Key Engineering Materials Vols. 326-328

Abstract: As the fluid dynamic bearing spindles are to be actively adopted to various small form factor mobile applications, mechanical specifications for the motors have been aggressively changed to pursue the fierce information technology sector market trend. One of the major technological challenges for the spindles to be successfully employed in the applications is the reduction of power consumption since the most of the mobile applications operate with a limited power source at relatively lower voltage. Recognizing implication of the power consumption that of course affects stiffness of the spindle, few of options for mechanical designers are available but either lowering rotational speed or adopting thinner lubricant. In the present work, a novel design solution for alleviating side effect of the lower stiffness spindle is introduced and verified.

Abstract: High-speed machining (HSM) is very useful method as one of the most effective manufacturing processes because it has excellent quality and dimensional accuracy for precision machining. Recently micromachining technologies of various functional materials with very thin walls are needed in the field of electronics, mobile telecommunication and semiconductors. However, HSM is not suitable for microscale thin-walled structures because of the lack of their structure stiffness to resist high-speed cutting force. A microscale thin wall machined by HSM shows the characteristics of the impact behavior because the high-speed cutting force works very shortly on the machined surface. We propose impact analysis model in order to predict the limit thickness of a very thin-wall and investigate its limit thickness of thin-wall manufactured by HSM using finite element method. Also, in order to verify the usefulness of this method, we will compare finite element analyses with experimental results and demonstrate some applications.

Abstract: This study contains an estimation of the dynamic buckling load for the spacer grid of fuel assembly in pressurized water reactor. Three different estimation methods were proposed for the calculation of the dynamic buckling loads of spacer grid. The dynamic impact tests and analyses were performed to evaluate the impact characteristics of the spacer grids and to predict the dynamic buckling load of the full size spacer grid. The estimation results were compared with the test results for the verification of the estimation methods.

Abstract: This paper presents a discrete analysis approach to investigate performance of the DMF. An arcspring installed between the flywheels is modeled as n - discrete elements. Each element consists of mass, spring and nonlinear friction element. The nonlinear friction model is proposed to describe Stribeck effect and viscous friction depending on the relative sliding velocity. The DMF performance such as hysterisis characteristics are investigated by comparing the experimental result. In addition, the torque characteristics transmitted to the driveshaft are evaluated by comparing the test result from manual transmission bench tester. It is found that discrete DMF model described the automotive driveline behavior closely. It is also found that the friction characteristics of the arcspring depends on the relative sliding velocity between the friction surfaces, which varies depending on the relative position of the DMF arcspring.

Abstract: The instability of the roadway is a general problem for most of the deep mine roadways due to high geo-stress and large deformation, which require that the more reasonable and effective support measures are designed and employed. By applying the 3-D explicit finite difference software FLAC3D, this paper establishes the numerical calculation model of a roadway located in about 700m depth based on the geologic condition of the site which the roadway is in as well as the results of the in-situ stress measurement and the laboratory tests for the physical-mechanical properties of rock. Furthermore, three different support scenarios are raised and the optimum one is determined by calculating and analyzing the distribution of the plastic zone and displacement field in the rock surrounding the roadway with the above three scenarios.

Abstract: An experimental modal analysis is the process to identify structure's dynamic characteristics. For investigating vibrational characteristics of cylindrical shell with multiple supports, modal testing is performed using impact exciting method. The frequency response function(FRF) measurements are also made on the experimental model within the frequency range from 0 to 4kHz. Modal parameters are identified from resonant peaks in the FRF’s and animated deformation patterns associated with each of the resonances are shown on a computer screen. The experimental results are compared with analytical and FEA results.

Abstract: The experimental studies on the dynamic buckling of the perfect bars with three kinds of lengths under impulsive axial compression were completed and the boundary condition of clamped-fixed was realized firstly in present studies. The time-history curves of axial strain of bars under different impact velocity were recorded. According to the magnitudes of the axial strain and bifurcate time, the quantitative relation of dynamic buckling load and critical bifurcate length are achieved; according to the curves recorded, the lateral velocity of bars are computed also. The experimental results show that the dynamic buckling load of the bar is distinctly greater than the static one, the front of stress wave can be regarded as fixed and the effect of the axial stress wave in the dynamic buckling of bar must be considered.

Abstract: In this paper, experiments are conducted to determine the non-ideal boundary conditions (BCs) of example beam structures. The spectral element (SE)-model is used for the beam structures, and the non-ideal BCs are represented by the frequency-dependent effective boundary springs. The boundary spring constants are then determined from the measured FRF-data. It is shown that the vibration responses analytically predicted by using experimentally identified BCs are very close to the measurements.

Abstract: A spectral element (SE)-model based frequency-domain method was proposed in the previous work [1] to identify the dynamic characteristics of a structural joint within onedimensional structures. In the present work, experimental work is conducted to verify the proposed method. The bolt-joint is represented by an equivalent joint model with four parameters, and the four parameters are determined by experimentally measured FRF data. The experimentally identified bolt-joint is shown to provide the dynamic responses which are in good agreement with measured dynamic responses.

Abstract: Split Hopkinson pressure bar (SHPB) and one-stage light gas gun are utilized to study the dynamic mechanical properties of reinforced concrete (RC) subjected to shock loading. The former experimental results show that the strength and stiffness of RC decrease but the ductibility increases with increasing the volume fractions of reinforced fibers due to more damage in the concrete and interface. For the latter experiment, three stress-time curves are recorded by three manganin pressure transducers embedded in the targets. With the stress-time records, complete histories of particle velocity and strain etc. can be obtained at any point within the gauged regions of RC using the path line principle of Lagrangian analysis method. The stress-strain curves of RC present stagnant-return properties. And some other dynamic properties can be gained, such as strain rate hardening, wave shape dispersion effects and the rheological properties of the concrete.