Vibration Fatigue
The breaking of a conductor or a solder joint over time as a result of repeated small bends. It appears after millions of cycles without any single overload. The break most often starts where the rigid and flexible regions meet, for example where the solder ends.
Metal accumulates a permanent change in its microstructure with every bend. If the stress is above a certain threshold, a crack nucleus forms and grows a little with each cycle. When the cross-section has been reduced enough, the conductor breaks.
- Why solder is risky: solder wicks between the wires of a stranded conductor by capillary action and stiffens that region. The point where the solder ends becomes a rigid-to-flexible transition, and the bending stress concentrates exactly there. That is why a crimped connection is preferred in a vibrating environment.
- Prevention: using stranded flexible cable, fixing the cable at regular intervals, leaving service slack at the terminal exit, using a cable bellows on moving connections.
- Symptom: an intermittent fault appearing months later; measurement values that change when the cable is flexed by hand.
All electronic installations working on vehicles and construction machines are under constant vibration. Planning the cable route correctly from the start is far cheaper than repeated break repairs afterwards.
Context in which this term is used: Installation, redundancy and field continuity