查看更多>>摘要：Results of residual stress measurements on Inconel 718 turbine components after machining are here presented. The work is focused on the experimental detection of the residual stress state produced after turning (orthogonal cutting and standard) and milling. The aim of the experimental activity was to supply an experimental data base of proved reliability for milling and turning model validation. This activity was performed inside the EU STREP project VERDI. The residual stresses were detected by means of X-ray diffraction technique. The experimental plan of measurements was performed on components worked with different working parameters (cutting velocity and feed rate) and by means of new and worn tool. The trends of residual stress versus depth are presented.
查看更多>>摘要：This paper is devoted to the analysis of the dynamics and vibrations of wing-like structures with bonded piezoelectric strips and subjected to unsteady aerodynamic loads for crack detection. Pairs of piezoelectric strips, acting as strain sensors, are bonded at the same locations on the opposite sides of a thin structure executing flexural oscillations. In this crack detection strategy, the measured voltage outputs of the two piezoelectric sensors forming a pair are conveniently subtracted in order to eliminate the voltage corresponding to the same level of strain on both sides. This differential voltage output is used to indicate the presence of a crack in the structure. The nonlinear mechanical behavior of the crack in the compression and extension phases of the oscillatory cycle increases substantially the sensitivity of this detection procedure. Furthermore, this crack detection method can take advantage of the aeroelastic oscillations of the wing structures, which are always present during normal flight evolutions of an aircraft. The numerical analysis of the dynamics of structure subjected to unsteady aerodynamic loads uses a finite element formulation for the structure and the piezoelectric strips and a panel method is used to compute the unsteady aerodynamic loads acting on the oscillating wing structure. Numerical simulation results are presented in the paper to explore the feasibility of this crack detection strategy by using the aeroelastic oscillations of the wing-like structures with bonded piezoelectric strips.
查看更多>>摘要：Application of composite laminates was very wide in aerospace engineering, civil engineering, wind energy, auto industry, etc. Low cost glass fiber textile was often applied into composite laminates by many composites companies. It is of import that investigation of mechanical properties and damage mechanism of this composites laminates. Two types of composite laminates were studied in this paper. One type of composite laminates was made of glass fiber biaxial cloth. The other was made of glass fiber composite felt. Each type composite laminates has different direction aligned. Many specimen were tested in compression with universal testing materials machine model INSTRON 5500R. Strength of composite laminates and stress-strain diagram was obtained in these experiments. Effect of fiber different orientation on compression strength of laminates was found. Shear stresses between two laminas were calculated. Fracture mechanism of composites laminates was analyzed by macro-method. Fractography of laminates was applied into analysis of mechanism. SEM photo was acquired and observed in detail. The result is that strength and failure mechanism of different types composite laminates varied with fiber orientation and different textiles.
查看更多>>摘要：With the increasing investigation on reliability and stability of engineering structures, it becomes important for reseach on mechanical properties of materials under fracutre conditions. Concerning to fracture problems of large deformation materials, deformation characteristics of the crack tip field is necessarily needed. This paper presents an experimental analysis on a double-cracked rubber disk under the I-II mixed-mode fracture condition. Deformation properties around the crack tip are described through analyzing displacement information acquired by digital moire method of circular and radial gratings. Also the existence of sector division mode under mixed loading condition is verified, and it is also found experimentally that the shear component makes the sectors shift.
查看更多>>摘要：Smoothed particle hydrodynamics (SPH) is a mesh-free numerical approximation technique for simulating various physical problems. A calculation system for transient heat transfer problem by SPH has been improved to deal with various boundary conditions and several model calculations are performed to verify it. As a practical application, the transient temperature field of a brake disk under emergency braking is analyzed. Both solid and ventilated disks are modeled with a moving heat source on the sliding surface. The numerical results show that the temperature sharply fluctuates because of the cyclic loading. Improvement of the calculation model is also discussed.
查看更多>>摘要：Two hollow rectangular bridge columns with Reactive powder concrete (RPC) were tested under a cyclically reversed horizontal load. Based on the test results, the seismic behavior of such columns was presented. An analytical model was developed to predict the force-displacement relationship of specimens. The test results were also compared to the proposed analytical model. It was found that the ductility factors of the specimens are over 4.0, and the proposed analytical model can predict the force-displacement relationship of such columns with acceptable accuracy.
查看更多>>摘要：In this research, damage spectra to quantify the damage of reinforced concrete (RC) bridges under earthquakes are proposed. The spectra are computed for hundreds of horizontal ground motions recorded during past several earthquakes. The damage spectra proposed are promising for performance-based seismic assessment of existing RC bridges as well as performance-based design of new systems.
查看更多>>摘要：In this paper some results of 3D-fmite element analyses of a modified CTS-specimen(MCTS) with an inclined crack front are presented. It will be shown, that through the inclination of the crack front, even under pure in-plane shear loading of the specimen, mixed-mode II and III loading conditions can be generated along the straight inclined crack front. Furthermore a superposition of all fracture modes I, II and III can be generated, if this MCTS-specimen is subject to an in-plane tension/shear loading. The computational fracture analysis is based on the calculation of separated energy release rates GI, GII and GIII along the crack front by the numerically highly effective modified virtual crack closure integral(MVCCI)-method and for the finite element(FE)-modelling the commercially available FE-code ANSYS is utilized.
查看更多>>摘要：Many damage models of concrete have been put forward till now, of which some models are applied in engineering practices. The damage parameters play an important role in the calculations of damage with these models, which is determined during experiments. However, the tests of damage on concrete are rarely made, especially about the measuring method of initial damage. The initial damage is an essential parameter to study on the damage of concrete. Being based on the theory of damage, this paper analyze of the damaged and undamaged elastic modulus of concrete. The new method of determining undamaged elastic modulus from test results has been put forward, and then the initial damage has been quantified.
查看更多>>摘要：There are several difficulties associated with the numerical simulation of the stretch bending process of extruded components; the main ones are non-linear material behavior, geometrical non-linearities, modeling of boundary conditions, contact between die and specimen, springback during the unloading phase. Another very complex aspect is the calibration of the numerical model, as rather few experimental results are generally available. This paper deals with a numerical simulation of a complete stretch bending process with the aim to select the most suitable numerical procedure oriented to the evaluation of the process-induced distortions and residual stresses; to validate the proposed procedure, numerical-experimental comparisons have been performed. The activities reported have been developed in collaboration with ALENIA Finmeccanica s.p.a. within the VI FP's research project called COMPACT.
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