Fatigue Fracture Mechanism, Inducement and Long-Term Improvement Solution of High-Strength Bolts

Fatigue Fracture Mechanism, Inducement and Long-Term Improvement Solution of High-Strength bolts

More than 80% of high-strength bolt fractures in mechanical equipment are fatigue fractures rather than overload fractures. Fatigue failure occurs suddenly without obvious deformation, which is the most hidden and dangerous equipment fault. Mastering fatigue mechanism is essential for long-term equipment safety.

1. Micro Mechanism of Fatigue Failure

After fastening, bolts bear continuous preload stress. Long-term vibration and alternating load produce micro stress circulation at thread roots, leading to micro crack generation and gradual expansion, finally causing sudden fracture.

2. Three Main Fatigue Modes

Vibration fatigue is caused by long-term equipment operation and thread micro slip. Stress fatigue results from uneven contact surface and eccentric force. Installation fatigue is induced by excessive tightening torque and over preload.

3. Common Inducements of Fatigue Fracture

Unstandard torque, uneven fitting surface, missing anti-loosening structure and mismatched bolt grade are the main reasons for early fatigue failure in industrial sites.

4. Comprehensive Improvement Measures

Adopt standardized torque assembly, ensure flat contact surface, upgrade anti-loosening structure, select matched high-strength bolts, and implement regular re-inspection to eliminate fatigue risks fundamentally.