“…Specifically, the range of σ d for the tested saturation specimens and optimal moisture content specimens are 50-250 kPa and 100-400 kPa, respectively. Moreover, the operation speed of heavy-haul freight trains is much less than the normal and high-speed passenger trains; for instance, the operation speed of heavy-haul freight trains in China is mainly in the range of 20-80 km/h [52][53][54], and the freight train speed in Australia is generally within 40-80 km/h [55,56]. The wagon length of freight trains in China is 12-14 m [57].…”
Critical dynamic stress (σcri) and accumulative plastic strain (εp) are primary indicators regarding the dynamic stability of unbound granular materials (UGMs). This study aims to seek an effective method to evaluate the dynamic stability of UGMs used in railway subgrades. First, the dynamic characteristics of an UGM used in railway subgrade bed construction were investigated by performing a series of large-scale cyclic triaxial tests, with the results showing that εp versus cycle number (N) curves can be categorized into stable, failure, and critical patterns. Grey relational analyses were then established, where the analyzed results demonstrated that the εp–N curve pattern and final accumulative plastic strain (εs) of the stable curves are strongly correlated with the moisture content (w), confining pressure (σ3), and dynamic deviator stress (σd). The analyzed grey relational grades distributed in a narrow range of 0.72 to 0.81, indicating that w, σ3, and σd have similar degrees of importance on determining the εp–N curve patterns and the values of εs of the UGM. Finally, a data processing method using a back-propagation (BP) neural network is introduced to analyze the test data, and an empirical approach is developed to evaluate the σcri (considering the effects of σ3 and w) and εs (considering the effects of σ3, w, and σd) of the UGM. The analyzed results illustrated that the developed method can effectively reflect the linear/non-linear relationships of σcri and εs with respect to σ3 and/or σd. The σcri approximately increases linearly with increasing σ3, and a simple empirical formula is proposed for the σcri. In addition, εs and its variation rate increase non-linearly with increasing σd but decrease non-linearly as σ3 increases.
“…Specifically, the range of σ d for the tested saturation specimens and optimal moisture content specimens are 50-250 kPa and 100-400 kPa, respectively. Moreover, the operation speed of heavy-haul freight trains is much less than the normal and high-speed passenger trains; for instance, the operation speed of heavy-haul freight trains in China is mainly in the range of 20-80 km/h [52][53][54], and the freight train speed in Australia is generally within 40-80 km/h [55,56]. The wagon length of freight trains in China is 12-14 m [57].…”
Critical dynamic stress (σcri) and accumulative plastic strain (εp) are primary indicators regarding the dynamic stability of unbound granular materials (UGMs). This study aims to seek an effective method to evaluate the dynamic stability of UGMs used in railway subgrades. First, the dynamic characteristics of an UGM used in railway subgrade bed construction were investigated by performing a series of large-scale cyclic triaxial tests, with the results showing that εp versus cycle number (N) curves can be categorized into stable, failure, and critical patterns. Grey relational analyses were then established, where the analyzed results demonstrated that the εp–N curve pattern and final accumulative plastic strain (εs) of the stable curves are strongly correlated with the moisture content (w), confining pressure (σ3), and dynamic deviator stress (σd). The analyzed grey relational grades distributed in a narrow range of 0.72 to 0.81, indicating that w, σ3, and σd have similar degrees of importance on determining the εp–N curve patterns and the values of εs of the UGM. Finally, a data processing method using a back-propagation (BP) neural network is introduced to analyze the test data, and an empirical approach is developed to evaluate the σcri (considering the effects of σ3 and w) and εs (considering the effects of σ3, w, and σd) of the UGM. The analyzed results illustrated that the developed method can effectively reflect the linear/non-linear relationships of σcri and εs with respect to σ3 and/or σd. The σcri approximately increases linearly with increasing σ3, and a simple empirical formula is proposed for the σcri. In addition, εs and its variation rate increase non-linearly with increasing σd but decrease non-linearly as σ3 increases.
“…Freight cars are mainly composed of four wheelsets, two bogies and one car body. 20 The main dimensions of car body are wheelbase (L1), adjacent wheelbase (L2), fixed distance (L3) and car body length (L4) as shown in Figure 3.Figure 3.Wagon structure diagrams.…”
The Bowed plates weld device (BPWD) is a new type of rail weld reinforcement device, which has been widely applied in heavy haul railway lines in China. It changes the service state and vibration characteristics of a weld. In order to explore the BPWD vibration influence on the track, static, and dynamic on-site tests were carried out on a heavy haul line. The vibration influence and spectrum characteristics of the track between BPWD and unplated weld (UW) was compared. At the same time, a 3D coupling model of heavy haul train-rail weld was established and optimization of service performance of the BPWD was carried out. The results showed that the average acceleration of rail, sleeper and ballast at the BPWDwere 52.7%, 43.5%, and 50.2% lower than that of UW. In comparison with UW, peak value of the periodic frequency spectrum and dominant frequency distribution in the BPWD track structure could be effectively reduced from rails to ballast. Length of 0.8 m for plate was found to be optimum in order to reduce the rail stress effectively. The material of the insulating interlayer should preferably be nylon.
“…Beaty et al established a model for lipping phenomenon at IRJs by twin-disc testing and offered a number of reinforcement suggestions [14]. Xiao et al utilised both field tests and 3D FE modelling to explore deformation of IRJs and estimate the wheel-rail impact force within the region [15].…”
Vehicle-track interaction at insulated rail joints (IRJs) plays a significant role in the wear evolvement and damage of the IRJ components. It is, however, challenging to characterise the contact conditions within the region non-destructively and accurately using experimental tools, especially when the IRJ contact involves both wheel-rail and wheel-endpost contact pairs. This study presents an ultrasonic technique to monitor and characterise static IRJ contacts in a non-invasive manner. The proposed ultrasonic reflectometry technique can realise high-resolution visualisation of contact patch and contact pressure distribution for both wheel-rail contact and wheel-endpost contact, by striking a beam of focused ultrasonic signals at the contact interface. Different data post-processing strategies are applied for the two types of contacts and a deconvolution algorithm is applied to rectify the measurements near the railendpost boundary. The ultrasonic measurements are verified through FE simulations and the results show good agreement with each other in terms of both contact area and contact pressure level. It is expected that the proposed ultrasonic approach can be a reliable tool to assist in revealing the contact behaviour of IRJs more profoundly.
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