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The mechanical properties of a material can be positively or negatively affected by its applied or residual stress. In this article, a series of molecular dynamic simulations were adopted to investigate the nanoindentation response of monocrystalline copper under tensile pre-deformation. Nanoindentation simulation under stress-free condition was compared with those under pre-tension strain values of 1.2%, 2.4% and 3.6%. Load–displacement curves with hardness value and recovery rates of total work for nanoindentation based on various tensile pre-deformations were obtained and discussed. It indicated that tensile pre-deformations resulted in a higher potential energy in substrate and a lower external energy will be introduced to realize the same elastic or plastic deformation during indentation. Moreover, the evolution of interior defects during indentation was also observed and analysed. The results showed that tensile pre-strain can influence dislocation nucleation behaviour of material during indentation. This article proposed a special molecular dynamic simulation method to characterize the mechanical properties of the material under tensile pre-deformations via nanoindentation, which gives an effective approach to characterize residual stresses in micro- and nanoscale and will have promising application in mechanical characterization of Microelectro Mechanical Systems devices and structures. Further analysis based on experiments will be done in our further research work.

In this article, the specimen of Q235 (low carbon steel, C ≤ 0.22%, Mn: 0.3%–0.8%, Si ≤ 0.3%, P ≤ 0.045%, S ≤ 0.05%) has been tested in in situ tensile tests. Especially, different types of scratches are prefabricated with 1, 2, and 3 µm in depth. In addition, three scratch angles ( θ = 0°, 45°, and 90°) are adopted to explore the changes of tensile strength. The cross profile of the scratch groove is measured with in situ observation method (Olympus DSX500), which is taken as an important indicator to verify the experiments. According to the results of experiments, scratch depth and angle can influence the tensile strength of material. When the depth and scratch angle increase, there is a decrement in the value of tensile strength. This indicates that the surface damage really has effect on the tensile strength of specimen.