In view of the deflection of metal bars in low-stress cropping process, which leads to serious extrusion damage on the surface of bar and difficulty to apply loads effectively, a “five-segment type” discontinuous variable cross-section bar model is established in this paper. The strain energy method is developed to establish the influence of V-shaped notch parameters on the deflection, and its accuracy is elevated with XFEM method, which is used to quantify the influence of crack depth. Finally, the characterization formula of deflection in the low-stress cropping process is established theoretically. The dynamic and static strain-deflection test and analysis platform is built on the low-stress cropping machine. The experimental results of 45# steel bar confirm the validity of the formula. On this basis, the law ${\theta }_i$ of follow-up rotation angle of loading die is analyzed, and the effective method to apply desirable loads is obtained. The evaluation parameter ${\omega }_i(L_B/2R_0)$ of allowable value of deflection at crack initiation is proposed, and the allowable deflection range $\left({\omega }_1,{\omega }_2\right)\text{=}\left(\text{0.02343mm,0.15383mm}\right)$ of 45# steel bar with a diameter of 15 mm is given, which can be applied to low-stress cropping and meet the requirements of industrialization.

针对低应力种植过程中金属棒的变形，导致棒材表面严重的挤压破坏和难以有效施加载荷的问题，建立了“五段型”不连续变截面棒材模型。这篇报告。开发了应变能方法以建立V型缺口参数对挠度的影响，并通过XFEM方法提高了其精度，该方法用于量化裂纹深度的影响。最后，从理论上建立了低应力种植过程中挠度的表征公式。动静应变变形测试分析平台建立在低应力种植机上。45＃钢筋的实验结果证实了该公式的正确性。在此基础上，法律${\theta }_{\mathrm{一世}}$分析了加载模的跟进旋转角，确定了施加理想载荷的有效方法。评估参数${\omega }_{\mathrm{一世}}（{\mathrm{大号}}_{乙}/\mathrm{2个}{\mathrm{[R}}_0）$ 提出了裂纹萌生时的允许挠度值，并给出了允许挠度范围 $\left({\omega }_{\mathrm{1个}}，{\omega }_{\mathrm{2个}}\right)\text{=}\left(\text{0.02343毫米，0.15383毫米}\right)$ 给出直径为15mm的45＃钢筋，可用于低应力作物种植，满足工业化要求。