Abstract
A difference in subgrade settlement between two rails of a track manifests as lateral differential subgrade settlement.
This settlement causes unsteadiness in the motion of trains passing through the corresponding area. To illustrate the effect of lateral differential subgrade settlement on the dynamic response of a vehicle-track coupling system, a three-dimensional vehicletrack-subgrade coupling model was formulated by combining the vehicle-track dynamics theory and the finite element method. The wheel/rail force, car body acceleration, and derailment factor are chosen as evaluation indices of the system dynamic response. The effects of the amplitude and wavelength of lateral differential subgrade settlement as well as the driving speed of the vehicle are analyzed. The study reveals the following: The dynamic responses of the vehicle-track system generally increase
linearly with the driving speed when the train passes through a lateral subgrade settlement area. The wheel/rail force acting on a rail with a large settlement exceeds that on a rail with a small settlement. The dynamic responses of the vehicle-track system increase with the amplitude of the lateral differential subgrade settlement. For a 250-km/h train speed, the proposed maximum amplitude for a lateral differential settlement with a wavelength of 20 m is 10 mm. The dynamic responses of the vehicle-track system decrease with an increase in the wavelength of the lateral differential subgrade settlement. To achieve a good operation quality of a train at a 250-km/h driving speed, the wavelength of a lateral differential subgrade settlement with an amplitude of 20 mm should not be less than 15 m. Monitoring lateral differential settlements should be given more emphasis in routine highspeed railway maintenance and repairs.
Key Words
ballastless slab track; finite element method; high-speed railway; lateral differential settlement of subgrade;
vehicle-track coupling dynamics
Address
Keping Zhang, Xiaohui Zhang and Shunhua Zhou: Shanghai Key Laboratory of Rail Infrastructure Durability and System Safety, Tongji University, No.4800, Caoan Road, Shanghai, PR China; Key Laboratory of Road and Traffic Engineering of the Ministry of Education, Tongji University, No.4800, Caoan Road, Shanghai, PR China
Abstract
This paper investigates experimentally and numerically the influence of drilling process on the mechanical and thermomechanical behaviors of woven glass fiber reinforced polymer (GFRP) composite plate. Through the experimental analysis, a CNC machine with cemented carbide drill (point angles o=118o and 6 mm diameter) was used to drill a woven GFRP laminated squared plate with a length of 36.6 mm and different thicknesses. A produced temperature during drilling "heat affected zone (HAZ)" was measured by two different procedures using thermal IR camera and thermocouples. A thrust force and cutting torque were measured by a Kistler 9272 dynamometer. The delamination factors were evaluated by the image processing technique. Finite element model (FEM) has been developed by using LS-Dyna to simulate the drilling processing and validate the thrust force and torque with those obtained by experimental technique. It is found that, the present finite element model has the capability to predict the force and torque efficiently at various drilling conditions. Numerical parametric analysis is presented to illustrate the influences of the speeding up, coefficient of friction, element type, and mass scaling effects on the calculated thrust force, torque and calculation's cost. It is found that, the cutting time can be adjusted by drilling parameters (feed, speed, and specimen thickness) to control the induced temperature and thus, the force, torque and delamination factor in drilling GFRP composites. The delamination of woven GFRP is accompanied with edge chipping, spalling, and uncut fibers.
Key Words
drilling of composite; finite element analysis; mass scaling and speeding up; thrust force and torque; woven glass fiber
Address
Mohamed S. Abd-Elwahed: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia
Usama A. Khashaba: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia; Mechanical Design and Production Engineering Department, Faculty of Engineering, Zagazig University, Egypt
Khaled I. Ahmed: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia
Mohamed A. Eltaher: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia; Mechanical Design and Production Engineering Department, Faculty of Engineering, Zagazig University, Egypt
Ismael Najjar: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia
Ammar Melaibari: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 22254-2265, Saudi Arabia
Azza M. Abdraboh: Physics Department, Faculty of Science, Benha University, Banha, Egypt
Abstract
The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution numerical models, namely surface-wetting model, core-wetting model and uniform-wetting model, were established to explore the water distribution influences. The feasibility and validity of the surface-wetting model were further demonstrated by comparing the simulation results with laboratory results. The investigation reveals that coal mechanical properties are affected by both water saturation coefficient and water distribution condition. For all water distribution models, micro-cracks always initiate and nucleate in the water-rich area and thus lead to distinct macro fracture characteristics. With the increase of water saturation coefficient, the failure of coal tends to be less violent with less cracks and ejected fragments. In addition, the corewetting specimen is more sensitive to water than specimens with other water distribution models.
