What type of failure occurs when a bolt is over-tightened, causing it to break?

When a bolt is over-tightened, it experiences excessive stress beyond its yield strength, which can lead to what is termed as bolt fracture. This type of failure results from the tensile forces exceeding the material's capacity to withstand them, typically leading to the bolt snapping or breaking under the load.

Understanding this type of failure is essential, particularly in applications where proper torque specifications are critical to ensuring the integrity of connections. Bolt fracture often occurs suddenly and can be dangerous if not recognized during the installation process.

Each of the other types of failure listed has its own distinctive characteristics. Shear failure typically occurs when a bolt is subjected to forces acting parallel to its length, leading to a shearing effect rather than a fracture due to tension. Fatigue failure is a gradual process resulting from repeated loading and unloading cycles, which can eventually weaken a bolt even if it has not been over-tightened. Creep rupture refers to material deformation and eventual failure under constant stress at high temperatures over time, which is a different mechanism entirely.

Recognizing bolt fracture as a direct consequence of over-tightening emphasizes the importance of adhering to prescribed torque values during assembly to avoid compromising connection strength and reliability.