Based on the over versus under tightening example, properly torqued fasteners can withstand how many more force application cycles before failure?

• A. 100 times
• B. 1000 times
• C. 5000 times
• D. 10000 times

Answer: (B)

When a fastener is tightened to the proper specification, the preload it creates helps keep the joint clamped tightly together throughout repeated loading. That clamping reduces relative movement at the interface, which minimizes fretting wear and the initiation and growth of fatigue cracks. If the bolt is over-tightened, it can yield or incur thread damage, introducing plastic deformation and stress concentrations that hasten failure under cyclic loads. If it’s under-tightened, the clamp force is insufficient, allowing movement and loosening that also promote fatigue failure. In the over versus under tightening example, properly torqued fasteners last about one thousand times more force application cycles before failure than joints that are not tightened correctly. This illustrates why following the specified torque is so important for extending the life of a joint under repeated loading.