Ultrasonic welding is an effective ways to achieve a non-reactive/immiscible heterogeneous metal connection, such as the connection of magnesium alloy and titanium alloy. But the thermal mechanism of magnesium alloy/titanium alloy ultrasonic welding has not been defined clearly. In this paper, the experimental and the finite element analysis were adopted to study the thermal mechanism during welding. Through the test, the temperature variation law during the welding process is obtained, and the accuracy of the finite element model is verified. The microscopic analysis indicates that at the welding time of 0.5 s, the magnesium alloy in the center of the solder joint is partially melted and generates the liquid phase. Through the finite element analysis, the friction coefficient of the magnesium–titanium ultrasonic welding interface can be considered as an average constant value of 0.28. The maximum temperature at the interface can exceed 600 °C to reach the melting point temperature of the magnesium alloy. The plastic deformation begins after 0.35 s and occurs at the magnesium side at the center of the interface.

This paper presents a test device to explore the influence of geometric attributes of the contact surface on a friction coefficient along with sliding speed and contact pressure. Friction tests were conducted on a third-generation high-strength steel QP980. The friction coefficients for different surface curvatures, contact pressures, and sliding speeds were calculated, and the influences of these factors were analyzed. The formula for calculating the friction coefficients between curved contact surfaces was derived. The relationship between bending-induced surface roughness increase and friction coefficient was established. An enhanced friction coefficient model with pressure, velocity, and curvature dependence was proposed. The enhanced friction model was applied to simulate the stamping of an automotive part, and a better correlation was achieved.

In response to the challenges of supporting fractured and weak surrounding rock in deep coal mines in the Huainan region of China, a self-moving hydraulic support system for roof support was designed and developed. This innovative solution addresses the difficulties encountered in providing continuous support to roof structures. Based on the theory of elastoplastic mechanics, a numerical analysis model was established to calculate the mechanical parameters such as the displacement, stress, and strain of hydraulic supports during the stepping process under multiple operating conditions. The results of the numerical simulation were compared and verified with those from an actual working site. The results show that the maximum equivalent stress is 245.33 MPa for operating condition 1, 246.82 MPa for operating condition 2, and 245.27 MPa for operating condition 3. The maximum stress values under the three working conditions do not exceed the yield strength of the material, satisfying the requirements for normal bracket support operations. These research findings can establish a theoretical framework for the comprehensive assessment of the reliability and stability of hydraulic supports and the optimization of construction processes.

Skid lines on the outer panels of automobiles seriously affects their appearance and are a common surface manufacturing defect. In the die and process design stages, numerical simulation is needed to predict skid lines to take prevention measures. However, it is still a challenge to predict skid lines accurately. The simulation-based skid line criteria need further verification and improvement. Therefore, this paper takes a lightweight aluminum alloy AL6061-T6 sheet as its research object, uses a set of U-shaped dies to explore the influence of process parameters on skid lines, and establishes the correlation between skid lines and surface roughness based on visual and microscopic measurements. The relationships between contact pressure/inverse bending strain and surface roughness are established through simulation. Thus, a contact pressure and inverse bending strain dependent skid line criterion is constructed. The skid line criterion based on the simulation results has theoretical, guiding significance for the practice of engineering.