Damage Mechanism of Broad-narrow Joint of CRTSII Slab Track under Temperature Rise

Xiaokai Liu,Wenhao Zhang,Jieling Xiao,Xueyi Liu,Wei Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5

There is two typical damage pattern at broad-narrow joint of CRTSII slab track breakage of narrow joint and fracture at junction between broad joint and narrow joint. This paper aims to study the damage mechanism and develop of broad-narrow joint of CRTSII slab track and put forward the methods to reduce the damage. Based on damaged plasticity model for concrete and cohesive zone model, the damage mechanism and development process of broad-narrow joint are analyzed in this study. The unequal width of broad joint and narrow joint, different concrete strength between broad-narrow joints and slab and slab integrity reducing due to the interface are the main reason for the typical damage. It is suggested to set the same width of broad joint and narrow joint, set the same strength of broad-narrow joint and slab and enhance the integrity of the slab by chipping or adding adhesives, among which the former two methods are more effective. Breakage of narrow joint is a gradual compression damage due to the lower concrete strength than slab. Fracture at the junction between narrow joint and broad joint is a mutational tension damage due to the unequal width of broad joint and narrow joint. The temperature gradient has significant effect on the compression damage, but small to the tension damage, it has the risk of complete destruction under extreme conditions.

Shear-Wave Elastography of the Breast: Added Value of a Quality Map in Diagnosis and Prediction of the Biological Characteristics of Breast Cancer

Xueyi Zheng,Yini Huang,Yubo Liu,Yun Wang,Rushuang Mao,Fei Li,Longhui Cao,Jianhua Zhou 대한영상의학회 2020 Korean Journal of Radiology Vol.21 No.2

Objective: To determine the added value of a shear-wave elastography (SWE) quality map (QM) in the diagnosis of breast lesions and in predicting the biological characteristics of invasive breast cancer. Materials and Methods: Between January 2016 and February 2019, this study included 368 women with 368 pathologically proven breast lesions, which appeared as poor-quality regions in the QM of SWE. To measure shear-wave velocity (SWV), seven regions of interest were placed in each lesion with and without QM guidance. Under QM guidance, poor-quality areas were avoided. Diagnostic performance was calculated for mean SWV (SWVmean), max SWV (SWVmax), and standard deviation (SD) with QM guidance (SWVmean + QM, SWVmax + QM, and SD + QM, respectively) and without QM guidance (SWVmean - QM, SWVmax - QM, and SD - QM, respectively). For invasive cancers, the relationship between SWV findings and biological characteristics was investigated with and without QM guidance. Results: Of the 368 women (mean age, 47 years; SD, 10.8 years) enrolled, 159 had benign breast lesions and 209 had malignant breast lesions. SWVmean + QM (3.6 ± 1.39 m/s) and SD + QM (1.02 ± 0.84) were significantly different from SWVmean - QM (3.29 ± 1.22 m/s) and SD - QM (1.46 ± 1.06), respectively (all p < 0.001). For differential diagnosis of breast lesions, the sensitivity and areas under the receiver operating characteristic curve (AUC) of SWVmean + QM (sensitivity: 89%; AUC: 0.932) were better than those of SWVmean - QM (sensitivity, 84.2%; AUC, 0.912) (all p < 0.05). There was no significant difference in sensitivity and specificity between SD + QM and SD - QM (all p = 1.000). Among the biological characteristics of invasive cancers, lymphovascular involvement, axillary lymph node metastasis, negative estrogen receptor status, negative progesterone receptor status, positive human epidermal growth factor receptor status, and aggressive molecular subtypes showed higher SWVmean + QM (all p < 0.05), while only lymphovascular involvement showed higher SWVmean - QM (p = 0.036). Conclusion: The use of QM in SWE might improve the diagnostic performance for breast lesions and facilitate prediction of the biological characteristics of invasive breast cancers.

Experimental Study on Bond Performances of Track Slab and Mortar Based on DIC Technology

Chengguang Su,Dan Liu,Chenxu Ding,Chuang Gong,Pingrui Zhao,Xueyi Liu 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.9

In order to guarantee the normal long-time service performance of CRST II slab track, it is necessary to study the interface parameters between track slab and CA mortar layer of CRTS II slab track. Thus the splitting and shearing model test of concrete and mortar bonded composite specimens were conducted. Based on the Digital Image Correlation (DIC) technology, the stress-strain relationship and cohesion model parameters were obtained from the interface displacement and distribution of strain. The results showed that: The displacement and the strain field distribution of the composite specimens as well as the whole interlaminar cracking process of initiation, propagation and failure can be well described with DIC. The bond failure between the track slab and the CA mortar layer is part of the brittle failure, and the normal and tangent interface tension-displacements are both bilinear. The shear strength between the track slab and the CA mortar layer is 1.82 MPa with the peak strain of 2.49 × 10−4 and the secant modulus of 7.30 × 103 MPa; While the shear strength is 2.40 MPa with the peak strain of 6.17 × 10−3 and the secant modulus of 3.89 × 102 MPa. When the shear strain is about 7.5×10-4, the shear stress-strain curve tends to remain stable. At this point, the shear strain is 0.12 times of the peak strain. Parameters of the cohesive zone model between the track slab and the CA mortar layer are suggested as follows: the normal cohesive strength is 1.792 MPa with the interface stiffness of 708.485 MPa/ mm and the critical fracture energy of 0.0252 mJ/mm2; the tangential cohesive strength is 0.956 MPa with the interface stiffness of 63.039 MPa/mm and the critical fracture of 0.018 mJ/mm2.

Numerical study of rock-breaking performance of cutters in heterogeneous sand cobble ground

Jin Guo,Xiangwei Kong,Liu Cheng,Xueyi Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6

Further research into tunneling performance in heterogeneous sand cobble ground demands an accurate numerical model of actual formation. In this paper, the ground model composed of spherical sand and ellipsoidal cobble was constructed to study the rockbreaking performance by using the discrete element method. The shape and physical parameters of sand and cobble were obtained on the basis of field test data. Then, the ground model was constructed to simulate the rock-breaking process of the cutterhead. The results show that the center cutter has a high flat wear percentage. With the decrease in cobble content (CC), the cracks between cutters are not connected effectively, thereby resulting in lower rock-breaking quantity. Finally, the influences of CC on the optimal parameters and crack propagation were analyzed. The results indicate that the rock-breaking performance in the ground with a low CC can be improved by increasing penetration and reducing cutter spacing.

Distribution characteristic of hydrodynamic pressure in the ballastless track crack under the train load

Shihao Cao,Rongshan Yang,Luhui Shi,Jiali Li,Xueyi Liu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2

In the areas which have rich rain and poor drainage, there may be obvious water damage existed in the interlamination of ballastless track. The damage is mainly caused by repeated hydraulic fracturing. Aimed at this problem, the calculation model of water pressure under the train load was established on the basis of fluid-structure interaction theory, and the influence of crack geometry and train operation condition on water pressure were analyzed. The results show that, when the train is close to and far away from the location of the crack, the water pressure changes periodically under the train load, and the pressure peak occurs at the crack front. Simultaneously, the positive and negative pressure may both exist in the crack. The crack geometry affects the distribution of water pressure significantly, the value of water pressure is inversely proportional to the vertical opening of crack, and proportional to the cubic polynomial of horizontal crack depth. The water pressure increases firstly with the increase of longitudinal crack length, then decreases gradually and tends to be stable finally. The train operation condition is also an important factor affecting the distribution of water pressure, the value of water pressure is linear with the axle load, and proportional to the square of train speed. These research results will provide a hydraulic boundary condition for further study of water damage mechanism.