Failure analysis and waveform structure optimization of bending and torsion composite deformation of metal bellows

Metal bellows in industrial pipeline systems are often subjected to complex loads, which are excellent in compensating for axial displacement, lateral dislocation, and torsional deformation in the system. Based on the finite element simulation of the bending–torsion composite deformation of metal bellows, this paper obtained the mutual coupling influence law between bending and torsion resistance and the influence law of waveform structure parameters on the bending–torsion resistance of metal bellows. Additionally, the waveform structure parameters with the best bending-torsion resistance were optimized. The bending–torsion composite deformation test and fracture microscopic characterization were performed, and the bending–torsion composite deformation characteristics and fracture failure mechanism of the metal bellows were analyzed. The results revealed that under the combined action of bending and torsion, the cracks first appeared in multiple trough positions, and with the enhancement of torsion, the cracks exhibited a spiral expansion to the adjacent waveforms on both sides. After optimization, the elastic limit bending line displacement and elastic limit torsion angle displacement of the metal bellows increased by 33 %, which improved the bending–torsion composite deformation performance of the metal bellows and the service life. After optimization, numerous dimples of similar size were evenly distributed on the fracture surface of the metal bellows. This indicated that the stress distribution was uniform, which effectively improved the bending–torsion composite deformation performance of the metal bellows.