Leon Mishnaevsky

Continuum Mesomechanical Finite Element Modeling in Materials Development: A State-of-the-Art Review

Advanced finite element techniques for the simulation of materials behavior under mechanical loading are reviewed. Advantages, limitations and perspectives of different approaches are analyzed for the simulation of deformation, damage and fracture of mate

PHYSICAL MECHANISMS OF HARD ROCK FRAGMENTATION UNDER MECHANICAL LOADING: A REVIEW

This Technical Note reviews a number of theoretical and experimental investigations, considers the diversity between them and determines some of the problems that need to be solved. Some of the conclusions of work on microindentation in ceramics can be extended to rocks. The stages of rock fragmentation under indentation are considered and physical mechanisms for the formation of the crushed zone are examined. The influence of the rate of loading, the shape of the indentor and cutting conditions is discussed. Mechanisms of chipping and crack formation are considered. The zone of crushed rock is of great importance in the fragmentation process. The main part of fragmentation energy is apparently consumed just by the formation of the zone and rock crushing within it. The energy of fragmentation increases as the size of the zone increases. The factors influencing the size of the crushed zone, and consequently the energy consumed in drilling, are discussed.

Computational mesomechanics of particle-reinforced composites

Abstract Numerical models of deformation, damage and fracture in particle-reinforced composite materials, based on the method of multiphase finite elements (MPFE) and element elimination technique (EET), are presented in this paper. The applicability of these techniques for different materials and different levels of simulation was studied. The simulation of damage and crack growth was conducted for several groups of composites: WC/Co hard metal alloys, Al/Si and Al/SiC composites on macro- and mesolevel. It is shown that the used modern techniques of numerical simulation (MPFE and EET) are very efficient in understanding deformation and damage evolution in heterogeneous brittle/ductile materials with inclusions.

Computational modeling of crack propagation in real microstructures of steels and virtual testing of artificially designed materials

A computational approach to the optimization of service properties of two-phase materials (in this case, fracture resistance of tool steels) by varying their microstructure is developed. The main points of the optimization of steels are as follows: (1) numerical simulation of crack initiation and growth in real microstructures of materials with the use of the multiphase finite elements (MPFE) and the element elimination technique (EET), (2) simulation of crack growth in idealized quasi-real microstructures (net-like, band-like and random distributions of the primary carbides in the steels) and (3) the comparison of fracture resistances of different microstructures and (4) the development of recommendations to the improvement of the fracture toughness of steels. The fracture toughness and the fractal dimension of a fracture surface are determined numerically for each microstructure. It is shown that the fracture resistance of the steels with finer microstructures is sufficiently higher than that for coarse microstructures. Three main mechanisms of increasing fracture toughness of steels by varying the carbide distribution are identified: crack deflection by carbide layers perpendicular to the initial crack direction, crack growth along the network of carbides and crack branching caused by damage initiation at random sites.

Methods of the theory of complex systems in modelling of fracture: A brief review

Abstract Theoretical investigations of damage and fracture of materials which are based on the concepts of the theory of complex systems are reviewed and analyzed. The models of fracture, which have been developed with the use of the methods of following theories, are considered: theory of phase transitions and statistical physics, percolation and fractals theories, theories of dynamical systems, bifurcations and self-organization. The main achievements, perspectives and limitations of the applications of these methods in modelling of fracture are analyzed.

IN-SITU OBSERVATION OF DAMAGE EVOLUTION AND FRACTURE IN ALSI7MG0.3 CAST ALLOYS

The mechanisms which occur during damage initiation, evolution and crack growth in A1Si7MgO.3 cast alloys are studied by in-situ tensile testing in a scanning electron microscope. It is shown that microcracks in these alloys are predominantly formed in the Si particles. Shear bands are seen to precede the breaking of the Si particles and the dislocation pile-up mechanism can thus be confirmed as the dominant damage initiating process in the matrix. Both micro- and macrocrack coalescence have been observed in the course of the experiments. The effect of the microstructure of the A1Si7Mg cast alloys on damage nucleation, crack formation and compliance reduction is analysed. @. 1999 Elsevier Science Ltd. All rights reserved.

DAMAGE EVOLUTION AND HETEROGENEITY OF MATERIALS: MODEL BASED ON FUZZY SET THEORY

Abstract A mathematical model of damage evolution in heterogeneous materials is developed using the methods of the theory of fuzzy sets. The fuzzy concept of damage is formulated and some applications of this concept are considered. The influence of the material heterogeneity on the damage as well as the heterogenization of the material due to the damage evolution are studied. On the basis of the fuzzy concept of damage, it is shown that the greater the heterogeneity of material, the closer is the material to failure under loading.

Investigation of the cutting of brittle materials

Abstract A mechanism describing brittle material destruction in cutting is investigated. A mathematical model for the cutting of brittle material is developed. It is shown that the zone containing large pennyshaped cracks forms during the cutting process. It is concluded that cutting efficiency can be increased through the interaction of zones of different cuts.

Strength and Reliability of Wood for the Components of Low-Cost Wind Turbines: Computational and Experimental Analysis and Applications

This paper reports the latest results of the comprehensive program of experimental and computational analysis of strength and reliability of wooden parts of low cost wind turbines. The possibilities of prediction of strength and reliability of different types of wood are studied in the series of experiments and computational investigations. Low cost testing machines have been designed, and employed for the systematic analysis of different sorts of Nepali wood, to be used for the wind turbine construction. At the same time, computational micromechanical models of deformation and strength of wood are developed, which should provide the basis for microstructure-based correlating of observable and service properties of wood. Some correlations between microstructure, strength and service properties of wood have been established.

A Simple Method and Program for the Analysis of the Microstructure-Stiffness Interrelations of Composite Materials

A simple efficient method for the estimation of stiffness of materials with arbitrarily complex and irregular microstructures is developed on the basis of a combination of Reuss and Voigt estimates for the stiffness of a composite. A program which designs complex microstructures as an array of cells in an interactive session, and then estimates the Young’s modulus of designed arbitrary microstructures is developed. A combined Reuss-Voigt model is developed for the calculation of Young’s modulus of bilayers with inclined interfaces. A subroutine, which links the developed program and the commercial FE codes and allows the automatic generation of micromechanical finite element models of the designed microstructures is built-in in the program. Using this model, the effect of the smoothness of the transition region in graded composites on the stiffness of the materials is studied. It is shown that the stiffness of graded composites increases with increasing the smoothness of the transition region between the phases.