Projected Contact Area Research Articles

Orientation-dependent hardness of Mo3Si studied by cube-corner nanoindentation

Mo3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document}Si crystals having crystallographic out-of-plane orientations close to (001)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(0\\,0\\,1)$$\\end{document}, (011)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(0\\,1\\,1)$$\\end{document} and (123)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(1\\,2\\,3)$$\\end{document} were studied by nanoindentation to better understand the hardness anisotropy. The Mo3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document}Si precipitates were grown in a Mo-17.5Si-6B alloy and identified by electron backscatter diffraction. Pronounced material pile-up around the indents was observed, which causes inaccuracies in the projected contact area determined using the Oliver–Pharr method of around 30% compared to the real one. Based on the analysis of scanning electron micrographs, the projected contact areas and thus the hardness values were determined. To rationalize the observed pronounced orientation dependence of the hardness of Mo3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document}Si, we suggest an easy-slip-cutting model accounting for the available slip systems as well as the upward flow of material along the surface of the cube-corner indenter tip.

Towards Determining an Engineering Stress-Strain Curve and Damage of the Cylindrical Lithium-Ion Battery Using the Cylindrical Indentation Test

Mechanical internal short circuit (ISC) is one of the significant safety issues in lithium-ion battery design. As a result, it is possible to subject LIB cells to thorough mechanical abuse tests to determine when and why failure may occur. The indentation test is a recommended loading condition for evaluating mechanical damage and ISC. In this study, 18,650 cylindrical battery cells underwent indentation tests and a voltage reduction following the peak force identified by the ISC. Due to the complexity of the contact surface shape between two cylinders (LIB cell and indenter), a new phenomenological analytical model is proposed to measure the projected contact area, which the FEM model confirms. Moreover, the stress-strain curve and Young’s modulus reduction were calculated from the load-depth data. In contrast to previously published models, the model developed in this paper assumes anisotropic hyperelasticity (the transversely isotropic case) and predicts the growing load-carrying capacity (scalar damage), whose variation is regulated by the Caputo-Almeida fractional derivative.

New Analytical Model for Determining the Roll Pitch Diameter in Three-Roll Continuous Retained Mandrel Rolling

The continuous tube-rolling method has been widely used to manufacture high-quality seamless pipes and tubes. However, the analytical model for determining the roll pitch diameter in three-roll continuous retained mandrel rolling from first principles has not yet been presented, which has, thus, hindered the development of rolling control technology in tube manufacturing. In this work, a new analytical model has been established from the force–equilibrium principles. The modelling has taken the tube-roll contact geometry, roll pressure, mandrel pull forces, inter-stand tensions, and friction coefficients into account for its formulations. Seen from the experimental results of the rolling at the plant, the maximum deviation of the predicted projected contact area is less than 6% and the maximum deviation of the calculated roll speed from the satisfactory data in field operation is less than 3.9%. The proposed model has enabled the influence of the friction coefficients on the roll pitch diameter to be quantified in theoretical analysis, and it was found that the changing amplitude of the theoretical roll pitch diameter corresponding to the commonly used data range of the friction coefficients can be above 9%. Having overcome the shortcomings of the empirical model, this model has the required prediction accuracy and flexibility for being applied to flexible tube rolling. By building the key algorithms around physical models, this modelling has advanced not only the rolling control at the plant, but also our scientific understanding of the mechanics of the continuous tube-rolling process.

