Four stage tensile test of small-diameter
seamless steel pipe
(1) elastic stage: the deformation of the sample at this stage is completely elastic, and the original length of the sample will be restored when all load is written. The modulus of elasticity of the material can be determined at this stage.
(2) yield stage: the elongation of the specimen suddenly increases, while the load reading on the universal testing machine fluctuates in a very small range (the zigzag line in the picture). If the slight fluctuation of the load reading is omitted, the stage can be represented by the horizontal line segment in the graph. If the sample is polished, the surface of the sample will see a stripe of about 45 degrees in the axis direction, which is called the slip line.
(3) strengthening stage: the specimen continues to stretch after the yield stage, because the material is continuously strengthened during the plastic deformation process, so the resistance in the sample increases continuously.
(4) at the necking stage and the fracture stage, the sample elongated to a certain extent and the load reading gradually decreased.
