer scale. The variation of these two parameters causes unexpected qualitative and quantitative effects: shift of PT away from the crack tip, "wetting" of the crack surface by martensite, change in the structure and geometry of the transformed region, crack trajectory, and process of interfacial damage evolution, as well as transformation toughening. The results suggest...