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1.
A cohesive law for carbon nanotube/polymer interfaces based on the van der Waals force 总被引:2,自引:0,他引:2
L.Y. Jiang H. Jiang H. Gao B. Liu 《Journal of the mechanics and physics of solids》2006,54(11):2436-2452
We have established the cohesive law for interfaces between a carbon nanotube (CNT) and polymer that are not well bonded and are characterized by the van der Waals force. The tensile cohesive strength and cohesive energy are given in terms of the area density of carbon nanotube and volume density of polymer, as well as the parameters in the van der Waals force. For a CNT in an infinite polymer, the shear cohesive stress vanishes, and the tensile cohesive stress depends only on the opening displacement. For a CNT in a finite polymer matrix, the tensile cohesive stress remains the same, but the shear cohesive stress depends on both opening and sliding displacements, i.e., the tension/shear coupling. The simple, analytical expressions of the cohesive law are useful to study the interaction between CNT and polymer, such as in CNT-reinforced composites. The effect of polymer surface roughness on the cohesive law is also studied. 相似文献
2.
Meshfree particle simulation of the detonation process for high explosives in shaped charge unlined cavity configurations 总被引:8,自引:0,他引:8
The numerical simulation of the detonation of a high explosive (HE) is generally not an easy task for traditional grid based methods. Smoothed particle hydrodynamics (SPH) method, as a meshfree, Lagrangian and particle method, provides a very attractive approach in dealing with large deformations and large inhomogeneities in the extremely transient high explosive detonation and later expansion process. This paper presents the application of SPH to simulate and analyze the detonation process of high explosive in shaped charge. A three-dimensional SPH code is developed and applied to simulate the shaped charge detonation process in different scenarios. It is observed that for high explosive in a shaped charge, the detonation produced gaseous products experience strong convergence that forms an extremely high-pressure gas jet. Factors such as different charge cavity shapes and different detonation models lead to quite different behavior of the gas jet convergence and later divergence. Further analyses reveal that a critical value for the charge head length exists. Beyond this critical value, increasing the charge head length will not result in improvement on the gas jet convergence performance.Received: 11 March 2002, Accepted: 9 December 2002, Published online: 28 April 2003 相似文献
3.
Dislocation events are seen as excursions or pop-in events in the load–displacement curve of nanoindentation experiments. Two nanoindenters have been used to examine the difference between quasi-static and dynamic loading during indentation. Yield excursions were present in the load–displacement curves of both the statically and dynamically loaded single crystal nickel samples. Only one major excursion occurred in each quasi-static indent, nominally loaded at 100 μN/s while staircase yielding was observed under dynamic loading indentation with a 45 Hz oscillation of 2 nm superimposed on a 60 μN/s loading rate. Thermal activation analysis is used to explain the arrest and reinitiation of the yielding with activation volumes being modeled. For nanoindentation experiments differences between quasi-static and dynamic loading are described by the models presented. It is proposed that insight into the plastic deformation mechanisms associated with such plastic instabilities will provide one of the keys to length scale effects necessary to understanding nanostructures. 相似文献
4.
In this paper we consider the elastoplastic behavior of the 304L stainless steel under cyclic loading at room temperature. After the experimental investigations presented in Taleb and Hauet (2009), the present work deals with modeling in the light of the new observations. An improved version of the multimechanism model is proposed in which the isotropic variable is revisited in order to take into account the non-proportional effect of the loading as well as the strain memory phenomenon. A particular attention has been paid to the identification process in order to capture the main important phenomena: relative parts of isotropic and kinematic hardening, time dependent effects, non-proportionality effect, strain amplitude dependence. Only strain controlled tests have been used for the identification process. The capabilities of the model with “only” 17 parameters are evaluated considering a number of proportional and non-proportional stress and strain controlled tests. 相似文献
5.
