Indentation Analysis Research Articles

Preparation and properties of double-layer phenolic/polyurethane coated isophorone diisocyanate self-healing microcapsules

Single-layer isophorone diisocyanate (IPDI) are one of the most popular self-healing microcapsules but suffers from low shell strength, poor heat resistance, stability and aging properties. In this paper, IPDI microcapsules were encapsulated into double-layer phenolic (PF)/polyurethane (PU) by a two-step process involving interfacial polymerization and in-situ polymerization. The prepared microcapsule composites were comprehensively characterized for their physical and chemical properties using optical microanalysis, scanning electron microscope, Fourier transform infrared spectroscopy, thermal gravimetric analysis and depth-sensing indentation analysis. Compared with the single-layer PU-IPDI microcapsule counterpart, the mechanical performance, thermal resistance, aging property and environmental stability of double-layer PF/PU-IPDI microcapsules were significantly improved. The epoxy coating was enhanced with the incorporation of 10 wt.% PF/PU-IPDI microcapsules, whose self-healing performance was evaluated by scratch corrosion test. The results demonstrated successful repair of coating scratches, along with the absence of corrosion on the coated steel substrate soaked in a 10 wt.% NaCl solution for 7 days. By comparing the tensile strength of epoxy coating before and after crack formation, it could be found that the self-healing efficiency was 57.9% when loaded with 10 wt.% of PF/PU-IPDI microcapsules in coating. This study highlights that the rational design of double-layer microcapsules integrated into the epoxy coating matrix could provide excellent anti-corrosion and self-healing properties.

Formation mechanism and property of interface microstructure between surface (TiNb)C-reinforced layer and TiNb substrate

The interface microstructure between the surface (TiNb)C-reinforced layer and TiNb substrate was fabricated through an in situ diffusion reaction in a vacuum environment. Microstructure, element composition, and phase distribution were investigated to elucidate the reaction process and formation mechanism of the transition phase at the interface. Indentation and fracture analysis were performed to assess the interface properties. The results indicated that there is a clearly banded microstructure existed between the surface-reinforced layer and TiNb substrate and that the phase in the transition region had an orthorhombic structure. The analyses revealed that the transition region formed at the front of the reaction interface, in which the main phase was (TiNb)2C. The structure of (TiNb)2C could be approximated as that of α-Nb2C, and (TiNb)2C reacted to form (TiNb)C with the further diffusion of C. Indentation analysis indicate that the apparent fracture toughness of the interface at different loads was 2.57–3.44 MPa m1/2, higher than that of the surface-reinforced layer. The bending experiment further proved that the microstructure in the transition region was brittle but showed good resistance to interface crack propagation.

Removal of the infrapatellar fat pad and associated synovium benefits female guinea pigs in the Dunkin Hartley model of idiopathic osteoarthritis.

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease. Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS). Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC. Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

On elastoplastic behavior of porous enamel–An indentation and numerical study

The micro/nano pores in natural mineralized tissues can, to a certain extent, affect their responses to mechanical loading but are generally ignored in existing indentation analysis. In this study, we first examined the void volume fraction of sound and caries lesion enamels through micro-computed tomography (micro-CT). A Berkovich indentation study was then carried out to characterize the effect of porous microstructure on the mechanical behavior of the human enamels. The indentation tests were also modeled using the nonlinear finite element analysis technique to simulate indentation load-displacement curves, which showed reasonable agreement with the experimental measurements. From the simulation results, the extent of densification in the plastic zone was identified and the corresponding stress and contact pressure evolutions were quantified. Further, a conventional elastic-perfectly plastic material model without considering micropores was also developed to investigate the compaction effect of the porous structure. The simulation results reveal that conventional elastic perfect-plastic constitutive models become less reliable to model the mechanical behavior of carious lesion enamel with increasing loss of mineral content as it underestimates the yield stress and plastic energy dissipation. This study divulges the importance of compaction of porous enamel structure beneath the indented area. Note that understanding the effect of porous microstructures on plastic behavior is vital as the involved inelastic deformation mechanism associated with irreversible processes, such as wear and localized microcracking, has a significant bearing on wear and fatigue behavior of enamel. Statement of significanceBased on micro-CT and nano-indentation characterization, a numerical model was developed aiming to precisely describe the deformation behavior of naturally porous enamel. Inelastic properties and energy dissipation characteristics of porous enamel were investigated in detail. This work demonstrated that the existence of micro-pores in White Spot Lesions (WSLs) contributes to mechanical stability, which can mitigate the reduction in Young's modulus and fracture toughness resulting from loss of mineral components. The knowledge gained from this study can be used to explain the mechanisms related to irreversible processes, such as contact induced cracking and wear, and strengthen understanding of the mechanical behavior of porous mineralized tissues.

