2024-03-21 
169
The Purpose ,Influence Mechanism and Failure Mode of The Random Vibration Test
Most of the vibrations encountered by products in transportation and actual use are random vibration. For example, the vibration of the astronauts and missiles during the launch and booster stage; the noise and pneumatic noise of the rocket engine cause the vibration of the structure; Vibration and atmospheric turbulence causes the vibration of the wings; the vibration of the aircraft landing and taxiing; the vibration generated when the vehicle is driving on an uneven road; the variety of vibrations produced by the ship are random vibration. Therefore, the trial of random vibration test machine can truly reflect the product's anti -vibration resistance.
Compared with sine vibration, the frequency domain of the random vibration test machine is wide, and there is a continuous spectrum. It can motivate the product at the same time. Frequency or continuous frequency sweeping simulation of the above vibration test is more severe, more real, and more effective. In addition, the dynamic characteristics of the product and the transmission function of the product with random vibrations are simpler and superior to use sine vibration methods.
Random vibration and sine vibration can also cause wire friction, loosening of fasteners, and stuck in activity, thereby destroying the connection, installation and fixing of the product. When the stress caused by random vibration incentives is too large, the structure will cause cracks and breaks, especially more significant in the resonance state. For a long time of random vibration, the cumulative damage caused by alternating stress will cause fatigue damage to the structure. Random vibration can also lead to poor contact contacts, contact or short circuit of charged components, welding joints off, wiring breaks, and generating strong electricity noise, which affects the normal work of the product, reduces product performance, fails, and even fails.
Description of random vibration test machine: In the random vibration test, because the mass of the vibration is in an irregular motion state, it will never repeat it. A series of measurements are made. cycle. At any determination, the amplitude, frequency, and phase cannot be known in advance, so it is impossible to describe the combination of simple cycle functions and functions.
Random process: According to the shape of the spectrum density spectrum, that is, according to the frequency structure of the random process, the random vibration of the product scene is mainly in the form.
1) Broadband random vibration
Broadband random vibration test machine refers to the vibration that can be distributed in a wide range of frequency range. Generally, the carrier tools, especially air carrier tools, such as jet aircraft, the vibration generated is a broadband random vibration.
2) Narrow band random vibration
Narrow -band random vibration refers to the vibration that can be distributed in a narrow frequency range, such as propeller aircraft. Due to the rotating pressure field driven by the propeller leaves, the narrow band is random vibration. The frequency of the leaves and its harmonics (generally to the 4th level), and its narrow bandwidth is ± 5%(drift) of the frequency (central frequency) and its various harmonics.
3) Broadband+Narrow Random Vibration
In addition to the random vibration of narrow bands, the most important thing is the broadband random vibration caused by various vibration sources. If it is installed on the swelling belt and through the track: the transportation of the car: the transportation of the vehicle, it usually receives a random vibration with broadband+narrowband. Broadband random vibration comes from the basic movement, support system, and pavement of the vehicle. The narrow -band random vibration comes from the motion of the crawler to hit the ground.
4) Broadband random vibration+cycle vibration
Broadband random vibration+cyclical vibration refers to superimposed sine vibration on the broadband random vibration. The vibration of helicopter aircraft is often superimposed on the signs of sinosatutra on the basis of the broadband random vibration. The broadband random vibration test machine comes from various vibration sources of helicopter aircraft. The sine vibration is generated by the rotating parts of the helicopter, such as the vibration of the main rotor, tail rotor, engine and gearbox.
The national standards and IEC standards, the random vibration of the broadband+narrowband and the random vibration of the broadband+cycle vibration is called a hybrid incentive vibration. In the hybrid inspiration vibration, the random component is represented by acceleration spectrum density, and the acceleration amplitude of sine component is represented by the acceleration amplitude.
