The Experts below are selected from a list of 1662 Experts worldwide ranked by ideXlab platform
Earl David Reedy - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics based cohesive zone law for brittle Interfacial fracture under mixed loading conditions effects of elastic constant mismatch
Acta Materialia, 2009Co-Authors: Xiaowang Zhou, N R Moody, Reese E Jones, Jonathan A Zimmerman, Earl David ReedyAbstract:Abstract One approach for performing a finite-element simulation of Interfacial fracture is to use a cohesive zone model. The cohesive zone model defines the Interfacial Traction–separation relation. Experimental determination of such a relation has been difficult. Most previous work has been confined to tensile loading, and much less has been devoted to mixed-mode loading conditions. Even so, specific laws are often assumed rather than predicted. Our recent work has used molecular dynamics (MD) simulation methods to derive a general cohesive zone law for the fracture between two brittle materials under any mixed-mode loading conditions. Here we extend our method and use it to explore the effect of elastic constant mismatch between adjacent materials. In particular, we construct two bilayer structures where the cohesive energies and lattice constants of the constituent materials are kept the same, but the elastic constant mismatch of the two materials in one structure differs from that in the other. We then use MD simulations to study the fracture and to derive the cohesive zone laws for both structures. The effect of elastic constant mismatch on fracture will then be discussed.
Huajian Gao - One of the best experts on this subject based on the ideXlab platform.
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probing mechanical principles of focal contacts in cell matrix adhesion with a coupled stochastic elastic modelling framework
Journal of the Royal Society Interface, 2011Co-Authors: Huajian Gao, Jin Qian, Bin ChenAbstract:Cell–matrix adhesion depends on the collective behaviours of clusters of receptor–ligand bonds called focal contacts between cell and extracellular matrix. While the behaviour of a single molecular bond is governed by statistical mechanics at the molecular scale, continuum mechanics should be valid at a larger scale. This paper presents an overview of a series of recent theoretical studies aimed at probing the basic mechanical principles of focal contacts in cell–matrix adhesion via stochastic–elastic models in which stochastic descriptions of molecular bonds and elastic descriptions of Interfacial Traction–separation are unified in a single modelling framework. The intention here is to illustrate these principles using simple analytical and numerical models. The aim of the discussions is to provide possible clues to the following questions: why does the size of focal adhesions (FAs) fall into a narrow range around the micrometre scale? How can cells sense and respond to substrates of varied stiffness via FAs? How do the magnitude and orientation of mechanical forces affect the binding dynamics of FAs? The effects of cluster size, cell–matrix elastic modulus, loading direction and cytoskeletal pretension on the lifetime of FA clusters have been investigated by theoretical arguments as well as Monte Carlo numerical simulations, with results showing that intermediate adhesion size, stiff substrate, cytoskeleton stiffening, low-angle pulling and moderate cytoskeletal pretension are factors that contribute to stable FAs. From a mechanistic point of view, these results provide possible explanations for a wide range of experimental observations and suggest multiple mechanisms by which cells can actively control adhesion and de-adhesion via cytoskeletal contractile machinery in response to mechanical properties of their surroundings.
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lifetime and strength of periodic bond clusters between elastic media under inclined loading
Biophysical Journal, 2009Co-Authors: Jin Qian, Jizeng Wang, Yuan Lin, Huajian GaoAbstract:Focal adhesions are clusters of specific receptor-ligand bonds that link an animal cell to an extracellular matrix. To understand the mechanical responses of focal adhesions, here we develop a stochastic-elasticity model of a periodic array of adhesion clusters between two dissimilar elastic media subjected to an inclined tensile stress, in which stochastic descriptions of molecular bonds and elastic descriptions of Interfacial Traction are unified in a single modeling framework. We first establish a fundamental scaling law of Interfacial Traction distribution and derive a stress concentration index that governs the transition between uniform and cracklike singular distributions of the Interfacial Traction within molecular bonds. Guided by this scaling law, we then perform Monte Carlo simulations to investigate the effects of cluster size, cell/extracellular matrix modulus, and loading direction on lifetime and strength of the adhesion clusters. The results show that intermediate adhesion size, stiff substrate, cytoskeleton stiffening, and low-angle pulling are factors that contribute to the stability of focal adhesions. The predictions of our model provide feasible explanations for a wide range of experimental observations and suggest possible mechanisms by which cells can modulate adhesion and deadhesion via cytoskeletal contractile machinery and sense mechanical properties of their surroundings.
