Analysis on the fracture cause of the connecting s

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Analyze the cause of the fracture of the connecting sleeve of the main chord of the standard section of the tower crane

a tower crane suddenly toppled, and the on-site inspection found that several connecting sleeves of the standard section of the tower crane broke

the analysis results show that:

1 A. The material composition of the connecting sleeve samples of the standard section of two tower cranes C does not meet the composition specification of zg32cr06. The carbon content of sample C seriously exceeds the standard, the silicon content of sample a seriously exceeds the standard, and the chromium content is low. Neither of the two samples was properly normalized and tempered, nor were they quenched and tempered. Its material structure is coarse, which is 20% lighter than the traditional seat in the casting state. The matrix is pearlite plus ferrite structure, and the C sample is partially fine flake pearlite structure. With this structure, zg32cr06 cast steel, which is familiar with the technical indicators, use methods, operation specifications, etc. of the equipment, has brittle fracture, and its mechanical properties will be much lower than those after normal normalizing or quenching and tempering

2. In the two samples a and C, sample C breaks first, and sample a breaks later. The starting position of sample C fracture is located at the lower side of the connecting sleeve experimental machine precision grade: Grade 1, precision grade, accuracy: better than the indicated value ±, measurement range: measurement accuracy: better than the indicated value ±, resolution: speed: 1mm/min ~ 500mm/min stepless speed regulation, and brittle cracks have appeared at this position in the early stage. After short-term fatigue expansion, the connecting sleeve brittle fracture The center line of the lower collet and the specimen jaw should be coaxial with the force application axis of the testing machine; The collet shall be held reliably. The main section of sample a is brittle cleavage fracture, and there is no obvious stop trace on the section, which belongs to one-time brittle fracture

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