Propagating guided waves in a homogeneous, isotropic, prestressed, hyperelastic plate show nonlinear characteristics that depend on the state of initial prestress. These nonlinear phenomena include higher harmonic generation, occurring when Lamb wave modes of different frequencies ( $$\omega _a$$ω a and $$\omega _b$$ω b ) are allowed to mix within the material generating secondary waves at frequencies $$2\omega _a,2\omega _b\, \text {and}\,\omega _a\pm \omega _b$$2 ω a , 2 ω b and ω a ± ω b . Further, if prescribed internal-resonance conditions are satisfied, the amplitude of secondary waves increases in space, providing a response quantity which is dependent on prestress and easy to be observed. Using the finite element method, in this paper we investigate the time and space evolution of higher harmonics arising in one-way wave mixing. The influence of prestress on the response is elucidated, observing the nonlinear parameter $$\beta $$β . It is further shown that the nonlinear ultrasonic technique called sideband peak count-index (SPC-I) can provide an effective monitoring tool for prestress.

The efficiency of track utilization is one of the important factors for train operation in marshalling stations, and it can not only affect the turnover efficiency of trains, but also determine the capacity of railway stations. This paper presents an optimization method for track utilization in the arrival yard of a marshalling station considering Arrival and Break-up Coordination Operation (ABCO). The interaction between the push operation of trains and track utilization efficiency is investigated. First, the case of crossing the running route for shunting locomotives is analyzed. Whether the shunting route crosses or not can greatly affect the duration of trains occupying tracks in the station. Then, a nonlinear integer programming model (NLPM) is established based on the above analysis. The ultimate goal is to minimize the number of crossovers of the shunting route by adding a constraint condition for ensuring traffic safety. A track assignment algorithm based on ABCO for solving the NLPM is proposed. Train operations in the downlink arrival yard of station A are simulated with the proposed method. The results after applying the optimization method show that the average duration of trains on the tracks is reduced by 49.1%, and the degree to which tracks utilization is balanced is also significantly improved. The proposed method optimizes and extends the current achievements that have been reported in the literature.

Tube/Pipe (TP) 304 stainless steel has been widely used in industry, but a change in its microstructures may endanger its service safety, and it is essential to evaluate its microstructural evolution. In this work, a pulse-echo nonlinear method is proposed to characterize the microstructural evolution of the TP304 stainless steel. The detailed pulse-echo nonlinear experimental process is presented, and it is shown that the absolute nonlinear parameter can be determined when the effect of attenuation is taken into account. The microstructural evolution of TP304 stainless steel is artificially controlled by annealing treatments before it is evaluated by using nonlinear ultrasonic method and metallographic method. The results show that the grain sizes increase as the annealing time increases, which leads to the performance degradation of the TP304 steel and an increase in the nonlinear parameters, with the reason discussed considering the variation in the microstructure. The present pulse-echo nonlinear method is easier to conduct than the traditional transmission-through method and the absolute nonlinear parameter can be determined for quantitative characterization. The variation in determined nonlinear parameters provides a reference to evaluate the microstructural evolution of TP304 stainless steel.

Ductile metallic materials such as aluminum alloy, brass, and steel are widely used in engineering structures. Monitoring elastoplastic deformation in these materials is important for structural health monitoring (SHM) to ensure the safety of structures made of metallic materials. This article presents a newly developed and promising nonlinear ultrasonic (NLU) technique called sideband peak count-index (or SPC-I) for monitoring the early stages of elastoplastic deformation in ductile metallic alloy Al6061. Experimental results presented in this article show that the elastic range of the Al6061 SPC-I values shows slight changes due to the inherent inhomogeneities (imperfect grain boundaries or dislocations at the grain boundaries under loadings) of Al6061. Then the SPC-I value changes rapidly as the material enters the plastic range zone. Compared to the linear ultrasonic (LU) parameters (wave velocity and attenuation changes), the SPC-I shows a noticeable advantage (higher sensitivity) for monitoring the early stages of the elastoplastic deformation in these ductile metallic specimens investigated in this study. It is concluded that the SPC-I technique is useful for monitoring deformations in ductile metallic materials, especially in their plastic zone. This work extends the applicability of the SPC-I technique for monitoring elastoplastic deformations in metallic specimens that have not been reported in earlier works and can provide some guidelines for SHM related to elastoplastic deformation in metallic structures.