Evaluation of bonding strength of dissimilar material joints by fracture mechanics

本文研究了由不同力学性能材料组成的粘结接头中界面裂纹的j积分。采用有限元法计算了两种粘结节点在均匀拉应力和三点弯曲荷载作用下的j值。一种是双材料接头，材料B直接与材料A结合；另一种是三材料接头，材料B通过插入材料c与材料A结合。讨论了材料A与材料B的杨氏模量比、材料A与材料B的线膨胀系数差、裂纹长度等因素对j值的影响。此外，断裂试验是使用使用插入材料粘合的试样进行的。得到的结果如下：1。阐明了双材料接头的归一化J值J/J_<A=B>可以由两种材料的杨氏模量之比E_A/E_B和线膨胀系数之差（alpha_A-alpha_B）确定。J_<A=B>为同材质节点的j值。这只受裂纹长度的影响。三材料接头的j值受插入材料厚度、d、E_A/E_B和E_C/E_B比值的影响。j值可由下式计算。利用上述方程计算的j值，从断裂试验的断裂载荷出发，分析临界j值。发现临界j值是评价不同材料接头结合强度的合理参数。

In this study, J-integral of interfacial crack in the bonded joint which is composed of the materials with different mechanical properties, is studied. J-values of two type of bonded joints under the uniformly tensile stress and the three-point bending load are calculated by finite element method. One type is the bi-materials joint, in which the material B is bonded directly to the material A,and the other type is the tri-materials joint, in which the material B is bonded to the material A by using the insert material C.The effect of several factors (Young's modulus ratio of material A and B,difference in coefficient of linear expansion of material A and B,crack length etc.) on J-value is discussed. Furthermore, fracture tests are carried out using specimens that are bonded using an insert materials.The results obtained are as follows.1. It is clarified that the normalized J-values of bi-materials joint, J/J_<A=B> are able to be determined by the ratio of Young's modulus of both materials, E_A/E_B and difference in coefficient of linear expansion, (alpha_A-alpha_B). J_<A=B> is the J-value of same material joint. This is affected only by crack length.2. J-values of tri-materials joint are affected by the thickness of insert materials, d, and the ratio of E_A/E_B and E_C/E_B. J-values can be calculated by the followed equation.3. Critical J-value is analyzed from breaking load of fracture test by using J-values which is calculated by above equation. It is found that the critical J-value is reasonable parameter for evaluating bonding strength of dissimilar material joints.