Instrumented Indentation Testing Research Articles

Calibration of machine platform nonlinearity in Instrumented Indentation Test in the macro range

Instrumented Indentation Test (IIT) is a non-conventional mechanical characterization technique to evaluate hardness, Young modulus, creep and relaxation of materials. In the macro range, it represents a cheaper and faster alternative to conventional tensile-based tests. IIT is a metrological scale; thus, to establish traceability, calibration is essential. Frame compliance calibration is critical because it is a major contribution to the measurement uncertainty. This work discusses the limits of the current state-of-the-art and proposes a novel methodology for frame compliance calibration. The introduced approach demonstrates the source of common systematic errors in the mechanical characterization reported in the literature, i.e. edge effect, while first highlighting a relevant frame compliance nonlinearity. The proposed procedure is cost-effective and relies upon constitutive spring modelling of IIT and calibration of reference block by nanoindentation. Results show that the novel approach corrects systematic trends in the characterization and yields a relative measurement uncertainty of 5%.

Improvement of instrumented indentation test accuracy by data augmentation with electrical contact resistance

Instrumented Indentation Test allows thorough surface multi-scale mechanical characterisation by depth-sensing the indenter penetration and correlating it with the indenter-sample contact area and the applied force. Localised plastic phenomena at the indentation edge, i.e. pile-up and sink-in, may bias the characterisation results. Current approaches attempt correcting related systematic errors by numerical simulation and AFM-based techniques. However, they require careful tuning and complex and expensive experimental procedures. This work proposes a methodology based on in-situ Electric Contact Resistance which augments information on the contact area and allows edge effect correction. The methodology is demonstrated and validated on industrially relevant metallic materials.

A new instrumented spherical indentation test methodology to determine fracture toughness of high strength steels

A new instrumented spherical indentation test (ISIT) methodology is proposed to determine fracture toughness of metallic materials that their strain hardening can be adequately described by a power-law function. Firstly, tensile properties, including Young’s modulus (E), yield stress (σy) and strain hardening exponent (n) are determined by an improved representative stress–strain method with the Meyer power-law correction. Secondly, by performing dimensional analysis and finite element computation, a new dimensionless function of critical indentation contact pressure (Pmcr) versus tensile properties is developed. To generalize the above dimensionless function to a broad scale of metallic materials, 100 different combinations of tensile properties have been implemented in the finite element computation of spherical indentation tests. Consequently, Pmcr of various tested metallic materials can be calculated conveniently by substituting the corresponding tensile properties into the dimensionless function. The critical indentation depth (hccr) of metallic materials can then be determined by identifying Pmcr on the curve of mean contact pressure versus indentation depth. Finally, fracture toughness is calculated by the concept of indentation energy to fracture at hccr. To demonstrate the repeatability of the above methodology, it has been applied to predict fracture toughness of three different high strength steels by two research groups, independently. The best measurement capacity of the present approach could be optimized in a relative small error, as ±6 % in tensile properties and ±10 % in fracture toughness, that is close to the conventional standard testing results upon multiple samples of the same group.

Εffect of cleansers on the composition and mechanical properties of orthodontic aligners in vitro

BackgroundThe aim of the study was to investigate the effect of three aligner cleaners on the composition and mechanical properties of two types of orthodontic aligners.Materials and methodsThe cleaners tested were two alkaline peroxide solutions (Retainer Brite—RB; Retainer Cleaner—RC) and one peroxide-free (Steraligner—ST) and the aligners Clear Aligner (C, polyester) and Invisalign (I, polyester–urethane). The aligners were immersed in the cleaner solutions as instructed every day (15 min for RB, RC; 5 min for ST) for a two-week period. The acidity of the solutions was tested with a pH meter. The changes in the chemical composition of the aligners were studied by attenuated total-reflection Fourier transform infrared spectrometry (ATR-FTIR), while Instrumented Indentation Testing (IIT) was used for assessment of changes in Martens Hardness (HM), modulus (EIT), elastic index (nIT) and relaxation (RIT).ResultsRB and RC were weakly acidic (pH = 6.3), whereas ST was mildly acidic (pH = 4.8). The ATR-FTIR analysis demonstrated evidence of acidic hydrolysis of C in ST and I in RB. The IIT-derived properties of I were not affected by the cleaners. However, for C a significant change was found in HM (all cleaners), nIT (all cleaners) and RIT (RB, ST). Although the chemical changes support a hydrolytic material deterioration, the results of mechanical properties may interfere with the material residual stresses during fabrication.ConclusionsCaution should be exerted in the selection of aligner cleaners. The mild acidic cleanser was more aggressive to the polyester, whereas an alkaline peroxide to the polyester–urethane aligner.

