The nonlinear load of the axle box bearing and the spatially coupled relationship of vehicles have seldom been considered in the dynamic modeling of vehicle-track systems in recent years. Therefore, based on the time-varying nonlinear contact load of an axle box bearing, a vehicle spatially coupled dynamic model is established. Subsequently, the vehicletrack spatially coupled dynamic model is established by the dynamic coupled relationship between the wheel and rail. Finally, the vehicle wheelset testbed is set up to verify the correctness of the theoretical model. Experimental results show that (1) the vibration of an axle box has a strong nonlinear coupled relationship. The axle box vertical amplitude aroused by lateral alternating load is approximately 0.108 mm, which was approximately 22.2% of the lateral vibration and (2) the lateral displacement and acceleration errors of axle box between the simulation and experiment are about 5.7% and 6.9%, respectively, which validates the theoretical model. The vehicle-track spatially coupled dynamic model accurately reflects the vibration characteristics of locomotives under track irregularity and provides theoretical support for the design of key components, such as axle box bearings.

The crack propagation mechanism of thick plates is difficult to describe accurately, and thus, it is difficult to predict the lifetimes of thick plate structural cracks in extreme construction environments. In this paper, a theoretical model of the time-integrated crack propagation that accounts for the thickness effect is established. The constraint factor is introduced to characterize the thickness effect of crack propagation, and the constraint factor formula was obtained by fitting the experimental results. The results of the fatigue crack growth tests and the crack propagation theoretical predictions for Q345D specimens showed the time-integrated crack propagation model predicts the crack propagation more accurately in the initial stage and during the stable expansion stage of crack propagation. These results have guiding significance for the fatigue life prediction of equipment with thick plate structural features.INDEX TERMS Thick plate, crack propagation, crack closure, fatigue test, time integration method.

Lubrication failures of axle box bearings can lead to accidents, such as bearing burnout and hot axle cutting. Presently, the modeling of the vehicle-track system dynamics rarely considers the nonlinear contact load of axle box bearings, and this leads to imperfection in the vehicle-track system dynamics calculation. And then, the load distribution and lubrication characteristics of axle box bearings are difficult to obtain. Therefore, in this paper, we fully consider the time-varying nonlinear contact load of bearings and track irregularity in establishing the bearing-wheel-rail system coupling-dynamics model. The dynamic response of axle box bearings is obtained by taking the vertical, strong impact-time-varying load on the carrying saddles as the external excitation. The load-balance equation of dynamic pressure lubrication is then obtained, according to the slicing method of bearing rollers. Finally, the elastohydrodynamic lubrication (EHL) model of axle box bearings is established considering thermal and scale effects. The results show that the central film thickness under thermal EHL was decreased by 13.61% compared with that under isothermal EHL. As the velocity of the contact pair increases, the thickness difference between thermal and isothermal EHL became larger. Thermal effects should be considered in the EHL model, in order to truly reflect the characteristics of EHL under a high speed.

In this paper, the nonlinear dynamics of a single degree of freedom system for the rolling mills with clearance is investigated. The boundary conditions of the self-excited vibration system basically involve discontinuities, and the effects of boundary conditions on the vibrating system are analyzed by using asymptotic method and numerical simulation. Different forms of nonlinear vibrations such as periodic, quasi-periodic and chaotic motions are detected. Influence of the system parameters on the nonlinear vibration behaviors is also examined by applying the Poincare sections, phase portraits, waveforms, the bifurcation diagram and the largest Lyapunov exponent. New phenomena are observed in nonlinear motions of the rolling mill mechanism.

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Fatigue damage is one of the most common failure modes of large-scale engineering equipment, especially the full-face tunnel boring machine with characteristics of a thick plate structure bearing strong impact load. It is difficult to predict the location and propagation life of crack of cutterhead under strong impact load. Unseasonal maintenance of equipment caused by inaccurate prediction of life cycle of cutterhead seriously affects the construction efficiency of the equipment and the life safety of the operators. Determining the crack location of tunnel boring machine cutterhead structure under strong impact load and predicting the crack propagation life are difficult scientific problems. To solve them, first, the location of the stress concentration of the cutterhead is determined by using finite element analysis method of statics. Second, prediction model for crack propagation life of tunnel boring machine cutterhead characteristic substructure based on time integration is built. And the test of crack growth of cutterhead characteristic substructure is performed. The feasibility and accuracy of the prediction model are verified by contrasting crack prediction models and the results of the test. Finally, the life prediction of tunnel boring machine cutterhead of water diversion project in Northwest Liaoning Province is carried out by using crack propagation model based on time integration. Results show that the maximum error of theoretical prediction and experimental results of crack propagation is 16%. So the feasibility of crack propagation model based on time integration in predicting the crack growth of cutterhead is verified. It is predicted that the tunnel boring machine cutterhead panel can work normally for 5.9 km under the condition of ultimate load. Building the crack propagation model considering the influence of plate thickness and strong impact load has important research value for improving the working efficiency of engineering equipment, prolonging service time, and improving the working safety.

The accurate performance evaluation of a cutterhead is essential to improving cutterhead structure design and predicting project cost. Through extensive research, this paper evaluates the performance of a tunnel boring machine (TBM) cutterhead for cutting ability and slagging ability. This paper propose cutting efficiency, stability, and continuity of slagging as the evaluation indexes of comprehensive cutterhead performance. On the basis of research of true TBM engineering applications, this paper proposes a calculation method for each index. A slagging efficiency index with a ratio of the maximum difference between the slagging amount and average slagging is established. And a slagging stability index with a ratio of the maximum slagging fluctuation and average slagging is presented. Meanwhile, a cutting efficiency index by the weighed average value of multistage rock fragmentation of a cutter's specific energy is established. The Robbins and China Railway Construction Corporation (CRCC) cutterheads are evaluated. The results show that under the same thrust and torque, the slagging stability of the CRCC scheme is worse, but the slagging continuity of the CRCC scheme is better. The cutting ability index shows that the CRCC cutterhead is more efficient.