一、前言金属材料拉伸和扭转时的流动极限是一个基本的材料机械性质参数。根据有关资料介绍,矩形截面杆件弯曲由于应力分布不均匀,按弹性公式计算能提高试件外层纤维拉压流动极限10～20%,16Mng钢能提高30～40%。对于碳钢圆截面弯曲试件将提高60%。此外,圆轴扭转 I. INTRODUCTION The flow limit of metallic materials during stretching and twisting is a basic material mechanical property parameter. According to relevant information, the bending of rectangular section bars due to uneven stress distribution, according to the elastic formula can increase the outer layer of the specimen tension and compression flow limit of 10 to 20%, 16Mng steel can be increased by 30 to 40%. For carbon steel round section bending specimen will increase by 60%. In addition, the shaft twists