Determining the elastic modulus of film/substrate materials from instrumented indentation testing based on machine learning

<p indent="0mm">Instrumented indentation testing has been widely used to determine the mechanical properties of materials. However, due to the substrate effect, the mechanical properties of each layer of film/substrate material becomes complicated to determine using this method. Through the finite element simulation, combined with a classic neural network method of multi-output multilayer perceptron (MLP), the relationship between the film/substrate material parameters (elastic modulus of film and substrate), normalized indentation depth (indentation depth/film thickness), and composite modulus is established. This established relationship is used to develop an indentation method to determine the elastic modulus of film/substrate. Prediction results through deep learning and the finite element simulation results are compared. The comparison results indicate that the predicted values of hard film/soft and soft film/hard substrate materials obtained from MLP are in good agreement with the simulation results. Indentation tests of Ni/304 and Cu/304 stainless steel were conducted to verify the trained neural network. The results indicate that elastic modulus of each layer predicted using the MLP is close to those obtained in the test. The results of this study can provide alternative research methods for evaluating the properties of film/substrate materials.

Characterization of the local mechanical properties of 5083-5383 MIG welded joints

act. Due to the heat input effect, the weld seam and heat-affected zone (HAZ) are strength weakened phases in 5xxx aluminum welded joints. Therefore, the local mechanical properties of the 5xxx aluminum welded joint are worth studying for structural design. In this paper, the local mechanical properties of 5083-5383 MIG joints were studied. Through instrumented indentation and tensile tests with digital image correlation (DIC), the yield strength of the same area of the weld center, heat-affected zone, and the base metal (BM) was respectively characterized. The two methods show good consistency in the characterization of the yield strength in each region. The tensile strength of the weld zone and BM characterized by two methods also represent good consistency. The HV0.1 and HV10 Vickers hardness distribution of welded joints was studied, and the differences in the characterization of local mechanical properties of 5083-5383MIG welded joints by instrumented indentation test, tensile test with DIC and Vickers hardness are analyzed. The instrumented indentation test can be used for approximate non-destructive quantitative characterization of the local mechanical properties of 5083-5383 MIG welded joints.

Resin-Based Bulk-Fill Composites: Tried and Tested, New Trends, and Evaluation Compared to Human Dentin.

A more-and-more-accepted alternative to the time-consuming and technique-sensitive, classic, incremental-layering technique of resin-based composites (RBCs) is their placement in large increments. The so-called bulk-fill RBCs had to be modified for a higher polymerization depth and already have a 20-year history behind them. From the initial simple mechanisms of increasing the depth of cure by increasing their translucency, bulk-fill RBCs have evolved into complex materials with novel polymerization mechanisms and bioactive properties. However, since the materials are intended to replace the tooth structure, they must be comparable in mechanical behavior to the substance they replace. The study compares already established bulk-fill RBCs with newer, less-studied materials and establishes their relationship to dentin with regard to basic material properties such as hardness and indentation modulus. Instrumented indentation testing enables a direct comparison of tooth and material substrates and provides clinically relevant information. The results underline the strong dependence of the measured properties on the amount of filler in contrast to the small influence of the material classes into which they are classified. The main difference of RBCs compared to dentin is a comparable hardness but a much lower indentation modulus, emphasizing further development potential.

Damping Behaviour and Mechanical Properties of Restorative Materials for Primary Teeth.

The energy dissipation capacity and damping ability of restorative materials used to restore deciduous teeth were assessed compared to common mechanical properties. Mechanical properties (flexural strength, modulus of elasticity, modulus of toughness) for Compoglass F, Dyract eXtra, SDR flow, Tetric Evo Ceram, Tetric Evo Ceram Bulk Fill, and Venus Diamond were determined using a 4-point bending test. Vickers hardness and Martens hardness, together with its plastic index (ηITdis), were recorded using instrumented indentation testing. Leeb hardness (HLD) and its deduced energy dissipation data (HLDdis) were likewise determined. The reliability of materials was assessed using Weibull analysis. For common mechanical properties, Venus Diamond always exhibited the significantly highest results and SDR flow the lowest, except for flexural strength. Independently determined damping parameters (modulus of toughness, HLDdis, ηITdis) invariably disclosed the highest values for SDR flow. Composite materials, including SDR flow, showed markedly higher reliabilities (Weibull modulus) than Compoglass F and Dyract eXtra. SDR flow showed pronounced energy dissipation and damping characteristics, making it the most promising material for a biomimetic restoration of viscoelastic dentin structures in deciduous teeth. Future developments in composite technology should implement improved resin structures that facilitate damping effects in artificial restorative materials.

