Advanced Materials Research Vol. 842

Abstract: According to the special engineering requirement, a novel luffing mechanism with variable degree of freedom is presented in this study. The mechanism is assumed to be an ideal rigid body system and the degrees of freedom in different work conditions are calculated. Then the kinematic equations of mechanism are obtained by the geometrical and motional relationship of the components; meanwhile, the dynamic equations of mechanism are deduced by the Newton's mechanical law. The analytic model can be employed for the calculation and analysis of the mechanism features; furthermore, it can be used for the design of hydraulic and electric control system.

Abstract: This part mainly focuses on the calculation, analysis and verification of the analytic model of the novel mechanism obtained in Part I. An indirect solution method is presented to simplify the calculation of the motional quantities. Then the kinematic and dynamic equations are solved and some interested results representing the kinematic and dynamic features of mechanism are figured out. A virtual prototype model of mechanism is established in ADAMS to verify the validity of the analytic model and the calculation process. Good agreements between the two models are found from the comparing of trajectory curves, which implies that the modeling, calculation and analysis in this study are accurate.

Abstract: This paper describes the results of numerical work to determine the flow structures of the slipstream and wake of a high speed train on platforms of underground rail station using three-dimensional compressible Euler equation. The simulations were carried out on a model of a simplified three-coach train and typical cross-section of Chinese high-speed railway tunnel. A number of issues were observed: change process of slipstreams, longitudinal and horizontal distribution characteristics of train wind. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Maximum and minimum velocity values were also noticed near to the nose rear tip. These structures extended for a long distance behind the train in the far wake flow. The slipstream in platform shows the typical three-dimensional characteristics and the velocity is about 4 m/s at 6 m away from the edge of platform.

Abstract: Mesh-free particle (Lagrangian) methods such as Moving Particle Semi-Implicit (MPS) are the latest generation of methods in the field of computational fluid dynamics where large interfacial deformations and fragmentations exist. Due to their mesh-free nature, these methods are capable of simulating any kind of boundary/interface deformation and fragmentations. In this study the weakly compressible corrected MPS (WCC-MPS) method is used to simulate dam break over a dry bed, which is a highly erosive and transient flow problem. The developed numerical model is first validated using a dry bed dam break problem by comparing with experimental data. Comparisons between the model results and experimental data showed that the developed numerical model with WCC-MPS method can well represent the dam break problems with very large free surface deformation and fragmentations.

Abstract: Elastic–plastic finite element analyses have been performed to study the compressive stress effect on fatigue crack growth under applied tension–compression loading. The near crack tip stress, crack tip opening displacement and crack tip plastic zone size were obtained for a kinematic hardening material. The results have shown that the near crack tip local stress, displacement and reverse plastic zone size are controlled by the maximum stress intensity factors Kmax and the applied compressive stress σmaxcom under tension–compression. Based on the finite element analysis results, a fatigue crack propagation model using Kmax and σmaxcom as a parameters under tension–compression loading has been developed.The models under tension–compression loading agreed well with experimental observations.

Abstract: The article deals with the elastic-plastic state of inhomogeneous array with a spherical cavity. Model is used thick-walled ball of an elastic-perfectly plastic material (Prandtl diagram). It is shown that in the inhomogeneous material, depending on the inhomogeneity functions describing the change of the modulus of elasticity and yield stress of soil plastic deformation may appear on both the inner and outer surface of the ball and inside it. Are found values of the limit loads, displacement diagrams are constructed in an array.

Abstract: AA7050and AA2024 aluminum alloys used in aviation were jointed by friction stir welding, and the tensile properties and fracture surfaces were investigated. The results show that the ultimate strength and the yield limit of welded materials can reach 90% and 75% for AA7075and AA2024 respectively, while the ultimate strength of AA7050/AA2024 FSW can reach 60.5% of AA7050 and 70.8% of AA2024, the yield limit can reach 46.2 % of AA7050 and 75.5% of AA2024. The equiaxial fine grains were found in weld nugget, the coarsen and distorted grains in the thermo-mechanically affected zone, and coarse grains in heat affected zone. The fractures occur at the advancing side between thermo-mechanically affected zone and heat affected zone. Dimples appeared on the fracture surfaces means that the fracture is ductile fracture.

Abstract: The propagation of cracking in concrete is a mechanism governing many physical and mechanical properties of the material. The aim of this study was to experimentally investigate the crack propagation of new concrete compositions using image analysis. Several concrete mixes containing microsilica and nanosilica were made. For each composition, Compact Tension (CT) specimens were prepared with dimensions 150x150x12mm. Specimens were subjected to a tensile load. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The compression strength and modulus of elasticity were also determined for reference. The results obtained with this method have shown that it is possible to monitor relatively small displacements on the specimen surface regardless of the scale of the representative area of interest and to evaluate the influence of filler on the cracking properties of concrete.

Abstract: In this paper, the numerical simulation procedure of the reinforced concrete (RC) structure is purposed using SAP2000 software. The plastic hinge model (PHM) is using SWPH code. This PHM is to simulate the nonlinear responses of the RC structure under seismic. The numerical structural models are established using FEM models. The test specimen under shake table is two-span RC structure. In order to demonstrate the accuracy of RC structural model, comparisons between the experimental and numerical results are close. The proposed procedure can be used to simulate the nonlinear responses of RC structure under seismic.

Abstract: In order to determine the parameters of a stress relaxation model based on Altenbach-Gorash-Naumenko creep equations, an efficient parameter identification scheme is discussed. The differential evolution (DE) algorithm is used in the identification procedure with a modified forward-Euler scheme. The model parameters of 1Cr-0.5Mo-0.25V stainless steel bolting material at 500°C have been determined, and the creep and stress relaxation behaviors have been calculated. Comparing with a step-by-step model parameter determination technology and the genetic algorithm (GA), it shows that the DE algorithm has better convergence property and suitability for parallelization, and no need of initial guesses close to the solution. Results indicate that the optimum solutions can be obtained more easily by DE algorithm than others.