Determining materials yield strength with Lüders behavior of existing steel structures using instrumented indentation approach

The instrumented indentation approach has become popular to characterize the mechanical properties of metals on-site. Although the evaluation of the materials' strength of metal structures is possible using the instrumented indentation approach, a few research studies have been reported to determine the strength of the steels presenting Lüders behavior. This paper presented a series of experiments including instrumented indentation and tensile tests, and proposed a method to evaluate the yield strength of steels presenting Lüders behavior. A steel truss bridge is used in the on-site benchmark experiment to verify the feasibility and reliability of the instrumented indentation approach. Tensile tests in the laboratory were conducted to obtain the accurate strength of steel from the steel truss bridge. The instrumented indentation tests were done on members of the steel truss bridge and the tensile test specimens. The strength from the instrumented indentation tests was compared with those from tensile tests. The comparison results are used to discuss the accuracy and precision of the instrumented indentation approach. The results indicate that the instrumented indentation approach is a feasible and sufficiently accurate method for measuring the strength of steel components. The difference of the yield strength is about 10%, and the difference of the tensile strength is around 5%. A method to improve the measured accuracy of yield strength is proposed. By using the proposed method, the difference of the yield strength for steels presenting Lüders behavior is less than 5%.