The requirement for reproducing (referring to approximate simulation) random vibration in the laboratory is the reproduction of the random vibration self-power spectrum, and the parameters describing a power spectrum are:
1) Frequency range
The frequency range of the power spectrum test first depends on the working environment of the product installation platform. The highest and lowest excitation frequencies given to the product on the installation platform must be included in the frequency range of the product’s broadband random vibration test. For example, the national military standard GJB150.16A stipulates the vibration environment test conditions for military equipment laboratories:
a) The frequency range of the ship is 1~100Hz;
b) The frequency range of the railway cargo is 1~350Hz;
e) The frequency range of helicopter is 10~500Hz;
d) The frequency range of the jet aircraft and propeller aircraft is 15~2000Hz
e) The frequency range of general low-limit integrity random vibration environment is 20~2000Hz
2)Acceleration power spectral density (g2/Hz)
Acceleration power spectral density (ASD) is usually referred to as power spectral density (PSD). The unit of power spectral density is (g2/Hz). Power spectral density (PSD) is the most important parameter in random vibration testing. It is marked on the total energy of random vibration within a certain frequency range (bandwidth). If the frequency bandwidth approaches zero, the power spectral density is the mean square value of all acceleration peaks that occur at this frequency point within an infinite (-∞~+∞) statistical average time.
3)Total root mean square (RMS) acceleration ARMS
The total root mean square (RMS) acceleration is a parameter that measures the total energy of a random vibration. It is the square root value of the integral of all areas under the random vibration power spectrum. The unit is (g or m/s2). Since the total root mean square acceleration does not contain “spectral” information and cannot express the distribution of vibration energy on the spectrum, this parameter cannot be used to specify and control random vibration tests. However, during the random vibration test, the total root mean square acceleration is a very useful parameter, and its functions are as follows:
a) Used to monitor the status of vibration in real time
b) Used to check errors in power spectrum settings for testing
c) Used to calculate the excitation force required for vibration tests
d) Auxiliary monitoring of the control accuracy of the power spectrum in vibration tests
4) Random vibration duration
The duration of a random vibration test depends on the type of random vibration test. It also depends on the magnitude of the test. The main types of random vibration tests include “functional test”, “durability test” and “life test”
a) Functional test: It is to assess whether the function of the product fails under vibration conditions and whether the performance index drops to the point that it cannot complete the work task.
b) Endurance test: Focus on the assessment of product structural damage caused by vibration environment, so the endurance test time is closely related to the test method. When random vibration is used to perform endurance tests, the duration of the test can be shortened by increasing the magnitude of the functional test.
c) Life test: Pay attention to whether there is failure during the entire life cycle under the action of vibration or other environmental conditions, the maximum number of failures, the maximum number of repair failures