Tensile Tests of Small Diameter Seamless Steel Tubes in Four Stages


(1) Elastic stage: In this stage, the deformation of the sample is entirely elastic, all of which are written into the load, and the original length of the sample will be restored. At this stage, the elastic modulus of the material can be determined.


(2) Yield stage: the elongation of the specimen increases suddenly, while the load readings on the universal testing machine fluctuate in a very small range (the zigzag line in the figure). If the light microwave motion of the load reading is omitted, the stage can be represented by the horizontal line segment in the figure. If the sample is polished, the surface of the sample will see about 45 degrees of fringes along the axis direction, which is called slip line.


(3) Strengthening stage: The sample passes through the yield stage and continues to stretch, because the material strengthens continuously in the plastic deformation process, so the resistance in the sample is getting bigger and bigger.


(4) At necking and fracture stages, the sample was elongated to a certain extent, but the load readings gradually decreased.