Papers by Keyword: Cohesive Model

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Authors: Bo Wu, Yue Guang Wei
Abstract: By means of finite element method which is based on the conventional theory of mechanism-based strain gradient plasticity, cohesive interface model is used to study the intergranular fracture in polycrystalline metals with nanoscale and ultra-fine grains. A systematical study on the overall strength and ductility of polycrystalline aggregates which depend on both grain interiors and grain boundaries for different grain sizes is performed. The results show that the overall strength and ductility of polycrystalline aggregates with nanoscale and ultra-fine grains are strongly related to the competition of grain boundaries deformation with that in grain interiors. Finally, the deformation and failure behavior of nanocrystalline nickel are described by using the computational model.
Authors: Bing Xue, Heng An Wu, Xiu Xi Wang, Zhi Long Lian, Jin Zhang, Shi Cheng Zhang
Abstract: Three-dimensional finite element simulations were carried out to investigate the hydraulic progressive damage and associated flow behavior in rock. In this study cohesive elements were used to simulate the damage of rock. A three-dimensional coupled pore fluid flow and stress model was proposed. The commercial engineering software ABAQUS is employed to simulate the damage process in rock along several predefined paths. A user-subroutine named FLOW was developed to enhance the capability of ABAQUS to deal the moving loadings. With the proposed coupling model, we studied the stress distribution, the pore pressure, the fluid loss, the geometry of the progressive damage. The results show that the length and the width of the path of the progressive damage are strongly influenced by both the hydraulic pressure and the injection time. The results provide good interpretation and understanding of the mechanism of hydraulic progressive damage in rock. This study is very useful and important to the oil engineering and some other rock engineering fields.
Authors: Toshio Nakamura, Zi Qiang Wang
Abstract: Accurate crack propagation simulation requires critical fracture parameters to be known a priori. For elastic-plastic materials, two fundamental parameters are the separation energy and the peak stress required to generate new crack surfaces. In general, both are difficult to quantify since direct determinations are not possible in experiments. For inhomogeneous materials, such as graded materials, determination is even more complex since these parameters vary spatially. In this paper, a novel method based on an inverse analysis technique is proposed to estimate the fracture parameters of elastic-plastic and graded media. The method utilizes the Kalman filter to process measured data and extract best estimates of the unknown parameters. The accuracy of the method is examined in a verification study where a dynamically propagating crack in double cantilever beam type specimen is modeled. In the study, time variation records of crack opening displacement, opening strain, crack advance distance, and load point reaction force are used as possible measurements. Despite large noises in data, the results confirm accurate estimation. The estimates improve when multiple measurements are supplied to the inverse technique.
Authors: A. Ríos, A. Martín-Meizoso
Abstract: A micromechanical model is employed to investigate the influence of the interface between the fibre and the matrix of a metal matrix composite with long fibre, which is elaborated through finite element method. Also, transverse properties of composite are studied in the present work. The interface, between the fibre and the matrix, is studied employing cohesive elements. These elements employ a cohesive zone model, which follows a bilinear law.
Authors: R. Kabir, Alfred Cornec, Wolfgang Brocks
Abstract: Quasi-brittle fracture of fully lamellar two phase (α2+γ)TiAl is investigated both experimentally and numerically. Fracture tests are conducted at room temperature, which fail in a quasi-brittle and unstable manner but exhibit significant variations in crack initiation and propagation prior to unstable failure. Fractographic investigations are performed which elucidate the micromechanical causes of the macroscopic behaviour. The observed deformation and fracture behaviours of the specimens are simulated by a finite element model containing cohesive elements for modelling the material separation. In order to capture the scatter of the macroscopic behaviour, a stochastic approach is chosen, in which local variations of cohesive parameters are taken into account. The model can describe and explain the physical phenomena of the specific material.
Authors: He Zhu, Gang Wang, Zhen Yue Ma, Yi Kang Su
Abstract: A cohesive model (CM) was introduced in this paper. The constitutive response of cohesive behavior depends on a traction-separation description characterized by the initial stiffness, damage initiation threshold, and damage evolution properties.Through the aseismic analysis of a gravity dam, the displacement, stress and anti-sliding safety factor were discussed in the paper, the results were also compared between elastic model (EM) and plastic model (PM). The results shown that the displacement amplitude computed by PM and CM was nearly twice larger than that by EM, and the area of stress concentration became not so obvious. The cohesive model could efficiently simulate the discontinuous structure and the responses of seismic computed by PM and CM were more correspond to actual situation.
Authors: Jarosław Galkiewicz
Abstract: In this study, two cases of crack growth initiation from a foreign particle in a representative elementary volume are analyzed. The task is completed with a cohesive model implemented in ABAQUS. The results are compared with those obtained for an inclusion-free cell.
Authors: Rainer Falkenberg, Wolfgang Brocks, Wolfgang Dietzel, Ingo Schneider
Abstract: The effect of hydrogen on the mechanical behaviour is twofold: It affects the local yield stress and it accelerates material damage. On the other hand, the diffusion behaviour is influenced by the hydrostatic stress, the plastic deformation and the strain rate. This requires a coupled model of deformation, damage and diffusion. The deformation behaviour is described by von Mises plasticity with pure isotropic hardening, and crack extension is simulated by a cohesive zone model. The local hydrogen concentration, which is obtained from the diffusion analysis, causes a reduction of the cohesive strength. Crack extension in a C(T) specimen of a ferritic steel under hydrogen charging is simulated by fully coupled diffusion and mechanical finite element analyses with ABAQUS and the results are compared with test results.
Authors: Ning Hu, Yutaka Zemba, Hisao Fukunaga
Abstract: In this paper, we have proposed a new cohesive model to stably and accurately simulate delamination propagations in composite laminates under transverse loads. In this model, we set up a pre-softening zone in front of the original softening zone. In this pre-softening zone, the initial stiffness is gradually reduced as the interface strength decreases. However, the onset displacement for starting the real softening process is not changed in this model. The fracture toughness of materials for determining the final displacement of complete decohesion is not changed too. This cohesive model is implemented in the explicit time integration scheme. A DCB problem is employed to analyze the characteristics of the present cohesive model. Moreover, an experimental example of laminates under impact loads is employed to illustrate the validity of the present method.
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