Dual flat-spherical indentation for extracting elastic–plastic properties from rough metallic surfaces

•A dual flat-spherical indentation (DFSI) technique is developed for rough metallic surfaces.•Effects of surface roughness on spherical indentation (SI) techniques are numerically demonstrated.•Flattening of rough surface by flat indenter varies with surface roughness Ra and material properties.•For Ra = 0~20 μm, load-depth curves from flattened rough surfaces are comparable to those from SI.•DFSI technique is demonstrated for evaluating material properties from rough metallic surfaces.