Applied Mechanics and Materials Vols. 444-445

Abstract: Investigation and potential analysis of low-slope hilly land resources is a foundational work for carrying out land development and utilization scenically. In this paper, based on status of land use change survey data in 2011 and satellite remote sensing data of study area, at the same time,we combined with the practical situation of study area, by using superposition analysis, spatial clustering and fuzzy comprehensive evaluation, did an investigation to low-slope hilly land resources which slopes between 8 degree and 25 degree, analyzed theoretical potential and actual potential of low-slope hilly development and utilization, in order to provide the basis and reference for land use work. The results of the project show: (1) development potential of low-slope hilly land resources is large; (2) the discrepancy beteen theoretical potential and actual potential is obvious; (3) the strategic of development and utilization must be adjust measures to local conditions, pay equal attention to ecological benefit, social benefit and economic benefit and considerate landscape and ecological balance comprehensively.

Abstract: The selected high-span continuous rigid frame bridge for studying is Mangjiedu Bridge in this paper. Based on the principle of structure dynamics and the method of seismic response analysis, the finite element model of the main bridge in Mangjiedu Bridge under Midas-civil was built according to the structural features, site conditions and seismic fortification intensity of the bridge. Then the characteristics of main bridge structure were studied using Lanzcos modal analysis method, and the seismic responses of main bridge are studied by earthquake response spectrum analysis and time history analysis respectively. The results show that the fundamental frequency of the main bridge is 0.1943Hz, and the transverse vibration mode shapes are most remarkable in the former 10 ordered types of vibration of main bridge. The main bridge is in the conditions of elastic range and does not failure under E1 earthquake. Both response spectrum analysis and time history analysis show that the largest displacement along the main bridge appears at the top of pier and the largest transverse displacement appears in the central position of main span. It also shows that the maximum shear and maximum moment occur at the bottom of main pier.

Abstract: On the basis of a performance emulation model of turbofan engine, a relation curve was first employed to fix the efficiency of compression components. With the turbine blade cooling efficiency being a restriction, an optimization algorithm was developed on the premise that engine cycle parameters match. The calculation results show that when the turbine blade cooling efficiency was improved at a fixed bypass ratio, the engine overall pressure ratio corresponding to the lowest specific fuel consumption (sfc) grows on a large scale, while the lowest sfc slightly drops and the specific thrust significantly boosts.

Abstract: The aerodynamic shape optimization design system was established in this paper. In the system, the RANS equation was used for solving the flowing; the free form deformation (FFD) method was used for the geometry parameterization, and the genetic algorithm was used for the optimization search. For the reducing of the time cost, the Kriging model was used for the surrogate model instead of the CFD simulation during the optimization design. The aerodynamic shape design of a swept wing was presented which used the system, and the result indicated that the 14% drag coefficient was reduced at the cruise conditions, which proved the validity of the system.

Abstract: The total consolidation process in the construction of hydraulic fill fly ash dam is calculated and analyzed by using the Biots consolidation theory and Cam-Clay model. Meanwhile, some problems such as characteristics of subsidence, excess pore pressure and stress of dam, influences coming from consolidation of hydraulic fill fly ash dam caused by drainage layer in dam foundation, etc, are analyzed. Results show that constructing hydraulic fill fly ash dam in saturated fly ash ground is feasible, and setting drainage layer in the dam foundation can greatly expedite the consolidation speed of dam, which is propitious to the safety of dam.

Abstract: In order to simulate the thermal stresses, thermal strains and residual stresses of steel during quenching by numerical means, it is necessary to obtain an accurate boundary condition of temperature field. The explicit finite difference method, nonlinear estimate method and the experimental relation between temperature and time during water and nitrogen-spray water quenching have been used to solve the inverse problem of heat conduction. The relations between surface heat-transfer coefficient in water and nitrogen-spray water quenching and surface temperature of cylinder have been given. In numerical calculation, the thermal physical properties of material were treated as the function of temperature. The results show that the relations between surface heat-transfer coefficient and surface temperature are non-linear during water and nitrogen-spray water quenching, the heat-transfer coefficient is bigger when water quenching than when nitrogen-spray water before 580°C, the heat-transfer coefficient is smaller when water quenching than when nitrogen-spray water after 400°C. The results of calculation coincided with the results of experiment. This method can effectively determine the surface heat-transfer coefficient during water and nitrogen-spray water quenching.

Abstract: Suspenders are main force-transmission components of half-through and through arch bridge, It is crucial for safety of bridges to its reliability and durability. Safety of the arch bridge will change when a suspender sudden failure, and affect the safety of the structure. Selecting a through arch bridge in Yunnan Province as the research object, it based on the three-dimensional finite element, this paper studied the dynamic response of arch bridge suspenders sudden failure on the failure-safety theory.

Abstract: The length of crack extension under stable crack extension is measured by digital image correlation technology and based on mixed-mode I/II fracture test. Quantitative analyses of the fracture properties are provided for thin sheet metals at stable crack extension under mode I, mode II and mixed-mode I/II loading conditions. The strain field of the crack tip at crack initiation is calculated by VIC-2D. It is suggested that the location of crack initiation is not at the crack tip. The fracture of recycled thin sheet metals is tough due to the large plastic deformation; mode I crack is the most difficult to extend; the load-carrying capacity is the minimum in 45° loading.

Abstract: A coupled model of damage and plasticity to describe the complex behavior of concrete subjected to impact loading is proposed in this paper. The concrete is assumed as homogeneous continuum with pre-existing micro-cracks and micro-voids. Damage to concrete is caused due to micro-crack nucleation, growth and coalescence, and defined as the probability of fracture at a given crack density. It induces a decrease of strength and stiffness of concrete. Compaction of concrete is physically a collapse of the material voids. It produces the plastic strain in the concrete and, at the same time, an increase of the bulk modulus. In terms of crack growth model, micro-cracks are activated, and begin to propagate gradually. When crack density reaches a critical value, concrete takes place the smashing destroy. The model parameters for mortar are determined using plate impact experiment with uni-axial strain state. Comparison with the test results shows that the proposed model can give consistent prediction of the impact behavior of concrete.

Abstract: The finite element model of multi-span continuous beam track is established to research the stress and strain fields of rail under the wheel-rail force. On this basis, according to the practical observation of crack shape, a three-dimensional semi-elliptical crack model was established, the singular element method was employed to simulate the stress field singularity of crack tip, and the transverse crack propagation characteristics of rail bottom under wheel-rail force was studied. The results show that: with the increase of wheel-rail force (vertical, lateral and longitudinal force), K_I shows an increasing trend, and with the increase of lateral force, the increase rate of K_I is maximum; with the increase of vertical force, both of the K_II and K_III show a decreasing trend. However, with the increase of lateral and longitudinal force, both of them show an increasing trend. From the range of stress strength factor of crack tip, the amplitude of K_I at the crack tip of rail outer edge is maximum , but the crack tip amplitude of K_II and K_III is maximum at partial to the rail centerline.