Finite Element Analysis Of Hardness Calculation Method For Material In Micro-nano Scale

With the development of micro-nano machining and manufacturing technology,completely testing methods is required to evaluate mechanical properties ofmaterials in nano scale. Hardness could characterize the mechanical properties ofmaterial, and it is relevant to yield stress, elastic modulus and other materialproperties. However, size effect, quantum effect becomes apparent in nano scale,and measure conditions, macrostructure of materials will also affect the calculatedhardness. There is an urgent requirement to study these factors’ effect on hardnessmeasurement.FEA method was used to analyze the hardness calculating methods such as OP(Oliver-Pharr) method, different indentation area methods and work of indentationmethods. The chosen of hardness calculation methods was discussed andexplanations were given on the hardness distinctions calculated by different methods.Pile up is always a problem and there is still not a good theory or model available totake it into consideration. Pile up and sink in effect were studied and the resulteddifferences in hardness calculated by OP method and work of indentation methodwere analyzed. Moreover, FEM models with different indentation residual stressstates were built and the semi-experimental model with different residual stressstates, indenter geometry and surface tilt degrees were deduced. Based on Hertzcontact mechanics, single factor method and finite element analysis (FEA) wereused to study the main factors including residual stress, indenter tip radius andsample tilt that affected hardness calculation and the sensibility of these parameterson the hardness calculation was discussed.Indentation creep was modeled and analyzed based on Maxwell viscoelastictheory. The effect of loading time and holding time on the load-displacement curveswas discussed. The two hardness calculating methods also present differentsensibility to indentation creep. Two types of film/substrate system which were softfilm/hard substrate system and hard film/soft substrate system were built. Thesubstrate effect on film deformation compared with bulk material was analyzed. Theelastoplastic zone in the film spread to substrate with different manners in softfilm/hard substrate and hard film/soft substrate systems and its effect on hardnesscalculation was studied. The substrate effect became pronounced with increasingrelative indentation depth and its effect on composite hardness was discussed. Thedistinctions between hardness calculating methods which applied to film/substratesystem were analyzed. The results showed that work of indentation method was a reliable method tocalculate material hardness in nano scale. The material surface residual stress, theindenter tip radius and the sample surface inclination have little effect on hardnesscompared with OP method. Also, work of indention method show great prospect incalculating material hardness with indentation creep and soft film/hard substratesystem.