Papers by Keyword: Micromechanical Model

Abstract: This study presents an accurate and easy-to-use micromechanical model to predict the ultimate strength of unidirectional polymer composites under an arbitrary load condition only upon independently measured constituent properties. In this model, the micromechanical method based on generalized model of cells (GMC), which effectively predict the nonlinear deformation of unidirectional composites, is used to analyze the repeating unit cells of composites. At the same time, a unified plastic theory (i.e. modified Ramaswamy-Stouffer model) is incorporated into the GMC's analytical framework to describe viscoplastic behaviors of matrix phase. Additionally, because of the stress concentration effect which causes the difference between the matrix in-situ and original strength behaviors, a stress concentration factor is introduced in order to utilize the measured constituent properties directly. The prediction results with SCF match better with the experimental results than the prediction results without SCF. In addition, the prediction results show that the presence of thermal residual stress and material plastic effects generally has important influence on the strength prediction of a composite.

Abstract: The mechanical properties of a cementitious composite are strongly affected by interfacial transition zone (ITZ) between the matrix and the aggregates, mainly by its strength and thickness. A micromechanical model based on Mori-Tanaka scheme coupled with an estimation of deviatoric stress in ITZ was developed for evaluation of the effect of selected secondary cementitious materials (SCMs – silica fume, fly ash and metakaolin) on the properties of ITZ in high-strength concrete (HSC). The model was validated by means of comparison of predicted ITZ thickness with direct ITZ thickness measurements performed by a combination of scanning electron microscopy and grid nanoindentation. Very good agreement between the theoretical and experimental results was reached, therefore the developed micromechanical model can be used for further research and optimization of HSC containing SCMs. Silica fume was determined to be the most efficient supplementary cementitious material from the point of view of ITZ thickness reduction.

Abstract: A new micromechanical modelling approach for brittle damage in initially orthotropic materials is presented. The proposed strain-based energy formulation allows to derive a fully anisotropic multilinear model for microcracked materials with arbitrary oriented defects. The thermodynamics framework provides a standard procedure for the damage evolution law. The new model explicitly accounts for the interaction between primary and induced anisotropies. Moreover, the very challenging issue of opening-closure effects (unilateral behavior) is addressed in this framework.

Abstract: Based on the connection between macroscopic and microscopic characteristics of carbon black filled rubber composites, Representative Volume Element (RVE) containing one single particle has been proposed, and three dimensional cubic RVE has been established to study and analyze the macroscopic mechanical properties of the carbon black filled rubber composites by the micromechanical finite element method. The research shows that the stiffness of the composite is increased with the increase of the volume fraction of carbon black filler particles. By comparison, it is shown that the results of the predictions on the stress-strain behavior of the rubber composite made with the cubic RVE numerical models containing one spherical particle are in good agreement with the experimental results for seven and fifteen percent carbon black filler content, but there is some discrepancy between them for twenty-five percent carbon black filler content. The results of the predictions on the stress-strain behavior of the rubber composite made with the cubic RVE numerical models containing one cubical particle are higher than the experimental results, and the higher the carbon black filler content, the greater is the discrepancy between them.

Abstract: Three dimensional (3D) cubic models with spherical pores ranged as Face-Centered Cubic (FCC) lattices are constructed to simulate the microstructures of rubber foams with various relative densities. The Mooney-Rivlin strain energy potential model is adopted to characterize the hyperelasticity of the constituent solid from which the foams are made. Large compressive deformations of closed-celled rubber foams are calculated by the iterative algorithm. Numerical results show that with the decreasing of foam relative densities, the effects of air pressures in cells on foam compressive stresses increase. When the ratio of initial Yangs modulus of cell material to the initial air pressure in cells reaches 2 order of magnitude, the influence of air pressures in cells can neglect.

Abstract: Fibre-reinforced polymer (FRP) composites have been widely used in industry. However, the machining of FRP products is difficult, because of very different properties of the fibres and matrix. This paper discusses the development and implementation of a microstructure-based three-dimensional finite element model for the elliptic vibration-assisted (EVA) cutting of unidirectional FRP composites. The results showed that the EVA cutting has a good potential to the machining of FRP composites, featured a much reduced cutting force, better surface integrity and controllable chip size.

Abstract: A convenient method to predict the macroscopic elastic performance of composite containing interphase was proposed in this paper. Firstly, a 3-D three-phase micromechanical model with randomly distributed fibers was established with the Moving Window Method (MWM), and the macroscopic elastic properties of T300/914C were predicted using energy method. Secondly, the multiple nonlinear regression correlation between the macroscopic elastic properties and micromechanical characteristic parameters of the interphase was established based on numerical data. Finally, the macroscopic elastic properties of T300/914C containing interphase were predicted using the regression model. Results indicate that the relative error for the longitudinal modulus is within ±1% while it is within ±3.5% for the transverse modulus, and shear modulus.

Abstract: In this paper, Representative Volume Element with random distribution pattern has been built and applied to study and analyze the macro mechanical properties of the carbon black filled rubber composites by the micromechanical finite element method. And numerical simulations under uniaxial compression have been made by two-dimensional plane stress model. The periodic boundary conditions are imposed on each Representative Volume Element in order to ensure the compatibility of the deformation field. The dependence of the macroscopic stress-strain behavior and the effective elastic modulus of the composites, on particle distribution pattern, particle volume fraction and particle stiffness has been investigated and discussed. It is shown that the stiffness of the composite is increased considerably with the introduction of carbon black filler particles, and the effective elastic modulus of the composite is increased with the increase of the particle volume fraction.

Abstract: In this paper, the micromechanical finite element method based on Representative Volume Element has been applied to study and analyze the macro mechanical properties of the carbon black filled rubber composites by using two-dimensional plane stress simulations and three-dimensional axisymmetric simulations under uniaxial compression respectively. The dependence of the macroscopic stress-strain behavior and the effective elastic modulus of the composites, on particle shape, particle area/volume fraction and particle stiffness has been investigated and discussed. Additionally, the simulation results of the two-dimensional plane stress model and the three-dimensional axisymmetric model are evaluated and compared with the experimental data, which shows that the two-dimensional plane stress simulations generate poor predictions on the mechanical behavior of the carbon black particle reinforced rubber composites, while the three-dimensional axisymmetric simulations appear to give a better prediction.

Abstract: Talus deposit is often seen in the hydropower projects in the southwest of China. Its mechanical properties are so complex that microstructure study is often used to reveal the essence of deformation and damage. The digital image processing technology (DIPT) is introduced to the simulation of talus deposits. Based on the study of DIPT, a Photo-To-Flac3D (PTF) auto-modeling program is developed. It is able to realize the whole process: analyzing and processing the digital image, acquiring the information and establishing the micro-model files. A new modeling method is developed for the mechanical behavior simulation of talus deposit. As an example, some talus deposit data of Gushui hydropower station is used, the micro-model of talus deposit can be established fast and correctly by the PTF from the digital photo on-site. The mechanical properties are studied by the numerical simulation of triaxial test. The results show that the talus deposit has the feature of bully in deformation while that of Unicom band under force.