Discrepancies in Nanoindentation Hardness and Modulus with a Berkovich, a Cube-corner, and a Conical Tip in a Cu(In,Ga)Se2 Light-Absorption Layer

In this study, we tried to understand the difference in the mechanical properties (elastic modulus, E & hardness, H) values of CIGS compound semiconductors measured using the Berkovich indenter and the sharper cube corner and conical indenter. Adopted continuous stiffness measurement technique to characterize it along with the indentation depth. The depth was up to 1000 nm, and E and H values w ere obtained according to the depth. The projected contact area of the cube edge and the conical indenter was calculated assuming the two indenters had an ideal shape. In the case of the Berkovich indenter, which is the subject of comparison, both calculated values assuming an ideal shape and experimental values were used. Cube-corner and conical tip showed lower load at the same depth of 1000 nm compared to Berkovich indenter. This means that the same depth of indentation was achieved even at a low load, which could affect the value of the mechanical properties of the thin film. The cube-corner tip and the conical tip have a sharp shape with a projected contact area about 6 times smaller than that of the Berkovich tip. It was observed that not only the effect of grain boundaries of the microstructure of the CIGS thin film, but also the effect of reflecting the characteristics of the Mo substrate had a significant effect on the mechanical properties of the CIGS thin film.

Characterization of power-law constitutive relationship of nickel-based single crystal superalloys under different loading rates by nanoindentation with different types of indenters

This work attempts to explore a method to characterize the effect of loading rate on the power-law constitutive parameters of nickel-based single crystal superalloys (NBSX) by nanoindentation, which avoids the influence of indentation sinking-in or piling-up and indentation size effects. Specifically, combing the reduced modulus obtained from a cylindrical flat punch indentation test with the indentation contact stiffness obtained from two pyramidal indentation tests with different equivalent half cone angles, the actual indentation projected contact area of two pyramidal indenters can be acquired. Based on the actual projected contact area and the intrinsic hardness results calculated by Nix-Gao model, the corrected indentation load-depth curves from two pyramidal indenters are constructed. The elastic modulus can be known from the reduced modulus in advance, and then according to the equivalent half cone angle of the pyramidal indenters and the corrected indentation load-depth curves, the representative strain and stress of two pyramidal indenters are obtained, respectively. The power-law constitutive parameters of NBSX along [001] orientation under different loading rates are accomplished by inverse analyses of the representative stress and strain of two pyramidal indenters, and verified by the test results of a pyramidal indenter with another equivalent half cone angle. Results demonstrate the effectiveness of the explored method.

Revealing nanoscale material deformation mechanism and surface/subsurface characteristics in vibration-assisted nano-grinding of single-crystal iron

Ultrasonic vibration-assisted grinding (UVAG) has attracted extensive attention as it can significantly improve the surface integrity of the machined workpiece. However, the atom-scale material deformation mechanism with the presence of ultrasonic vibration is still unclear, which hider the application of the UVAG to the ultra-precision machining process. To fill this gap, we present a molecular dynamics (MD) model for the vibration-assisted nano-grinding process (VANG) of single-crystal iron. The characteristics of the material deformation process induced by ultrasonic vibration are studied, including material accumulation, temperature, dislocation, subsurface damage (SSD), contact area, and grinding force. The results show that vibration changes the dislocation distribution in the plastic zone, forms the phenomena of expansion and contraction and causes the fluctuation of SSD depth. Due to the different distribution of stress and temperature during VANG, the details of plastic deformation, such as dislocation movement, dislocation nucleation and phase transformation, change with the varying vibration frequency. In addition, the reduction of the projected contact area is the main reason for the reduction of grinding force. However, dislocation pileup in the grinding zone and chips further increase the grinding hardness. This research could enrich the understanding of nano-scale deformation mechanisms in vibration-assisted processing of metallic materials.

A Combined Numerical and Experimental Study of Evaporative Cooling for Polymer Electrolyte Fuel Cells

