| In recent years, depth-sensing indentation (DSI) technique has shown broadapplication prospects in investigating the mechanical properties at the grain (meso-)scale of the material. In this paper, some preliminary research work around thenumerical simulation of the indentation force-penetration depth (F-h) curves usingFEM, the procedure for determining the mechanical properties based on theindentation force-penetration depth (F-h) curves and the application of DSItechnique in analyzing mesoscopic mechanical properties of polycrystalline solidsubjected to low-cycle fatigue loading have been carried out.Firstly, the current research work regarding the procedure for determining themechanical properties using DSI technique, including descriptions of the indentationforce-penetration depth (F-h) curves, formulas of the projected contact area andthree representative procedures for determining mechanical properties based on theforce-penetration (F-h) curves, were reviewed simply and evaluated properly.Both the three-dimensional model and the axisymmetric model were used tosimulate the indentation procedure by using the general-purpose finite elementsoftware (ABAQUS). According to the agreement of the F-h curves determinedusing the two models, the following results were obtained: the axisymmetric modelwith a conical indenter, which has the same area function of the real tip, is an effectivetool for simulating indentation procedure with a Berkovich indenter. Theaxisymmetric model was used to simulate the F-h curves of the 18Cr-SNi austeniticsteel. Comparison between the numerical results and experimental data demonstratedthat the finite element approach is capable of reproducing the loading-unloadingbehavior of an indentation test. A comprehensive parametric study of 28 additionalcases was conducted. It was shown that, when the Yong's modulus and yield strengthremain the same, the loading curvature increases with increasing strain hardeningexponent. Piling-up and sinking-in phenomena are determined by Y/E, as well as thestrain hardening exponent (n). By observing large numbers of different materials'plastic zones developed during indentation, as might be expected, larger plastic zonesare associated with larger strain hardening exponent, the increase in zone size occursprimarily in the depth dimension. Overlapping phenomena of plastic zones occursnear the tip of the indenter. The main reason of producing overlapping phenomena ofplastic zones is that "piling-up" and "sinking-in" are occurred. The F-h curves of the meso-structures of 18Cr-SNi austenitic steel subjected tolow-cycle fatigue loading were measured using DSI technique. Using above threerepresentative procedures, the variation of the mechanical properties, such as hardness,Young's modulus, yielding strength, strain hardness exponent and plastic work, atgrain (meso-) scale of material with applied strain amplitudes were further obtained. Itwas shown that, with increasing strain amplitudes, the indentation hardness, Young'smodulus, yield strength and strain hardness exponent increase while the indentationplastic work decreases. In the above three approximation methods, T.A.Venkateshreverse analysis algorithm yields accurate estimates of hardness and yielding strengthwhich agree well with those of 18Cr-SNi austenitic steel, derived from uniaxial tests.It is also shown that A.Venkatesh reverse analysis algorithm gives better predictionsof Young's modulus and it is more stable than the other algorithms.The above results were analyzed by means of Taylor's hardening theory based ondislocation mechanisms, combined with the observations of the micro-structures ofthe material subjected to low-cycle fatigue loadings.The research work in this paper provides the fundamental numerical simulationand experimental investigation for further exploiting the application of depth-sensingindentation (DSI) technique in mesoscopic mechanical properties of polycrystallinesolid subjected to cyclic loading.
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