Instrumented Indentation Testing Research Articles

New method to differentiate surface damping behavior and stress absorption capacities of common CAD/CAM restorative materials

ObjectivesTo assess energy dissipation capacities and surface damping abilities of different CAD/CAM restorative materials (CRMs) to characterize stress resistance during load peaks. MethodsUsing instrumented indentation testing (IIT), Martens hardness (HM) together with its elastic (ηIT) and plastic index (ηITdis) and Leeb hardness (HLD) together with its deduced energy dissipation (HLDdis) were determined for eight ceramic, eight composite, and four polymer-based materials as well as three metals. The results were compared to those of bovine enamel. Ten indentations per material were performed at room temperature (23 ± 1 °C) on two separate specimens (12.0 × 12.0 × 3.5 mm3) after water storage (24 h; 37.0 ± 1.0 °C). Hardness parameters were recorded, and data were analyzed with one-way MANOVA (Games-Howell post hoc tests, α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05). ResultsIndependently determined HLDdis, and ηITdis values substantiated different energy dissipation characteristics of CRM, whereby a strong correlation was observed for the two datasets (r = 0.956, p = 0.011). Ceramics had the significantly lowest values (p < 0.001) while both parameters revealed the highest surface damping effects for metals (p < 0.001), followed in both cases by bovine enamel. Energy dissipation of polymer and composite CRM was in between ceramics and bovine enamel (p < 0.001), whereas only for HLDdis did both show no significant difference (p > 0.05). SignificancePromising new HLDdis and ηITdis data allow a reliable differentiation of energy dissipation and surface damping capacities of CRMs. Previously published rankings of edge chipping and loss tangent results were perfectly reproduced, especially by HLDdis.

Data-driven estimation of plastic properties of alloys using neighboring indentation test

A data-driven estimation method for the plastic properties of alloys was proposed using indentations at neighboring positions. An instrumented indentation test is an efficient approach to measure m...

Verification of radial displacement correction effect in instrumented indentation testing

The radial displacement had been ignored in the analysis of unloading curve of instrumented indentation test. There are two representative methods of radial displacement correction, proposed by Hay et al. [J. Mater. Res., 14, 2296, (1999)] and Chudoba-Jennett [J. Phys. D, 41, 215407, (2008)]. In this study, we examine the effect of radial displacement corrections in finite element analysis and experiments.

Tungsten-Copper Composites for Arcing Contact Applications

The study presents the research findings on electrical contact materials based on tungsten-copper (W-Cu) composites containing 72 ± 3 wt.% W, rest Cu, and up to 1.5 wt.% Ni. Cylindrical sintered parts with 57 ± 0.5 mm in diameter and 12 ± 0.5 mm in height were manufactured by pressing, sintering, and liquid infiltration route, then were mechanically polished and processed as complex shape protection rings used as arcing contacts in high voltage circuit breakers (HVCBs). The surface elemental composition of the sintered parts was determined by wavelength dispersive X-ray fluorescence spectrometry. The density was determined by hydrostatic weighing in ethanol. The arithmetic mean surface roughness was measured by contact profilometry. The microstructure was studied by scanning electron microscopy. The electrical conductivity was measured by eddy current method. The thermal diffusivity and specific heat were determined by laser flash analysis. Instrumented indentation testing and two computational methods (Oliver &amp; Pharr, and Martens hardness) were employed to study the mechanical properties under quadratic loading and continuous multi cycle (CMC) indentation mode. The functional behavior of the arcing contacts was assessed in terms of static and dynamic contact resistance in operation in minimum oil HVCBs of 110 kV. The properties investigation revealed highly dense contact parts with homogeneous microstructure, Vickers hardness of 260-374, elastic modulus of 185-311 GPa, as well as good electrical and thermal conductivity. The arcing contacts proved a good functional behavior. in service, too. The results endorse the developed sintered contact materials for implementation in practical applications.

