Effect of symmetrical position notching on cracking and cross-section quality of thick-walled metal tube under low-stress cropping

Aiming at the problem of prominent tear marks in the inner ring of the low-stress cropping cross-section of thick-walled metal tubes, a low-stress cropping method based on symmetric position notching is proposed. The optimal internal notch shape is determined by the XFEM method as V-shape. Combined with the orthogonal experimental method, it is concluded that the bottom corner radius of the internal notch has the greatest impact on cracking force and cracking quality, and the flare angle of the internal notch has the smallest impact. The optimal internal notch parameters of the typical tube are obtained through the optimization analysis. The cropping results of comparing the tubes with an optimal internal notch of 45# steel and 304 stainless steel with the traditional tube show that the fatigue tear marks of inner rings are significantly reduced by the proposed cross-section quality evaluation method, and the cropping time is also obviously shortened. Considering those notch parameters related to cracking force and deflection, the critical cracking force formula and discontinuous variable section deflection formula of the tube with annular notches and different parameters are established. The evaluation parameters of deflection allowable value ω i (2 L B /( D - d )) are proposed. The allowable ratio of length to the wall thickness of 45# steel tube in cropping with common wall thickness is given, and the allowable deflection range which meets the cropping requirements before cracking is obtained.