Aude Hauert 《Journal of the mechanics and physics of solids》2009,57(11):1781-1800
Weibull parameters of angular alumina particles are determined from experimental tensile test data on high-ceramic-content metal matrix composites using a micromechanical model that accounts for internal damage in the form of particle cracking, the dominant damage mode in these composites. The fraction of broken particles is assessed from the drop of Young's modulus and particle fracture is assumed to be stress controlled. Two extreme load-sharing modes, namely a purely local and a global load-sharing mode, are considered to account for the load redistribution due to particle fracture. Consistent powder strength parameters can be thus “back-calculated” for particles that are embedded in different Al-Cu matrices. On the other hand, this calculation fails for pure Al matrix composites, which exhibit a much larger strain to failure than Al-Cu matrix composites. It is shown that for Al matrix composites, the role of plastic (composite) strain on particle fracture constitutes a second parameter governing particle damage. This finding is rationalized by particle-particle interactions in these tightly packed ceramic particle-reinforced composites, and by the increase of matrix stress heterogeneity that is brought with increasing plastic strain. Failure of the alloyed matrix composites is well described by the (lower bound) local load-sharing micromechanical model, which predicts a catastrophic failure due to an avalanche of damage. The same model predicts failure of pure aluminium matrix composites to occur at the onset of tensile instability, also in agreement with experimental results once the role of plastic strain on damage accumulation is accounted for. 相似文献
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The present paper investigates a mechanism of compressive fracture for heterogeneous incompressible non-linear materials with special kinds of defects of interfacial adhesion under large deformations. The analysis finds the lower bounds for the critical load. In order to calculate the bounds, the problem of the internal instability is considered within the scope of the exact statement based on the application of the model of a piecewise-homogeneous medium and the equations of the 3-D stability theory. The solution of the 3-D problem is found for the most general case accounting for large deformations and the biaxiality of compressive loads. The characteristic determinants are derived for the first four modes, which are more commonly observed. Special attention is given to the calculation of critical loads for hyperelastic layers described by a simplified version of Mooney's potential, namely the neo-Hookean potential. 相似文献
8.
In the present paper, we attempt to explain the macroscopic flow law evolution in porous media according to the Reynolds number.
A crenellated channel, considered as an element of such a medium, is used to perform numerical simulations in stationary and
non-stationary cases. In the case of non-stationary laminar flows, we point out flow instabilities occurring in the channel
at high Reynolds numbers and we focus on their influence on the macroscopic law. We qualitatively prove that they generate
an additional quadratic contribution to Forchheimer’s law. We use two methods to study this contribution: first, a periodic
disturbance, for which the instabilities appearing at the beginning of disturbance become regular oscillations; then a pulse
disturbance of the entry velocity field which enables us to link the additional quadratic contribution to the existence of
an accumulation of fluid at low velocity in the channel. 相似文献
9.
A model is proposed that deals with the transient mechanical anisotropy during strain-path changes in metals. The basic mechanism is assumed to be latent hardening or softening of the slip systems, dependent on if they are active or passive during deformation, reflecting microstructural mechanisms that depend on the deformation mode rather than on the crystallography. The new model captures the experimentally observed behaviour of cross hardening in agreement with experiments for an AA3103 aluminium alloy. Generic results for strain reversals qualitatively agree with two types of behaviour reported in the literature – with or without a plateau on the stress–strain curve. The influence of the model parameters is studied through detailed calculations of the response of three selected parameter combinations, including the evolution of yield surface sections subsequent to 10% pre-strain. The mathematical complexity is kept to a minimum by avoiding explicit predictions related directly to underpinning microstructural changes. The starting point of the model is a combination of conventional texture and work hardening approaches, where an adapted full-constraints Taylor theory and a simple single-crystal work-hardening model for monotonic strain are used. However, the framework of the model is not restricted to these particular models. 相似文献
10.
