Shock testing outputs a sharp transfer of energy to a mechanical system to test the system’s capability to survive a drop, hit, impact, fall, explosion, or any other source of transient vibration. Classical shock pulses are the standard method of generating shock.
The following shock test procedure outlines the necessary steps to running a basic shock test.
Shock Testing Software
- Define the test item – The test item size, weight, and construction help the engineer determine the correct test setup. The engineer can also use its predicted in-service damage to define the test’s acceptance criteria (the desired condition of the test item after testing).
- Identify the test criteria – The testing software uses a test profile to output the shock pulse to the test item. The engineer will use a test standard to create the test profile or use a pre-defined profile within their test laboratory.
a. Select a shock test standard – A shock test standard provides direction for setting up a test. Its parameters help the engineer determine which equipment is suitable to use and how to configure the test in the software. Selecting a shock test standard can be influenced by several factors:
- An industry may expect engineers to use an accepted standard within their field.
- Regulations may require a test laboratory to conform to a specific standard.
- A company may prefer a specific test standard that they know imposes enough damage to ensure the quality of their product.
- An engineer may customize a test standard that meets industry and internal requirements.
- Well-known shock test standards include MIL-STD-810 Method 516, DO-160 Section 7, and IEC 60068-2-27. ISTA, ASTM, and SAE also have shock test methods for various product types.
b. Identify the test profile – The engineer may not need a reference test standard if their test laboratory has a pre-defined test profile. It is still good practice to review the profile before running the test.
- Characterize the shock pulse – The parameters of a shock pulse are a helpful reference when setting up equipment. A test standard may require the engineer to choose from several parameter options; for example, ASTM D4169 − 16 includes three test intensity levels. It may also call for multiple shock pulses with different amplitudes and durations.
- Set up the equipment – Classical shock tests can run on mechanical shock machines, electrodynamic shakers, or servo-hydraulic shakers. When selecting a system, the engineer must consider the test item mass, the peak amplitude of the pulse, and the defined pulse shape.
Accelerometers are typical sensors for shock testing. Depending on the characteristics of the shock pulse, the setup may require different accelerometers to measure the test results.
a. Pre-test considerations – Considering the parameters of the shock pulse, the engineer should:
- Design a test fixture without resonances within the frequency range of the test
- Determine the appropriate mounting location for the accelerometer(s)
- The engineer should also mount an accelerometer to the shaker to monitor system limits.
b. Test setup checklist – When prepared to set up the equipment, the engineer should follow Vibration Research’s “Vibration Test Setup Checklist” as follows:
- Turn off all equipment before making any adjustments to the system
- Turn down the amplifier Gain
- Check cable connections
- Secure the transducers
- Turn on and check equipment
- Verify the system parameters in the software
- Turn on the amplifier Gain
- When possible, run the VibrationVIEW System Check Procedure (pass/fail) prior to testing
- Define the pulse in the software – The engineer will define a new test profile in the software. In VibrationVIEW, the minimum information needed to run a shock test is as follows:
- Pulse width
- Pulse type
- Peak amplitude
- Pulse direction
- Total pulses
- Delay between pulses
- Pulse limits
If running the test on an electrodynamic or servo-hydraulic shaker, the engineer may also add pulse compensation.
Example Test Profile
The following is an example test profile from the VibrationVIEW Syllabus.
- Output 10mS wide
- Positive Trapezoid shock pulse with a peak amplitude of 5G
- Trapezoid ramps up in 2mS
- Trapezoid ramps down in 2mS
- Square shape
- Allow up to 20% of the peak acceleration prior to the pulse
- Allow up to 30% of the peak acceleration after the pulse
Run for 100 pulses at 100% with 1-second pulse intervals
- Starting drive limits:
- Max Output: 2V
- Max System Gain: 10V/G
- Running drive limits:
- Max Output: 2V
- Max System Gain: 10V/G