Direct answer
Look at three things only: whether the shaker's force rating and table size can take your sample plus fixture, whether combined temperature-vibration testing is available, and which spectral profiles the controller supports. The combined weight of sample plus fixture exceeding the table rating is the most common cause of re-work — fixtures often weigh as much as or more than the sample.
Three hard criteria
Force rating. Required force ≈ (sample mass + fixture mass) × target acceleration × safety factor. The safety factor is usually taken as 1.3 or above. It is easy to count only the sample, whereas in practice the fixture is often the deciding term.
Table size and fixture design. A table that is too small cannot take the sample, and a poorly designed fixture produces a non-uniform table response — the control point and a single measurement point can differ by several dB. Ask whether the laboratory designs fixtures in-house, or has an acceptance process for customer-supplied fixtures.
Frequency range. Automotive random vibration generally has to be covered up to 2000 Hz. The low end tests displacement capability, the high end the first resonance of the table.
Is combined temperature-vibration testing mandatory?
More and more automotive projects require temperature and vibration applied simultaneously, because it is closer to real conditions. Doing them separately (vibration first, then temperature cycling) underestimates certain failure risks, particularly solder joint fatigue and material interface failures.
If the customer standard says "combined vibration and temperature", you can only use a laboratory with combined capability — an ambient-temperature shaker cannot do it.
Control and measurement: four questions to ask
- Where the control accelerometer is mounted (table / fixture / sample) — the results differ substantially by location
- Whether there are enough monitoring channels (multi-point monitoring is the only way to find local response amplification)
- Whether multi-point averaging control is supported
- How the shock waveform is generated (drop type or electrodynamic) and the peak level reachable
Three mounting methods, three different results
- Rigid mounting: bolted directly to the table, high transmission efficiency, conservative levels.
- Simulated vehicle bracket: uses the real bracket and damping parts, closer to the vehicle, but the fixture itself becomes a variable.
- Purpose-built fixture: designed for the test, requiring modal verification so that fixture resonance does not contaminate the data.
Whichever is used, the mounting method and fixture details must be stated in the report. Otherwise the customer cannot reproduce it and the data cannot be compared.
Common failure modes to expect
- Solder joint cracking (thermal expansion mismatch plus vibration fatigue)
- Connector micro-breaks and terminal fretting corrosion
- Harness chafing against structural parts, wearing through the jacket
- Bracket resonance leading to fracture
- Bolts loosening (insufficient preload)
Where we stand
TMC LAB holds both CMA and CNAS accreditation and is equipped for vibration, shock and combined temperature-vibration testing, all performed in our own laboratory. Send us the sample weight, its envelope, the target profile and the customer standard, and we will calculate the force requirement first and then confirm the setup.
Related pages for this question
Last updated Technical criteria follow the current standards and the agreed scope; please confirm the specific project with the lab.
