High Strength Steel The Pros And Cons To Load The Mechanical Properties Testing And Theory

This paper addresses a problem of the yield strength deduction of the X80 pipeline steel during the manufacture. The material was from a steelworks. Forward and reverse axial loading schemes were taken by the researchers to investigate the role of deformation history. Experiments were performed at the room temperature on a hydraulic universal machine (WEW-300C). A typical curve of X80 steel in simple tension testing was then drawn. The stress-strain response displays that X80 has the character of perfectly-plastic material. Then, reverse loading experiments were performed subsequently and the stress-strain curves were also recorded. It was found that the yield strength under the reverse loading was lower than that of the first forward loading test. This is the Bauschinger effect (BE). The yield strength difference increased as the pre-stain grew. When the pre-strain increased to 0.95%, the reverse yield strength reached to a constant. On the basis of elastic-plastic mechanics theory, experiential formulas that describe the. yield strength with the pre-plastic deformation were derived.Considering the process of the X80 pipeline steel, the researchers designed the experiments of bending test. It were shown that the BE was increased with pre-strain added when the reverse bending were carried on after the first bending unloaded. Then numerical calculation on the yield strength was taken considering the residual stress. The calculation results almost agreed with the experiment results.In order to prove the BE of the X80 pipeline steel, torsion tests were carried by the researchers. The specimens were taken reverse loading after they got some pre-deformation. And strain gauge can measure ±45° shearing strain. The result shows that the BE also exists on X80 specimens. The numerical calculation was also carried. And the results of the calculation and the experiment are agreed.