The strength of butt joints weakened by soft interlayer under bending load

The problem of mechanical heterogeneity of butt joints, that is, the influence of the soft interlayer parameters on the stress-strain state of the joints under bending load was studied. It is known, that the regulation of the geometrical dimensions and mechanical properties of the soft interlayer can improve mechanical properties of a joint by local strengthening. It can even provide the joints of uniform strength. The purpose of this work was to determine the ranges of parameters of the soft interlayer, providing butt joints of uniform strength under static bending. The following tasks had to be solved: 1) to determine the parameters of the soft interlayer in order to get joints of uniform strength without defects; 2) to assess the possibility of obtaining joints of uniform strength that are mechanically heterogeneous with lack of fusion. The research was performed using the finite element analysis based on the theory of plastic flow and the glide lines method. This paper describes the most characteristic interlayer stress states with defect and without it. The mathematical solutions were verified and boundary conditions of their application were refined. In particular, it was found that in reality it is possible to obtain a significant effect of local strengthening only on thick parts with the requirements for the thickness of the parts under bending load being one and a half times higher than for tension. It is possible to reduce these requirements with the help of special welding methods. There is also a possibility to get joints of uniform strength if there is a central defect in soft interlayer of a lack of fusion type. The results of this research can be used in mechanical engineering in the production of designs for the chemical and petrochemical industry, power equipment, and structures for the aerospace industry.