板料n值测量方法的研究

Research on measuring work-hardening exponent of sheet metal

在板料冲压成形过程中 ,板料的硬化指数n值具有十分重要的意义 ,因而n值的测量无论对理论研究还是对工程实践都非常必要。因此 ,涌现出众多的硬化指数n值的测量方法。到目前为止 ,常用的测量方法主要有一点法、两点法、阶梯形试件拉伸法等。这些方法各有其优缺点 ,其共同不足就是用这些方法测定的n值反映的只是均匀塑性变形阶段的硬化性能。为此 ,本文基于常规单向拉伸试件在拉断后出现的锥形现象 ,以拉伸过程中的3个特征点 (屈服之后靠近屈服的一点、最大载荷时刻的点和断裂时刻的点 )为基础 ,提出了一种测量n值的新方案———三点法。在此方案中 ,用 3个特征点表征的两个n值分别描述了板料在均匀塑性变形阶段和随后大塑性变形阶段的硬化性能 ,而大塑性变形在板料成形过程中是必不可少的。本文通过对软钢板、紫铜板等进行的试验研究 ,证明了此方案是可行的。而且 。

The work\|hardening exponent (n) of sheet metal has essential effects on sheet deformation, so to accurately determine n is important to the theory study and actual production Up to now, many methods have been put forward to measure n, such as one\|point method, two\|point method, three\|stepped specimen method, etc Each method has its merits and faults,and the common shortage is that n calculated from these methods only reflects the hardening property in the uniform plastic deformation In this paper, the three\|point method is proposed to determine n based on tapered phenomena of fractured tensile specimen and three characteristic points (a point that just after the yield point, the point when the load reaches maximum, and the point when the fracture happens) With this method, two values of n calculated by three characteristic points describe the hardening property in the uniform plastic deformation and that of the following large plastic deformation necessary to the sheet forming In this paper, experiments have been carried out with sheet materials of soft steel and red copper, which testified the proposal The coefficient of normal anisotropy (r), the important parameter in sheet forming, can be obtained in the experiment as well