Study on Strength Evaluation of Ceramic/Metal Joints

对Si_3N_4/S45 C和Si_3N_4接头光滑和预裂纹试样进行了四点弯曲试验。通过有限元方法对焊接残余应力进行了分析研究。结果表明：（1）Si_3N_4/S45 C接头断裂强度的降低除了与界面和中间层的存在有关外，还存在着其它原因。(2)在焊接后的机械切割过程中，由于固有缺陷容易产生裂纹。(3)当界面附近的陶瓷存在裂纹和残余拉应力时，强度急剧下降。用Si_3N_4的平面应变断裂韧性，用应力强度因子来评价接头的强度。(4)在压痕预裂纹在界面附近的陶瓷侧引入的情况下，预裂纹朝向界面扭结，因此，压痕方法不适合在界面附近引入预裂纹。(5)axi-sy的结果 ...更多信息 对接头残余应力的平面应力分析结果与三维应力分析结果吻合较好，并可通过两个平面应力分析结果的叠加近似估算出接头的包封应力。(6)陶瓷/金属接头切割后，残余应力重新分布，在界面附近的陶瓷新的自由表面上出现拉应力峰值。强调了同一点的残余应力在切削后有所降低，但最大值不变。其效果与改变接头试件尺寸和长宽比的效果基本相同。(7)用X射线法对Si_3N_4/S45 C接头切割前后陶瓷界面残余应力进行了无损测量。本研究中所使用的PSPC/RSF系统可以无损地测量界面附近的局部残余应力分布。残余应力在切削过程中重新分布。虽然同一位置的残余应力的绝对值减小，但分布特征没有改变。X射线测量结果与有限元分析结果的比较表明，定性上吻合较好。(8)陶瓷和镶块材料的弹塑性特性决定了界面附近陶瓷残余应力的奇异性。弹塑性奇异性指数大于弹性奇异性指数。(9)Si_3N_4/S45 C接头断裂强度较Si_3N_4 /Si_3N_4接头断裂强度低的原因，可以用接头界面附近陶瓷层的残余应力和外加应力的奇异应力场来解释。少

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