Crimping Defect State Evaluation and Fracture Failure Mechanism of Strain Clamps

The crimping defects of strain clamps are the main reasons that cause their fracture failure, which seriously affect the safety of transmission lines. Till now, there is still lacking of scientific and effective state evaluation method on the crimping defects, and the fracture failure mechanism of the strain clamps with different defects is ambiguous, immensely hindering the fast diagnosis of operation defects and effective formulation of protection technologies. Using the NY-400/35 type strain clamps commonly applied in transmission lines, firstly, simulated experiments were carried out to obtain the tensile mechanical properties and X-ray defect detection images, by means of which the correlation between failure characteristics and crimping defects was constructed. On this basis, fuzzy clustering algorithm was improved to realize the defect state evaluation. Finally, crimping-tensile finite element simulation model was established to analyze the fracture failure mechanism. Results show that the neglected crimping of two anti-skid grooves, the insertion depth of the steel core with 30%, and the neglected crimping of the aluminum tube with 70% are major defects; The insertion depth of the steel core with 50%, and the neglected crimping of the aluminum tube with 50% are emergent defects; Other defects are determined to be ordinary defects. Different defects cause the shift of normalized stress concentration zone to various extent, which therefore leads to the change of failure modes. This work provides theoretical foundation and technical support for the operation estimation and failure prevention of strain clamps.