Mechanics

Dynamic Behavior of Rack Vehicle System Subject to Gravity Center Offset

2025-02-20T11:51:03+02:00

During the operation of rack vehicles, gravity center offset is usually induced by the passenger distribution and the equipment layout, which greatly deteriorates the gear-rack dynamic meshing effect and the wheel/rail nonlinear friction contact behavior, and further threatens the safety and stability of the vehicle. Aiming at this problem, dynamic behavior of rack vehicle system subject to gravity center offset is investigated in this work. Considering the disturbance effect of gear-rack meshing impact and wheel/rail dynamic contact behavior, a complete dynamic model of rack vehicle is established based on multi-body dynamics, adopting which the influence of the carbody gravity center offset on the dynamic characteristics of rack vehicle and nonlinear meshing behavior of driven gear-rack system are explored. Results show that: The gear-rack dynamic contact force results in an impact under the rack vehicle carbody gravity center offset, and the impact increases with the increase of running speed. The gear-rack dynamic contact force reaches 73kN when the speed reaches 30km·h-1. The lateral offset of the gravity center has a linear effect on rack vehicle running safety, and the wheel/rail vertical force is affected by the gear-rack dynamic meshing and produce vibration. The rack vehicle running stability is more sensitive to the longitudinal offset of the gravity center. The carbody acceleration increases by 4.8 times when the carbody gravity center is 3.0m forward. The vertical Sperling index of the vehicle is optimal when the carbody gravity center is behind in 0~1 m. The conclusions of this study provide theoretical support for the worldwide rack railway design and safe operation.

Real-Time Swing-up of a Linear Inverted Pendulum Using Reinforcement Learning

2025-03-12T14:16:42+02:00

This study focused on applying and enhancing the Deep Deterministic Policy Gradient (DDPG) algorithm to effectively control a Single Inverted Pendulum (SIP) system. The primary objective was to improve the algorithm's performance by addressing common challenges such as overestimation of Q-values and convergence to local optima. The system's behaviour was analyzed through simulation and real-world experiments, showcasing the algorithm's ability to offer faster responses, enhanced stability, and reduced pendulum displacement. The research introduced key modifications to the experience replay mechanism and the Critic network, which played a significant role in improving the efficiency of the learning process and the robustness of the control strategy. By combining Reinforcement Learning with traditional control methods, this approach successfully managed the nonlinear dynamics of the SIP system. Nevertheless, certain challenges persist, particularly in terms of
the efficiency of deep reinforcement learning algorithms and their stability in real-world environments. These findings suggest that future research should focus on further refining DRL algorithms to increase their practical application in physical control systems. In conclusion, the research highlights the potential of combining DRL techniques with conventional control strategies for tackling complex control problems. The success achieved in controlling the SIP system indicates a promising direction for further exploration and development in this field.

Optimization of Static Three-Dimensional Stiffness of Non-Pneumatic Tire with Composite Spokes Based on Response Surface Method

2025-02-28T12:03:36+02:00

This study aimed to investigate the relationship between the static stiffness of non-pneumatic tires (NPTs) and the design parameters of composites spokes and shear bands using the finite element (FE) method. The stress–strain curve of the rubber material was fitted using the neo-Hookean constitutive model. Subsequently, key design parameters, including the reinforcement plate thickness and constitutive parameters of the spoke and shear band materials, were selected based on the NPT structure. FE simulations were performed on multiple sets of different parameter design schemes for the NPTs, and polynomial models for the vertical, lateral, and longitudinal stiffnesses were established using response surface analysis. The sensitivity analysis results indicated that the thickness of the reinforcement plate significantly influenced the three-dimensional stiffness, whereas the constitutive parameters of the spoke and shear band materials had a relatively minor impact. Finally, multi-objective optimization was employed to determine a design scheme with maximum longitudinal stiffness while ensuring vertical load-bearing capacity. Under the premise of ensuring the vertical load-bearing capacity, the longitudinal stiffness increased by 39.1% and 32.9% in the forward and backward directions, respectively. This method can be used to predict the three-dimensional stiffness of NPTs under different design parameter schemes or to optimize the setting parameters of NPTs based on the desired target stiffness, facilitating the rapid design of the three-dimensional stiffness of NPTs.

