Indentation Technique Research Articles

Determination of elastic moduli of polymeric materials using microhardness indentation

Young's modulus of elasticity (or stiffness, E) is an important material property for many applications of polymers and polymer-matrix composites. The common methods of measuring E are by measuring the velocity of ultrasonic pulses through the material or by resistance to flexure, but it is difficult for ultrasound to penetrate polymers that contain filler particles, and flexural measurements require large specimens that may not mimic the clinical case. Thus, it may be difficult to determine E using conventional techniques. It would be useful to have a relatively rapid technique that could be applied to small specimens, highly filled materials, and even specimens cured in situ. We suggest using a microhardness indentation technique that was originally developed for ceramic materials. We tested two unfilled rigid polymers, four resin composites, and four unfilled polymers with lesser hardness for this study. The study found that greater Vickers hardness loads yielded more consistent results than lesser loads. We developed a modified equation for E based on Knoop microhardness indentations. We concluded that laboratories may use a microhardness indenter to estimate the elastic moduli of polymers and resin composites. The results support our initial hypotheses that the slope of the equation relating the indentation parameter and the hardness/elastic modulus ratio was different for polymers and resin composites than for ceramics; however, the intercept is the same irrespective of the material tested.

Adapting high-speed indentation mapping for investigating microstructure-property correlations in chromium carbide-nickel alloy coatings: Challenges and solutions

This study investigates the microstructural and mechanical characteristics of chromium carbide‑nickel rich alloy coatings produced through laser cladding, detonation spraying, and plasma spraying techniques. While all three processing techniques used the same feedstock powder, each method yields coatings with unique microstructures encompassing varying compositions and length scales. Employing Field Emission Scanning Electron Microscopy (FE-SEM) in combination with Energy Dispersive Spectroscopy (EDS) and nanoindentation mapping, local microstructure and mechanical properties were assessed at the micrometre length scale. Laser-clad coatings exhibit a typical metal matrix composite microstructure with high carbide content, distinct (MoNb)C2 phases, and Fe in the metallic matrix, while the thermal sprayed coatings showed carbides of varying sizes and metallic matrix with varying degrees of chromium dissolved in it. The instrumented indentation technique helped precisely record the microstructural features in all the coatings. Chromium carbide consistently emerges as the hardest phase across all coatings, with variations in metallic matrix hardness. Higher matrix hardness in thermal sprayed coatings correlates with increased Cr content, attributed to extended solid solubility of Cr and the presence of Mo and Nb. Energy dispersive spectroscopy and transmission electron microscopy provided clearer insight into the microstructure. This study highlights a direct one-to-one correlation between microstructure and mechanical properties mapped using instrumented indentation techniques in chromium carbide‑nickel rich coatings across different deposition methods.

Deep Indentation Tests of Soft Materials Using Mobile and Stationary Devices.

Measurements of the properties of soft materials are important from the point of view of medical diagnostics of soft tissues as well as testing the quality of food products and many technical materials. One of the frequently used techniques for testing such materials, attractive due to its non-invasive nature, is the indentation technique, which does not puncture the material. The difficulty of testing soft materials, which affects the objectivity of the results, is related to the problems of stable positioning of the studied material in relation to the indentation apparatus, especially with a device held by the operator. This work concerns the comparison of test results using an indentation apparatus mounted on mobile and stationary handles. The tested materials are cylindrical samples of polyurethane foams with three different stiffnesses and the same samples with a 0.5 or 1 mm thick silicone layer. The study presented uses an apparatus with a flat cylindrical indenter, with a surface area of 1 cm2, pressed to a depth of 10 mm (so-called deep tests). Based on the recorded force changes over time, five descriptors of the indentation test were determined and compared for both types of handles. The tests performed showed that the elastic properties of foam materials alone and with a silicone layer can be effectively characterized by the maximum forces during recessing and retraction and the slopes of the recessing and retraction curves. In the case of two-layer materials, these descriptors reflect both the characteristics of the foams and the silicone layer. The results show that the above property of the deep indentation method distinguishes it from the shallow indentation method. The repeatability of the tests performed in the mobile and stationary holders were determined to be comparable.

