Papers by Keyword: Micromechanics

Abstract: Advancements in the numerical modelling of 3D woven composites have allowed improved understanding of the mechanical behaviour and in turn aided the design and analysis of new materials. The objectives of this paper are to utilise FEA (Finite Element Analysis) methods to determine the elastic properties of a given woven composite. The investigation focuses on satin weaves, considering both 5-harness and 8-harness varieties. Multi-scale analysis results of an RVE are used to formulate the stiffness matrix and consequently determine the elastic properties; these will be compared to published analytical methods and experimental results. Further investigations considering the effect of weave parameters on the elastic properties are conducted.

Abstract: This paper describes using of silicon carbide for micromechanical systems. Low stressed sensitive membrane signal converters, thin film transducers and piezoresistive sensors were formed based on silicon carbide films. The mechanical properties of silicon carbide films were determined.

Abstract: Based on the micromechanics principle, establish concrete random aggregate, constitutive model choose HJC model and K&C model, numerical Simulation for the part of the S.J.Hanchak projectile penetrating into concrete targets test. Through the bullets remaining projectile velocity and target plate failure compared, it is concluded that Concrete mesostructure uneven impact of its macro mechanics; flaking and spallation phenomena on the HJC model simulation of the target body front and back by the impact appears less effective, and K&C model is in good agreement with the experimental conditions; K&C model is a simple and effective way to predict the dynamic response of the projectile penetrating into concrete targets.

Abstract: The hydrated products, unhydrated cement and water (capillary pores) in the cement paste are seen as matrix, inclusion, Equivalent medium respectively, We used the micromechanics theories and Power’s Volume model to develop a multi-phase micromechanics model capable of simulating the elastic properties of cement-based materials, and the evolution of elastic properties in the hydration process was calculated at different water-cement ratio. The final experimental results show that this model can be used to predict the elastic properties of cement-based materials.

Abstract: Recycled Aggregate Concrete (RAC) is referred to as Recycled Concrete (RC). In this paper, the compression performance of recycled concrete was researched using the micromechanics. The recycled concrete was taken as a five-phase composite material consisting of recycled coarse aggregate, old hardened cement paste, new hardened cement paste, the old interfacial transition zone (Old ITZ) and the new interfacial transition zone (New ITZ) on meso-level. A random aggregate model was used to simulate the meso-structure of recycled concrete. The propagation process of cracks and the mechanical properties of uniaxial compression specimens of recycled concrete were simulated using finite element method (FEM) with damage model. The numerical simulation results agree well with the corresponding experimental results. The results show that the specimen usually damaged along the old interfacial transition zone and the new interfacial transition zone.

Abstract: Laboratory experiments and numerical simulations, using Particle Flow Code (PFC2D ), were performed to study the behavior of marble under tri-axial loading and pre-existing fissure uniaxial compression. The laboratory tri-axial compression results of marble was analyzed, and the calibration of the micro-properties of BMP (Bonded particle model ) in PFC2D with the test data was carried out successfully. The pre-existing fissure was simulated by smooth joint contact, and the cracking propagation mode of pre-existing fissure was carried out with the calibrated BMP properties and single smooth joint contact. The simulation show that the tensile crack firstly initiated along the vertical direction to pre-existing fissure, and then gradually departs towards the direction of axial stress, and finally develops along the direction of axial during compression. The numerical simulation coincide with our understanding of fracture mechanics.

Abstract: Textile composites have increasingly been used as a structural material because of their balanced properties, higher impact resistance, and easier handling and fabrication compared with unidirectional composites. However, the complex architecture of textile composites leads to difficulties in predicting the response in spite of the fact that there is the need to determine mechanical properties in product design. Micromechanical analysis, using the Finite Element Method, was conducted in order to evaluate the effective mechanical properties of plain woven and 3D woven composites. In this study, numerical models of unit cells were used and it is shown that the predicted values of homogenized mechanical properties using the developed procedure were in good agreement with experimental results.

Abstract: The melt spun ribbons of ferromagnetic shape-memory alloy (FSMA) Ni₅₃Mn₂₄Ga₂₃ have been prepared by rapid quenching. Thermomechanical properties have been studied by multi-point technique and perfect shape memory effect (SME) observed. The magnetic field effect on thermomechanical behavior was studied by placing multi-point press into Bitter magnet. A giant (1.2%) bending strain, due to magnetic field-induced martensitic transformation (magnetic-field-induced SME), has been observed at a constant temperature T= 56 °C in a field of 6 T. At least 80% of martensitic transformation reversibly induced by the external field was observed experimentally. Submicron sized samples of the alloy with thicknesses down to 300 nm have been milled by focused ion beam (FIB) technique. The deformation behavior of these samples was studied by Omniprobe micromanipulator in the vacuum chamber of FIB device. The SME response was tested in situ by heating the samples with a semiconductor laser. Strong two-way SME was observed due to bending strains of the samples under study.

Abstract: Series of biaxial compression simulations are carried out to investigate the effects of boundary condition on the deformation of granular materials by using DEM. The parameters used in DEM are validated by the biaxial compression experiments on elliptical steel bars. The effects of boundary condition on the stress-strain relationship are analyzed. And special focus are put in the analysis of particle displacement, particle rotation, void distribution, particle long axis orientation and contact force with the development of deformation.

Abstract: A micromechanical model for single-fiber pull-out test of fiber-reinforced viscoelastic matrix composites is established. It includes fiber, interphase and viscoelastic matrix. The formulas to calculate the fiber axial stress, the interphase shear stress, and the matrix axial and shear stress are obtained. Moreover, for Kevlar aramid fiber reinforced viscoelastic matrix composites, the influences of the interphase thickness, the fiber embedded length and volume fraction on the stress distributions of fiber and interphase is studied. Some analysis results show that, with the increase of normalized fiber axial distance, the fiber axial stress increases monotonically, but the interphase shear stress decreases. The stress distributions of fiber and interphase change with the variation of the interphase thickness, the fiber embedded length and volume fraction.