Determining if a bolt has failed requires a comprehensive analysis of its appearance, stress state, and operating environment. Common failure modes include fracture, loosening, corrosion, and fatigue cracking. Prevention hinges on scientific selection and standardized assembly.
You're not just concerned with whether it's broken, but also with how to detect potential problems early and prevent accidents. Especially in equipment maintenance or engineering safety scenarios, a minor bolt problem can trigger a chain reaction. Understanding failure signs and mastering prevention logic are essential for truly reliable connections.
How to Determine if a Bolt Has Failed?
Visual Inspection
Cracks or Fractures: Obvious fractures or small cracks appear on the bolt shank or at the head-shank transition fillet (can be detected with a magnifying glass or penetrant testing).
Signs of Loosening: Misaligned anti-loosening markings, deformed washers, and increased gaps between connectors.
Corrosion Marks: Reddish-brown rust, pitting, and green oxides appear on the surface (especially in marine or humid environments). Thread damage: Threads are worn down, stripped, difficult to screw in, or jammed during disassembly.
Case reference: Wind turbine flange bolt fractures often originate at the headstock transition fillet, with the fracture surface exhibiting both fatigue bands and brittle fracture zones.
Abnormal operating conditions: Increased vibration, abnormal noise, and displacement of connection parts.
Preload monitoring shows a clamping force decrease exceeding 15%.
Torque re-inspection reveals a significant decrease in torque (more than 20% below the initial value).
