Investigation on insertion mechanism of ultrasound guided insertion process based on numerical simulation

The insertion of finer Z-pins is the key factor for increasing the reinforcement effects of Z-pinned composite laminates. This paper presents a three-dimensional cohesive zone finite element (FE) model for revealing the insertion mechanism of the ultrasound guided insertion process of fine Z-pins. The prepreg fracture is modeled based on the cohesive elements, where fracture toughness is obtained from the double insertion method. The contact between the needle and prepreg is simulated by LuGre dynamic friction model. According to model simulation and relevant experiments, compared with nonvibratory insertion, smaller insertion force, earlier surface fracture and slighter ply crimp can be observed in the ultrasound guided insertion process. In addition, the prepreg forms an initial crack firstly after needle insertion, followed by a final crack due to needle extraction and prepreg springback. The effects of needle diameter on the insertion force and crack length are discussed. It can be concluded that larger needle diameter can lead to greater insertion force and initial crack length, but has little effect on the final crack length.