Characterization of strain rate effects on the plastic properties of structural steel using nanoindentation

SM490, a structural steel, has been widely used in the construction of buildings, bridges, and tunnels due to excellent machinability and weldability. Since the mechanical properties of structural steel are important material input data in engineering design as well as in both static and dynamic analyses of structure, the important task is to deeply understand the mechanical properties of structural steel and the effecting factors on these properties, in which the strain rate effect is most important. In this study, the indentation strain rate effects on the mechanical properties of SM490 steel, including hardness, yield strength, the strain hardening exponent and shear stress were investigated using the nondestructive indenting technique. The dynamic tensile tests were performed at different strain rates to demonstrate that the strain rate effects on the hardness and yield strength investigated by using indentation are reliable. The strain rate sensitivity value of SM490 steel obtained using the nondestructive indentation experiment was reported. The linear relation between the indentation strain rate (ε̇I) and uniaxial strain rate (∈̇) was discovered, and the coefficient C2 of 0.15 relating to both strain rates was well estimated. A modified method was also proposed to determine the values of plastic properties considering uncertain contact stiffness at high indentation strain rates. The results were used to assess and understand the variation of mechanical properties of SM490 as the indentation strain rate changes.