Study on Strength Evaluation of Ceramic/Metal Joints

点击翻译按钮获取中文摘要

Four-point bend tests were conducted for Si_3N_4/S45C and Si_3N_4 joint smooth and precracked specimens. Analytical studies on joining residual stresses were also performed by the FEM method. The results obtained are as follows :(1) There is a reason for the decrease of the fracture strength in the Si_3N_4/S45C joint additional to the existence of the interface and interlayer.(2) Cracks are easily initiated from the inherent defect during mechanical cutting after joining.(3) In the case that there is a crack and tensile residual stresses at the ceramic near the interface, the strength decreases drastically. The strength of the joint can be evaluated by the stress intensity factor using the plane strain fracture toughness of Si_3N_4.(4) In the case that an indentation precrack is introduced at the ceramic side near the interface, the precrack is kinked toward the interface, so, the indentation method is not suitable to introduce a precrack near the interface.(5) The result of the axi-sy … More mmetric analysis on the joining residual stresses shows a good agreement with the results of the three dimensional analysis and the pack stress can be approximately estimated by superposing results of the two plane stress analysis.(6) The residual stresses redistribute after cutting of the ceramic/metal joint and the peak tensile stress occurs on the new free surface at the ceramic near the interface. It is emphasized that the residual stress at a same point decreases after cutting, but the maximum value does not change. The effects is almost the same as that of the changing the size and aspect ratio of the joint specimen.(7) Residual stresses at the ceramic near the interface were measured nondestructively by the X-ray method for the Si_3N_4/S45C joints before and after cuttings. The local residual stress distribution near the interface can be measured nondestructively by the PSPC/RSF system used in this study. The residual stresses redistribute by the cutting. The distribution characteristics do not change, although the absolute value of the residual stresses at the same position decreases. The comparison between the results of the X-ray measurement and the result of the FEM analysis shows a good agreement qualitatively.(8) The singularity of residual stresses at the ceramic near the interface is characterized by elastic-plastic properties of ceramic and insert materials. The exponent of the elastic-plastic singularity is larger than that of elastic singularity.(9) The decrease in the fracture strength for the Si_3N_4/S45C joints compared with those for the Si_3N_4 /Si_3N_4 joints is explained by considering the singular stress field of residual and applied stresses at the ceramic near the interface of the joint. Less