State-of-the-art liquid cooling of polymer electrolyte fuel cells (PEFC) requires a complex multi-layer design of bipolar plates [1] which is responsible for about 75 % of stack volume and approximately 80 % of its mass [2]. Additionally, an external humidifier is often required to ensure a proper humidification and thus ionic conductivity of the proton exchange membrane [3] at elevated temperatures.Evaporative cooling shows the potential to reduce the stack volume, mass, complexity and cost by up to 30 % by simplifying the design of bipolar plates. Additionally, it allows a better internal humidification which enables higher operating temperatures without external humidification [4]. In our concept, liquid water is fed to each cell through dedicated water channels in the anode flow-field. Subsequently, the water is distributed in a specially designed gas diffusion layer with a mixed hydrophilic and hydrophobic pattern (Figure 1) [5]. Once in contact with the gas flow, the water in the hydrophilic lines evaporates, cools the cell and is eventually released as vapor with the exhaust gases.In our previous work [6] we have elaborated the potentials and limits of this concept on the stack and system level. In this study, we focus on the experimental and numerical investigation of water evaporation from GDLs with patterned wettability [7] in a technical cell environment. Ex-situ evaporation experiments have been carried out with a patterned Toray 060 GDL (7 x 3 cm2, 14 hydrophilic lines, pattern: 500 µm hydrophilic, 940 µm hydrophobic) and nitrogen as a carrier gas. The operating temperature (22 to 90 °C) as well as the gas velocity (0.2 to 7 m/s) has been varied whereas the pressure is kept constant (ambient at cell outlet).In order to further foster the understanding of the underlying evaporation phenomena, a simplistic 2-D water vapor transport model has been developed in this study. Fickian diffusion is taken into account in the GDL and gas channel, while convection is only considered in the channel. Water evaporation is modeled according to the Hertz-Knudsen-Schrage equation [8]. The projected contact area between hydrophilic lines and gas channel is an input parameter to the model and has been determined by ex-situ X-Ray tomographic imaging (XTM).Figure 3 shows that the evaporation rate and thus the related cooling power increases significantly with temperature. This fact is attributed to the higher water saturation pressure as well as to the increased diffusivity at higher temperature. Further, it can be seen that the evaporation rate increases with gas speed. We attribute the strong increases at low gas speed to the fact that the evaporation is only limited by the saturation of the gas channels in this regime. At higher gas speeds, however, the increase in evaporation rate is less pronounced. We hypothesize that the water vapor transport through the GDL is limiting the evaporation rate. Evaporation kinetics have not been a limiting factor in the investigated parameter space, since the interface between hydrophilic and hydrophobic lines is fully saturated in the conducted simulations.Furthermore, the modelling results show that the evaporation rate and thus cooling power is not homogenous along the channel (Figure 2). Based on these results, an optimized pattern structure is proposed to achieve a more uniform cooling and evaporation distribution.Finally, a cooling power density of more than 1 W/cm2 can be achieved which is sufficient for cooling state-of-the-art fuel cell systems.

On the effective load during nanoindentation creep testing with continuous stiffness measurement (CSM)

The ability to accurately determine the applied load is critical in measuring hardness, which is traditionally defined as the ratio of the applied load to the projected contact area in the case of instrumented indentation. The magnitude of the applied load is unambiguous when the load is monotonically increased or held constant. However, in the case of nanoindentation testing with continuous stiffness measurement (CSM), wherein an oscillatory load is superimposed on the primary load, what one should use for the load has significant implications especially for rate-dependent materials. In this work, a concept of an effective load during nanoindentation creep testing with CSM is proposed based on a theoretical analysis. The analytical model is experimentally validated, and good agreement is found with the experimental results, even when the material exhibits a strong indentation size effect (ISE). The findings of this work have important implications for accurately measuring the rate dependence of hardness, especially during high-temperature nanoindentation testing.

Effects of particle distribution and calculation method on results of nano-indentation technique in heterogeneous nanocomposites-experimental and numerical approaches

