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接接头中界面裂纹的J积分。用有限元方法计算了两种粘接接头在均布拉应力和三点弯曲载荷作用下的J值。一种是双材料连接，即B材料直接与A材料粘结；另一种是三材料连接，即B材料通过插入材料C与A材料连接。关于J值的讨论。此外，还使用使用镶件材料粘结的试件进行了断裂试验。阐明了双材料接头的归一化J值J/J&lt；A=B&gt；可以由两种材料的杨氏模数之比E_A/E_B和线膨胀系数之差(α_A-α_B)来确定。J_lt；A=B&gt；是同种材料接头的J值。这只受裂纹长度的影响。三种材料接头的J值受镶嵌材料厚度d以及E_A/E_B和E_C/E_B比值的影响，J值可由下式计算。利用上述公式计算出的J值，由断裂试验的断裂载荷分析出临界J值。结果表明，临界J值是评价异种材料接头粘结强度的合理参数。

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.