Evaluation of Cryogenic Mechanical Properties of Resistance Seam-Welded Invar Alloy Sheet by Instrumented Indentation Test

Invar alloy sheet was welded by resistance seam welding (RSW) with a constant electrode force and three different welding currents. Tensile properties were evaluated using instrumented indentation testing (IIT) with a spherical indenter and microstructure observations were obtained under an optical microscope. IIT performed on the base material at room temperature (RT) and −163 °C, a cryogenic temperature (CT), gave results in good agreement with those of tensile testing. The strength of each zone was higher in the order of heat-affected zone (HAZ) &lt; weld nugget (WN) &lt; base material (BM) because the amount of cold working was least in the BM, heavy metal elements and carbon vaporized during melting, and the WN was formed more tightly than the HAZ, effectively constraining the plastic zone generated by the indentation. As for the welding current, the nugget, which becomes larger and tighter as the current increases, more effectively constrained the plastic zone in the indentation, and this soon increased the strength. Generally, Invar is known to consist of single-phase austenite, and microstructure observations have confirmed that the average grain size is ordered as BM &lt; HAZ &lt; WN. Fan-like columnar grains developed in the direction of the temperature gradient, and equiaxed grains were observed near the BM. It was confirmed that the grain size in the WN also increases as the current is increased. Interestingly, the constraint effect with increasing nugget size was more important for strength than the grain size.

Evaluation of the Elastic Compliance of the Hardness Tester in Instrumented Indentation Tests

The elastic compliance of the instrument (hardness tester) should be taken into account when determining the mechanical properties of materials by means of instrumented indentation with registration of indentation diagrams. The values of Young’s modulus of the tested materials significantly depend on the method for evaluating and accounting for elastic compliance. Therefore, the methods should be verified during instrumented indentation of materials with known but very different Young’s moduli. Successful experience in evaluating and accounting for elastic compliance of the instrument during the instrumented indentation of materials with a diamond pyramid has already been accumulated to date. This is reflected in the relevant standards. However, this experience cannot be applied to instrumented indentation with a steel ball or hard-metal ball without additional research and experimental verification. We propose a method for evaluating the elastic compliance of the hardness tester using the instrumented diagram of ball indentation based on the Hertz equation in the case of elastic contact of the ball with the plane. It is found that additional elastic deformations of the links of instrument are directly proportional to the indentation load; this dependence is typical of each instrument and the diameter of the ball does not affect it. This dependence allows one to take into account the elastic compliance of the instrument using software when registering and processing diagrams of ball indentation. Experiments to determine Young’s modulus and hardness by instrumented ball indentation of various materials (steel, aluminum alloy, magnesium alloy, and titanium alloy) using the known and proposed methods to account for the elastic compliance of the instrument are performed. The main criterion confirming the reliability of the method is the coincidence or proximity of the values ​​of Young’s modulus of the same material determined from the diagram of ball indentation and the diagram of tension of the sample. The advantages and disadvantages of the known and proposed methods are described. Practical recommendations for use of these methods are given.

Mechanical properties and wear behaviour of alumina/tricalcium phosphate/titania ceramics as coating for orthopedic implant

This research work reports the impact of adding synthesized Tricalcium Phosphate (β-TCP) and commercial Titania powder (TiO2) on the mechanical and tribological properties of Alumina (Al2O3). In fact, the commercial Al2O3 mingled with β-TCP and commercial (TiO2) to obtain a mixture which considered as a bioactive coating that may be used in orthopedic implants. Representative bioceramic samples of such blends were prepared with different formulations and then tested using numerous methods and techniques. Mechanical properties, hardness and fracture toughness were evaluated by semi-circular bending (SCB) and instrumented indentation tests. A pin-on-disk tribometer was retained to ensure friction and wear experiments against zirconia ball. A 2D profilometer was used to measure and estimate the wear volume generated after sliding tests. Scanning electron microscopy (SEM) was equally used to examine wear mechanisms for worn surfaces of the tested samples.From the main results, it was found that the best wear resistance was measured for Al2O3-10 wt% TCP-5 wt% TiO2 formulation under dry conditions. Also, the lowest friction coefficient was found to correspond to the same biocomposite. Finally, the best mechanical and fracture properties, in terms of micro-hardness and fracture toughness, were obtained for Al2O3-10 wt% TCP −5 wt% TiO2 composition.