Effect of Cycling on the Physical Properties of the Garnet Solid Electrolyte, LLZO

Solid-state energy storage is the future of high performance, high-energy-dense battery systems. A common solid electrolyte, argued to be viable for such a system is the ceramic garnet solid oxide solid electrolyte, LLZO. LLZO is preferred due to its high ionic conductivity and stability against lithium metal. To date, most mechano-electrochemical studies of this solid electrolyte only focus on the fabrication and cell performance of the solid electrolyte. For the first time, this work explores the effect cycling has on the physical properties of the LLZO solid electrolyte, where, after cycling, surface characterization is completed to understand the degradation effects of cycling, as well as the grain boundary-grain modifications that occur. Initial results indicate lithium nucleation in the grain boundaries occurs, where elemental mapping will allow for quantification of lithium concentration changes in the grain boundaries, indicating whether lithium exists in the grain as a pure metal or as an alloying compound. Indentation techniques are used to show that molecular stoichiometric changes of the solid electrolyte at the grain boundaries create a softer material, which would be more susceptible to dendrite protrusions, allowing for premature cell failure. This work provides valuable insight into the chemo-mechanical response of LLZO to lithium-ion migration across grain-grain boundary interfaces, helping guide materials engineering decisions for a more robust, electrochemically stable solid electrolyte. Figure 1

Evaluation method of dynamic indentation behavior of glass based on electromagnetic induction phenomena

AbstractContact damage of glass is one of the most crucial issues for glass products. To develop strong and tough glass products and to compare damage resistance among glass compositions, a simple method for evaluating the mechanical response of glass during contact is required not only for glass mechanists but also for glass customers and suppliers. Although it is well known that the quasi‐static Vickers indentation test is one of the simplest and most useful methods to evaluate hardness and brittleness in glass, the indentation response of glass under the indenter at higher impact velocities remains to be quantitively understood because of the difficulty of measurement and limited experimental works. In this study, therefore, the dynamic indentation behavior of soda‐lime glass is evaluated by using a lab‐made free‐drop indentation set‐up with the coils for detecting electromotive forces (EMFs). The cono‐spherical indenter made of tungsten carbide attached with a neodymium magnet was employed to generate the EMFs when the indenter passed through the coils located near the glass sample. The impact load versus indentation depth curve during the impact within a few tens of microseconds was successfully obtained both for an elastic contact and for an inelastic contact. Under an elastic condition, where no residual indent nor any cracks were left on the glass surface after the test, it is confirmed that there is almost no hysteresis in the impact load versus indentation depth curve and that the curve can be reproduced by the Hertzian analytical solution. Under an inelastic condition, on the other hand, it is found that the hysteresis in the impact load versus indentation depth curve stems from inelastic phenomena, such as plastic deformation (shear flow and/or permanent densification) and cracking. These results suggest that the dynamic indentation technique based on electromagnetic induction phenomena is a useful and effective tool for evaluating the mechanical responses of glasses during the impact.

Influence of the Surface Topography of Titanium Dental Implants on the Behavior of Human Amniotic Stem Cells.

The dental implant surface plays a crucial role in osseointegration. The topography and physicochemical properties will affect the cellular functions. In this research, four distinct titanium surfaces have been studied: machined acting (MACH), acid etched (AE), grit blasting (GBLAST), and a combination of grit blasting and subsequent acid etching (GBLAST + AE). Human amniotic mesenchymal (hAMSCs) and epithelial stem cells (hAECs) isolated from the amniotic membrane have attractive stem-cell properties. They were cultured on titanium surfaces to analyze their impact on biological behavior. The surface roughness, microhardness, wettability, and surface energy were analyzed using interferometric microscopy, Vickers indentation, and drop-sessile techniques. The GBLAST and GBLAST + AE surfaces showed higher roughness, reduced hydrophilicity, and lower surface energy with significant differences. Increased microhardness values for GBLAST and GBLAST + AE implants were attributed to surface compression. Cell viability was higher for hAMSCs, particularly on GBLAST and GBLAST + AE surfaces. Alkaline phosphatase activity enhanced in hAMSCs cultured on GBLAST and GBLAST + AE surfaces, while hAECs showed no mineralization signals. Osteogenic gene expression was upregulated in hAMSCs on GBLAST surfaces. Moreover, α2 and β1 integrin expression enhanced in hAMSCs, suggesting a surface-integrin interaction. Consequently, hAMSCs would tend toward osteoblastic differentiation on grit-blasted surfaces conducive to osseointegration, a phenomenon not observed in hAECs.

