Interfacial debonding of coated-fiber-reinforced composites under tension-tension cyclic loading

A new degradation function of the friction coefficient is used. Based on the double shear-lag model and Paris formula, the interfacial damage of coated-fiber-reinforced composites under tension-tension cyclic loading is studied. The effects of strength and thickness of the coating materials on the debond stress, debond rate as well as debond length are simulated. The subject supported by the National Natural Science Foundation of China (No.59778034), Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE, China and The Hong Kong Polytechnic University (G-S737)     

Interfacial drag of two-phase flow in porous media

In this paper, the influence of the interfacial drag on the pressure loss of combined liquid and vapour flow through particulate porous media is investigated. Motivation for this is the coolability of fragmented corium which may be expected during a severe accident in a nuclear power plant. Cooling water is evaporated due to the particles decay heat. To reach coolability, the outflowing steam has to be replaced by inflowing water.     

Experimental simulation of matrix cracking and debonding in a model brittle matrix composite

A model composite material system was designed to simulate typical damage mechanisms in unidirectional fiber reinforced brittle matrix composites. Experiments were performed at low to high quasistatic, macroscopic loading rates . At all loading rates reversal of the transverse strain was observed and was correlated to matrix cracking and debonding. The optical method of coherent gradient sensing (CGS) was used to obtain qualitative information regarding the stress fields and to observe the progression of damage. It was found that the sequence of damage formation (damage path) depended on the macroscopic loading rate. At lower loading rates periodic matrix cracks developed; minimal debonding of the reinforcement-matrix interface occurred only much later in the experiment. At higher loading rates extensive debonding followed propagation of the initial matrix crack, and periodic cracking was not observed. Several features of the material response of the model material system were also observed in a previously studied unidirectional ceramic matrix composite.     

The effective properties of piezoelectric composite materials with transversely isotropic spherical inclusions

ＩｎｔｒｏｄｕｃｔｉｏｎＷｉｔｈｔｈｅｄｅｖｅｌｏｐｍｅｎｔｏｆｉｎｆｏｒｍａｔｉｏｎｉｎｄｕｓｔｒｙａｎｄｔｈｅａｐｅａｒａｎｃｅｏｆｓｍａｒｔｍａｔｅｒｉａｌｓａｎｄｓｍａｒｔｓｔｒｕｃｔｕｒｅｓ,ｉｔｂｅｃｏｍｅｓｍｏｒｅａｎｄｍｏｒｅｉｍｐｏ...     

Transfer matrix approach of vibration isolation analysis of periodic composite structure

The transmission properties of elastic waves propagating in a three-dimensional composite structure embedded periodically with spherical inclusions are analyzed by the transfer matrix method in this paper. Firstly, the periodic composite structures are divided into many layers, the transfer matrix of monolayer structure is deduced by the wave equations, and the transfer matrix of the entire structure is obtained in the case of boundary conditions of displacement and stress continuity between layers. Then, the effective impedance of the structure is analyzed to calculate its reflectivity and transmissivity of vibration isolation. Finally, numerical simulation is carried out; the experiment results validate the accuracy and feasibility of the method adopted in the paper and some useful conclusions are obtained. Project (No. 50075029) supported by the National Natural Science Foundation of China.     

Modeling of two-phase flow in porous media with heat generation

The main purpose of this work is investigation of coolability of a boiling debris bed. The main governing equations are derived using volume averaging technique. From this technique some specific interfacial areas between phases are appeared and proper relations for modeling these areas are proposed. Using these specific areas, a modification for the Tung/Dhir model in the annular flow regime is proposed. The proposed modification is validated and the agreements with experimental data are good. Finally, governing equations and relations are implemented in the THERMOUS program to model two-phase flow in the debris bed in the axisymmetric cylindrical coordinate. Two typical configurations including flat and mounted beds are considered and the main physical phenomena during boiling of water in the debris bed are studied. Comparing the results with the one-dimensional analysis shows higher specific power of the bed.     

Interfacial stress analysis and prediction of debonding for a thin plate bonded to a curved substrate

This paper focuses on the analytical and numerical modeling of the interface between a rigid substrate with simple constant curvature and a thin bonded plate. The interfacial behavior is modeled by independent cohesive laws in the normal and tangential directions, coupled with a mixed-mode fracture criterion. The newly developed analytical model determines the interfacial shear and normal stress distributions as functions of the substrate curvature, during the various behavioral stages of the interface prior to the initiation of debonding. The model is also able to predict the debonding load and the effective bond length. In the numerical model the interface is modeled by zero-thickness node-to-segment contact elements, in which both the geometrical relationships between the nodes of the discretized problem and the interface constitutive laws are suitably defined. Numerical results and comparisons between the predictions of the two models are presented.     