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lifetime and strength of adhesive molecular bond clusters between elastic media
Langmuir, 2008Co-Authors: Jin Qian, Jizeng Wang, Huajian GaoAbstract:With a long-term objective toward a quantitative understanding of cell adhesion, we consider an idealized theoretical model of a cluster of molecular bonds between two dissimilar elastic media subjected to an applied tensile load. In this model, the distribution of Interfacial Traction is assumed to obey classical elastic equations whereas the rupture and rebinding of individual molecular bonds are governed by stochastic equations. Monte Carlo simulations that combine the elastic and stochastic equations are conducted to investigate the lifetime of the bond cluster as a function of the applied load. We show that the Interfacial Traction is generally nonuniform and for a given adhesion size the average cluster lifetime asymptotically approaches infinity as the applied load is reduced to below a critical value, defined as the strength of the cluster. The effects of elastic moduli, adhesion size, and rebinding rate on the cluster lifetime and strength are studied under strongly nonuniform distributions of Interfacial Traction. Although overly simplified in a number of aspects, our model seems to give predictions that are consistent with relevant experimental observations on focal adhesion dynamics.
Guoqiang Li - One of the best experts on this subject based on the ideXlab platform.
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on approximately realizing and characterizing pure mode i interface fracture between bonded dissimilar materials
Journal of Applied Mechanics, 2011Co-Authors: Zhenyu Ouyang, Gefu Ji, Guoqiang LiAbstract:Bimaterial systems in which two dissimilar materials are adhesively joined by a thin adhesive interlayer have been widely used in a variety of modern industries and engineering structures. It is well known that Interfacial fracture is the most common failure mode for these bimaterial systems. Particularly, the interface fracture is a mixed mode in nature mode-I (pure peel) and mode-II (pure shear) due to the disrupted symmetry by the bimaterial configuration. Obviously, characterizing individual fracture modes, especially mode-I fracture, is essential in understanding and modeling the complex mixed mode fracture problems. Meanwhile, the J-integral is a highly preferred means to characterize the Interfacial fracture behaviors of a bimaterial system because it cannot only capture more accurate toughness value, but also facilitate an experimental characterization of Interfacial Traction-separation laws (cohesive laws). Motivated by these important issues, a novel idea is proposed in the present work to realize and characterize the pure mode-I nonlinear interface fracture between bonded dissimilar materials. First, a nearly pure mode-I fracture test can be simply realized for a wide range of bimaterial systems by almost eliminating the mode-II component based on a special and simple configuration obtained in this work. Then, the concise forms of the J-integral are derived and used to characterize the Interfacial fracture behaviors associated with classical and shear deformation beam theories. The proposed approach may be considered as a promising candidate for the future standard mode-I test method of bimaterial systems due to its obvious accuracy, simplicity, and applicability, as demonstrated by the numerical and experimental results.
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effects of bondline thickness on mode ii Interfacial laws of bonded laminated composite plate
International Journal of Fracture, 2011Co-Authors: Gefu Ji, Zhenyu Ouyang, Guoqiang LiAbstract:For a variety of modern industries, Interfacial delamination is a critical issue for the design and application of laminated composite structures. Numerous global experimental studies have been conducted to characterize the toughness of adhesively bonded composite structures. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions. The local Interfacial Traction–separation laws as the fundamental input are crucial for the successful applications of CZMs. Several local tests have also been conducted to determine the Interfacial Traction–separation laws in adhesively bonded joints. However, very few tests have been employed to investigate the dependency of the local Interfacial Traction–separation laws on the bondline thickness, particularly, for the laminated composite joints under Mode-II loading conditions. In this work, the effects of bondline thickness on the Interfacial behavior have been systematically investigated at various typical bondline thicknesses (from 0.1 to 0.8 mm). The effects of adhesive thickness on the Interfacial toughness, Interfacial strength, and shapes of the local Interfacial Traction–separation laws have also been evaluated. The test results indicated that the measured Mode-II (shear test) Interfacial shear strength of the composite joints increases as the adhesive layer becomes thicker. It was found a significant dependency of the measured shapes of the Mode-II Interfacial laws on the bondline thickness. Several other interesting issues were also reported in this work. This work may provide valuable baseline test data for analytical and numerical modeling of fracture and failure of laminated composite structures.
