Search

A density functional theory (DFT) calculation is carried out in this work to investigate the effect of vacancies on the behavior of Al(111)/6H SiC composites. Generally, DFT simulations with appropriate interface models can be an acceptable alternative to experimental methods. We developed two modes for Al/SiC superlattices: C-terminated and Si-terminated interface configurations. C and Si vacancies reduce interfacial adhesion near the interface, while Al vacancies have little effect. Supercells are stretched vertically along the z-direction to obtain tensile strength. Stress–strain diagrams illustrate that the tensile properties of the composite can be improved by the presence of a vacancy, particularly on the SiC side, compared to a composite without a vacancy. Determining the interfacial fracture toughness plays a pivotal role in evaluating the resistance of materials to failure. The fracture toughness of Al/SiC is calculated using the first principal calculations in this paper. Young's modulus (E) and surface energy (Ɣ) is calculated to obtain the fracture toughness (KIC). Young's modulus is higher for C-terminated configurations than for Si-terminated configurations. Surface energy plays a dominant role in determining the fracture toughness process. Finally, to better understand the electronic properties of this system, the density of states (DOS) is calculated. [ABSTRACT FROM AUTHOR]

Fracture toughness, bending strength, Young's modulus, hardness and subcritical crack growth were determined for six different alumina/zirconia composites. The bending strength was modelled using Weibull distribution. The fracture toughness, bending strength and resistance to subcritical crack growth increase as a function of ZrO 2 content (stabilized with 3 mol% Y 2 O 3). The authors claim that a threshold stress in a three-parameter Weibull distribution may correspond to a threshold stress intensity factor in which the subcritical crack growth is negligible. [ABSTRACT FROM AUTHOR]

The damage behaviour of unfired dry earth is determined experimentally under compression by means of loading-unloading cyclic tests. The scalar damage parameter is determined and its evolution law is related to the applied strain - $${d (\varepsilon)}$$ . Interpolating functions are determined, permitting to estimate how the damage depends on the deformation process of the considered material. Different aspect-ratios of the specimens are considered. [ABSTRACT FROM AUTHOR]

Abstract: In the fabrication process of ceramic composite materials or in service interface cracks could appear in one of the constituents. This work reports the stress intensity factors solution of a kinked crack whose corner is on the interface of two bonded dissimilar ceramic materials subjected to tension parallel to the interface and to tension normal to the interface. The finite element method was used to calculate the stress intensity factors at the tips of the crack. The effects of the material properties of the ceramic composite constituents, the kinked crack length, the interface crack length, and the kinked angle were investigated. A convergence study was carried out in order to find the proper distance r for collecting the displacement data for the crack flank displacement method. Results for the modulus of the complex stress intensity factors for the bi-material combinations with the homogeneous case, based on Suo and Hutchinson approach show consistent agreement for a range of interface crack lengths, kinked crack lengths and kinked angles. [Copyright &y& Elsevier]

Abstract: This paper is a first attempt to determine the dynamic fracture toughness of polyurethane foam and to study the effect of impregnation on the fracture toughness. Instrumented impact tests were performed using notched specimens. In order to study the effect of impregnation on the impact properties two different resins were used. The obtained results show that the impregnation increases the dynamic fracture toughness by 27%. [Copyright &y& Elsevier]

The fracture mechanics concepts were applied to describe the experimental results of three-points bending tests to investigate fracture characteristics and crack resistance of unfired earth material. [ABSTRACT FROM AUTHOR]

Stress intensity factors for a kinked crack originating at interface of two bonded dissimilar materials subjected to normal tension are found by the finite element method. [ABSTRACT FROM AUTHOR]

Abstract: Analysis and fracture interpretation (using the strain energy density criterion) of Compact Shear specimen for Mode II fracture testing of materials is presented in the paper. Two approaches are used. One is based on singular integral equations for the problem of the interaction of two parallel cracks under Mode II loading corresponding to the loading in the Compact Shear specimen (CS specimen). Approximate analytical formulas for the stress intensity factors at the crack tips are derived. A numerical calculation using Gauss-quadrature formulae for the corresponding integral equations is presented. The influence of geometry of the problem on the stress intensity factors and on the angles of the initial propagation direction of the cracks is investigated. The other approach is Finite Element Method implemented in FRANC2D/L code. Numerical analysis was done for plain strain conditions. Different geometries of the specimen are considered for two models of the CS specimen and compared with results available in the literature. Analytical and FEM calculations are also compared and discussed. [Copyright &y& Elsevier]

Abstract: The fracture behaviour of unfired dry earth has been investigated by means of an experimental approach supported by some numerical simulations. Three-points bending tests, both with monotonic and cyclic loads, have been performed experimentally, and the related force–displacement diagrams are interpreted theoretically to characterize the fracture parameters of the considered material. Both Linear Elastic Fracture Mechanics and a Two Parameter Model are considered. In the latter case, based on the post-peak softening behaviour, the R-curve is determined, which shows how the critical stress intensity factor depends on the fracture length. [Copyright &y& Elsevier]

Many efforts have been made in recent years to determine the fracture toughness of different types of foams in static and dynamic loading conditions. Taking into account that there is no standard method for the experimental determination of the fracture toughness of plastic foams different procedures and specimens were used. This paper presents the polyurethane foam fracture toughness results obtained for different foam densities. Two types of specimens were used for determining fracture toughness in modes I, II and a mixed one, and also the size effect, loading speed and loading direction were investigated. The paper proposed correlations for density, cell orientation and mixed mode loading based on the experimental testing results. [ABSTRACT FROM AUTHOR]