Role of crystalline orientations and additive layers on bulk tensile response of wire-arc directed energy deposited (WDED) single phase titanium

A significant challenge in improving metal-based wire-arc directed energy deposition (WDED) for additive manufacturing is the lack of knowledge about microstructure evolution and its correlation with layer-wise plastic response and bulk tensile behavior. For the first time, this paper establishes the role of crystalline orientation, dislocation densities, and layer-by-layer strength on the anisotropy of bulk uniaxial tensile deformation in commercially pure titanium (cp-Ti) processed by WDED. An integrated approach that combines microscopy, spectroscopy, millimeter-scale indentation and centimeter-scale uniaxial tensile techniques is adopted. The variation in thermal cycles during WDED results in a higher grain orientation spread greater than 5° in the longitudinal direction (LD) parallel to arc motion compared to about 4° along the normal direction (ND) of additive buildup. Similarly, the statistically stored dislocation density in LD, 1.8 x 1016 m−2, is double that in ND, 0.9 x 1016 m−2. These factors result in a greater strain localization in the LD than in ND. The higher strain localization results in plastic anisotropy manifested as material buildup and ductility, which are 40 μm and 33 % higher in ND than in LD. On the other hand, the monolithic macrostructure and absence of weak points at layer interfaces of the cp-Ti component led to comparable yield and ultimate tensile strengths across the individual layers and the bulk component at 311–328 MPa and 369–385 MPa, respectively. These properties are about 90 % of those in conventionally cast commercially cast titanium. Thus, the comprehensive understanding of titanium's nuanced isotropic strength and anisotropic ductility constitutes a major step in advancing WDED as a large-scale additive manufacturing technology and establishing a standardized database of mechanical properties.

Study on methods measuring mechanical properties of arterial wall by macroscopic indentation

Accurately evaluating the local biomechanics of arterial wall is crucial for diagnosing and treating arterial diseases. Indentation measurement can be used to evaluate the local mechanical properties of the artery. However, the effects of the indenter's geometric structure and the analysis theory on measurement results remain uncertain. In this paper, four kinds of indenters were used to measure the pulmonary aorta, the proximal thoracic aorta and the distal thoracic aorta in pigs, and the arterial elastic modulus was calculated by Sneddon and Sirghi theory to explore the influence of the indenter geometry and analysis theory on the measured elastic modulus. The results showed that the arterial elastic modulus measured by cylindrical indenter was lower than that measured by spherical indenter. In addition, compared with the calculated results of Sirghi theory, the Sneddon theory, which does not take adhesion forces in account, resulted in slightly larger elastic modulus values. In conclusion, this study provides parametric support for effective measurement of arterial local mechanical properties by millimeter indentation technique.

Tribological behaviour of microindented 100Cr6 steel surfaces in dry contact conditions

In the present work, we studied the dry tribological behaviour of a 100Cr6 steel, the spherical surface of which was texturized with microindentation. The purpose of adopting a mechanical indentation technique on a non-planar surface was to simultaneously evaluate the effectiveness of adopting a fast, deformation-based technique for improving the contact tribological properties. Specifically, dimples were created using an automatic microhardness tester equipped with a Vickers indenter, setting a load of 0.5 N. Friction tests were performed at different speeds considering textured surfaces with two different void ratios (VRs). Textured and untextured surfaces were tested using a ball-on-disc tribometer. In addition, the effect of dimple size was evaluated by producing Vickers indented surfaces at a load of 5 N per each indentation, while keeping the VR values unchanged and testing the frictional properties of such surfaces at a fixed speed of 4.18 mm/s. Textured surfaces were deeply investigated to motivate the improvement of tribological properties. Notably, compared to the untextured samples, the microindented samples exhibited a much lower coefficient of friction (COF), with a friction reduction compared to the untextured case ranging from 45 to 65%, depending on the VR values. The adoption of large dimples allowed the reduction of the COF, already at smaller VR value but, in such a case, the presence of bulges at the edge of the dimple worsens the wear resistance of the counter surface. In addition to reducing the contact area and the capability to trap any debris in the dimples, the local measurement of strength allowed to clarify that the friction reduction is also determined by the work hardening effect produced by the microindentation texturing. Considering the significant improvements recorded in terms of COF and the high ability to indent even non-planar surfaces, the proposed approach can be considered very promising and, therefore, industrially applicable (e.g. using a specifically designed multi-indenter tool) to affect the friction behaviour of components, even locally, during both their use and their production.