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effects of adhesive thickness on global and local mode i Interfacial fracture of bonded joints
International Journal of Solids and Structures, 2010Co-Authors: Gefu Ji, Zhenyu Ouyang, Guoqiang Li, Samuel Ibekwe, Suseng PangAbstract:The Interfacial fracture of adhesively bonded structures is a critical issue for the extensive applications to a variety of modern industries. In the recent two decades, cohesive zone models (CZMs) have been receiving intensive attentions for fracture problems of adhesively bonded joints. Numerous global tests have been conducted to measure the Interfacial toughness of adhesive joints. Limited local tests have also been conducted to determine the interface Traction-separation laws in adhesive joints. However, very few studies focused on the local test of effects of adhesive thickness on the Interfacial Traction-separation laws. Interfacial toughness and Interfacial strength, as two critical parameters in an Interfacial Traction-separation law, have important effect on the fracture behaviors of bonded joints. In this work, the global and local tests are employed to investigate the effect of adhesive thickness on Interfacial energy release rate, Interfacial strength, and shapes of the Interfacial Traction-separation laws. Basically, the measured laws in this work reflect the equivalent and lumped Interfacial fracture behaviors which include the cohesive fracture, damage and plasticity. The experimentally determined Interfacial Traction-separation laws may provide valuable baseline data for the parameter calibrations in numerical models. The current experimental results may also facilitate the understanding of adhesive thickness-dependent interface fracture of bonded joints.
Yung C Shin - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics based cohesive zone representation of ti6al4v tic composite interface
Materials & Design, 2018Co-Authors: Mohamed G Elkhateeb, Yung C ShinAbstract:Abstract In this paper, Molecular Dynamics (MD) simulation is used to simulate the crack propagation along the interface of Ti6Al4V/TiC in Titanium metal matrix composites under Mode-I and II loadings and at different temperatures. MD simulation can then determine the Interfacial Traction-separation relationship between Ti6Al4V and TiC. The interatomic potential between the atoms in Ti6Al4V/TiC composite is defined by the second-nearest neighborhood modified embedded atom method (2NN MEAM) and the Morse potential. For Vanadium-Carbon (V-C) interatomic potential, the 2NN MEAM parameters are developed and validated based on previous first principle calculations conducted on VC structure. MD simulation results show asymmetrical crack propagation along the interface between Ti6Al4V/TiC and the crack propagates in Ti6Al4V than along the interface. The obtained Traction-separation relationship is used to parametrize the cohesive zone model (CZM) for modeling the interface in finite element analysis. Validation of the parameterized relationship is done by finite element simulation of the compression test of Ti6Al4V/TiC at different volume fractions of TiC. A good agreement is shown between the stress-strain results obtained from simulation and the experimental data under the same conditions.
Xiaowang Zhou - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics based cohesive zone law for brittle Interfacial fracture under mixed loading conditions effects of elastic constant mismatch
Acta Materialia, 2009Co-Authors: Xiaowang Zhou, N R Moody, Reese E Jones, Jonathan A Zimmerman, Earl David ReedyAbstract:Abstract One approach for performing a finite-element simulation of Interfacial fracture is to use a cohesive zone model. The cohesive zone model defines the Interfacial Traction–separation relation. Experimental determination of such a relation has been difficult. Most previous work has been confined to tensile loading, and much less has been devoted to mixed-mode loading conditions. Even so, specific laws are often assumed rather than predicted. Our recent work has used molecular dynamics (MD) simulation methods to derive a general cohesive zone law for the fracture between two brittle materials under any mixed-mode loading conditions. Here we extend our method and use it to explore the effect of elastic constant mismatch between adjacent materials. In particular, we construct two bilayer structures where the cohesive energies and lattice constants of the constituent materials are kept the same, but the elastic constant mismatch of the two materials in one structure differs from that in the other. We then use MD simulations to study the fracture and to derive the cohesive zone laws for both structures. The effect of elastic constant mismatch on fracture will then be discussed.