Mechanical and electrochemical characterization of 3D printed orthodontic metallic appliances after in vivo ageing.

Three-dimensional (3D) printing technology is a promising technique for fabricating custom orthodontic metallic appliances. Aim of this study was to assess the effect of intraoral aging on the mechanical / electrochemical properties of 3D-printed orthodontic metallic appliances. Twelve molar orthodontic distalization appliances 3D-printed from cobalt chromium (Co-Cr) alloy were retrieved after intraoral use and twenty blocks fabricated under similar conditions were used as control. The samples' microstructural / elemental composition assessment was assessed with SEM/EDS, while their mechanical properties (modulus of elasticity [EIT], Martens hardness [HM] and the elastic index [ηIT]) were measured by instrumented indentation testing. Finally, the samples' electrochemical features were assessed with a potentiostat-connected cell arrangement in terms of open circuit potential (OCP), corrosion potential (Ez), current density (I300) and breaking potential (Epit). Results were analyzed by t-test / Mann-Whitney test (α=0.05). The used Co-Cr alloy was found to have a highly homogenous structure with no significant differences between retrieved and new specimens in HM (4037.7±215.6 vs 4090.9±259.8N/mm2), EIT (120.0±13.2 vs 123.8±12.9GPa), or nIT (28.4±2.6 vs 28.6±2.9 %) (P>0.05 in all instances). Metallic surfaces retained the same oxidation tendency and oxide dissolution rate in passive region in both groups (P>0.05 for OCP, Ez, and I300). However, intraorally-aged specimens had a significantly lower breakdown potential due to degraded protection efficacy of surface oxide (P=0.003 for Epit). The tested 3D-printed Co-Cr orthodontic appliances present clinically-acceptable mechanical properties that remained unaffected by intraoral ageing, which however degraded the protection of surface oxide against pitting corrosion.

Data-driven estimation of plastic properties in work-hardening model combining power-law and linear hardening using instrumented indentation test

Data-driven estimation of plastic properties in work-hardening model combining power-law and linear hardening using instrumented indentation test

The P-h2 relationship as a function of (hf/hm) in indentation

In the present study, a semi-empirical modeling of the mechanical response in pile-up mode is obtained by deriving the load-depth relationship during the indentation loading cycle. The advantage compared to the relations previously used is that this new expression is a function of the predictable criterion of the mode of deformation, (hf/hm), which makes it possible to distinguish the sink-in mode from the pile-up mode. A comparison between the proposed expression and the results of the instrumented indentation tests shows excellent agreement.

Instrumented indentation based methods to assess fracture toughness (KIC) of self-compacting concrete: Influence of water to binder (w/b) ratio and type of concrete

The main objective of this paper is to compare the fracture toughness determined by instrumented indentation tests of a variety of self-compacting concretes (SCCs) and normal vibrated concretes (NVCs). For this purpose, five mixing compositions of self-compacting concrete (SCC) with different water/binder ratios of 0.33 to 0.41 (water/cement ratio = 0.44 to 0.56) and two mixing compositions of normal vibrated concrete (NVC) were prepared. The fracture behaviors of both (SCCs) and (NVCs) with laboratory-size specimens under the instrumented indentation test (IIT) were investigated. It was found that the fracture toughness values of the self-compacting concrete increased with the decreasing w/b ratio. The largest values of the stress intensity factor (KIC) were showed on the concretes with the lowest (w/b) ratio (w/b = 0.33, the case of SCC5). Moreover, it is confirmed that the self-compacting concretes exhibit larger fracture toughness than those of the normal vibrated concretes at the same compressive strength. The obtained results indicated that there existed a remarkable relationship between the water/binder (water/cement) ratio, fracture behavior and mechanical properties of these materials. It is shown that the instrumented indentation technique can be very useful for determination of the fracture parameters.

Solid-State Rotary Friction-Welded Tungsten and Mild Steel Joints

This paper is a study of the microstructure and other selected properties of solid-state, high-speed, rotary friction-welded tungsten and mild steel (S355) joints. Due to the high affinity of tungsten for oxygen, the welding process was carried out in a chamber with an argon protective atmosphere. Joints of suitable quality were obtained without any macroscopic defects and discontinuities. Scanning electron microscopy (SEM) was used to investigate the phase transformations taking place during the friction welding process. Chemical compositions in the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). The microstructure of friction welds consisted of a few zones, fine equiaxed grains (formed due to dynamic recrystallization) and ultrafine grains in the region on the steel side. A plastic deformation in the direction of the flash was visible mainly on the steel side. EDS-SEM scan line analyses across the interface did not confirm the diffusion of tungsten to iron. The nature of the friction welding dissimilar joint is non-equilibrium based on deep plastic deformation without visible diffusive processes in the interface zone. The absence of intermetallic phases was found in the weld interface during SEM observations. Mechanical properties of the friction-welded joint were defined using the Vickers hardness test and the instrumented indentation test (IIT). The results are presented in the form of a distribution in the longitudinal plane of the welded joint. The fracture during strength tests occurred mainly through the cleavage planes at the interface of the tungsten grain close to the friction surface.

