Numerical Analysis And Experimental Study On Heterogeneous Interface Intensity

Bonded components are widely used in the automotive, aerospace, and electronic industries. Measurement of bi-materials interface bonding strength is crucial for the design and application of structures with two or more materials since bi-material interface debonding is one of the major modes of failures for these structures. However, accurate determination of the interface bonding strength is not an easy task due to the discontinuity of material properties at the interface. So reducing or eliminating the stress singularity of the bi-material interface can improve the interface strength. It is important theoretical and practical significance to improve the safety and reliability of bonded components. In this work, the interfacial strength of bi-material bonded scarf joints is investigated by an integrated theoretical calculation, numerical and experimental method. The specific contents are as follows.The beam joint consists of two elastic, isotropic, homogeneous and perfectly bonded materials, each material (denoted by A and B) occupies a part of the joint. The material A is PMMA or polycarbonate and the B is always aluminum. Based on characteristic equation, contours of the combination of wedge angles are obtained for plane stress and plane strain problems. The theoretical analysis for three dimensional structures will be limited. The singular stress analyses for three-dimensional bi-material structure with various geometric factors are performed using FEM (finite element method) sub-modeling technique. The focus is on the effects of the wedge angle upon the order of stress singularity at bi-material interface corner. Compared with the theoretical values in two-dimensional condition, the stress singularity of interface point can’t be estimated by the theoretical values and the value of interface edge can be estimated by the theoretical values sometimes. The other is on the effects of the vertex angle between two side free surfaces upon the order of stress singularity at bi-material interface corner. The numerical results show that the vertex angle has a significant effect on stress singularity at bi-material interface corner. Larger the vertex angle is, bigger the characteristic value of stress singularity becomes, and the value of singularity order at the corner will converge to the level of the edge singularity when the vertex angle is close to 180°, which is also coincident with that estimated by using two-dimensional theory under plane strain. It is found that after eliminating the interface corner by generating a round fillet at the intersection of two side free surfaces, the values of singularity order along the interface edges become continuous, i. e. the strength of the corner singularities can be reduced to the level of the edge singularities. The next work is designing the beam joint of different scarf angles of joint and interface dimensions, using a series of aluminum/PMMA and aluminum/polycarbonate bi-material specimens. The samples are carried on the four-point bending test. The experimental results show that interface dimensions have no distinct effects on the interfacial strength and the measured maximum failure bending stress decreases as the scarf angle increases. For the further study, design the other group samples with a circular-arc fillet carried on the four-point bending test. The experimental results show that the strength of the samples with a fillet can be increased. Finally, an empirical equation based on interface fracture mechanics is determined by curve fitting of the experimental results to predict the interfacial strength of bonded scarf joints. We have designed scarf joints with circular-arc fillet and experiments are under way.