Safety Warning For Transmission Lines: In-depth Analysis Of Metal Fatigue Failure Of Bolt-type Tension Clamps

Transmission lines are exposed to the elements for extended periods, and alternating stress caused by wind vibration is a hidden killer of hardware. As a crucial component for securing wires, the internal metal structure of component bolted type strain clamp is highly susceptible to performance degradation under cyclic loading. This physical damage process is extremely insidious, and early microstructural changes are difficult to detect visually during routine inspections.

Microscopic Initiation Process of Fatigue Cracks

The metal matrix undergoes localized plastic deformation under cyclic stress. The root of the dead end strain clamp bolt thread or the bend of the U-bolt creates natural stress concentration zones due to abrupt changes in cross-section. These locations are the preferred initiation sites for cracks. Initially, tiny slip bands gradually accumulate. Over time, the crack slowly propagates along a direction perpendicular to the maximum tensile stress.

Operating Condition Variables Inducing Shortened Fatigue Life

The evolution rate of metal fatigue is influenced by multiple complex factors:

• The frequency distribution of conductor micro-amplitude vibrations.

• The grain size and inclusion content of the metal material itself.

• The prestress distribution during bolt installation.

• The corrosive intensity of the atmospheric environment on the crack tip.

These variables persist throughout bolted dead end clamp operation. Excessive initial installation loads accelerate the coupling process of stress corrosion and fatigue.

The failure cross-section of bolt-type tension clamps typically consists of a fatigue initiation zone, a propagation zone, and a momentary fracture zone. The propagation zone exhibits fine fatigue arcs. These are the physical imprints left by the material under cyclic loading. By analyzing these characteristics, technicians can trace the specific causes and operational history of the fitting failure.