In this investigation, a new three-dimensional nonlinear train car coupler model that takes into account the geometric nonlinearity due to the coupler and car body displacements is developed. The proposed nonlinear coupler model allows for arbitrary three-dimensional motion of the car bodies and captures kinematic degrees of freedom that are not captured using existing simpler models. The coupler kinematic equations are expressed in terms of the car body coordinates, as well as the relative coordinates of the coupler with respect to the car body. The virtual work is used to obtain expressions for the generalized forces associated with the car body and coupler coordinates. By assuming the inertia of the coupler components negligible compared to the inertia of the car body, the system coordinates are partitioned into two distinct sets: inertial and noninertial coordinates. The inertial coordinates that describe the car motion have inertia forces associated with them. The noninertial coupler coordinates; on the other hand, describe the coupler kinematics and have no inertia forces associated with them. The use of the principle of virtual work leads to a coupled system of differential and algebraic equations expressed in terms of the inertial and noninertial coordinates. The differential equations, which depend on the coupler noninertial coordinates, govern the motion of the train cars; whereas the algebraic force equations are the result of the quasi-static equilibrium conditions of the massless coupler components. Given the inertial coordinates and velocities, the quasi-static coupler algebraic force equations are solved iteratively for the noninertial coordinates using a Newton–Raphson algorithm. This approach leads to significant reduction in the numbers of state equations, system inertial coordinates, and constraint equations; and allows avoiding a system of stiff differential equations that can arise because of the relatively small coupler mass. The use of the concept of the noninertial coordinates and the resulting differential/algebraic equations obtained in this study is demonstrated using the knuckle coupler, which is widely used in North America. Numerical results of simple train models are presented in order to demonstrate the use of the formulation developed in this paper.
Additive Manufacturing (AM) discrete patterns made of stainless steel 316 L offer potential energy absorption for engineering applications, including blast and impact protection systems and aircraft structure. Herein, three different superimposed stainless steel 316 L lattice structures varying rod diameter are manufactured by selective laser melting (SLM). Compression experiments and split Hopkinson pressure bar (SHPB) tests are conducted to determine the quasi‐static and impact behavior of different lattice structures for the strain rate from 10−3 to 1000 s−1. The compressive response, strain rate dependency, and energy absorption capacity of the lattice structures are mechanically characterized. In addition, numerical simulations are conducted to complement the experimental work in which the deformation modes of the lattice under mechanical responses have been studied. The results indicate that vertical truss in structure plays a bearing role in the whole process of compression, which is better than inclined truss structures. Due to the combined effect of two deformation modes in the superimposed structure, it has shown superior energy absorption capacity compared with other structures. The superiority of the superimposed structure provides a new idea for the design of lattice structure.
Through surface nanocrystallization and low-temperature ion sulfurization, the nanocrystalline/FeS thin film with excellent friction-reduction and antiwear properties was fabricated on the surface of AISI321 stainless steel. The nanocrystallization treatment formed the high hardness and active nanocrystalline structure on the surface of AISI321, with the harness increased from 4.6 GPa to 7.56 GPa. Furthermore, the significantly refined nanostructure strongly increased the concentration of S element in comparison with the single-sulfurized layer on the substrate. Tribological tests reveal that both the original AISI321 substrate and the single-sulfurizing-treated samples are subject to severe abrasion. Single nanocrystallization treatment can improve the wear resistance of AISI321, while the compound treatment can obviously improve the comprehensive tribological properties. The compound-modified layer presents excellent tribological properties with the lowest coefficient of friction (COF) of 0.33, which is related to the increased hardness of the substrate and increased thickness, density, and homogeneity of the sulfurized layer. Furthermore, a physical model is developed for the vacuum tribological behavior of the samples after different treatments. This model provides a reference for revealing the tribological mechanism of the compound-modified layer treated using surface nanocrystallization-assisted chemical heat treatment.
Through compound treatment of surface nanocrystallization and low-temperature ion sulfurization, the compound-modified layer (nanocrystalline/FeS film) with excellent friction-reduction and anti-wear properties was fabricated on the surface of AISI321 stainless steel. A comparative study is conducted on the element distribution, microstructure, and vacuum tribology properties (1 × 10‒4 Pa) of compound-treated samples, single-related samples (surface nanocrystallization or low-temperature ion sulfurization), and original substrate samples. The nanocrystallization treatment formed the high hardness, high activity nanocrystalline structure on the surface of AISI321, which results in significantly refined microstructure, increased thickness and concentration of S element in the compound-sulfurized layer compared to the single-sulfurized layer on the substrate. Tribological tests reveal that both the original AISI321 substrate and the single-sulfurizing treated samples are subject to severe abrasion. Single nanocrystallization treatment can improve the wear resistance of AISI321, while the compound treatment can obviously improve the comprehensive tribological properties with milder wear and lower friction of coefficient. The good tribological properties of the compound-modified layer are related to the enhancement of substrate hardness and the increase of the thickness, density, and homogeneity of the sulfurized layer. Furthermore, a physical model is developed for the vacuum tribological behavior of the samples after different treatments. This model provides a reference for revealing the tribological mechanism of the compound-modified layer treated by surface nanocrystallization assisted chemical heat treatment.
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