Key Words
coal mechanical behaviour; discrete element method; nuclear magnetic resonance imaging; waterweakening effect; water distribution model
Address
Lihai Tan: School of Resource Environment and Safety Engineering, University of South China, Hengyang, 412001, PR China; School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW 2522, Australia
Xin Cai: School of Resources and Safety Engineering, Central South University, Changsha 410083, PR China
Ting Ren: School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW 2522, Australia
Xiaohan Yang: School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW 2522, Australia
Yichao Rui: School of Resources and Safety Engineering, Central South University, Changsha 410083, PR China
Abstract
With the continuous increase of computational capacity, more and more complex nonlinear elastoplastic constitutive models were developed to study the mechanical behavior of elastoplastic materials. These constitutive models generally contain a large amount of physical and phenomenological parameters, which often require a large amount of computational costs to determine. In this paper, an inverse parameter determination method is proposed to identify the constitutive parameters of elastoplastic materials, with the consideration of both strain rate effect and temperature effect. To carry out an efficient design, a hybrid optimization algorithm that combines the genetic algorithm and the Nelder-Mead simplex algorithm is proposed and developed. The proposed inverse method was employed to determine the parameters for an elasto-viscoplastic constitutive model and Johnson-cook model, which demonstrates the capability of this method in considering strain rate and temperature effect, simultaneously. This hybrid optimization algorithm shows a better accuracy and efficiency than using a single algorithm. Finally, the predictability analysis using partial experimental data is completed to further demonstrate the feasibility of the proposed method.
Key Words
elastoplastic constitutive model; hybrid Genetic-Simplex algorithm; inverse problem; strain-rate dependency; temperature dependency
Address
Xin Li, Chao Zhang: Department of Aeronautical Structure Engineering, Northwestern Polytechnical University, Xi'an, Shaanxi, 710072, China; Shaanxi Key Laboratory of Impact Dynamics and its Engineering Applications, Xi'an, Shaanxi, 710072, China; Joint International Research Laboratory of Impact Dynamics and its Engineering Applications, Xi'an, Shaanxi, 710072, China
Zhangming Wu: Cardiff School of Engineering, Cardiff University, Wales, CF23 4AA, UK
Abstract
In this paper, a hybrid scaled boundary finite element and finite volume method (SBFEM-FVM) is proposed for simulating hydraulic-fracture propagation in brittle concrete materials. As a semi-analytical method, the scaled boundary finite element method is introduced for modelling concrete crack propagation under both an external force and water pressure. The finite volume method is employed to model the water within the crack and consider the relationship between the water pressure and the crack opening distance. The cohesive crack model is used to analyse the non-linear fracture process zone. The numerical results are compared with experimental data, indicating that the F-CMOD curves and water pressure changes under different loading conditions are approximately the same. Different types of water pressure distributions are also studied with the proposed coupled model, and the results show that the internal water pressure distribution has an important influence on crack propagation.
Key Words
concrete crack propagation; coupling; finite volume method; hydraulic fracture; scaled boundary finite element method
Address
Peng Zhang: Nanjing Institute of Technology, Nanjing 211167, China; Department of Engineering Mechanics, Hohai University, Nanjing 211100, P.R. China
Chengbin Du, Wenhu Zhao: Department of Engineering Mechanics, Hohai University, Nanjing 211100, P.R. China
Deheng Zhang: Nanjing Institute of Technology, Nanjing 211167, China
Abstract
Composite materials, composed of multiple constituent materials with dissimilar properties, are actively adopted in a wide range of industrial sectors due to their remarkable strength-to-weight and stiffness-to-weight ratio. Nevertheless, the failure mechanism of composite materials is highly complicated due to their sophisticated microstructure, making it much harder to predict their residual material lives in real life applications. A promising solution for this safety issue is structural damage detection. In the present paper, damage detection of composite material via electrical resistance-based technique and infrared thermography is reviewed. The operating principles of the two damage detection methodologies are introduced, and some research advances of each techniques are covered. The advancement of IR thermography-based non-destructive technique (NDT) including optical thermography, laser thermography and eddy current thermography will be reported, as well as the electrical impedance tomography (EIT) which is a technology increasingly drawing attentions in the field of electrical resistance-based damage detection. A brief comparison of the two methodologies based on each of their strengths and limitations is carried out, and a recent research update regarding the coupling of the two techniques for improved damage detection in composite materials will be discussed.
