Applied Mechanics and Materials Vol. 684

Abstract: There is very rich fault information in vibration signals of rotating machineries. The real vibration signals are nonlinear, non-stationary and time-varying signals mixed with many other factors. It is very useful for fault diagnosis to extract fault features by using time-frequency analysis techniques. Recent researches of time-frequency analysis methods including Short Time Fourier Transform, Wavelet Transform, Wigner-Ville Distribution, Hilbert-Huang Transform, Local Mean Decomposition, and Local Characteristic-scale Decomposition are introduced. The theories, properties, physical significance and applications, advantages and disadvantages of these methods are analyzed and compared. It is pointed that algorithms improvement and combined applications of time-frequency analysis methods should be researched in the future.

Abstract: Due to the high precision and strong molding capacity, micro-milling plays an important role in the field of micro-machining. The components machined in micro-machining is smaller than conventional components, and sometimes the generated burrs are as large as the feature size of components, so the study of micro burr control is very important. In the reseach, cutting-direction burrs are based on the traditional milling characteristics, also combined with the characteristics of micro-milling. The experimental data verify the correctness of the model well, so it provides theoretical guidance for the burrs control in micro-milling.

Abstract: By the MATLAB software the article simulated the local irregularity, the new harmonic excitation superimposed on the initial harmonic to simulate track settlement deterioration, the new uplift excitation superimposed on the initial harmonic to simulate track raised deterioration, as the locomotive model external excitation, using the SIMPACK multi-body dynamics simulation software to analyze the influences of the deterioration of harmonic local irregularity on locomotive wheel-rail vertical force, on the basis of the locomotive wheel-rail interaction dynamics index by the locomotive vehicle dynamics theory. The simulation results show that when the deterioration of harmonic local irregularity occurs, even if the amplitude of deterioration is small, which will cause serious deterioration of wheel-rail dynamic response and strong shock and vibration of wheel-rail .The larger amplitude of harmonic local irregularity, the greater of the maximum wheel-rail vertical force. When deterioration of the amplitude exceeds a certain value, the maximum of the wheel-rail vertical force exceedes the limit, which will cause derailment. The wheel-rail dynamic interaction increases with the speed increasing. At the same speed (such as 120km/h), harmonic local irregularity settlement deterioration compareing to harmonic local irregularity raised deterioration, the maximum of the wheel-rail vertical force increases 14.4%. Therefore, local irregularity deterioration or the speed of the locomotive should be strictly controlled.

Abstract: The evolutions of physical properties of composites during the curing process of the carbon fibre reinforced resin composite, such as density, modulus, coefficient of thermal expansion, specific heat capacity and thermal conductivity, were analyzed and those evolutions were introduced into the numerical simulation. The new approach to construct the curvilinear coordinate system by streamline equation of steady flow was proposed with the complex curved structure composite as the study object. By using the finite-element method and building the curvilinear coordinate system, the distribution of internal temperature, degree of cure, internal stresses and evolutions of physical properties during the curing process of the composite skin plate of a light aircraft wing were calculated. The deformation of the skin plate caused by the uneven distributions of temperature field and cure degree field, anisotropic thermal expansion coefficients and volumetric shrinkage of resin were calculated in the same model. From the numerical simulation results, it can be concluded that the curing process will be more reasonable and more accurate when the evolutions of physical properties of composites are adopted and the curvilinear coordinate system constructed by streamline equation of steady flow is fully applicable to finite element analysis of composite curved structure.

Abstract: The paper is devoted to a theoretical study of nonlinear wave on a free-surface thin film down an inclined uneven plane. The problem is quite different from that of a viscous films flow along a smooth surface. Thus nondimensional variables are introduced in two ways according to the different relationship of the shallow water parameter and the topography parameter. Further, the zero-order and first-order stream function are derivated on the basis of perturbation method. Finally, the equations which govern the surface height of surface wave on a viscous fluid film down an inclined uneven wall are obtained.

Abstract: Finite element formulation using semiloof shell element for initially stressed vibration of Functionally Graded Material (FGM) plates and shells are presented. The influence of volume fraction index on the vibration frequencies of thin functionally graded plates and shells and variation of temperature on frequency are studied. New results are presented for initially stressed vibration of FGM plates and shells.

Abstract: The flight process often in turbulence. Atmospheric turbulence causes flight bump, long time will cause damage to the aircraft structure fatigue. This paper establishes a model for atmospheric disturbance, flight simulation. Based on the aircraft through all kinds of atmospheric disturbance is studied. The use of embedded database and real-time simulation platform, built a run, in the PC machine can be used for dynamic model for real-time simulation of flight simulator.

Abstract: A probabilistic methodology for modeling fatigue damage accumulation and fatigue life under variable amplitude loading is proposed in this paper. With probabilistic modifications, the calculative consistency between fatigue damage and life is achieved in the model and the load sequence effects are properly accounted for variable amplitude loading. This damage model overcomes the inherent deficiencies in the linear damage accumulation rule but still preserves its simplicity for engineering application. With Monte Carlo sampling method, numerical verification of this model is conducted under two-level spectrum loading. The predicted probabilistic distributions of fatigue life are validated by the fatigue tests on Al-alloy straight lugs.

Abstract: This paper aims at evaluating the damage resistance of thin core sandwich structures, composed of aramid paper honeycomb core and carbon/ epoxy laminates face-sheets subjected to low velocity impact. The impact tests are performed using the instrumented impact-testing machine and resulting impact damages are inspected by Ultrasonic C-scan. In order to study the failure process of the core, which is important in the damage of the structures, flatwise compression test was carried out. Four parameters have been analyzed as follows: maximum load, total energy absorbed during impact, impact dent depth, and impact damage area. Nearly all impact force histories of panels have “twin peaks”, but the second peak of the 3mm-core structure is much larger than the first, which is quite different from others, when impact energy reached 5J, which were caused by the thickness of the core. Impact damages of thin-core sandwich structures are mainly delamination in the face-sheet and core crushing at low energy, and fiber breakage at relatively high energy. The damage processes of different groups of structures are essentially different and the impact resistance of the sandwich structure is greatly influenced by the face-sheet and core thickness.

Abstract: Free vibration of functionally graded materials (FGMs) Euler beam with elastically restrained edges is investigated. The material properties of the FGMs beam vary continuously in the thickness direction according to the power law form. The neutral axis site of the FGMs beam is determined by the static equilibrium condition. The governing equation and boundary conditions are found by applying the Hamilton’s principle. The linear combination of a Fourier cosine series and auxiliary Legendre polynomial function is used to obtain the natural frequencies of the FGMs beam. The effects of the rotational spring stiffness, the translational spring stiffness and the gradient index on the natural frequencies are discussed and analyzed for different material properties and different boundary conditions, indicating that the frequencies are sensitive to the gradient variation of material properties and the spring stiffness.