Process and Experimental Research of Controllable Pneumatic Rotary Bending Cropping of 304 Stainless Steel Bar

doi:10.3901/JME.2018.22.047

Abstract

Abstract: A new controllable pneumatic rotary bending cropping technology is proposed aiming to reduce the disadvantages of the traditional bar cropping methods such as bad cross-section quality, low material utilization and high energy consumption. It skillfully utilizes the notch effect of the V-groove, the crack-tip stress concentration effect of the initiated micro-crack and the propagating macro-crack. The working principle of the cropping method is introduced. The experimental setup is successfully designed and manufactured according to the principle. The mechanical model of the bar cropping process, which is loaded by the bending moment, is established by using the theory of material strength and linear elastic fracture mechanics. The theoretical formulas of the V-groove notch-root micro-crack initiation load, the propagating crack initiation load and the transient-breaking load are obtained. The cropping experiments of the 304 stainless steel metal bars with 30 mm diameter are studied under three different load control curves with different levels of the constant stress intensity factor range. Moreover, the cross-section quality of the cropped-billets are quantitatively assessed by the new proposed cross-section quality assessment method. The results show that the cropping process can be accurately controlled and implemented by keeping the crack-tip under a constant stress intensity factor range level. The cross-section quality of the cropped-billet and the cropping time decrease with increasing the range level. The ideal load control curve is △K=0.7K_c. The cropping process uses the fracture mechanics theory to establish the rotating bending cropping mechanism, which can not only guide the actual cropping experiments, but also provide theoretical support for the establishment of the subsequent cropping process database.

Key words: crack, cropping, stainless steel bar, stress concentration effect, stress intensity factor

CLC Number:

TG316

ZHONG Bin, LI Xuewu, YU Zhengyang, ZHANG Chuanwei. Process and Experimental Research of Controllable Pneumatic Rotary Bending Cropping of 304 Stainless Steel Bar[J]. Journal of Mechanical Engineering, 2018, 54(22): 47-54.

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