M. Basista

Micromechanically Inspired Phenomenological Damage Model

The theory is based on the micromechanics of brittle deformation processes. The inelastic change of the compliance is identified as the flux and a properly averaged energy release rate as the affinity. The paper identifies conditions under which the damage potential exists

Chemically Assisted Damage of Concrete: A Model of Expansion Under External Sulfate Attack:

A micromechanical model is proposed to simulate the deformation of cementitious composites exposed to external sulfate attack. The model involves coupled physico-chemical processes of nonsteady diffusion with reaction, topochemical reaction of ettringite formation, expansion of ettringite inclusions, microcracking of hardened cement paste and percolation of sulfates through heavily deteriorated mortar. The Ficks second law with reaction term is assumed to govern the transport of the sulfate ions. The Eshelby solution and the equivalent inclusion method are used to determine the eigenstrain of expanding ettringite crystals in microcracked hardened cement paste. The degradation of transport properties is studied in the effective medium and the percolation regime. An initial boundary value problem (2D) of expansion of a mortar specimen immersed in a sodium sulfate solution is solved and compared with available test data.

Chemo-micromechanics of brittle solids

Abstract A s imple micromechanical model is formulated for a brittle solid reacting with water-borne aggressive chemical substances. Underlying physicochemical processes, diffusion, chemical reaction, expansion of reaction products and microcracking, are modeled on the microscale. The microscale models are homogenized into a governing set of equations relating macrovariables of the problem. Sulphate attack on concrete is used to illustrate the efficiency of the derived model.

Elastic moduli of perforated plates in the neighborhood of critical state

Abstract Percolation theory was applied to determine the critical surface urea density for a random distribution of circular voids in a two-dimensional elastic medium. Additionally, the percolation theory provides the scaling laws characterizing nonlinear dependence of elastic moduli on lacunity in the neighborhood of critical slate. It is also argued that the percolation theory complements the traditional effective continua models providing a measure of their accuracy.

Recent advances in research on magnesium alloys and magnesium–calcium phosphate composites as biodegradable implant materials

Magnesium alloys are modern biocompatible materials suitable for orthopaedic implants due to their biodegradability in biological environment. Many studies indicate that there is a high demand to design magnesium alloys with controllable in vivo corrosion rates and required mechanical properties. A solution to this challenge can be sought in the development of metal matrix composites based on magnesium alloys with addition of relevant alloying elements and bioceramic particles. In this study, the corrosion mechanisms along with corrosion protection methods in magnesium alloys are discussed. The recently developed magnesium alloys for biomedical applications are reviewed. Special attention is given to the newest research results in metal matrix composites composed of magnesium alloy matrix and calcium phosphates, especially hydroxyapatite or tricalcium phosphate, as the second phase with emphasis on the biodegradation behavior, microstructure and mechanical properties in view of potential application of these materials in bone implants.

Internal Variable Representation of Microcrack Induced Inelasticity in Brittle Materials

For brittle materials strained in compression, nonlinear constitutive equations are developed within the thermodynamic framework with microstructural internal variables. The sliding crack dissipative micromechanism, activated on preexisting dilutely distributed flaws, is assumed to govern the macroscopic deformation. The losses of energy resulting from frictional sliding on closed preexisting flaws, wing crack propagation, and wing crack rotation are included in the analysis. Two models (displacement-driven vs traction-driven) of the basic deformational micromechanism are considered in detail. The obtained incremental stress-strain relations are compared with the corresponding kinematic solutions available in the literature.

Numerical modeling of deformation and fracture of reinforcing fibers in ceramic–metal composites:

This paper is concerned with numerical modeling of deformation and fracture of a metal ligament bridging the crack faces in ceramic–metal composites, as a prerequisite for the determination of the J integral for composites with interpenetrating microstructure. A finite element model is proposed of an elasto-plastic crack-reinforcing fiber undergoing large plastic deformations and progressive debonding from the elastic matrix through a cohesive matrix–fiber interface. The σ-u relationships are derived first in the case of pullout of an elasto-plastic fiber embedded in an elastic matrix and then in uniaxial tension of the elasto-plastic fiber bridging the crack faces in elastic matrix. The obtained numerical results are discussed and compared with the theoretical predictions reported by other authors.

Thermal Residual Stresses Generated during Processing of Cr-Al2O3 Composites and their Influence on Macroscopic Elastic Properties

This work is focused on the modeling of thermal stresses induced during the fabrication of the metal/ceramic composites. On example of Cr-Al2O3 composite processed by powder metallurgy, thermal stresses after fabrication are determined by FEM model for different contents of metal and ceramic phases. Numerical model of microcracking induced by thermal stresses is then proposed and applied to compute the overall elastic properties of the damaged composite. Comparison of the model predictions with the measured data for Youngs modulus is presented.

Brittle deformation of disordered solids

Abstract The presented study summarizes the current state-of-art in the modeling of brittle deformation of solids containing a large number of microcracks. The discussion emphasizes micromechanical considerations and their limitations. It is further argued that the statistical methods may be used in a complementary manner to model the response near the critical point. Finally, it is suggested that an appropriate phenomenological model can be derived from micromechanical considerations.

The sliding crack model revisited

Abstract Two-dimensional micromechanical sliding crack model of inelastic deformation in brittle solids under compression is reexamined within the thermodynamic framework with microstructural internal variables ( Rice, 1971, 1975 )Incremental stress-strain equations are derived for an elastic solid weakened by non-interacting sliding microcracks. Preliminary results of crack-crack interactions in the presence of frictional and cohesive resistance are also presented.