Issue 53

L. Hadid et alii, Frattura ed Integrità Strutturale, 53 (2020) 1-12; DOI: 10.3221/IGF-ESIS.53.01

in the electronics industry and electro-technical due to its interesting electrical properties such as great resistivity, significant dielectric constant and weak dielectric loss factor. Very often to benefit the maximum of these advantages, it is necessary to bind ceramics and more particularly alumina with metals and their alloys. Under the simultaneous action of the temperature and the elaboration constraint of the bimaterial, the metal deforms plastically and becomes encrusted in the roughness defects of the ceramic. This incrustation leads to a good mechanical attachment between these two protagonists and ensures very good adhesion between metal and ceramic. The joining of ceramics with metals is inherently difficult because of their distinctly different properties. During recent past years, considerable studies have been devoted to the technology development of ceramic/metal joining. It has been led to significant successes [1]. Dissimilar materials need to be joined together in many technical areas. One example of the ceramic to metal joint combines the wear resistance, high temperature strength and thermal or electrical resistance of the ceramic with the ductility of the metal. Due to the difference of the elastic properties and the thermal expansion coefficients of the ceramic and metal, high stresses occur at the intersection of edges which leads the interface of the joint under mechanical or thermal loading [2-3]. The joining of ceramics with metals is a critically important technology for the effective use of advanced materials [4]. Metal-ceramic interfaces have wide applications, and the interface fractures play an important role in determining mechanical behaviours of related structures [5]. The study of the interface separation behaviours of interfaces with the atomic vacancy and dislocations indicates that the interface strength decreases for the interfaces with defects, and the defects decrease the catastrophic tendency [5]. Joining dissimilar materials implies property mismatches and structure discontinuities [6]. Interfaces must typically sustain mechanical and thermo-elastic stresses without failure. Consequently, they exert an important influence on the performance of the material [7-8]. Due to differences in thermal and mechanical properties, the stresses and strains can develop near a ceramic-metal interface stress concentration. This can result in the plastic deformation of metal during both fabrication and under subsequent thermal or mechanical loading (cracking within the ceramic). Tremendous efforts have been made to understand these phenomena [7–12]. Nevertheless, the effects of material properties and specimen geometry on stress and strain distributions, and fracture mechanisms are reasonably well understood. The realization of Silver-Alumina junction is made in solid state. The mechanical resistance of this assembly depends primarily on the conditions of its elaboration, particularity on the atmosphere of elaboration. The fracture resistance is generally determined according to the nature of the elaboration the atmosphere of this kind of junctions [12–14]. Silver is a noble metal and reacting with the alumina does not give an intermediate compound. The assembly of this metal in alumina form no-reactive junction. The objective of this study is to numerically analyse silver-alumina junction by the finite element method. The effect of the interface defect between the metal and ceramic on the stress level has been studied in this work. he finite element model is already explained in our previous work [15-17]; however, salient features of the model which is used in this work are discussed here. A three-dimensional finite element analysis is developed for this investigation. A 2–D schematic view of the metal / ceramic bi-materials with an interface defect is shown in Fig. 1(a). One half of the model is selected as the analysis model (because of the symmetry) in order to reduce the calculation time (see Fig. 1(b)). The geometrical characteristics of the structure are the length L (L= 350 µm), the width w and the thickness ( e 1 and e 2 ) such as L / e 1 = 7, e 2 / e 1 = 6, L / w = 2. The plate is subjected to a uniformly distributed tensile load with P = 70 MPa. The diameter of the interface defect is 50 µm which characterize an average size of interface defect site. These defects are simulated with half-spherical cavities located at alumina interface with well-defined size ((see Fig. 1(e)). Numerical modelling has been taken using the ABAQUS [18] finite element program. The precision of numerical computation is strongly related to the quality of the mesh in the structure. Additionally, due to the stress concentrations expected at the metal/ceramic interface, the mesh is refined at this zone and a 4-node linear tetrahedron (C3D4) finite element is used for the model (see Fig. 1(c)). The finite element model with 75801 elements is shown in Fig. 1(c). It has a fine grid at the metal/ceramic interface. The refinement of the mesh also shows its influence on the accuracy of numerical results, and number of elements higher than 75801 leads to similar and much more precise values (Fig. 2). The surface between the metal and the ceramic is defined as the surface to surface contact (perfect surface). Here, the ceramic has been selected as a slave and the metal as a master surface. T F INITE ELEMENT MODEL

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