Francesco Dal Corso Massimiliano Gei 《Journal of the mechanics and physics of solids》2008,56(3):815-838
A lamellar (zero-thickness) rigid inclusion, so-called ‘stiffener’, is considered embedded in a uniformly prestressed (or prestrained), incompressible and orthotropic elastic sheet, subject to a homogeneous far-field deformation increment. This problem is solved under the assumption of plane strain deformation, with prestress principal directions and orthotropy axes aligned with the stiffener. A full-field solution is obtained solving the Riemann-Hilbert problem for symmetric incremental loading at infinity (while for shear deformation the stiffener leaves the ambient field unperturbed). In addition to the full-field solution, the asymptotic Mode I near-tip representation involving the corresponding incremental stress intensity factor are derived and these results are complemented with the Mode II asymptotic solution. For null prestress, the full-field stress state is shown to match correctly with photoelastic experiments performed by us (on two-part epoxy resin samples containing an aluminum lamina). Our experiments also confirm the fracture patterns for a brittle material containing a stiffener, which do not obey a hoop-stress criterion and result completely different from those found for cracks. Issues related to shear band formation and evaluation of energy release rate for a stiffener growth (or reduction) are deferred to Part II of this article. 相似文献
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Theoretical analysis on the local critical stress and size effect for interfacial debonding in particle reinforced rheological materials 总被引:1,自引:0,他引:1
The mechanisms of interfacial debonding of particle reinforced rheological materials are studied. Based on an energy criterion, a simple formula of local critical stress for interfacial debonding is derived and expressed in terms of the interfacial energy. The particle size effect on interface debonding can then be analyzed easily owing to the fact that critical stress is inversely proportional to the square root of particle radius. By taking PP/CaCO3 system as an example, the present energy criterion is compared with the mechanical debonding criterion, and it is found that under the condition that bond strength is equal to matrix strength and particle radius not over 0.2μm, the mechanical debonding criterion can be automatically satisfied if the energy criterion is satisfied. A relation between critical time and interface energy is calculated by using the energy criterion. The influences of the particle volume fraction and the parlicle size, the loading rate and the relaxation time of the matrix on the critical time of interfacial debonding are also discussed. Supported by the National Natural Science Foundation of China (19632030 and 19872007) and Natural Science Foundation of Jiangsu Province. 相似文献
13.
In this paper, a general and simple way was found to solve the problem of an arbitrary hole with edge cracks in transversely isotropic piezoelectric materials based on the complex variable method and the method of numerical conformal mapping. Firstly, the approximate mapping function which maps the outside of the arbitrary hole and the cracks into the outside of a circular hole is derived after a series of conformal mapping process. Secondly, based on the assumption that the surface of the cracks and hole is electrically impermeable and traction-free, the approximate expressions for the complex potential, fields intensity factors and energy release rates are presented, respectively. Thirdly, under the in-plane electric loading together with the out-plane mechanical loading, the influences of the hole size, crack length and mechanical/electric loading on the fields intensity factors and energy release rates are analyzed. Finally, some particular holes with edge cracks are studied in numerical analysis. The result shows that, the mechanical loading always promotes crack growth, while the electric loading may retard crack growth. 相似文献
14.
An experimental study on oligo-cyclic fatigue of rubber-like materials submitted to tension test in large deformation, to constant amplitude of loadings, brings to the fore that the stress during the loading, at a given cycle, is always smaller than during the previous cycle. These tests highlight that this phenomenom, called stress-softening, depends on the maximal stretch and on the number of cycles to which the materials has been submitted. A model, taking into account these two parameters is proposed and experimental validations are proposed. To cite this article: M. Brieu et al., C. R. Mecanique 332 (2004). 相似文献
15.
Bilel Ben Boubaker Bernard Haussy Jean-François Ganghoffer 《Comptes Rendus Mecanique》2003,331(4):295-302
The coupling between yarns in a piece of fabric has been analysed at the mesoscopic scale, in terms of its impact on the macroscopic unidirectional behaviour. Starting from a discrete model of a woven structure associated to a variational formulation of the equilibrium of the structure, the coupling between both yarns is introduced, the potential energy of which is calculated. The initial shape of the yarn, represented by a planar undulated beam supposed to be periodic, is described by a Fourier series. The coefficients of the series are expressed vs. the contact force exerted at the top of the undulations, and vs. the mechanical properties of the solicited yarn. The contact force is then expressed vs. the mechanical properties of the transverse yarn and vs. the vertical displacement of the contact point. The potential energy of the coupling is then built, assuming the continuity of the displacement at the contact points. The equilibrium shape of the yarn submitted to unidirectional traction is obtained numerically as the minimum of the total potential energy. The simulated traction curve reproduces in a satisfactorily manner the observed behaviour. The respective contributions of the flexional and extensional effects of the yarn are analysed. The consideration of the coupling enhances the rigidity of the response of the yarn; one demonstrates the effect of the geometrical and mechanical parameters of the transverse yarn. To cite this article: B. Ben Boubaker et al., C. R. Mecanique 331 (2003). 相似文献
16.
This Note presents a new approximate scheme for nonlinear composites. The approximation which is made preserves certain features of the original second-order scheme of Ponte Castañeda, exactness to second-order in the contrast and existence of an effective energy, but improves on one drawback, which is the gap between the strain-energy formulation and the affine formulation. A numerical example shows the accuracy of the present method. To cite this article: N. Lahellec, P. Suquet, C. R. Mecanique 332 (2004). 相似文献