Micromechanics and indentation creep of magnesium carbon nanotube nanocomposites: 298 K–573 K

In the present study, the time-dependent plastic deformation (creep) response of magnesium/carbon nanotube (CNT) nanocomposites containing 0.25, 0.5, and 0.75 vol% of CNTs is investigated through instrumented indentation tests against monolithic pure magnesium. The Mg-CNT nanocomposites were synthesized via powder metallurgy coupled with microwave sintering followed by hot extrusion. Indentation creep tests were performed at 298, 373, 473, and 573 K with a cubic boron nitride Berkovich indenter. Creep tests are dual-stage, i.e., all tests involve loading to a prescribed peak load (50 mN), holding this peak load constant for a set dwell period (120 s), and finally unloading. Three load rates of 0.5, 5, and 50 mN/s were tested. Results are explained through hardness, microstructure, and CNT volume fraction in each sample. Mg reinforced with 0.25–0.5 vol% CNTs exhibit the best creep resistance. At the ambient temperature of 298 K, dislocation creep is the dominant creep mechanism. At elevated temperatures, multiple creep mechanisms are identified. However, diffusion creep mechanisms are expected to prevail when temperatures exceed 573 K. These materials are promising candidates for aerospace, automotive, military, and many other industrial applications. To this end, the findings of this study can be used for material selection in these industries. This work may also be used as a baseline for future high-temperature nanoindentation creep studies on other nanocomposites.

Determining the constitutive behavior of nonlinear visco-elastic-plastic PMMA thin films using nanoindentation and finite element simulation

Understanding the nonlinear visco-elastic-plastic behavior and properties of PMMA thin films during nanoindentation is helpful for predicting the plastic deformation of thermoplastic polymer products during manufacture and evaluating stress to predict the reliability and failure behavior of their service structures. This article reports a study on the nanoindentation of PMMA thin films via instrumented indentation testing and numerical simulation to determine its constitutive behavior. It is found that both the loading curve and the unloading curve at any depth can be generated from one indentation depth for the indentation tests of PMMA thin films with Berkovich indenter. By coupling experimental investigation and finite element simulation, we investigated the possibility of applying the Oyen-Cook constitutive equation to nonlinear viscous-elastic-plastic PMMA thin films. The results of finite element analysis show that the time-dependent elastic-plastic deformation of the unloading curves becomes more conspicuous when the quadratic viscosity term of the Oyen-Cook constitutive equation is decreased. Finite element simulations using the Oyen-Cook constitutive model reproduce the experimentally-measured indentation load-displacement curves with reasonable accuracy.

Analysis of the Thermomechanical Fatigue Behavior of Fully Ferritic High Chromium Steel Crofer®22 H with Cyclic Indentation Testing

The 22 wt.% Cr, fully ferritic stainless steel Crofer®22 H has higher thermomechanical fatigue (TMF)- lifetime compared to advanced ferritic-martensitic P91, which is assumed to be caused by different damage tolerance, leading to differences in crack propagation and failure mechanisms. To analyze this, instrumented cyclic indentation tests (CITs) were used because the material’s cyclic hardening potential—which strongly correlates with damage tolerance, can be determined by analyzing the deformation behavior in CITs. In the presented work, CITs were performed for both materials at specimens loaded for different numbers of TMF-cycles. These investigations show higher damage tolerance for Crofer®22 H and demonstrate changes in damage tolerance during TMF-loading for both materials, which correlates with the cyclic deformation behavior observed in TMF-tests. Furthermore, the results obtained at Crofer®22 H indicate an increase of damage tolerance in the second half of TMF-lifetime, which cannot be observed for P91. Moreover, CITs were performed at Crofer®22 H in the vicinity of a fatigue crack, enabling to locally analyze the damage tolerance. These CITs show differences between crack edges and the crack tip. Conclusively, the presented results demonstrate that CITs can be utilized to analyze TMF-induced changes in damage tolerance.

