Effect factors of stress distribution and failure behavior of threaded connection for carbon materials

Understanding the stress distribution of threaded connection can help to predict the damage and failure behavior of the joints under actual working conditions. However, due to the brittle nature of carbon materials and the fact that deformation under load mainly occurs in the internal threads, commonly used stress analysis methods such as digital image method (DIC) are not applicable. In this paper, a finite element simulation method was used to investigate the internal and external connection structure of a homogeneous graphite stud-nut under load. The effects of pitch P and the number of thread bite teeth n on the stress change of the structure during the elastic phase were investigated, and the damage process was analyzed. The results show that when the value of thread bite teeth is small, the load distribution is more uniform and a slight stress concentration occurs at the root of the thread on the loaded end face of the nut. With the increase of the number of teeth of the thread, the stress distribution at the root of the connecting part shows a U-shaped distribution, and the two ends of the thread bear more stress. At the same time, the number of carrying threads increases, resulting in the increase of the strength of the thread connection. The pitch for threaded connections has little impact on the overall stress distribution. The von Mises stress distribution chart shows that the stress concentration at the ends of the nut is most serious, and with the increase of load, the internal and external screw thread root stress concentration increased, at the ends of the thread area will be the first failure happened.