A Comparative Study of Metaheuristic Optimization Approaches to Optimize Laser Welding Process Parameter with Pre-Set Weld Size Magnitude for AISI 416 and AISI 440 FSe Stainless Steels

2025-03-14T14:59:29+02:00

Optimization methods are used to accurately predict laser welding process parameters, helping to save material effort and time in determining the desired output variables. Based on a mathematical model, parameter selection is considered a binding optimization problem. The work involved is closely related to evolutionary optimization algorithms. This article proposes highly effective meta-heuristic methods: the GA (Genetic Algorithm), the JAYA optimization algorithm, and the MDE (Modified Differential Evolution) algorithm, which optimize the parameters of the laser welding to achieve the desired size for the weld. The performance of these three methods is evaluated on laser welds for AISI 416 and AISI 440 FSe stainless steels. With the same initial conditions, the MDE algorithm outperforms the other algorithms, GA and JAYA algorithms, regarding the best fitness value after ten runs. Thus, the MDE algorithm is used to optimize three parameters: Laser Power (LP), Welding Speed (WS), and Fiber Diameter (FD) to achieve two desired welding dimensions: the Width of the Weld Zone (WWZ) and the Penetration Depth of the Weld (PDW) for laser welds.

Tribological Characterization of AlCrN, TiAlN, TiSiN and AlTiN Coatings Against Mold Steel

2025-01-23T20:11:37+02:00

This study investigates the tribological performance of TiAlN, AlTiN, AlCrN, and TiSiN coatings under boundary lubrication conditions using a tribometer. The findings indicate significant reductions in average friction coefficients compared to uncoated tungsten carbide (0.2436), with TiSiN demonstrating the lowest friction coefficient of 0.2111, thus showcasing its superior performance. Optical microscopy and profilometry analyses further reveal that TiSiN coating effectively minimizes surface roughness and wear tracks, suggesting enhanced wear resistance. While the coatings successfully reduce friction, they tend to increase wear on the counter materials. This study highlights the critical role of these coatings in industrial applications, emphasizing the need to balance friction reduction with wear enhancement for optimal performance.

Effect of Nanoscale Amorphization on Edge Dislocation Emission from a Bifurcated Crack Tip in Deformed Nanocrystalline Solids

2025-02-20T12:01:17+02:00

The effect of nanoscale amorphization at the triple junction of grain boundaries on edge dislocation emission from a bifurcation crack tip in nanocrystalline materials has been suggested and theoretically described. A corresponding mechanical model has been established, and the exact analytical solution of the modified model was obtained using the complex potential method of elastic mechanics. The resultant force acting on the dislocation was calculated, and the analytical expression for the critical stress intensity factor corresponding to dislocation emission was obtained based on the dislocation emission criterion. The influence of the size, position, strength of nanoscale amorphization, and bifurcation crack shape on the critical stress intensity factor was discussed using numerical analysis. The study found that an increase in the angle between the main crack and the branched crack makes it more difficult for dislocations to emit from the bifurcation crack tip. The critical dislocation emission angle is independent of the angle between the main crack and the branched crack. The presence of nanoscale amorphization can reduce the high stress field near the bifurcation crack tip, making it difficult for dislocations to emit from the bifurcation crack tip, thereby reducing the toughness of the material caused by dislocation emission.

A Novel Principle Stress Model to Predict the Stress and Load in Sheet Drawing

2025-03-12T13:52:48+02:00

The solution of stress and load of metal sheet deep drawing serves as a primary basis for guiding production, verifying strength of dies, and optimizing technology parameters. Based on the differential equations, boundary conditions, theory simplification and solution equations, an principle stress model (PSM) to predict the stress distribution and deformation load in drawing processes with a blank holder were proposed, and then the results were compared with the predicted value by finite element method (FEM) under the same conditions. Due to the thickness of the flange in deformation zone remains basically unchanged under the action of blank holder, it is reasonable to simplify the solution of deformation to plane strain problem. The PSM and FEM predict that the radial tensile stress and circumferential compressive stress in the flange zones remain basically consistent trends, and the relative error of most of predicted results is less than 5%. The influence of the die fillet bending on the stress state of inner and outer sides is not consider, leads to the calculated stress and load by PSM slightly higher than those of FEM. The solution of stress and load solution by PSM is reliable and convenient, and the FEM predicts more detailed and accurate results but need consume much larger calculating time. This research is of great significance for improving the solution efficient and engineering applications of plastic mechanics in sheet deep drawing deformation.

Dynamics of Ferromagnetic Hybrid Nanofluids in the Presence of Permeable Surface

2024-12-11T17:15:20+02:00

This research examined the dynamics of ferromagnetic hybrid nanofluid with the consequence of heat generation, thermal radiation, and Soret-Dufour mechanisms. The thermal procedure was inspected with induced magnetism and permeable stretching surface. The physical model interpretation is represented by partial differential equations (PDEs). By implementing a suitable transformation function, the set of PDEs is changed into ordinary differential equations (ODEs). The spectral relaxation technique (SRM) is further implemented to solve the set of ODEs. The SRM was implemented to iteratively solve the equations of ODEs by considering the linear terms and nonlinear terms at current and previous iterations. Thermal analysis greatly enhances the thermal condition and the opacity of the thermal boundary layer (BL). The Dufour enhances the temperature contour while the Soret enhances the concentration contour. The current outcome as compared with previous work is discovered to be in good agreement.