This study aims to investigate the effects of two testing parameters on the results of the nano-indentation experiment in the heterogeneous particle reinforced composites: (1) the particle distribution pattern, and (2) the methods for calculating the residual projected contact area of the sample under the indenter. For this purpose, several nano-indentation experiments were performed by using Berkovich indenter on the specimens prepared from Filtek Z350 XT dental nanocomposite as a particle reinforced composite with a volume fraction of 63.3 percent. Then, the nano-indentation procedure on the dental nanocomposite was simulated using the finite element (FE) method. In the FE simulation, several representative volume elements (RVEs) of the nanocomposite were modeled by modifying the Lubachevsky-Stillinger algorithm to distribute particles randomly with a volume fraction of more than 50 percent in a cubic volume. The hardness and elastic modulus of the nanocomposite were calculated from the results of the nano-indentation experiment and the simulation. In these calculations, the projected contact area of the indenter on the specimen was obtained using two different approaches of the Oliver-Pharr method and direct measurement of the area. The results indicated that the distribution of particles around the indenter has significant effects on the nano-indentation results. According to the simulation results, the heterogeneity of the material causes the projected contact area of the indenter on the sample to distort from its equilateral triangle shape, which is assumed in the Oliver-Pharr method. Therefore, the method of direct measurement of the indenter projected contact area on the specimen is proposed to obtain more precise results from the nano-indentation test on heterogeneous materials.

Berkovich nanoindentation of Zr55Cu30Al10Ni5 bulk metallic glass at a constant loading rate

Berkovich nanoindentation experiments were conducted on Zr55Cu30Al10Ni5 bulk metallic glass under a constant loading rate. Indentation hardness decreased linearly with contact depth, which defied the direct application of conventional indentation size effect model for crystalline material. Elastic modulus remained invariant under small loads, but decreased linearly under large loads. The scaling relationships between indentation variables such as contact depth, permanent depth, the maximum indentation displacement, plastic energy, the total work of indentation and their ratios were investigated. The area of shear band circle, the projected contact area at the maximum load, and the residual projected area were all found to be proportional to one another. A new methodology to determine fracture toughness was proposed based on the total work of indentation, provided that the critical indentation displacement at the onset of fracture corresponds to zero value of elastic modulus extrapolated from curve fitting.

Compressive Properties of Nanoporous Gold Through Nanoindentation: An Analytical Approach Based on the Expanding Cavity Model

We investigated the analytic relation between hardness and compressive yield stress using an expanding cavity model (ECM) for nanoporous gold (np-Au). We prepared three np-Au samples with ligament sizes 30.61, 59.36 and 116.33 nm by free-corrosion dealloying and post heat treatment. The indentation contact morphology was examined to estimate the hardness accurately from the nanoindentation load-depth curve. Unlike conventional dense metals, the deformation was confined to the projected contact area, and the center of the residual impression was dominated by densification. The projected contact area estimated by the Oliver–Pharr method was overestimated, so that a new contact area function was proposed that considered the indentation contact morphology of np-Au. It was confirmed that a hardness value taking into account the indentation contact morphology of np-Au matches well with the hardness derived by direct measurement of the residual impression. We modeled the ratio of hardness to compressive yield stress for np-Au using an ECM. The scaling factors, which represent the extra strain-hardening in the core in the ECM, were analyzed for np-Au and dense metals. An ECM that better matches np-Au is suggested based on the scaling factor resulting from densification beneath the indenter.

Numerical Study on Shear Performance of a New Perfobond Connector with Controllable Stiffness

To improve the shear behavior and design applicability of rubber ring perfobond connectors (RPBLs), a new rubber ring that aims to make the shear stiffness of RPBLs controllable was proposed. Firstly, the conceptual design and configuration of the new rubber rings were presented and discussed. Subsequently, finite element (FE) models for modified push‐out tests of new RPBLs were established based on the validated modeling method. The initial shear stiffness is dominated by the horizontal projected contact area between hole walls and concrete dowels. γ is defined as the ratio of the horizontal projected length of hollows to the diameter of holes. The shear stiffness of new RPBLs is about 35%, 60%, and 82% of the shear stiffness of PBLs when γ equals 0.25, 0.5, and 0.75, respectively. Employing the new rubber rings with varying central angles on conventional PBLs is feasible to obtain the required stiffness for RPBLs. Further, the effects of the number of sectors, the size of side wings, the central angle of hollows, the offset angle, and the thickness of rubber rings were analysed. Based on the numerical results, the proper thickness of side wings is no larger than 2 mm. The thicker side wing could reduce the confinement effects provided by surrounding concrete on concrete dowels, resulting in a drop of the yield load of new RPBLs. The number of sectors is suggested to be no less than 6 so that the shear behavior of new RPBLs is irrelevant to the offset angle. Besides, the shear stiffness is not related to the thickness of rubber rings. To improve the yield load of RPBLs and obtain the moderate recovered stiffness, the thickness of rubber rings is recommended as 2 mm. Finally, the expression for the shear stiffness of new RPBLs was proposed.