Determination of local density in components made by fused deposition modeling through indentation test

The present study is aimed at determining the local density of components made by fused deposition modeling (FDM) through non-destructive indentation tests. An experimental campaign was performed to assess such a relationship. Specimens were made varying the amount of material flow and the direction of deposition. The specimen’s dimension and weight were measured to determine the average density. The internal porosity due to uncomplete filling produced due to the deposition process was also assessed through cross-sectioning. Instrumented indentation tests were conducted on the samples to determine a relationship between the density and the slopes during the loading and unloading phases. The tests were performed using flat cylindrical indenters of different diameters. The results indicated that the density of the specimens was strongly influenced by the adopted material flow and the orientation during deposition. An empirical relationship was determined between the slopes measured during indentation tests and the density. Such a relationship is independent of the deposition orientation. The optimized procedure represents a valuable tool to determine the local density of components made by fused deposition modeling through non-destructive indentation tests.

Identification Method for Material Constants in Johnson–Cook Model Associated With Strain-Rate and Temperature Sensitivities Using Ball Impact and Indentation Tests

Abstract The Johnson–Cook (JC) flow stress model can simply express the strain-rate and temperature dependencies of the flow stress. We previously proposed a concept of a simple identification method for material constants in the JC model associated with the strain-rate and temperature sensitivities (JC parameters C and m) at high-strain rates. However, several issues still exist in our method for practical use. In this study, we modified our method to identify both the JC parameters C and m. The fundamental concept was formulated based on the requirement that the normalized indentation depths obtained from the ball impact and instrumented ball indentation tests are equal to each other. In addition, the conversion factor was derived to transfer from the impact velocity to the strain rate. The ball indentation and impact analyses based on a finite element method were conducted to verify the established method. The analysis results obtained under idealized conditions demonstrated that C and m can be accurately identified using the established method, even at exceeding 104 s−1. Changes in the radius of the impactor are more effective in obtaining different strain rates than changes in the impact velocity because the identification accuracy can be ensured at lower than 200 m/s.

A new spherical indentation approach to determine fracture toughness of high strength steels

Fracture toughness indicates the resistance to unstable crack growth that is very important in the assessment of structural integrity. As the Instrumented Indentation Test (IIT) technique is relatively simple to perform, it has been suggested as an alternative way to determine fracture toughness of engineering materials. This paper presents a new spherical IIT approach to predicting fracture toughness of engineering materials using the critical contact pressure. Firstly, according to Johnson’s maximum strain energy theory under indentation, the formula of critical contact pressure under IIT is derived by considering strain hardening and fundamental tensile properties. Secondly, by using an automatic iterative procedure of translating the input and output data between MATLAB and ANSYS, finite element analysis is carried out to build a dummy database of critical contact pressure versus strain hardening and tensile properties for a broad scale of engineering materials. Finally, for the sake of engineering applications, a general analytical formula is put forward according to the dummy database, by which the critical contact pressure and thus the critical indentation depth can be read directly. Fracture toughness of engineering materials is then determined using the concept of indentation energy to fracture at the critical indentation depth. Validation of predicted fracture toughness and tensile properties of four high strength steels is taken out using compact tension (CT) and standard tensile tests, respectively. Good agreements are found between the standard tests and IIT.

Martens Hardness of CAD/CAM Resin-Based Composites

(1) Background: The properties of CAD/CAM resin-based composites differ due to differences in their composition. Instrumented indentation testing can help to analyze these differences with respect to hardness, as well as energy-converting capabilities due to viscoelastic behavior. (2) Methods: Eleven materials were investigated using instrumented indentation testing. Indentation depth (hr), Martens hardness (HM), indentation hardness (HIT), indentation modulus (EIT), the elastic part of indentation work (ηIT), and indentation creep (CIT) were investigated, and statistical analysis was performed using one-way ANOVA, Bonferroni post-hoc test, and Pearson correlation (α = 0.05). (3) Results: All of the investigated parameters revealed differences between the analyzed materials. Besides the differences in hardness-associated parameters (hr, HM, and HIT), instrumented indentation testing demonstrated differences in energy-converting properties. The subsequent one-way ANOVA revealed significant differences (p &lt; 0.001). A significant (p &lt; 0.01, Pearson correlation &gt;0.576) correlation between the materials and HM, HIT, or EIT was identified. (4) Conclusions: Due to the differences found in the energy-converting properties of the investigated materials, certain CAD/CAM resin-based composites could show superior stress-breaking capabilities than others. The consequential reduction in stress build-up may prove to beneficial, especially for implant-retained restorations or patients suffering from parafunctions.

