Micromechanics

About: Micromechanics is a research topic. Over the lifetime, 6000 publications have been published within this topic receiving 162635 citations.

Colloidal aggregate micromechanics in the presence of divalent ions.

Abstract: Colloidal gels exhibit rheological properties, such as a yield stress and elasticity, which arise from the manner in which stress is transmitted through the microstructure. Insight into the mechanisms of stress transmission is critical in developing a full understanding of the mechanics of these materials. Paramount to this is a thorough knowledge of the interparticle interactions. In this work, we use optical trapping to study interactions between poly(methyl methacrylate) (PMMA) particles in adhesive contact by measuring the bending elasticity of directly assembled colloidal aggregates under various physicochemical conditions. The simplified geometry of the aggregate enables us determine the single-bond rigidity, which can then be related to the work of adhesion, W(SL), through the Johnson-Kendall-Roberts (JKR) theory of adhesion. We find that W(SL) is independent of ionic strength in flocculating monovalent salt solutions. However, more complex behavior is observed for divalent salts. Using zeta-potential measurements, we show that divalent cations adsorb to the particle surface. This results in the formation of ionic bridges between particles in adhesive contact. A model of the aggregate micromechanics that considers the divalent ion contribution to the surface energy provides a direct link between the interfacial properties of the particles, nanoscale contact interactions between particles, and the bulk gel modulus.

Damage analysis of fiber reinforced Ti-alloy subjected to multi-axial loading—A micromechanical approach

Abstract: Effects of initiation and propagation of interface damage on the elastoplastic behavior of a unidirectional SiC/Ti metal matrix composite (MMC) subjected to multi-axial loading are studied using a three-dimensional micromechanics based analytical model. Effects of manufacturing process thermal residual stress (RS) are also included in the analysis. The selected representative volume element (RVE) consists of an r × c unit cells in which a quarter of the fiber is surrounded by matrix sub-cells. The constant compliance interface (CCI) model is used to model interfacial debonding and the successive approximation method together with Von-Mises yield criterion is used to obtain elastic–plastic behavior. Failure modes during multi-axial tensile/compressive loading in the presence of residual stresses are discussed in details. Results revealed that for more realistic predictions both interface damage and thermal residual stress effects should be considered in the analysis. Comparison between results of the presented model shows very good agreement with available finite element micromechanical analysis and experiment for uniaxial loading. Also, results are extracted and interpreted for equi-biaxial including transverse/transverse and axial/transverse and equi-triaxial loading.

An Analysis of Thermal Residual Stresses in Ti-6-4 Alloy reinforced with SiC and Al2O3 Fibres

Abstract: Thermal residual stresses in Ti6Al4V alloy reinforced with silicon carbide (SiC) and sapphire alumina (Al2O3) fibres are estimated based on an elastic-viscoplastic micromechanics analysis. Effects of fibre volume fraction and different manufacturing procedures are considered and comparisons made with published experimental results for the SiC fibre composite. Stress components in the Ti-6-4/Al2O3 are generally less than half the corresponding values in the Ti-6-4/SiC composite.

Three‐dimensional numerical modelling by XFEM of spring‐layer imperfect curved interfaces with applications to linearly elastic composite materials

Abstract: The spring-layer interface model is widely used in describing some imperfect interfaces frequently involved in materials and structures. Typically, it is appropriate for modelling a thin soft interphase layer between two relatively stiff bulk media. According to the spring-layer interface model, the displacement vector suffers a jump across an interface whereas the traction vector is continuous across the same interface and is, in the linear case, proportional to the displacement vector jump. In the present work, an efficient three-dimensional numerical approach based on the extended finite element method is first proposed to model linear spring-layer curved imperfect interfaces and then applied to predict the effective elastic moduli of composites in which such imperfect interfaces intervene. In particular, a rigorous derivation of the linear spring-layer interface model is provided to clarify its domain of validity. The accuracy and convergence rate of the elaborated numerical approach are assessed via benchmark tests for which exact analytical solutions are available. The computated effective elastic moduli of composites are compared with the relevant analytical lower and upper bounds. Copyright © 2011 John Wiley & Sons, Ltd.