Stress concentration and effective stiffness of aligned fiber reinforced composite with anisotropic constituents

The paper addresses the problem of calculation of the local stress field and effective elastic properties of a unidirectional fiber reinforced composite with anisotropic constituents. For this aim, the representative unit cell approach has been utilized. The micro geometry of the composite is modeled by a periodic structure with a unit cell containing multiple circular fibers. The number of fibers is sufficient to account for the micro structure statistics of composite. A new method based on the multipole expansion technique is developed to obtain the exact series solution for the micro stress field. The method combines the principle of superposition, technique of complex potentials and some new results in the theory of special functions. A proper choice of potentials and new results for their series expansions allow one to reduce the boundary-value problem for the multiple-connected domain to an ordinary, well-posed set of linear algebraic equations. This reduction provides high numerical efficiency of the developed method. Exact expressions for the components of the effective stiffness tensor have been obtained by analytical averaging of the strain and stress fields.     

Bending and buckling of a class of nonlinear fiber composite rods

An investigation of the mechanics of bending and buckling is carried out for a class of nonlinear fiber composite rods composed of embedded unidirectional fibers parallel to the rod axis. The specific class of composite considered is one in which the fibers interact with the matrix through a nonlinear Needleman-type cohesive zone [Needleman, A., 1987. A continuum model for void nucleation by inclusion debonding. ASME J. Appl. Mech. 54, 525-531; Needleman, A., 1992. Micromechanical modelling of interfacial decohesion. Ultramicroscopy 40, 203-214]. The primary decohesive mechanism active in bending and buckling of these composite rods is shear slip along the fiber-matrix interfaces allowing the use of a previously developed constitutive relation for antiplane shear response [Levy, A.J., 2000b. The fiber composite with nonlinear interface—part II: antiplane shear. ASME J. Appl. Mech. 67, 733-739]. The formulation requires the specification of a potential interface force-slip law that is assumed to permit interface failure in shear.Four cases of the bending and shearing of beams (concentrated or uniform load on a cantilever or a simply supported beam) are analyzed, each of which exhibits qualitatively distinct response. For certain values of interface parameters, the beam deflection or its gradient at a fixed location can change discontinuously with load. Furthermore, for interface parameter values within a certain range, singular surfaces will exist in uniformly loaded beams where there is a non-uniform distribution of shear stress along the beam length. These singular surfaces divide the beam into regions of maximal and minimal fiber slip and propagate with a rate that varies inversely as the square of the applied load. For other parameter values, singular surfaces will not exist and fiber slip will be diffuse.For the class of nonlinear composite considered, bifurcation and imperfection buckling of pinned-pinned columns is analyzed. For bifurcation buckling, a nonlinear eigenvalue problem is derived and the solution is obtained by Galerkin's method. It is demonstrated that critical loads are influenced by the initial slope, and hence the linear portion, of the interface force-slip relation but the post-buckling response, which in some sense resembles that of plastic buckling, is affected by the entire interface constitutive relation. Imperfection buckling is analyzed in a similar manner by assuming a slight initial curvature of the rod. Sensitivity of the response to imperfection magnitude is discussed as well.     

Effective properties of elastic periodic composite media with fibers

A series solution to obtain the effective properties of some elastic composites media having periodically located heterogeneities is described. The method uses the classical expansion along Neuman series of the solution of the periodic elasticity problem in Fourier space, based on the Green's tensor, and exact expressions of factors depending on the shape of the inclusions. Some properties of convergence of the solution are presented, more specifically concerning the elasticity tensor of the reference medium, showing that the convergence occurs even for empty fibers. The solution is extended for rigid inclusions. A comparison is made with previous exact solutions for a fiber composite made of cylindrical fibers with circular cross-sections and with previous estimates. Different examples are presented for new situations concerning the study of fiber composites: composites with elliptic cross-sections and multi-phase fibrous composites.     

Stability of plates made of a particulate composite with nonlinear elastic matrix and damaged inclusions

The bifurcation instability problem for rectangular plates made of particulate composites with nonlinear elastic matrix and damaged inclusions is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 7, pp. 79–89, July 2007.     

Stability of cylindrical shells made of a particulate composite with nonlinear elastic inclusions and damageable matrix

The bifurcation instability problem for cylindrical shells made of particulate composites with nonlinear elastic inclusions and damageable matrix is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 10, pp. 68–79, October 2007.     

Stability of cylindrical shells made of a particulate composite with nonlinear elastic matrix and damaged inclusions

The bifurcation instability problem for cylindrical shells made of particulate composites with nonlinear elastic matrix and damaged inclusions is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 8, pp. 80–91, August 2007.     

Stability of shells of revolution made of a particulate composite with nonlinear elastic inclusions and damageable matrix

The bifurcation instability problem for shells of revolution made of particulate composites with nonlinear elastic inclusions and damageable matrix is formulated and solved __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 11, pp. 55–65, November 2007.     

