Direct answer
Vibration is a continuous, repeated load that tests fatigue and resonance; shock is a single, transient, high-acceleration load that tests structural strength and instantaneous failure. Neither replaces the other — many products pass vibration and then fail shock, because the failure mechanisms are completely different.
The physical difference
| Dimension | Vibration | Mechanical shock |
|---|---|---|
| Load character | Continuous, periodic or random | Single, transient |
| Time scale | Minutes to hours | Milliseconds |
| What it examines | Fatigue, resonance, wear | Strength, displacement, instantaneous failure |
| Key parameters | Frequency, PSD, acceleration, duration | Peak acceleration, pulse duration, waveform |
| Typical consequence | Accumulated cracking, loosened connections, rising contact resistance | Fracture, detachment, functional glitches |
An analogy
Vibration is bending a piece of wire back and forth — it takes many cycles to break, and the fracture shows fatigue characteristics. Shock is one hard bend — it may break at the first attempt, and the fracture shows overload characteristics. So passing vibration does not mean passing shock: a structure may endure low stress for a long time and then fracture outright under a momentary high acceleration.
Failure modes side by side
Failures dominated by vibration
- Fatigue cracking of solder joints (cracks start at the edge and propagate through)
- Connector terminal fretting corrosion (contact resistance rising with mileage)
- Harness chafing against structural parts, wearing through the jacket
- Bracket resonance cracking
- Bolts loosening
Failures dominated by shock
- Instantaneous solder joint fracture (large brittle fracture surface)
- Leads of heavy components (inductors, electrolytic capacitors) cracking or detaching
- Housing deformation, clip fracture
- Connectors separating, terminals backing out
- Relay contacts chattering momentarily and causing false actuation
Where they sit in the standards
ISO 16750-3 covers both vibration and mechanical shock, but the test conditions are specified separately and the parameter systems differ: vibration is defined by a profile and a duration, shock by peak acceleration and pulse duration. The two are not convertible.
Some OEM standards specify the test sequence — for example temperature cycling before vibration, or shock after vibration. A different sequence means different accumulated damage and possibly a different result, so follow the standard or the customer requirement.
Three common misunderstandings
"If we run vibration hard enough, we can skip shock." No. The failure mechanisms differ and neither covers the other.
"Increasing the vibration level is equivalent to shock." No. Vibration is a frequency-domain problem, shock is a time-domain transient; they are not interchangeable.
"A single shock does not tell you much." The opposite is true: one shock often decides whether the product is usable at all, particularly for safety-related parts.
Where we stand
TMC LAB holds both CMA and CNAS accreditation, with in-house vibration and shock equipment and combined temperature-vibration capability. Send us the sample weight, the mounting method and the customer standard, and we will first determine which items are needed and in what order.
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.
