Interface Shape Effects on the Tensile Strength for T-type Structure Bonded Dissimilar Materials
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Masayoshi Tateno Department of Mechanical Engineering, Kogakuin University, 2665-1 Nakano, Hachiohji, Tokyo 193-0014 Japan (Received 21 May 2001; accepted 1 October 2001)
To estimate the effect of the spherical interface of the T-type joint structure on bonding strength, thermal residual stress on the outer surface and in the interface were investigated by thermal elastoplastic finite element analysis, in terms of principal stress and principal axis direction. These numerical results were compared with experimental fracture patterns and the tensile strength. The relationship between the maximum principal stress around the interface edge and the joint angle was studied. As a result, an optimal joint angle was shown by the experimental data and also by the principal stress calculated.
I. INTRODUCTION
The process of high-temperature diffusion bonding, a joining method of dissimilar materials such as ceramics and metal, is composed of pressurization at constant high temperature and decompression during the cooling process. Thus high residual stress occurs around the intersection of the ceramic/metal interface and the outer surface due to the discrepancy of thermal expansion coefficients and Young’s modulus. It is the primary cause in the decrease in the overall strength of joining. It is difficult in general to produce a joining structure having large bonding area because of the size effect. Many studies on high bonding strength have been undertaken for thermal residual stress.1–3 It was reported that improvement of the interface shape was one of the most effective factors for achieving high bonding strength.4,5 In those studies, a cylindrical straight type joint was investigated, changing the joint angle. The authors reported the principal stress distributions on the bonded interface or on the outer surface of several T-type joints, which have the spherically shaped interface, by using the elastoplastic finite element analysis.6 However, the correlation between actual strength and the failure modes were not yet discussed clearly. Due to the size effect on the residual stress generation, a large-sized joint has not fabricated. We assume that the T-type structure, which is bonded with multiply separated metal bars to a wide ceramics plate, is useful in producing a large joint structure because of its relatively small bonding area. It is important to estimate the stress distribution around the interface edge to achieve high bonding strength in the T-type structure because, since 20
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J. Mater. Res., Vol. 17, No. 1, Jan 2002 Downloaded: 02 Apr 2015
the T-type structure is used for connecting multiply separated metal bars to a wide ceramics plate, its relatively small bonding area allows a large joint structure. In this study, to reveal the actual effect of interface shape on bonding strength for a T-type joint (shown in Fig. 1), the tensile strength of T-type structure, composed of a Si3N4 (ceramic) thick plate and Ni (metal) cylindrical bar, was investigated experimentally, with a varyin
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