## 1 Introduction  
As threaded connections are easy to install, disassemble, and maintain, the connection between a projectile and fuse is typically a threaded connection. During penetration of a projectile into a hard target, owing to the discontinuity and friction damping of the threaded connection interface [1], there is significant uncertainty in the transmission of overload from the projectile to the fuse, which can cause damage to the key electronic components inside the fuse. Finite element (FE) simulation is an effective method for studying the response of projectile-fuse systems under penetration overload. Because commonly used structural dynamics analysis software cannot deal with nonlinear factors, the threaded contact is usually simplified as a rigid connection for modeling. However, this causes the calculation result to be larger than the actual value. In the field of signal recognition for high-speed penetration of multi-layer hard targets, it is crucial to evaluate the vibration response characteristics of the projectile-fuse system accurately. To improve the accuracy of the simulation, the contact stiffness and friction damping of the threaded connection should be accurately characterized. Therefore, establishing an accurate modeling method for the threaded contact is of great significance for studying the vibration response of the projectile-fuse system. Much research has been conducted on the response mechanism of projectile-fuse systems under external loading. [PERSON] et al. [2] used a split Hopkinson pressure bar (SHPB) to investigate the loosening response of a threaded connection under a series of impact loadings. The correlation between the preload variation and the loosening rotation angle was established using a high-speed camera and digital image correlation (DIC). [PERSON] et al. [3] proposed a collision model for threaded connections and obtained calculation methods for the collision time and collision force. An FE model was established to study the collision process of the threaded interface between the projectile body and the fuse body. In addition, the wavelet decomposition of the measured deceleration signal indicated the existence of a thread collision frequency between the projectile and the fuse. [PERSON] et al. [4] studied the vibration and energy dissipation efficiencies of flange connections under a series of impact loadings. High-frequency excitation amplified the nonlinear characteristics of the interface, resulting in shock-wave distortion and changes in the shock-wave frequency. As the excitation frequency decreased, the influence of the nonlinear characteristics of the interface also decreased. The above studies investigated the dynamic response of the projectile-fuse system experimentally, and demonstrated that the nonlinear characteristics of the connection interface had a significant impact on the dynamic response of the system. Some works in the literature [5; 6; 7] actively introduced nonlinear factors, such as contact stiffness and friction damping, which were in order to adjust the dynamic response characteristics of the combined system. During their works, they adopted a similar method which added coatings on the contact interface and changed the dynamic response characteristics of the combined system by adjusting the material properties of coatings. In addition, much research has been conducted on the FE simulation of threaded connection interfaces. In particular, to characterize the nonlinear characteristics of the contact interface, the current treatment is to establish a fine solid-thread model in the explicit calculation [8; 9]. The establishment of fine solid threads not only increases the complexity of the modeling, it also significantly increases the calculation time. Therefore, threaded connections are often ignored when the structural response is not of concern [10].