在拉伸试验中,有些单位为适应具体生产情况,自行设计了各式各样的卡具。而为了和这些卡具相配合,把试样的平行部分l加工成比标准规定的长一些或短一些(如图1所示)。这两种做法都会对延伸率δ产生较大的影响。见表1。分析拉伸时,试样l部分的两端点A外侧,由于截面积不同,A点及其内侧要受到三向拉应力。由于径向力的作用,使A点内侧附近不易发生径向变形,即和中间部分相比,直径不易变细。这样A点内侧附近的相对伸长量△δ和中间部分的△δ相比,要小一些。在拉伸时,在弹性变形阶段,A点内侧等于d_0长度处,应力已基本上沿轴向均匀分布,即基本上已不存在三向应力。但在发生塑性变形时,由于不受三向应 In the tensile test, some units to adapt to the specific production, self-designed a wide range of fixture. In order to cooperate with these tools, the parallel part of the sample is machined to be longer or shorter than the standard (as shown in Figure 1). Both of these approaches have a large effect on the elongation δ. See Table 1. Analysis of stretching, the sample l part of the two points outside the point A, due to the different cross-sectional area, A point and the inside to be subjected to three-way tensile stress. As a result of radial force, so that the inner A point near the radial deformation is not easy, that is, compared with the middle part, the diameter is not easy to slim. The relative elongation Δδ near the inner side of point A is smaller than that of Δδ in the middle portion. At the time of drawing, in the stage of elastic deformation, the stress inside the point A is equal to the length d_0, and the stress is distributed substantially in the axial direction, that is, the three-direction stress basically does not exist. However, in the event of plastic deformation, due to not be three-way response