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Equipment Requirements For Shock/Bump Tests

Requirements for Shock Test Machine


International standard IEC68-2-27 requires the following characteristics of the test equipment during shock test (that is, when the test machine and fixture are loaded with test samples):


(1) Basic pulse waveform: During the test, the shock test machine should be able to generate the specified basic pulse waveform (such as half sine pulse, trapezoidal pulse and sawtooth pulse at the back peak), and meet the requirements of the standard for the difference of various waves.


(2) Tolerance of speed variation: for all pulse waveforms, the actual speed variation should be within 15% of its corresponding nominal pulse value. When the speed change is determined by the integration of the actual pulse, it should be integrated from 0.4D before the pulse to 0.1D after the pulse. Here, d is the nominal pulse duration. For all pulse waveforms in the standard, the actual speed change is specified, which can be determined by many methods: for the impact pulse that will not cause rebound motion, it is determined by the collision speed; For free drop tester, it is determined by the height of drop and rebound. Can be determined by the integration of acceleration-time curve, etc. One of the purposes of specifying the speed change and its corresponding tolerance requirements is to promote the laboratory to achieve the same impact pulse as the nominal pulse, that is, to be in the center of the pulse tolerance range. Only in this way can the reproducibility of the test be guaranteed. The other purpose is related to the impulse response spectrum of the pulse.


(3) Lateral movement: the positive or negative peak acceleration perpendicular to the predetermined impact direction at the detection point should not exceed 30% of the nominal pulse peak acceleration in the predetermined direction.


Requirements for Shock Test Equipment


The international standard IEC68-2-29 requires the following characteristics of the test equipment during the collision test (that is, the test machine and fixture are equipped with test products):


(1) Basic pulse waveform: During the test, the shock test machine  should be able to generate the prescribed half-sine impact pulse, and meet the wave shape difference requirements specified in the standard.


(2) Repetition frequency: Repetition frequency should make the relative motion in the sample between two collisions basically zero, and the acceleration value at the detection point should be within the limit specified in the standard. Usually 1 ~ 3 times per collision.


(3) Tolerance of speed change l The actual acceleration change should be within 20% of the corresponding nominal pulse value. When the speed change is determined by the integration of the actual pulse, it should be integrated from 0.4D before the pulse to 0.1D after the pulse. As far as shock test is concerned, the actual speed change must be determined. The methods to determine the speed change are: for the pulse that will not cause rebound movement, it is determined by the collision speed, or by the integration of acceleration-time curve, etc. One purpose of specifying the tolerance requirements of the speed change and its pulse is to promote the laboratory to achieve the same impact pulse as the nominal pulse, that is, the pulse is in the center of the tolerance zone, so that the test can maintain high reproducibility. Another purpose is related to the impulse response spectrum, that is, when the normalized frequency FD = 0.2, the residual response spectrum is approximately proportional to the velocity variation of the pulse.


(4) Lateral movement: At the detection point, the positive or negative peak acceleration perpendicular to the predetermined direction should not exceed 30% of the nominal peak acceleration of the pulse in the predetermined direction. When the tolerance of pulse waveform, velocity variation, repetition frequency and lateral movement meet the requirements, the test method specified in the standard has high reproducibility, and the same is true for the shock test method.


Conditions and Functions of Shock/Bump Test Equipment


(1) It should be able to bear the specified load, and have a workbench with a considerable area for installing test samples.


(2) It should be able to produce the specified impact pulse waveform, and meet the requirements of wave shape tolerance and speed change tolerance.


(3) It should be able to adapt to certain environmental conditions including temperature, relative humidity, surrounding media, etc.


(4) After installation, the shock platform should have a solid foundation, and its working surface should have the specified levelness.


(5) Its structure should be able to withstand the specified impact acceleration.


(6) Should be able to work for a long time, the noise should be as small as possible. The shock/bump test methods of some test samples are relatively simple, so the conditions and functions of the corresponding test equipment can be appropriately reduced. In a word, the conditions and functions of the shock platform increase or decrease with the complexity or simplicity of the test method, which is also a problem that users should pay attention to when selecting and using the shock platform.

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