Tests for classical shock impact are implemented for elements, devices and electronic equipment in order to determine their resistance to single and multiple shocks impacts.

This clause will deal with the following issues:

tests performance

necessary equipment

parameters to be configured

In the process of its use and transportation, every electronic device is exposed to the impact of external factors including shocks (single or multiple) of various nature and impact degree. Shock impact test provides a convenient option for evaluation of samples resistance to shock impact.

First of all, it is necessary to realize that the test purpose is to detect mechanical defects and/or characteristics deterioration as well as to use the obtained information together with the applicable standards and technical documentation for evaluation of sample structural integrity and quality.

Test equipment

Depending on the test complexity, the shock impact on the sample can be performed by shock machine, electrodynamic shaker system, free drop, etc. On impact machines, the shock parameters are controlled by force meter values. In the case of electrodynamic shakers (vibration exciters), the accelerometer values enable acceleration control and diagram representation of acceleration time dependence used for required pulse form creation. As a criterion of pulse form conformity to the tolerance range, one can use vibrational acceleration value obtained by means of comparing acceleration-time curve to the value specified in table 1. In the case, if the sample is tested with the free drop method, the acceleration change is determined by drop height and rebound characteristics (in this method, the sample is exposed to constant acceleration).

Equipment selection

Testing equipment should provide repeatability of the required parameters and actual pulse detection.

Electrodynamic shaker systems enable reproducing all signal shapes specified by the applicable parameters. Shaker parameters determine tests severity rate. In order to perform tests using electrodynamic shaker system, you will also need the following instruments: accelerometer (for vibration parameters control), FFT spectrum analyzer (for shaker (vibration exciter) control and accelerometer signal measurement), software (for automatic tests performance in the specified mode with parameters control).

When choosing the test instruments, one should pay special attention to acceleration, velocity and speed parameters and frequency range of the shaker system, accelerometer, measuring and control equipment. Shaker payload is also an important parameter since some products are to be tested in the package with a weight comparable to that of the product.

Test parameters 

Severity rate and shape of the shock pulse should be determined by the external factors to which the tested object will be exposed during its use and transportation. However, since the samples are often exposed to shocks of various amplitude having complex and random nature, the tests are not used for the precise reproduction of such impacts. Tests parameters are specified by applicable standards and the tolerances are used for obtaining similar tests results in different laboratories.  Parameters value standardization enables dividing products into categories in accordance with their resistance to a particular severity rate specified in the applicable standards.

Definitions:

• shock severity grade — combination of peak acceleration and pulse duration;
• multiple shock severity grade — combination of peak acceleration, pulse duration and shocks number;
• pulse shape — time dependence of acceleration nominal level produced by the shaker and influencing the sample;
• velocity change (of shock acceleration pulse) — absolute value of instant velocity increment from the applied acceleration.

In order to perform tests for single shock impact, one should set the shape (half-sine, trapezoidal or saw-tooth), amplitude and duration of the pulse. Velocity change should be within the limit of 15% of the nominal pulse.

Tests for multiple shocks impact are performed by means of half-sine pulses having certain amplitude, duration, and frequency. Velocity change should be within the limit of 20% from the nominal pulse value.

For shock load impact tests the velocity of the sample in the direction transverse to the impact should not exceed 30% of the velocity in the set direction.

Tests performance 

In the course of shock tests performance, the sample should always be attached to a mounting fixture or a slip table of the testing machine.

During the test for single shock impact for each of three mutually transverse axes of the tested specimen there should be three consequent shocks, i.e. the total number of shocks is 18.

For testing of “element”- type samples for multiple shocks impact the number of shocks (see table 3) should be applied in the direction of three mutually transverse axes of the samples.

When testing equipment for multiple shocks impact the number of shocks (see table 3) should be applied in the direction of three mutually transverse axes of the samples. In the case, if the sample position during mounting and transportation is known and most active shock impact during installation is acting in one direction, then it is possible to apply the corresponding amount of impacts only in this direction.

Parameters selection

The table below specifies acceleration value and pulse duration for single shock impacts in compliance with the applicable standards as well as corresponding acceleration values for each pulse type. Recommended parameters combinations are highlighted.