Determination of the true projected contact area by in situ indentation testing — ERRATUM

Determination of the true projected contact area by in situ indentation testing — ERRATUM

Micro hardness determination on a rough surface by using combined indentation and topography measurements

Micro hardness determination on rough surfaces is a topic of interest e.g. in industrial applications where the component surface is of functional relevance. In most approaches, hardness on a rough surface is determined by including profile roughness parameters like Ra (e.g., [–]) to adjust measured hardness values or to get the minimum indentation depth value where the influence of the surface topography is assumed to become negligibly small. In the present study, local surface topography data were used instead to enable precise micro hardness measurements on a sample with arbitrary surface topography. Samples made of 1.457 1 stainless steel with different surface states were face milled by using an end mill with different feed rates. Instrumented indentation tests were performed on these samples as well as on comparative samples with polished surfaces. From the resulting load-indentation depth (F-d)-curves the averaged indentation hardness was calculated for all surface states. A method was applied to manipulate and to average the F-d-curves to eliminate deviations, occurring at the beginning of the indentation. The indentation hardness was calculated from these modified F-d-curves and compared to the indentation hardness from the actually measured F-d-curves of the polished samples with feasible results. Using surface topography measurements is considered to enable deriving more accurate indentation hardness values directly and to put the investigations to another level. The surface topography of the samples was evaluated by confocal microscope measurements before and after the indentation tests. From the surface topography data at the location of indentation, four parameters were calculated: volume, projected contact area and depth of the indentation mark, as well as the curvature of the surface topography before indentation. These parameters were correlated with the hardness value from the respective indentation and compared to the indentation hardness of the polished sample. The results of the present study are the basis for combining optical imaging techniques like confocal microscopy or white light interferometry and indentation testing equipment to broaden the field of application.

Nanoindentation of zirconium based bulk metallic glass and its nanomechanical properties

Nanoindentation experiments with a Berkovich tip are performed on zirconium based bulk metallic glass (Zr-BMG, Zr65Cu15Al10Ni10) to study its deformation and mechanical properties (elastic modulus and hardness) at nanoscale. Further to reveal indentation-size effect (ISE), the influence of loading rate and peak and cyclic loads on evaluated nanomechanical properties are investigated in detail. The loading rate has significant effect on serration flow (pop-in), which gets predominant at higher loads. According to the Oliver-Pharr method, hardness becomes peak load-independent, whereas elastic modulus increases with the load. The same phenomenon is observed with sinus and progressive multicycle indentation methods. However, observation of significant pile-up (the ratio of elastic and total energy We/Wt ≈ 0.33 < 0.5) questions the application of the Oliver-Pharr method to Zr-BMG; therefore, evaluated nanomechanical properties are corrected with the projected contact area measured by atomic force microscopic (AFM) and finite element analysis to reduce ISE.

Numerical analysis of the influence of friction conditions on the pile-up effect in Vickers hardness measurements

