An improved model for predicting stiffness of single-lap composites bolted joints using Matlab/Simulink

A novel model for predicting the stiffness of single-lap composites bolted joints is introduced on the basis of the analytical spring-mass model. While the previous spring-mass model shows three phases in the load–displacement curve of the jointed composites, the newly proposed model presents four steps in the curve after considering a transition of the contact force from static friction to sliding friction. It is found that the transformation happens firstly at the contact surfaces between the upper and lower laminates and then at the contact area between laminates and bolt heads, causing the change of the stiffness of joint during the friction phase. Moreover, since the linear relationship between the deformation and the external force of the spring is similar to the relation between current and voltage, the mechanical system of spring-mass model can be converted to circuit system and thus be solved in the Matlab/Simulink. After validating the proposed model by results of the single bolted laminates, a series of 3D finite element models with multi-bolts and different geometry parameters are established. The results of the numerical benchmarks prove the effectiveness of the proposed analytical method.