Uncertainty Quantification of a High-Throughput Profilometry-Based Indentation Plasticity Test of Al 7075 T6 Alloy

The quantification of spatially variable mechanical response in structural materials remains a challenge. Additive manufacturing methods result in increased spatial property variations—the effect of which on component performance is of key interest. To assist iterative design of additively manufactured prototypes, lower-cost benchtop test methods with high precision and accuracy will be necessary. Profilometry-based indentation plastometry (PIP) promises to improve upon the instrumented indentation test in terms of the measurement uncertainty. PIP uses an isotropic Voce hardening model and inverse numerical methods to identify plasticity parameters. The determination of the baseline uncertainty of PIP test is fundamental to its use in characterizing spatial material property variability in advanced manufacturing. To quantify the uncertainty of the PIP test, ninety-nine PIP tests are performed on prepared portions of a traditionally manufactured Al 7075 plate sample. The profilometry data and the Voce parameter predictions are examined to distinguish contributions of noise, individual measurement uncertainty, and additional set-wide variations. Individual measurement uncertainty is estimated using paired profilometry measurements that are taken from each indentation. Principal component analysis is used to analyze and model the measurement uncertainty. The fitting procedure used within the testing device software is employed to examine the effect of profile variations on plasticity predictions. The expected value of the error in the plasticity parameters is given as a function of the number of tests taken, to support rigorous use of the PIP method. The modeling of variability in the presence of measurement uncertainty is discussed.

Effect of the reduced graphene oxide on the tribological behavior of UHMWPE/rGO nanocomposites under sliding contact conditions

AbstractIn this work, the effect of the addition of reduced graphene oxide (rGO) nanofillers to UHMWPE was investigated. The UHMWPE/rGO nanocomposites were prepared at rGO contents of 0.010, 0.10, 0.25, and 0.50 wt%. The morphological, mechanical, and surface properties of the nanocomposites and the neat UHMWPE were evaluated and related with their tribological behavior. For that, DSC, SEM, contact angle, MO, and profilometry techniques, besides shore D hardness tests, instrumented indentation tests and pin‐on‐disc sliding wear tests were performed. The results showed that nanocomposites with rGO contents of 0.10 and 0.25 wt% exhibited higher crystallinity degree than the neat UHMWPE, which improved significantly their mechanical and tribological behavior through increases of around 40% in the instrumented hardness and the elastic modulus, and a significant reduction of up to 48% in the coefficient of friction when compared to the neat UHMWPE. Additionally, the presence of rGO decreased the work of adhesion of the nanocomposites/counterface pairs, resulting in friction and wear mechanisms changes in comparison with the neat polymer.

A New Approach to Estimate the Fatigue Limit of Steels Based on Conventional and Cyclic Indentation Testing

For a reliable design of structural components, valid information about the fatigue strength of the material used is a prerequisite. As the determination of the fatigue properties, and especially the fatigue limit σw, requires a high experimental effort, efficient approaches to estimate the fatigue strength are of great interest. Available estimation approaches using monotonic properties, e.g., Vickers hardness (HV), and in some cases the cyclic yield strength, only allow a rough estimation of σw. The approaches solely based on monotonic properties lead to substantial deviations of the estimated σw in relation to the experimentally determined fatigue limit as they do not consider the cyclic deformation behavior. In this work, an estimation approach was developed, which is based on a correlation analysis of the fatigue limit σw, HV, and the cyclic hardening potential obtained in instrumented cyclic indentation tests (CIT). For this, eleven conditions from five different low-alloy steels were investigated. The CIT enable an efficient and quantitative determination of the cyclic hardening potential, i.e., the cyclic hardening exponentCHT eII, and thus, the consideration of the cyclic deformation behavior in an estimation approach. In this work, a strong correlation of σw with the product of HV and |eII| was observed. In relation to an existing estimation approach based solely on HV, considering the combination of HV and |eII| enables the estimation of σw with an enormously increased precision.