Some Techniques Of Environmental Vibration Test Research

Ambient vibration test is an important research means in the assessment and evaluation ofproduct vibration environmental adaptability. In the process of test implementation, determination andinduction of vibration test conditions、fixture design and layout of sensors or other conditions directlyaffect the authenticity、reliability and validity of the product vibration resistance ability evaluation.This paper focus on the existing problems of environmental vibration test to study in the followingaspects, including:(1) In order to determine the vibration test conditions with processing of the measured data ofequipment vibration environment, the basic principle in induction of random environment measuredata was deduced from the theory. Then, based on equation of cumulative of frequency function underthe normal school, combining with the theory of unbiased evaluation, a new method was derived forinduction of random environment measure data under the given probability value. Consequently, themethod was used for dealing with data coming form an equipment, and an induction curve wasconcluded from the natural measure data of vibration environmnet.(2) Determining the acceleration factor which describes the equivalent relation between the timeand vibration level is one of the important steps during the vibration durability test. In order to obtainthe acceleration factor, based on the law of palmgren-miner fatigue cumulative damage and the theoryof cumulative damage under stationary narrow and wide band stress, the calculation equation ofacceleration factor is derived. The accelerated life equation, combining with the accelerated lifetesting theory, is used to design the prototype of the accelerated life test. The test is implemented, thenthe test data is verified by weillbull model and processed by least square method, finally the specimenmaterial vibration acceleration factor can be obtained.(3) In order to obtain the optimal acceleration sensor placing location, according to the electricvibration table multi-point control principle and the characteristic of transfer function, a sensorplacement optimization calculation model was established. A fixture was taken as an example toestablish it’s finite element model, nastran software was used to get the transfer function. Then anoptimal acceleration sensor placing location was obtained according to the optimization modelpreviously mentioned. Finally, the response of the connection place between the fixture and a testsample was measured with the fixture vibration test. The test results indicated that the mean squaredeviation of the response acceleration obtained with the optimization method is significantly smallerthan that with the traditional method. (4) In order to solve the phenomenon of the severely uneven vibration magnitude passed by thetest fixture to the Specimen and deviation from the reference spectral acceleration rms value,according to the electric vibration table multi-point control principle and the characteristics of afixture frequency response, a fixture design optimization model was established. Taking a specimenfixture design as an example, the fixture FRF value was calculated by Nastran software, then theoptimal design parameters of fixture was obtained according to the optimization model previouslymentioned. Optimization results indicated that the mean square deviation of response accelerationand the acceleration rms variation range obtained the optimization method are all significantly smallerthen that with the traditional method, while the vibration test results show that the variation range ofthe acceleration rms measured on the transfer point in the vibration test is basically the same with theresult coming form the optimization calculation.(5) In order to obtain the combined simulation model accurately in the design of fixture andlayout of sensors in the process of simulation, the calculating formula of real contact area in thecombination party was inferred with the Hertz contact theory and Greenwood-Williamson model.Then, the theory of finite element nodal rigid connecting mode was established. A clamp assembly ofa printed circuit board was taken as an example to establish the finite element simulation model, bycomparing the non translational first four modes measured modal with the modes of the simulationcalculation and calculating the MAC value, the fixture assembly model is demonstrated that it is rightand can meet the engineering need.