Reliability test: sinusoidal vibration test method and influence

Date：2021-07-27 16:07:00 Views：2412

The vibration test is mainly environmental simulation, and the test parameters are frequency range, vibration amplitude and test duration. The impact of vibration on products includes: structural damage, such as structural deformation, product crack or fracture; Product function failure or poor performance, such as poor contact, relay misoperation, etc., are not permanent damage, because once the vibration is reduced or stopped, the work can return to normal; Technological damage, such as loose screws or connectors and desoldering. From the development trend of vibration test technology, multi-point control technology and multi machine combined excitation technology will be adopted.

In the sinusoidal vibration test method, two test methods "sweep frequency test" and "constant frequency test" are specified.

 1. Sweep frequency test

Frequency sweep test refers to the test in which the magnitude of one or two vibration parameters (displacement, velocity or acceleration) remains unchanged while the vibration frequency continuously changes back and forth within a certain range. Linear scanning is linear, that is, how many Hertz are scanned per unit time, in Hz / s or Hz / min. this scanning is used for the test of fine finding resonant frequency

The logarithmic scanning frequency changes according to the logarithm. The scanning rate can be OCT / min and OCT is octave. If the upper limit frequency FH, lower limit FL, FH / FL = 2n, n is n octaves from the lower limit frequency to the upper limit frequency. The formula for n is:Logarithmic scanning means that the number of frequency octaves scanned at the same time is the same. For example, from 5-20hz is two octaves, and from 500-2000hz is also octaves. In the case of logarithmic scanning, the scanning time is the same. That is to say, during logarithmic scanning, the low-frequency scanning is slow and the high-frequency scanning is fast (of course, this refers to the frequency range scanned per unit time). Sometimes the logarithmic scan rate is also used for DEC / min, which means how many tens of octaves are scanned per minute. Frequency sweep test is mainly used for:

a) Check the product vibration frequency response (i.e. initial resonance inspection), determine the resonance point and working stability, and find out the product resonance frequency for vibration resistance treatment.

b) Frequency sweep resistance treatment: when the product has no resonance point within the use frequency range, or there are several unobvious resonance points, frequency sweep resistance treatment must be carried out. The frequency sweep treatment method adopts positioning shift amplitude in the low frequency band, and logarithmic continuous scanning of constant acceleration amplitude in the high frequency band. The crossover frequency is generally 55-72hz, and the frequency sweep rate is generally one octave per minute.

c) Finally, resonance inspection: use the same method of product vibration frequency response inspection to check whether each resonance point of the product has changed after vibration resistance treatment, so as to determine the reliability of the product after vibration resistance treatment.

2. Constant frequency test:

Fixed frequency test refers to the test of different orders of vibration parameters at the specified fixed frequency point. It is mainly used for:

(1) Resistant to resonance frequency processing. Apply the vibration with the specified vibration parameter amplitude to the obvious resonance frequency point found during the product vibration frequency response inspection, so as to evaluate the ability of the product to withstand resonance vibration.

(2) Treatment of resistance to predetermined frequency: when the vibration frequency of the product under known environmental conditions is used, the vibration test of resistance to predetermined frequency can be adopted. The purpose is to assess the ability of the product to withstand vibration at a predetermined dangerous frequency.

The impact of vibration on products mainly includes:

(1) Impact on structure

This effect mainly refers to deformation, bending, crack, fracture and mutual impact between components. This kind of damage can be divided into the damage caused by the stress caused by vibration exceeding the limit that the product structural strength can bear, and the damage caused by fatigue of the product caused by long-time vibration (such as the vibration of more than 107 stress cycles). This kind of damage is usually irreversible.

(2) Impact on Performance

This effect mainly refers to the abnormal action of moving parts, poor contact of contact parts, misoperation of relays, increased noise of electronic devices, flashing of indicator lights, etc. caused by vibration, resulting in abnormal and unstable operation, even failure and failure of operation. The severity of this effect often depends on the magnitude of vibration, and this kind of damage usually does not belong to permanent damage. Because in many cases, once the vibration stops, the work can return to normal. It can be seen that this damage is often reversible.

(3) Effect on process performance

This effect mainly refers to the loosening of screws, disconnection of connectors or solder joints, etc. This damage usually occurs within a short vibration time (e.g. half an hour).

Conclusion: the structural damage, performance degradation, poor work and failure of electronic and electrical products caused by vibration in China also occur frequently, and they are relatively serious. Therefore, sinusoidal vibration test is an effective method to determine whether the product can withstand the predetermined vibration conditions and work reliably under the predetermined vibration conditions without story and performance degradation.