Key Words
composite materials; damage detection; electrical impedance tomography; electrical resistance measurement; IR thermography
Address
Kundo Park, Junhyeong Lee and Seunghwa Ryu: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea
Abstract
Ductility is very important parameter in seismic design of RC members such as beams where it allows RC beams to
dissipate the seismic energy. In this field, the curvature ductility has taken a large part of interest compared to the deflection ductility. For this reason, the present paper aims to propose a general formula for predicting the deflection ductility factor of RC beams under mid-span load. Firstly, the moment area theorem is used to develop a model in order to calculate the yield and the ultimate deflections; then this model is validated by using some results extracted from previous researches. Secondly, a general formula of deflection ductility factor is written based on the developed deflection expressions. The new formula is depended on curvature ductility factor, beam length, and plastic hinge length. To facilitate the use of this formula, a parametric study on the curvature ductility factor is conducted in order to write it in simple manner without the need for curvature calculations. Therefore, the deflection ductility factor can be directly calculated based on beam length, plastic hinge length, concrete strength,
reinforcement ratios, and yield strength of steel reinforcement. Finally, the new formula of deflection ductility factor is compared with the model previously developed based on the moment area theorem. The results show the good performance of the new formula.
Key Words
curvature; deflection; ductility; mid-span load; moment area theorem; RC beam
Address
Haytham Bouzid: Sciences and Technology Department, University of Tissemsilt, Algeria; Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria
Benferhat Rabia, Tahar Hassaine Daouadji: Civil Engineering Department, University of Tiaret, Algeria; Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria
Abstract
To investigate the mechanical behavior of large stud shear connector embedded in hybrid fiber-reinforced concrete (HFRC), a refined 3D nonlinear finite element (FE) model incorporating the constitutive model of HFRC was developed using ANSYS. Firstly, the test results conducted by the authors (He et al. 2017) were used to validate FE model of push out tests. Secondly, a total of 27 specimens were analyzed with various parameters including fiber volume fractions of HFRC, diameter of studs and HFRC strength. Finally, an empirical equation considering the contribution of steel fiber (SF) and polypropylene fiber (PF) was recommended to estimate the ultimate capacity of large stud shear connector embedded in HFRC.
Key Words
composite bridge; FE analysis; HFRC; large stud; push-out test
Address
Yu Liang He, Chong Zhang: College of Civil Engineering, Shaoxing University, Shaoxing 312000, China
Li Chao Wang: Hua Hui Group, Shaoxing, 312000, China
Ying Yang: College of Civil Engineering, Shaoxing University, Shaoxing 312000, China
Yi Qiang Xiang: College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China
Abstract
Buckling restrained bracing (BRB) was firstly introduced in Japan construction industry in year 1989. With time, BRB performance has been advanced to self-centering BRB (SC-BRB) which has exceptional energy dissipation, addressing the improvement in the structure performance in post-seismic affect. Although the BRB performance specifications are defined in design codes of several countries, specific design provisions are not generally provided since BRBs are usually considered a manufactured device. Furthermore, most of review papers focused on BRB rather than SC-BRB. Thus, this paper explores the background of both BRB and SC-BRB. The importance of self-centering components in BRB and literature related to it have been studied. This review study also highlights the significance of corrosion-resistance materials in the configuring BRB and SC-BRB since most of such members are made of carbon steel that is susceptible to corrosion.
Key Words
bracing system; buckling restrained bracing (BRB); cyclic loading test; energy dissipation; residual deformation; self-centering BRB (SC-BRB)
Address
Syed Muhammad Bilal Haider: Department of Civil and Environmental Engineering, Incheon National University, Incheon, South Korea
Dongkeun Lee: Department of Civil and Environmental Engineering, Southern University and A&M College, Baton Rouge, Louisiana, USA
Abstract
In this paper, we present a new method to calculate interface warping functions for the analysis of beams with geometric and material discontinuities in the longitudinal direction. The classical Saint Venant torsion theory is extended to a three-dimensional domain by considering the longitudinal direction. The interface warping is calculated by considering both adjacent cross-sections of a given interface. We also propose a finite element procedure to simultaneously calculate the interface warping function and the corresponding twisting center. The calculated interface warping functions are employed in the continuum-mechanics based beam formulation to analyze arbitrary shape cross-section beams with longitudinal discontinuities. Compared to the previous work by Yoon and Lee (2014a), both geometric and material discontinuities are considered with fewer degrees of freedom and higher accuracy in beam finite element analysis. Through various numerical examples, the effectiveness of the proposed interface warping function is demonstrated.
Key Words
beams; continuum-mechanics based beam; finite element method; longitudinal discontinuity; torsion; warping
Address
Dong-Hwa Lee, Hyo-Jin Kim and Phill-Seung Lee: Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
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