A macro-pillar compression technique for determining true stress-strain curves of steels

Instrumented indentation testing (IIT) is extensively and successfullyused as an alternative technique for investigations of the mechanical properties of steels, where traditional specimens, such as round bar specimens for tensile tests, are not acquirable. The IIT is based on an assumption that the true stress-strain curve of the analyzed sample follows one of the known constitutive equations, such as the Hollomon, Ludwik, Swift, or other predefined equations. However, steel samples exposed to extreme conditions, such as media with high-temperature or neutron irradiation may exhibit a novel stress-strain relation that follows an unknown constitutive equation. In this situation, the accuracy of the IIT may be doubtful. This article proposes a constitutive model independent technique, called macro-pillar compression testing (MPCT), where constitutive equations are not necessary. The MPCT was conducted on a specimen with pillars and established on the theory of the compression testing. In this study, a modified imaginary radius function was proposed for the pillar to consider its sinking and barreling effect during the compression. Finally, three different types of steel (austenitic stainless, low-alloy and low-carbon steel) were used to verify the accuracy of the MPCT. Both MPCT and round bar tensile tests were performed on each type. The test results show that the true strain-stress curves obtained by MPCT have a good agreement with the corresponding curves by tensile tests.

Influence of growth defects on the running-in behavior of an a-C:H:W coating under pure sliding contact conditions

The mechanical and tribological behaviors of coated surfaces are affected by the presence of local variations on coating composition, morphology and microstructure. During the deposition process, irregular surface topography and/or process instabilities can produce regions with macroscale defects, including voids and macroparticles. The interface between those regions and other portions of the coating presents an irregular columnar structure, identified by discrepancies between two consecutive columns, which may lead to local lower mechanical properties. In this work, numerical and experimental analyses were conducted to explore the effect of growth defects with irregular columnar boundaries (GDICB) on the mechanical and tribological behavior of a Tungsten Carbide/Carbon (a-C:H:W) multilayer coating subjected to multiscale tribological tests, including macroscale reciprocating tests and microscale scratch tests. Samples consisted of a commercial a-C:H:W coating deposited onto polished AISI H13 discs and AISI 52100 steel balls. Mechanical properties and microscale surface topography were evaluated using a triboindenter capable of carring out instrumented indentation tests and scanning probe microscopy techniques, while the microstructure was observed by scanning electron microscopy analyses. Macroscale reciprocating tests revealed a variable GDICB mechanical behavior, including deformation and detachment of those regions inside the wear track in the beginning of the test. Microscale scratch test results indicated a load-dependent mechanical behavior of the GDICB, showing a transition from deformation to detachment mechanism with the increase in the normal load. The digital tribology package TriboCODE was applied to model a realistic representation of the microscale scratch test, allowing the identification of individual GDICB behavior dependence on the applied normal load and the local mechanical properties.

A Further Study on Knoop Indentation Plastic Deformation for Evaluating Residual Stress

A method for evaluating residual stress using an instrumented indentation test was developed some decades ago. More recently, another method was developed, using a Knoop indenter. The conversion factor ratio, which is one of the key factors in the evaluation algorithm, has been taken to be 0.34, although this value comes from an experimental result and its physical meaning has not been examined. Here we examine the physical meaning of this conversion factor from the previous residual stress model, and calculate its ratio using analytical model of the stress field beneath the indenter. In this process, we assumed that the conversion factor ratio was the ratio of the projected area of the plastic zone generated during the Knoop indentation test. An analysis of the stress field beneath the indenter was performed by FE simulation. Actual nanoindentation was conducted after Knoop indentation testing, using the interface-bonding technique, to identify the plastic zone. In addition, the conversion factor ratio was also calculated for the case where residual stress was present, and the geometric ratio of the Knoop indenter was different. A comparison of our results with those from previous studies showed that the conversion factor ratio obtained using our assumption was in good agreement with previous studies.

