According to the dimensionless formulae of DOP (depth of penetration) of a rigid projectile into different targets, the resistive force which a target exerts on the projectile during the penetration of rigid projectile is theoretically analyzed. In particular, the threshold Vc of impact velocity applicable for the assumption of constant resistive force is formulated through impulse analysis. The various values of Vc corresponding to different pairs of projectile-target are calculated, and the consistency of the relative test data and numerical results is observed

The effects of aging treatment and the volume fraction of precipitation particles on the nano-hardness and nano-indentation morphology of Ni-based single crystal superalloys are systematically investigated. Using nano-indentation tests and atomic force microscopy (AFM), this study examined the mechanical properties and related physical mechanisms of Ni-based superalloys that have two volume fractions of precipitation particles and four aging treatment times. Results analyzed using the Oliver–Pharr method indicate that prolonging the aging time or increasing the volume fraction of particles enhances the nano-hardness and creep resistance of Ni-based single crystal superalloys and reduces the indentation-affected area. Additionally, the nano-hardness and elastic modulus decrease gradually with increasing applied force, revealing an obvious indentation size effect. These variations are closely linked to the size and density of particles and work hardening rate, as well as to the topologically close-packed (TCP) phases, which influence dislocation movement and accumulation within the material and lead to various nano-indentation behavior in Ni-based single crystal superalloys. The related study provides theoretical guidance and experimental data to support the design and application of superalloys.

Integrated with high-speed oblique water entry tests of a large caliber conical-nosed projectile and numerical simulations based on the arbitrary Lagrange–Euler fluid–structure interaction method, the deflection behavior of projectile during the high-speed oblique water entry in various conditions is investigated systematically in the present paper. First, the rationality and practicality of related finite element method simulation are verified by the ballistic data in the oblique water entry tests. Then, the force mode and load variation characteristics in the projectile as well as the mechanism for the deflection of trajectory are discussed in detail regarding to the oblique water entry at a high-speed of 500 m/s. Furthermore, the influence of various factors, including impact velocity, oblique angle, and attack angle, on the deflection behavior of projectile is analyzed systematically. It is demonstrated that the instability of projectile motion is mainly due to the pitching moment, which is significantly affected by the actual water entry condition. The impact velocity mainly contributes to the projectile deflection rate, and a higher impact velocity generally results in a more rapid trajectory deflection. The water oblique angle affects both the rate and degree of projectile deflection, and the deflection degree displays different trends in different water oblique angle ranges: when the oblique angle is less than 15°, the projectile usually jumps out of the water, i.e., a yaw phenomenon occurs; when the oblique angle locates in the range of 30°–60°, the deflection trend is almost the same, and the projectile gradually deflects from the initial oblique state to a horizontal state, then to a vertical state, and eventually moves downwards in a “launch” posture with its nose opposite to the entry direction; and when the angle increases to 75°, the projectile can no longer rotate to a vertical state after it rotates to a horizontal state, instead it moves downwards in an oblique state with its nose facing upwards. Comparatively, the attack angle affects the deflection direction, and a positive attack angle usually leads to the increase in deflection degree, while a negative attack angle will change the deflection direction. Related research is of significance in predicting the ballistic evolution characteristics of projectile at high-speed oblique water-entry and optimizing the projectile configuration as well as the impact conditions.

Due to the nonlinearity of the contact interface, as well as the material, jointed structures exhibit complex mechanical behaviors under impact loading. In order to accurately characterize the dynamic response of a joint, this work presents a nonlinear dynamic model (DICF model). First, the effects of loading velocity, preload and friction coefficient on the displacement–load curve are discussed based on a validated finite element model. Numerical simulation results show that the critical load and critical displacement are linearly related to the normalized logarithmic velocity and linearly related to the normalized preload and friction coefficient. Subsequently, a DICF model that consists of sliding, collision and failure is proposed. The constitutive relations of the model are derived, and dynamic correction functions are introduced to characterize the effects of velocity, preload and friction coefficient. A parameter identification method for the model is also provided. Finally, the DICF model is compared with the finite element simulation results, with an error of 0.43% for quasi-static conditions, a minimum error of 0.17% and a maximum error of −1.41% for impact conditions, in addition to significantly improved accuracy compared to the EC3 model, which indicates that it can effectively capture the behavior of bolted joints under impact loading conditions.