Table 1. Acceleration, pulse duration and velocity change for different signal types.
Peak acceleration, А, g	Nominal pulse duration, D, ms	Corresponding pulse velocity change Δv, m·s-1
		Half-sine  Δv=(2/Π)AD×10-3	saw-tooth end peak Δv=0,5AD×10-3	trapezoidal Δv=0,9AD×10-3
5	30	1,0	—	—
15	11	1,0	0,8	1,5
30	18	3,4	2,6	4,8
30	11	2,1	1,6	2,9
30	6	1,1	0,9	1,6
50	11	3,4	2,7	4,9
50	3	0,9	0,7	1,3
100	11	6,9	5,4	9,7
100	6	3,7	2,9	5,3
200	6	7,5	5,9	10,6
200	3	3,7	2,9	5,3
500	1	3,1	—	—
1000	1	6,2	—	—
1500	0,5	4,7	—	—
3000	0,2	3,7	—	—

The table below specifies pulse shapes and severity grades recommended for testing materiel resistance to a single shock impact in compliance with the applicable standards.

Table 2. Example of shock pulse shapes and severity grades used for shock impact testing.
Severity grade		Pulse shape	Elements	Equipment
peak acceleration, g	duration, ms
15	11	Saw-tooth with fall at the end, half-sine, trapezoidal		Main test for integrity evaluation in the course of rigging works and transportation. Testing of fixed equipment transported by automobile, railway and air transport inside of protective, shock-proof package.
30	18	Saw-tooth with fall at the end, half-sine, trapezoidal		Test for the integrity of equipment mounting structures. Equipment transported or installed on railway, automobile or air transport.
50	11	Saw-tooth with fall at the end, half-sine, trapezoidal	Elements inside of protective package transported by wheel transport (via highways and railways), subsonic and supersonic aircrafts, merchant ships and light naval vessels.	Equipment integrated into and transported by cross-country vehicles. Equipment undergoing continuous swaying transportation via roadways and railways.
			Elements integrated into or transported by wheel transport (via highways and roadways), pre-sonic and ultrasonic aircrafts, merchant ships and light naval vessels.	Industrial equipment exposed to shocks during mechanical rigging works (dockside cranes, lift-trucks)
			Elements integrated into heavy industry equipment
100	6	Saw-tooth with fall at the end, half-sine, trapezoidal	Elements inside of protective package transported by cross-country vehicles.	Single shocks during riggings works (in the course of automobile and railroad transportation)
			Elements integrated into equipment, transported by or installed into cross-country vehicles.	Launching shocks, shocks caused by missile separation of spaceships, aerodynamic shock, impact, caused by atmosphere entry.
			Elements incorporated into devices for pre-sonic and ultrasonic aircrafts. Elements incorporated into devices undergoing continuous transportation in an unfixed state by means of automobile or railroad transport.	Portable equipment
500	1	Half-sine	Structural integrity tests of semiconductor devices, integrated circuits, microchips and chips assemblies	Impacts caused by underwater, surface and aerial explosions
1500	0,5	Half-sine	Structural integrity tests of semiconductor devices, integrated circuits, microchips and chips assemblies

The table below depicts severity grades recommended for sample tests for multiple shocks impacts in accordance with the applicable standards.

Table 3. Examples of severity grades for multiple shocks impact tests for various applications in accordance with the applicable standards
Severity grade			Elements	Equipment
Peak acceleration, g	Duration, ms	Number of shocks for each direction
10	16	1000	Fragile devices transportation via roadways (excluding cross-country transportation)	Normal structural integrity tests of the equipment installed or transported by wheel transport
15	6	4000	Minimal integrity test of general purpose devices exposed to main mechanical stress during transportation	Stationary equipment and equipment installed on mobile facilities (for instance, in close vicinity to a power plant)
25	6	1000	—	Equipment installed on or transported by all-purpose vehicles. Devices installed on rigging machinery (dockside-cranes, lift trucks)
40	6	1000	Transportation of devices in factory package for further use in non-stationary equipment	Equipment which can be transported in a non-fixed state by wheel transport (via roadway or railroad) in the course of ad-hoc transportations (for instance, during delivery)
40	6	4000	Devices for further integration into mobile facilities equipment	Mobile equipment transported by all vehicle types (via railroad, roadway, and cross-country) in a non-fixed way
100	2	4000	Electron tube and spring valves (to be used in key-switches, phones, switchboards)

For samples with weight below 100 kg, the recommended severity grade is 25 and 40 g.  For heavier samples – 10 g.

The table below specifies nominal values of velocity change for various severity grades during samples testing for multiple shocks impact.

Table 4. Acceleration, pulse duration, corresponding velocity change
Peak acceleration, g	Pulse duration, ms	Corresponding pulse velocity change Δv, m·s-1
10	16	1,0
15	6	0,6
25	6	0,9
40	6	1,5
100	2	1,5

See also

The Software Classical shock integrated into special ZETLAB Software complex is used for vibration shaker control and enables testing of the samples resistance to shock vibration impact. The Software is used for vibration shaker parameters control in accordance with the applicable requirements.

Article “Shock spectrum and Duhamel integrals”