Computational modeling of viscoplastic polymeric material response during micro-indentation tests

The computational modeling of instrumented indentation tests used to characterize material properties is challenging. It is mainly due to the computational techniques demanded to couple the complex physical mechanisms involved, such as, for example, the time-dependent inelastic material response to loads during contact. Therefore, this work aims to simulate the mechanical response of the poly vinylidene fluoride (PVDF) during a micro-indentation test considering a viscoplastic material model, and a prescribed load approach, using the finite element method. Further, model validation is performed based on experimental data measured during the contact between the indenter and the PVDF. Numerical analyses were performed using COMSOL Multiphysics finite element software considering the loading scheme of the experimental tests of 800 mN/min rate during loading and unloading, and a 400 mN constant load, held by 30 s. Finally, a viscoplastic Chaboche constitutive model is presented considering two cases: (1) a perfectly plastic behavior, and (2) a nonlinear isotropic hardening behavior based on Voce and Hockett–Sherby exponential laws. While the latter models exhibit some discrepancy in capturing the experimental behavior, the former one has shown excellent agreement with the load-depth curves obtained experimentally, achieving the best fitting for the set of Chaboche parameters: $$A=1\,{\mathrm{{s}}}^{-1}, {n}=4.62$$ and $$\sigma _\mathrm{{ref}}=132$$ MPa. Moreover, several phenomenological features of viscoplastic behavior such as rate dependence, plastic flow (or creep) and stress relaxation were accurately provided by the Chaboche model when describing the behavior of the PVDF material.

On the use of instrumented indentation to characterize the mechanical properties of functionally graded binary alloys manufactured by additive manufacturing

The mechanical properties of a Ti-xNb functionally graded material (FGM) created by using an additive manufacturing process (CLAD®) were obtained using a spherical instrumented indentation test (IIT). The aim of this paper is to demonstrate the great suitability of the indentation test coupled with FGM for not only obtaining the hardness of a material, but also obtaining other mechanical properties such as Young’s modulus, yield stress and the work-hardening exponent for heterogeneous materials. In the first step, results obtained from the instrumented indentation test were compared with those obtained from the tensile test for the same materials. These results show that these two tests highlight a similar evolution in the mechanical properties. In the second step, and after validating the efficiency of the IIT in obtaining mechanical properties, the FGM Ti-xNb was successfully identified using only IIT. This paper demonstrates that the different mechanical properties of all the compositions of a phase diagram can be measured very easily and quickly while minimizing the number of samples.

The Use of Laboratory Indentation Testing to Characterize Champlain Sea Clay

This paper presents a description, the results and analysis of instrumented indentation testing of intact specimens of a Champlain Sea Clay. Five indenters of different geometries and composed of different metals were used. Indentation was conducted to target loads that varied from 2 to 32 N with unloading and force, P, versus penetration, h, curves were recorded. Conventional geotechnical testing was also conducted on the clay. These included index property and characterization testing as well as consolidation, unconfined compression and consolidated undrained triaxial compression. Existing analytical and theoretical solutions were applied to the indentation test results to deduce the hardness, undrained shear strength and Young’s modulus. However, these were found to be not applicable to the clay for a few reasons. An innovative analytical solution that considers the behavior of the clay and the geometry of the indenters is proposed. It was found that a penetration of 4 mm is necessary for the hardness to reach a constant asymptotic value. The proposed solution was validated using indentation test data.

