Series Of Modal Tests Research Articles

Investigation of a cutting state-independent method for identifying in-process frequency response functions of the micro milling system

Conveniently obtaining the in-process frequency response functions (FRFs) of micro milling tool is a very difficult task due to the small diameter. This article presents a method to identify the in-process FRFs of micro milling tool based on actual cutting tests, which can be at either stable or chatter cutting state. According to mode superposition principle, the in-process FRFs are predicted by integrating the mode shape with the pole, which includes damping ratio and natural frequency. The in-process mode shape of tool is modeled as being consistent with that corresponding to static state, and thus, it is calculated from the tool’s static state by combining receptance coupling substructure analysis (RCSA) with Timoshenko beam theory. The poles of in-process FRFs are acquired by modal analysis of the response signals from actual micro milling tests. To do this, cutting forces are used as excitation signals, and the velocities of tool are selected as response signals and they are measured from actual micro milling tests. With the aid of editing cepstrum and hampel outlier processing methods, a filtering method is established to remove the harmonic and useless chatter components involved in the response signals. As a result, the finally obtained FRFs are not influenced by the noises in the measured response signals, and the effectiveness of this method is verified by a series of modal tests and micro milling tests.

Structural similitudes for the vibration characteristics of concave thin-walled conical shell

A structural similitude is proposed for the analysis of the vibration characteristics of concave thin-walled conical shell. The similitude laws are derived by invoking the least square method and transition models with different proportional input parameters. Analytical calculations show that satisfactory similitude in terms of natural frequency scaling can be achieved. Based on the analytical study, a series of modal tests is performed on the three-scaled thin-walled conical shell to verify the scaling laws. Emphasis is especially predicting and verifying the vibration characteristics of concave conical shell through the standard thin-walled conical shell to avoid manufacturing limitations.

Experimental Investigation of Dynamics of Assembly with Typical Mechanical Joint

Mechanical joints have a significant influence on the dynamics of assembled structure due to its discontinuity, uncertainty, frictional contact and micro-slip along the interface. To study the effect of mechanical interface on vibration behavior of industrial product, it is necessary to capture vibration data and investigate modal properties. In order to study effects of typical mechanical joints, double plates coupled with bolted joint are manufactured. Corresponding welded specimen was also manufactured for comparison and reference. Specimens were suspended by two flexible nylon cords for a free–free boundary condition and series of modal tests were carried out. Experimental results reveal that the preload in bolted joint affects the vibration behavior of assembly greatly, and the dynamic stiffness and natural frequency could be enhanced by increasing preload values of specimen. Bolted joints give rise to more frictional damping capacity within lower preload range in this test and welded specimen shows up much higher frequency and similar damping ratio.

비닐하우스 아치구조의 모달실험

To determine the static buckling loads and evaluate the structural performance of slender steel pipe-arches such as for greenhouse structures, a series of modal tests using a fixed hammer and roving sensors was carried out, by providing no load, then a range of vertical loads, on an arch rib in several steps. More attention was given to an internal arch where vertical and horizontal auxiliary members are not placed, unlike an end arch. Modal parameters such as natural frequencies, mode shapes and damping ratios were extracted using more advanced system identification methods such as PolyMAX (Polyreference Least-Squares Complex Frequency Domain), and compared with those predicted by commercial FEA (Finite Element Analysis) software ANSYS for various conditions. A good correlation between them was achieved in an overall sense, however the reduction of natural frequencies due to the existence of preaxial loads was not apparent when the vertical load level was about up to 38% of its resistance. Some difficulties related to the field testing and parameter extraction for a very slender arch, as might arise from the influences of neighboring members, are carefully discussed.

Line-of-sight Jitter Of SELEX Optical Terminals,Analysis And Verification Activities

The Semi-Conductor Laser Inter-Satellite Link Experiment (SILEX) is a very innovative program of the European Space Agency. Two optical terminals, PASTEL and OPALE, respectively on the SPOT4 satellite (low Earth orbit) developed by MATRA MARCONI SPACE under CNES contract, and on the ARTEMIS satellite (geostationary) developed by ALENIA under ESA contract, must be pointed to each other to within 2 microradians in the communication phase. To achieve this very high accuracy pointing, the Pointing, Acquisition and Tracking (PAT) system of each terminal provides high bandwidth (above 100 Hz), fine control capabilities so as to decrease the pointing jitter induced by host spacecraft disturbances. In this frequency band, the spacecraft and the optical terminal are no more rigid bodies, and the coupling of structural modes is a performance driver that requires detailed analysis and verification tests. The aim of the paper is to describe the activities carried out at MATRA MARCONI SPACE to predict and verify on the ground the high frequency line-of-sight pointing performances of the SILEX terminals, essentially focusing on the case of PASTEL. Due to the complexity of the problem (flexible bodies in a high frequency range, large angle azimuth/elevation motions of PASTEL, PAT control loop, on-board disturbing environment...), the pointing verification logic was built on a combined tests/analyses approach. A series of modal tests have been performed at terminal level, completed by a microvibration test on the SPOT4/PASTEL assembly. Their exploitation has led to Finite Element Model update, and definition of worst case transmissibility envelopes. In addition, the detailed characterisation of the main on-board disturbance sources (SPOT4 Reaction Wheels and Oblique Viewing Mirror mechanism) has provided the Transactions on the Built Environment vol 19, © 1996 WIT Press, www.witpress.com, ISSN 1743-3509