A Comprehensive Review of Indentation of Gels and Soft Biological Materials

Abstract Indentation measurement has emerged as a widely adapted technique for elucidating the mechanical properties of soft hydrated materials. These materials, encompassing gels, cells, and biological tissues, possess pivotal mechanical characteristics crucial for a myriad of applications across engineering and biological realms. From engineering endeavors to biological processes linked to both normal physiological activity and pathological conditions, understanding the mechanical behavior of soft hydrated materials is paramount. The indentation method is particularly suitable for accessing the mechanical properties of these materials as it offers the ability to conduct assessments in liquid environment across diverse length and time scales with minimal sample preparation. Nonetheless, understanding the physical principles underpinning indentation testing and the corresponding contact mechanics theories, making judicious choices regarding indentation testing methods and associated experimental parameters, and accurately interpreting the experimental results are challenging tasks. In this review, we delve into the methodology and applications of indentation in assessing the mechanical properties of soft hydrated materials, spanning elastic, viscoelastic, poroelastic, coupled viscoporoelastic, and adhesion properties, as well as fracture toughness. Each category is accomplished by the theoretical models elucidating underlying physics, followed by ensuring discussions on experimental setup requirements. Furthermore, we consolidate recent advancements in indentation measurements for soft hydrated materials highlighting its multifaceted applications. Looking forward, we offer insights into the future trajectory of the indentation method on soft hydrated materials and the potential applications. This comprehensive review aims to furnish readers with a profound understanding of indentation techniques and a pragmatic roadmap of characterizing the mechanical properties of soft hydrated materials.

Retracted: Micromechanical properties characterization of 4H–SiC single crystal by indentation and scratch methods

Growth and micromachining of single crystal silicon carbide (SiC) have drawn extensive attention in wide bandgap semiconductors and remained challenging. The micromechanical properties (i.e., hardness, elastic modulus, fracture toughness), which are the key to machinability and machining quality (and therefore the yield of the grown SiC), of 4H–SiC were assessed by nanoindentation, microhardness, and microscratch tests. Consistent values of true indentation hardness of 4H–SiC can be obtained by different approaches without the need for the area function of the indenter. Accurate determination of elastic modulus (i.e., 583.5 GPa) and indentation hardness (i.e., 38 GPa) of 4H–SiC by the instrumented indentation technique requires low loads with slight indentation-induced damage. Consistent values of fracture toughness Kc of 4H–SiC were obtained by different methods such as the Vickers/Berkovich indenter-induced cracking method (2.1 MPa·m1/2), energy-based nanoindentation approaches (the critical void volume fraction of 0.062 should be used for 4H–SiC when the deterioration of indentation hardness is used), and linear elastic fracture mechanics (LEFM)-based scratch approach with a spherical indenter (2.6 MPa·m1/2). This work provides the guidance for the mechanical machining of 4H–SiC wafers and the paradigm of micromechanical characterization of brittle solids by indentation and scratch technologies.

Understanding heterogeneity and anisotropy of Duplex Stainless Steel's elastic/plastic nature through property mapping technique

Accelerated property mapping, an advanced indentation technique was used to describe the nanomechanical behaviour of duplex stainless steel (DSS) surfaces prior to and post heat treatments. Heterogeneity in deformation responses and relative elastic and/or plastic nature of DSS was assessed on longitudinal and transverse directions through load–displacement curves, property maps, histograms of hardness (H), modulus (E) and indentation works. Empirical ratios such as H/E, (H/E)1/2, H3/E2 and plasticity index were employed to understand the anisotropy across the directions.