Size-dependent effective elastic moduli of particulate composites with interfacial displacement and traction discontinuities

This work aims at estimating the size-dependent effective elastic moduli of particulate composites in which both the interfacial displacement and traction discontinuities occur. To this end, the interfacial discontinuity relations derived from the replacement of a thin uniform interphase layer between two dissimilar materials by an imperfect interface are reformulated so as to considerably simplify the characteristic expressions of a general elastic imperfect model which is adopted in the present work and include the widely used Gurtin–Murdoch and spring-layer interface models as particular cases. The elastic fields in an infinite body made of a matrix containing an imperfectly bonded spherical particle and subjected to arbitrary remote uniform strain boundary conditions are then provided in an exact, coordinate-free and compact way. With the aid of these results, the elastic properties of a perfectly bonded spherical particle energetically equivalent to an imperfectly bonded one in an infinite matrix are determined. The estimates for the effective bulk and shear moduli of isotropic particulate composites are finally obtained by using the generalized self-consistent scheme and discussed through numerical examples.     

Second-order two-scale computational method for ageing linear viscoelastic problem in composite materials with periodic structure

The correspondence principle is an important mathematical technique to compute the non-ageing linear viscoelastic problem as it allows to take advantage of the computational methods originally developed for the elastic case. However, the correspondence principle becomes invalid when the materials exhibit ageing. To deal with this problem, a second-order two-scale (SOTS) computational method in the time domain is presented to predict the ageing linear viscoelastic performance of composite materials with a periodic structure. First, in the time domain, the SOTS formulation for calculating the effective relaxation modulus and displacement approximate solutions of the ageing viscoelastic problem is formally derived. Error estimates of the displacement approximate solutions for SOTS method are then given. Numerical results obtained by the SOTS method are shown and compared with those by the finite element method in a very fine mesh. Both the analytical and numerical results show that the SOTS computational method is feasible and efficient to predict the ageing linear viscoelastic performance of composite materials with a periodic structure.     

Influence of the Physical Nonlinearity of the Matrix on the Deformation of a Particulate Composite with Microdamageable Inclusions

The structural theory of short-term damage is generalized to particulate composites with nonlinearly elastic matrix and microdamageable inclusions. The basis for this generalization is the stochastic elasticity equations for a particulate composite with porous inclusions. Microvolumes of the material meet the Huber-Mises failure criterion. The damaged-microvolume balance equation and the equations relating macrostresses and macrostrains of a particulate composite with porous inclusions and physically nonlinear matrix constitute a closed-form system. This system describes the coupled processes of physically nonlinear deformation and microdamage. Algorithms for computing the microdamage-macrostrain relationships and deformation curves are proposed. Uniaxial tension curves are plotted for a particulate composite with linearly hardening matrix__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 3–11, April 2005.     

Metal matrix composite solidification in the presence of cooled fibers: numerical simulation and experimental observation

Attempts have been made to alter the solidification microstructures of fiber reinforced aluminum composites by cooling the ends of the fibers extending out of the mold. Experimental observations indicate that cooling the extended ends of the reinforcement results in finer microstructures in the matrix and changes the nature of the interface. In this paper, numerical simulation is performed on a two-dimensional axi-symmetric model to investigate the solidification process of metal matrix composite (MMC) with the extended ends of the fibers cooled by a heat sink. The numerical simulation is based on the source-based enthalpy method with finite volume discretization. The temperature profiles obtained by simulation are compared to the cooling curves measured experimentally in order to validate the current mathematical model. It is found that the simulation result matches the experimental data with reasonable agreement.     

纤维复合材料界面横向拉伸分析

以单纤维十字型横向拉伸试验为研究对象,对纤维/基体界面采用弹性-软化双线性内聚力模型,建立了纤维复合材料在横向拉伸作用下界面法向失效过程的解析模型。得到了沿纤维/基体圆周界面的法向应力分布,纤维/基体界面的状态与界面承载力和单纤维复合材料承载力的关系,以及内聚力参数和试件几何尺寸对它们的影响。结果表明:纤维/基体圆周界面在脱粘前经历全部弹性及弹性+软化两种状态;当界面为弹性状态时,界面法向应力随界面强度线性增加;当界面为弹性+软化状态时,界面软化范围随界面裂纹萌生位移的增加而增大;界面初始脱粘位置与拉伸荷载方向重合;界面初始脱粘时的界面承载力随界面强度及界面裂纹萌生位移的增加而增加,随界面裂纹生成位移的增加而降低;单纤维复合材料的脱粘荷载受基体截面尺寸的影响,当纤维体积含量相同时,沿荷载方向截面尺寸的增大对提高脱粘荷载更显著。     

Novel mechanical behavior of periodic structure with the pattern transformation

In periodic cellular structures, novel pattern transformations are triggered by a reversible elastic instability under the axial compression. Based on the deformation-triggered new pattern, periodic cellular structures can achieve special mechanical properties. In this paper, the designed architecture materials which include elastomer matrixes containing empty holes or filled holes with hydrogel material are modeled and simulated to investigate the mechanical property of the periodic materials. By analyzing the relationship between nominal stress and nominal strain of periodic material, and the corresponding deformed patterns, the influence of geometry and shapes of the holes on the mechanical property of architecture material is studied in more details. We hope this study can provide future perspectives for the deformation-triggered periodic structures.