薄壁扇形筋板挤压成形开裂抑制及翻转展宽策略

通过对大高厚比扇形筋板挤压成形机理进行数值模拟和物理实验，明确了扇形筋板局部变形不协调和角部应力集中是筋板角部产生开裂的主要原因。提出采用应力转移法在筋板成形初期提前预制局部切口，有效改变筋板内部拉应力分布形态，使筋板与侧壁的连接处拉应力由原有的120 MPa降低到50 MPa甚至更低。实验与模拟分析证明，预制切口可释放筋板自身变形约束，使筋板变形以切口为中心分界，左侧部分筋板向左侧面内弯曲，右侧部分筋板向右侧面内弯曲。得出在小拉应力作用下依靠筋板的面内弯曲可大幅度增加筋板长度的结论。

Cracking Suppression and Lateral Bending Broadening Strategy of Fan-shaped Thin-wall Ribs during Extrusion

Through numerical simulation and physical experiments on extrusion forming mechanism of fan-shaped ribs with large ratio of height to thickness, it is found that the main causes of corner cracking are local deformation disharmony and corner stress concentration. A stress transfer method was proposed, where the local incision was prefabricated in advance at the initial stage of the rib forming, which might effectively change the distribution pattern of tensile stress inside the ribs and reduce the tensile stress at the connection between the rib and the side wall from 120 MPa to 50 MPa or even lower. Experimental and simulation analysis show that the precast incision may release the deformation constraint of the rib itself, the rib deformation with the incision as the central boundary, the left part of the ribs in the plane bending towards left side, the right part of the ribs in the plane bending towards the right side. It is concluded that the length of ribs may be greatly increased by in-plane bending under the action of small tensile stress.