Identification of Temperature-Induced Deformation for HSR Slab Track Using Track Geometry Measurement Data.

Slab track is widely used in many newly built high-speed rail (HSR) lines as it offers many advantages over ballasted tracks. However, in actual operation, slab tracks are subjected to operational and environmental factors, and structural damages are frequently reported. One of the most critical problems is temperature-induced slab-warping deformation (SWD) which can jeopardize the safety of train operation. This paper proposes an automatic slab deformation detection method in light of the track geometry measurement data, which are collected by high-speed track geometry car (HSTGC). The characteristic of track vertical irregularity is first analyzed in both time and frequency domain, and the feature of slab-warping phenomenon is observed. To quantify the severity of SWD, a slab-warping index (SWI) is established based on warping-sensitive feature extraction using discrete wavelet transform (DWT). The performance of the proposed algorithm is verified against visual inspection recorded on four sections of China HSR line, which are constructed with the China Railway Track System II (CRTSII) slab track. The results show that among the 24,806 slabs being assessed, over 94% of the slabs with warping deformation can be successfully identified by the proposed detection method. This study is expected to provide guidance for efficiently detecting and locating slab track defects, taking advantage of the massive track inspection data.

A SAFT Method for the Detection of Void Defect inside a Ballastless Track Structure Using Ultrasonic Array Sensors.

High-precision ultrasound imaging of void defects is critical for the performance and safety assessment of ballastless track structures. The sound propagation velocity of each layer in the ballastless track structure is quite different. However, the traditional concrete Synthetic Aperture Focusing Technique (SAFT) ultrasound imaging method is based on the assumption that the concrete has a single constant shear wave velocity. Thus, it is not a suitable method for the ultrasonic imaging of multilayer structures. In this paper, a Multilayer SAFT high-precision ultrasound imaging method is proposed. It is based on the ray-tracing technique and uses the Fermat principle to find the refraction point that minimizes the delay of the acoustic wave propagation path at the interface of the discrete layers. Then, the acoustic wave propagation path is segmented by the position of the refraction point, and the propagation delay of the ultrasonic wave is obtained segment by segment. Thus, the propagation delay of the ultrasonic wave is obtained one by one, so that the propagation delay of the ultrasonic wave in the multilayer structure can be accurately obtained. Finally, the focused image is obtained according to the SAFT imaging algorithm. The finite element simulation and experimental results show that the Multilayer SAFT imaging method can accurately track the propagation path of the ultrasonic wave in ballastless track structures, as well as accurately calculate the propagation delay of the ultrasonic wave and the lengths of void defects. The high accuracy of the Multilayer SAFT imaging represents a significant improvement compared to traditional SAFT imaging.

Surface Crack Detection in Precasted Slab Track in High-Speed Rail via Infrared Thermography.

The surface crack of ballastless track slab can seriously reduce the serviceability and durability of high-speed railway (HSR). Aiming at accurately and efficiently detecting the slab cracks, this research proposes an infrared thermography (IRT)-based method for the surface crack, which is the most serious and common crack type in track slab. A three dimensional finite element (FE) model of IRT detection of concrete slab with surface cracks is established. The relation between the width of detectable cracks and the ambient temperature can be thereby obtained by inputting the measured thermodynamic parameters in the model. Parametric study shows that with ambient temperature higher than 15 °C, cracks with a width of no less than 0.2 mm can be well detected. Scale model test and field test are conducted, IRT method can effectively locate the slab surface cracks with width as small as 0.14 mm when ambient temperature is no less than 20 °C.

Mechanism for Solvent Exchange on trans-[Os(en)(2)(eta(2)-H(2))S](2+).

Solvent exchange on trans-[Os(en)(2)(eta(2)-H(2))S](2+) (S = H(2)O, CH(3)CN) has been studied in neat solvent as a function of temperature and pressure by (17)O NMR line-broadening and isotopic labeling experiments (S = H(2)O) and by (1)H NMR isotopic labeling experiments (S = CH(3)CN). Rate constants and activation parameters are as follows for S = H(2)O and CH(3)CN, respectively: k(ex)(298) = 1.59 +/- 0.04 and (2.74 +/- 0.03) x 10(-)(4) s(-)(1); DeltaH() = 72.4 +/- 0.5 and 98.0 +/- 1.4 kJ mol(-)(1); DeltaS() = +1.7 +/- 1.8 and +15.6 +/- 4.9 J mol(-)(1) K(-)(1); DeltaV() = -1.5 +/- 1.0 and -0.5 +/- 1.0 cm(3) mol(-)(1). The present investigation of solvent exchange when compared with a previous study on substitution reactions on the same complexes leads to the conclusion that substitution reactions on these compounds undergo an interchange dissociative, I(d), or dissociative, D, reaction mechanism, where solvent dissociation is the rate-limiting step.