Estimation of Fracture Toughness Using Flat-Ended Cylindrical Indentation

A method is proposed to predict the fracture toughness of in-service structures using the instrumented indentation test. While previous studies have attempted to predict fracture toughness using spherical indenters, we propose the method to predict fracture toughness using flat-ended cylindrical indenters. Using the geometric similarity of a cylindrical indentation test and the Cracked Round Bar (CRB) fracture toughness test, fracture toughness values were derived from a single indentation test by assuming that the load–depth curve of the indentation test is the same as the load–displacement curve of the CRB fracture toughness test. To determine the crack initiation point, the concept of limit load in CRB testing is adopted, and a new load–depth curve is obtained using a suggestion in the standard of fracture toughness test. In order to apply the proposed method directly to in-service structures, the model uses mechanical parameters that can be obtained by indentation testing. The model was verified on metallic materials primarily used in nuclear power plants.

A Damage Criterion to Predict the Fatigue Life of Steel Pipelines Based on Indentation Measurements

Abstract A study was conducted to investigate the effects of surface microhardness on different phases of fatigue damage. This helps to estimate the evolution of the material resistance from microplastic distortions and gives pertinent data about cumulated fatigue damage. The objective of this work is to propose a damage criterion, associated with microstructural changes, to predict the fatigue life of steel structures submitted to cyclic loads before macroscopic cracking. Instrumented indentation tests (IIT) were conducted on test samples submitted to high cycle fatigue (HCF) loads. To evaluate the role of the microstructure initial state, the material was considered in two different conditions: as-received and annealed. It was observed that significant changes in the microhardness values happened at the surface and subsurface of the material, up to 2 µm of indentation depth, and around 21% and 7% of the fatigue life for as-received and annealed conditions, respectively. These percentages were identified as a critical period for microstructural changes, which was taken as a reference in a damage criterion to predict the number of cycles to fatigue failure (Nf) of a steel structure.

Mechanical characterization of meso-porous alumina by micro- and nano-indentation

Meso-porous γ-alumina ceramics used as catalyst supports are characterized by high porosity fraction (>70 %) and specific surface area (>200 m²/g) targeted to ensure high catalytic performances, but at the expense of the mechanical strength. The aim of this work is to link the mechanical properties of three different catalyst supports with their microstructure. Instrumented indentation tests were performed at two different length scales to assess mechanical properties at both macroscopic scale (support) and at constituents scale (grains and matrices). The distribution of porosity fraction in grains and matrices is estimated with image processing on Scanning Electron Microscopy (SEM) pictures. The mechanical behavior of catalyst supports are strongly influenced by their microstructure. In spite of a larger porosity fraction, macro-and meso-porous grains exhibit higher mechanical properties than the matrices. Matrix of the three alumina supports have almost similar volume fraction of porosity but different mechanical properties. Finally, Focused Ion Beam (FIB) cross-sections of residual indents indicate a damageable behavior under contact loading, with densification of larger pores.

Application of a portable indentation rig with Rockwell indenter to determine mechanical properties and residual stresses on an aluminum plate

Measuring residual stresses is still a dilemma in many engineering applications. It is even more crucial when the industrial requirements demand for a non-destructive technique in order to avoid compromising the structural integrity of the engineering components. Furthermore, estimating the mechanical properties of the materials, especially when the components are aged, is of importance. Instrumented indentation has gained much interest in recent years. There are many studies in the literature which are focused on measuring residual stresses or mechanical properties using instrumented indentation. Since in many cases there is no possibility of transferring large samples or those under service, for possible measurements, having a portable rig can be very useful. Furthermore, indentation procedure is a low-cost non-destructive method with high accuracy which is able to measure the plastic properties of material as well as its residual stresses on which the designing and construction of the portable apparatus were based. The instrumented indentation testing details were followed according to the ASTM E2546-15 standard practice. In this research, a wide range of simulations were performed on a group of aluminum alloys in order to estimate the equi-biaxial residual stresses by analyzing the indentation load–displacement curves which were obtained from the experimental outcomes. Then neural networks were employed to estimate the unknown parameters. The performance accuracy of the designed portable apparatus and the acceptable precision of the introduced method were then verified with experimental tests performed on Al 2024-T351.