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Fracture criteria for prediction of extension of the interface crack and of the crack growth direction in a bimaterial consisting of a homogeneous and a functionally graded material (FGM) with systems of internal defects are studied. The bimaterial is subjected to a heat flux and a tensile load applied at infinity. It is assumed that the thermal properties of the FGM have exponential form. The Young’s modulus and Poisson’s ratio are assumed to be constant. In the previous papers (Petrova and Schmauder, 2011a,b, 2012a,b) asymptotic analytical formulas for the stress intensity factors (SIFs) at the interface crack tips were obtained as a series of a small parameter (the ratio between sizes of the internal and interface cracks). These SIFs are used in fracture criteria to obtain the possible direction of crack propagation and critical loads. The maximum circumferential stress criterion is used and some results for the fracture angles is obtained by the minimum strain energy density in order to compare the predictions for the fracture angles by two fracture criteria. The influence of geometry of the problem (location and orientation of cracks) and the parameters of non-homogeneity of FGMs on the main fracture characteristics is investigated. [ABSTRACT FROM AUTHOR]

Abstract: The work is devoted to the investigation of fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to tensile loading and a heat flux. A previously obtained solution () for the case of thermal loading on the same geometry is used as a part of the present solution. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) possess exponential form. An asymptotic analytical solution is derived for a special case where an interface crack is larger than internal cracks in the FGM. The stress intensity factors are presented as asymptotic analytical functions of geometry of the problem and material properties. Analyses of the effects of the location and orientation of the cracks and the material non-homogeneity parameters on the stress intensity factors in FGM/homogeneous bimaterials is performed in the presence of thermal and mechanical loading. Examples of some FGM/homogeneous bimaterial are discussed. [Copyright &y& Elsevier]

Abstract: The work is devoted to mathematical modeling of the fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to a thermal flux. A previously obtained solution (Petrova and Schmauder, 2009, 2011) is used and supplemented with the additional possibility to take into account the crack closure. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) have exponential form. For a special case where an interface crack length is much larger than the internal cracks in the FGM an asymptotic analytical solution of the problem is obtained as series of a small parameter (the ratio between sizes of the internal and interface cracks). Analyses of the effects of the location and orientation of the cracks, the material non-homogeneity parameters and the crack closure effects on the thermal stress intensity factors of the interface crack in FGM/homogeneous bimaterials are performed. Examples of some FGM/homogeneous bimaterial combinations (i.e., metal/metal, ceramic/metal) are discussed. [Copyright &y& Elsevier]

Abstract: The thermal fracture of a bimaterial consisting of a homogeneous material and a functionally graded material (FGM) with a system of internal cracks and an interface crack is investigated. The bimaterial is subjected to a heat flux. The thermal properties of FGM are assumed to be continues functions of the thickness coordinate, while the elastic properties are constants. The method of the solution is based on the singular integral equations. For a special case where the interface crack is much larger than the internal cracks in the FGM the asymptotic analytical solution of the problem is obtained as series in a small parameter (the ratio between sizes of the internal and interface crack) and the thermal stress intensity factors (TSIFs) are derived as functions of geometry of the problem and material characteristics. A parametric analysis of the effects of the location and orientation of the cracks and of the inhomogeneity parameter of FGM’s thermal conductivity on the TSIFs is performed. The results are applicable to such kinds FGMs as ceramic/ceramic FGMs, e.g., TiC/SiC, MoSi2/Al2O3 and MoSi2/SiC, and also some ceramic/metal FGMs. [Copyright &y& Elsevier]

• Overview of the available results for Mode III interface crack problems is presented. • Mode III interface crack problem is posed using analytic functions of complex variable. • Closed form analytical solution for interface crack- microcrack interaction is presented. • Solutions for SIFs are discussed with respect to their dependency on bimaterial constants. An overview of the results for Mode III interface crack problems available in the literature, as well as those obtained by the authors, is presented in the paper. The analytical and semi-analytical solutions for the main fracture characteristics (i.e. stress intensity factors and energy release rates) are discussed with respect to their dependency on bimaterial constants. Detailed formulation for the antiplane shear problem for an interface crack interacting with internal cracks is presented using the methods of complex potentials and singular integral equations. Some particular solutions (e.g. for the problem of a singularity interacting with an interface and for the Mode III interface crack) are obtained, and these can serve as benchmark solutions or as parts of other similar problems. The approximate closed-form solution is derived for a special case of the interaction between the interface crack and internal micro-cracks. The resulting form of the solution for the stress intensity factors is rather simple and its structure is easily analyzed. A theoretical analysis of the explicit form of expressions for the stress intensity factors shows the conditions under which the solution for the interface crack depends on the bimaterial mismatch, and those under which it does not depend. This formula also allows to define the condition, when a small internal crack does not influence the stress intensity factor of the interface crack (i.e. invisible for the interface crack). [ABSTRACT FROM AUTHOR]

Interfacial bonding of three different semi-coherent bcc-Fe(110)/graphene interfaces is investigated using the plane-wave pseudopotential method within density functional theory. The analysis of bond lengths, charge densities, charge transfer, magnetic moments and densities of states shows that interfacial adhesion can be understood from the electronic structure. Graphene is considered on Fe(110) surfaces as well as embedded in (110) planes of bulk Fe. Moreover, the influence of single vacancies in graphene is studied in case of graphene on the Fe(110) surfaces. It is found that a single vacancy in graphene leads to a strong increase of interfacial adhesion. The most important contribution to the adhesion is covalent bonding with hybridization of Fe states and C states which is most pronounced for neighboring atoms of the vacancy. [Display omitted] • bcc-Fe(110)/graphene interfaces exhibit strong adhesion due to covalent Fe–C bonds. • Single vacancies in graphene lead to a strong increase of adhesion. • Large magnetic moments are induced at C atoms neighboring a single vacancy. [ABSTRACT FROM AUTHOR]

• B substitution of a C atom increases the work of separation on the Fe(110) surface. • There is almost no effect of N on the graphene/Fe(110) interface. • B and N impurities affect the charge states of the nearest C atoms. • Impurities influence on the magnetic state of the nearest Fe atoms. Influence of B and N substitutional impurities on the adhesion properties, electronic and magnetic characteristics of the external and internal graphene/Fe(110) semi-coherent interface was investigated by the projector augmented-wave method within the density functional theory. The analysis of interatomic distances, charge densities, charge transfer and magnetic states of atoms was performed. It was shown that B-doped graphene has a higher adhesion energy on the Fe(110) surface and in the iron bulk in comparison with the undoped systems; whereas, N-doped graphene in the Fe bulk demonstrates the opposite trend and on the surface it has no effect. Boron acts as electron donor that increases charges of the nearest C atoms by 0.5–0.6 e. Nitrogen due to its high electronegativity is an acceptor and as a result the nearest C atoms lose 0.2–0.3 e. Both impurities, depending on the position, influence differently on the magnetic moment of the nearest iron atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

Co(0001)/TaC(01 2 ¯) interfaces with Re impurities are investigated using the plane-wave pseudopotential method within density functional theory. Two interface configurations and several interfacial sites for Re impurities are considered. The calculations reveal that Re doping can lead to more favourable interfaces with lower interface energies. It is shown that the decrease of interface energy can be understood from the electronic structure. Analyses of bond lengths, overlap populations, charge density distributions and densities of state demonstrate the importance of C-Co and C-Re bonds across the interface. Image 1 • Interfacial Re impurities increase interface strength. • Increased interface strength is mainly caused by strong C-Re covalent bonds. • Most favourable configuration of Co/TaC interface is changed by Re doping. [ABSTRACT FROM AUTHOR]