Vickers indentation load-depth curve may be used to determine basic mechanical properties of metallic materials such as hardness, yield stress, modulus of elasticity, and elastic and plastic work. The pile-up phenomenon observed during indentation causes underestimation of the projected contact area and the diagonal dimensions of the impression in different hardness measurement scales (nano-, micro-, and macro-). The aim of this paper is to conduct a numerical analysis of the effect of friction conditions on the pile-up phenomenon during testing of DC04 steel sheet. The mechanical properties of the sheet metal used for the modelling purpose were first characterized by tensile tests on samples cut along the rolling direction (0°), transverse to the rolling direction (90°) and at an angle of 45° to the rolling direction. The numerical computation was conducted using ABAQUS, which is one of the powerful finite element-based programs. A wide range of variation of friction coefficients, i.e. 0-0.3 has been used in the analysis. It has been observed that the results of indentation of anisotropic materials are significantly affected by friction. The difference in the pile-up height measured at rolling direction of sheet metal and transverse to the rolling direction decreases with the reduction of the maximum displacement of the indenter. For higher values of the coefficient of friction, the higher the value of the indenter displacement, the lower becomes the increase in the pile-up height value.

Determination of the true projected contact area by in situ indentation testing

Abstract

Molecular dynamics and experimental studies of nanoindentation on nanoporous silica aerogels

The nanomechanics during the indentation test on low-density nanoporous silica aerogels remains one of the least understood and explored areas of mechanics. In the present work, we performed nanoindentation using a spherical indenter on silica aerogels to investigate the mechanical properties, such as elastic modulus and hardness, and also, the deformation behaviour. Using all-atom simulations on large samples, the elastic modulus is computed from the elastic part of force–depth curves that can be fitted to the Hertz law, which shows that it increases with density. We proposed a novel approach to calculate the projected true contact area in nanoindentation and to estimate an accurate hardness of silica aerogel, which has a highly complex and randomly arranged network of atoms structure. The experimental studies of nanoindentation are performed on silica aerogel, which reveals that the measured elastic modulus is in good agreement with the simulations. However, the measured hardness values are nearly close to the projected contact area method. It suggests that in all-atom simulations the computed high hardness values using the proposed true area method are the actual local contact pressure. This new understanding may help to expand the use of computer simulations to explore the nanoindentation processes at the molecular level and to advance the macroscopic hardness calculation.

An extension of the general nanoindentation equation regarding cylindrical—shaped samples and a simplified model for the contact ellipse determination

The mechanical properties of biomaterials and biological samples at the nanoscale can be determined using the AFM nanoindentation method. Typical biological samples are the fibrous proteins which can be modelled as cylindrical—shaped samples. However, the nanoindentation method for such samples is a challenging procedure due to the fact that the projected contact area between a spherical indenter and the sample is elliptical and as a result advanced mathematical analysis is required. Several approximations are commonly used to avoid the complexity, which, however, result in significant errors in the analysis. The purpose of this paper is to present a new simplified technique which extends the applicability of the general nanoindentation equation for cases that concern cylindrical—shaped samples. The proposed analysis results in the accurate calculation of the projected contact area and can be generally applied when biological samples and biomaterials with cylindrical symmetry are being tested using spherical indenters.

A novel approach to extracting hardness of copper/niobium (Cu/Nb) multilayer films by removing the substrate effect

This article presents a novel method to eliminate the substrate effect in soft thin film on hard substrate by correcting the projected contact area in nanoindentation test. The hardness of sputtered Cu/Nb multilayer films on silicon substrate with different individual layer thickness was measured by nanoindentation in continuous stiffness mode (CSM) and was shown to be influenced by both indentation size effect (ISE) and substrate effect. Finite element modeling (FEM) and atomic force microscope (AFM) were used to investigate the influence of substrate to the hardness measurement, and the results showed that the hardness deviation induced by the substrate effect resulted from the pile-up can be reasonably removed. Silicon substrate was found to be crucial for the pile-up formation, as the vertical plastic flow of soft Cu/Nb film was restrained by hard silicon substrate with the increase of indentation depth. After applying our pile-up correction and revised Nix-Gao fitting, the hardness curves show a depth independent relation, which fulfills the requirement for accurate hardness measurement. We showed that the hardness deviation due to pile-up is about 14%. Meanwhile, some vague issues like the plateau region and “one-tenth rule” applied in many studies were discussed and clarified basing on our experimental and modeling results. The correcting methods and simulation results could be instructive and significant for nanoindentation hardness test of similar soft film on hard substrate system.