Study on fracture toughness of quasicrystalline phase in Mg-42Zn-7Y alloy based on indentation technique

The Mg-42Zn-7Y alloy, which contains an icosahedral quasicrystalline phase, was prepared using a conventional solidification process. The fracture toughness of this quasicrystalline phase in the Mg-42Zn-7Y alloy was nondestructively detected using in situ tensile and indentation techniques. The alloy exhibited a tensile strength of 99.17 MPa and an elongation of 3.9%. Microscopic observation and energy spectrum analysis confirmed the high-contrast lamellar structure as the quasicrystalline phase. Ultimately, under cyclic loading during indentation, the fracture toughness of the quasicrystalline phase was determined to be 35.08 MPa m0.5. The findings of the present study provided an effective basis for the determination of the fracture toughness of the quasicrystalline phase.

Fatigue crack growth of WC–Co cemented carbides: a comparative study using small indentation flaws and long through-thickness cracks

The fatigue crack growth behavior of a submicron-grained WC–Co hardmetal is investigated by artificially introducing small flaws by means of sharp indentation. Similar fatigue testing is also conducted on notched specimens with long through-thickness cracks for comparison purposes. The use of controlled small indentations flaws is shown to be a valid and successful approach for studying and describing crack growth behavior under cyclic loading for the material under consideration. This statement is based on the similitude found in fatigue mechanics and mechanisms between both crack types. Regarding the former, accounting of the indentation-induced residual stresses is key to rationalize the experimental findings. Concerning the latter, inspection of crack-microstructure interaction as well as fracture surfaces permit to discern similar features and scenarios, at both meso- and micrometric length scales. Results from this research yield an immediate practical implication, as indentation techniques may then be proposed as an alternative testing route for investigating fatigue crack growth behavior of hardmetal grades where sharp indentation is capable to induce well-developed radial crack systems.

A novel impact indentation technique with dynamic calibration method for measurement of dynamic mechanical properties

High strain rates and continuous real-time data acquisition are difficult to balance in existing impact indentation techniques. Meanwhile, the inaccuracy of the testing P-h curves limits the development of quantitative applications for dynamic testing of mechanical properties at micro region. This article develops a momentum exchange impact indentation testing method, which extends the testing range of strain rate to above 105 s−1, and at the same time avoids secondary impact. Impact indentation tests are conducted on single-crystal aluminum specimens with impact velocity from 76.9 to 176 mm/s. Based on calibrated data, the comparison of calculation methods for dynamic hardness is carried out. The dynamic elastic modulus is obtained by means of the Oliver-Pharr method, which increases from 71.9 to 89.4 GPa with increasing impact velocity. A multi-dimensional data analysis method is proposed based on the obtained experimental data to quantitatively study the damping and stiffness characteristics of materials. This testing method is particularly useful for quantitatively obtaining the micro region dynamic mechanical properties of solid materials at high strain rates.

Atomic force microscopy correlates mechanical and electrical properties of HepG2 cells with curcumin concentration

Hepatocellular carcinoma (HCC) is a highly prevalent cancer with a significant impact on human health. Curcumin, a natural compound, induces cytoskeletal changes in liver cancer cells and modifies the distribution of lipids, proteins, and polysaccharides on plasma membranes, affecting their mechanical and electrical properties. In this study, we used nanomechanical indentation techniques and Kelvin probe force microscopy (KPFM) based on atomic force microscopy (AFM) to investigate the changes in surface nanomechanical and electrical properties of nuclear and cytoplasmic regions of HepG2 cells in response to increasing curcumin concentrations. CCK-8 assays and flow cytometry results demonstrated time- and concentration-dependent inhibition of HepG2 cell proliferation by curcumin. Increasing curcumin concentration led to an initial increase and then decrease in the mechanical properties of nuclear and cytoplasmic regions of HepG2 cells, represented by the Young's modulus (E), as observed through nanoindentation. KPFM measurements indicated decreasing trends in both cell surface potential and height. Fluorescence microscopy results indicated a positive correlation between curcumin concentration and phosphatidylserine translocation from the inner to the outer membrane, which influenced the electrical properties of HepG2 cells. This study provides valuable insights into curcumin's mechanisms against cancer cells and aids nanoscale evaluation of therapeutic efficacy and drug screening.

Simulations of the effect of shot peening backstress on nanoindentation

Shot peening is a mechanical surface treatment that can introduce compressive residual stress and work hardening simultaneously. This work hardening, considered as a modification of the elastic region with plastic strain, can be modeled with two types of contributions: isotropic hardening and kinematic hardening. In order to characterize the mechanical properties of the treated surface using the instrumented indentation technique, the effect of the backstress associated with kinematic hardening should be studied, especially for works related to fatigue loading. In this paper, the distribution of three backstress components is obtained by shot peening simulations on a nickel-based alloy, Inconel 718, commonly used in the aerospace industry, and a series of indentation simulations are carried out using a spherical tip with different equivalent backstress levels. For Inconel 718, the third backstress component, which has the slowest evolution rate, is found to have the most significant influence on the response. However, compared to the effect of residual stress and cumulated plastic strain, the effect of backstress can be neglected.

Evaluation of the (Baha) technique of scleral indentation using a self-retained scleral indenter during vitrectomy surgery: a randomized trial

AimsThe current study compared a novel technique of scleral indentation using the self-retaining Leyla retractor to the conventional scleral self-indentation with the chandelier light.MethodsPatients with rhegmatogenous retinal detachment were randomized on a 1:1 basis to either have the (Baha) indentation using a tip of a thimble scleral indenter welded to the support for the Leyla retractor system or to have the conventional scleral indentation while using a 25-gauge chandelier light. A video was recorded for the surgery of all the cases and reviewed by another consultant masked to the type of indentation. The indentation duration (i.e., the time in seconds between the first appearance of a hump due to scleral indentation in the recorded video until its final disappearance) was measured for every case.ResultsThe current study included 60 eyes of 60 adults with a mean age of 59.6 ± 9.8 years. Thirty-nine of the eyes were phakic and 21 were pseudophakic. The mean indentation time was 618 ± 87 and 696 ± 72 s in (Baha) indentation and conventional indentation groups, respectively. The difference was not statistically significant (p = 38). There was a positive correlation between the vertical palpebral fissure height and the indentation duration for both (Baha) indentation (r = 0.58) and conventional indentation groups (r = 0.42). Readjustment of the chandelier endo-illumination was required in 19 cases (63.3%) in the conventional indentation group. Iatrogenic breaks or accidental crystalline lens touch did not occur in any case.ConclusionThe (Baha) technique is effective and safe, especially in patients with a larger palpebral fissure.

WC-based cemented carbide with NiFeCrWMo high-entropy alloy binder as an alternative to cobalt

In the current work, a nanostructured NiFeCrWMo high entropy alloy (HEA), synthesized by mechanical alloying, was used as the alternative binder phase for substituting Co to fabricate WC–HEA cemented carbides by electron–beam sintering (EBS). The microstructure and mechanical properties of initial powder mixtures and sintered samples were studied using X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), indentation technique and compression tests. NiFeCrWMo HEA does not have direct interaction with WC, but at the boundaries between WC and HEA particles (Ni, Fe, Cr)xWyCz complex carbide is formed as result of reduction processes during sintering. The results show that WC–HEA cemented carbide has better performances than the commercial WC–8Co-cemented carbide prepared by EBS. The NiFeCrWMo HEA binder significantly slows down the growth of WC grains due to the sluggish diffusion effect and the formation of a small amount of complex carbide, and, compared to Co, improves the mechanical properties, provides an excellent combination of microhardness (18.9 ± 0.4 GPa) and fracture toughness (11.4 ± 0.3 MPa m1/2). Therefore, the NiFeCrWMo high entropy alloy can potentially become a binder for WC cemented carbides.

Studies on the fatigue failure behaviour of novel carbon nanotube–glass composites

Single walled carbon nanotubes (SWCNTs) based glass composites were fabricated through a melt-quench process and their fatigue failure properties were studied using a repeated indentation technique. The SWCNT–glass composites were found to exhibit significantly reduced damage in comparison to their respective base glasses, as corroborated by field emission scanning electron microscopy (FESEM). The fatigue resistance parameter (n) of the samples was determined where considerable increment in ‘n’ values in case of composites than that of the base glasses was observed. Moreover, a mathematical equation was also proposed for the theoretical estimation of the percentage enhancement in fatigue resistance parameter (In) of the composites and it was found to be in good agreement with the experimental values. Finally, the superior fatigue resistant behaviour of the SWCNT-glass composites was well elucidated with the help of cushioning effect and enhanced plasticity of the nanotube bundles embedded within the glass structure.