Spherical Indentation and Implementation of S3/P for yield stress determination of brittle materials

A mathematically transparent and robust experimental method has been developed to estimate the yield stress of brittle materials through the analysis of depth-sensing spherical indentation. Employing Hertzian contact mechanics, an elastically invariant ratio based on the simple equation S3/P=6REr2, (where S and P are contact stiffness and indentation load, respectively) has been derived that enables more accurate and confident determination of the transition from elastic to inelastic deformation; a transition that the yield stress dictates and represents. Using two diamond spheres with radii of 3.2 and 8.6 μm, the indentation test method and analyses are applied to two vitreous silicates: Corning's HPFS 7980® fused silica and Vitro's Starphire® soda-lime silicate. The estimated yield strengths are 8.15 GPa ± 2.5 % for the fused silica and 6.1 GPa ± 3.3 % for the soda-lime silicate, and both were independent of indenter radius. Verification of this new experimental method is demonstrated with an as-drawn titanium by showing equivalence of measured yield stress by its spherical indentation and that from uniaxial compression testing. This method will enable easier and more confident estimation of yield stress in brittle materials - a property that historically has been elusive to measure for these materials using common laboratory mechanical test methods.

Comparative Analysis and Error Assessment of Nanoindentation Evaluation Techniques for NafionTM117

AbstractAdvances in the application of polymers for electrochemical cells require an understanding of their viscous deformation mechanisms and their interaction with moisture. Nanoindentation offers a localized, microscale testing alternative to traditional tensile testing. However, the viscoelastic nature of the polymers, combined with their increased compliance, presents challenges in the analysis of nanoindentation results. In addition, the dependence on moisture results in significant scatter and low repeatability. This study combines nanoindentation and tensile testing as a verification method and compares different correction protocols for static nanoindentation to investigate the mechanical behavior of polymer electrolyte membranes. Comparisons of different indentation devices, analysis methods, and indentation protocols show a significant overestimation of Young’s modulus using the classical Oliver–Pharr method compared to values determined from tensile tests. Nanoindentation at different humidity levels revealed different mechanisms leading to a decrease in Young’s modulus and hardness with increasing humidity.

High temperature hardness and thermal analysis of CoNiCrAlY alloys used as bond coats for thermal barrier coatings

CoNiCrAlY alloys, commonly used as the bond coat of thermal barrier coatings (TBCs), are often exposed to high temperatures of about 1000 °C, the evolution of mechanical and thermal properties is critical to the reliability and durability of TBCs. In this paper, the hardness and thermal properties (weight change and heat flow) of CoNiCrAlY alloys at temperatures within 1000 °C were evaluated by indentation and TGA-DSC thermal analysis. It was found that hardness and thermal properties change gradually within 600 °C but change sharply above 600 °C, exhibiting an approximately synchronized evolution. An illustrative explanation was given for the correlation in terms of the Boltzmann energy distribution theory of microscopic particles. Based on these findings, an idea of inter-calibration between the two evolutions was proposed.

Influences of hybrid fiber-reinforcement using wollastonite and cellulose nanofibers on strength and microstructure characterization of ultra-high-performance mortar

This paper presents the effect of incorporating wollastonite microfibers and cellulose nanofibers on mechanical properties and microstructure of ultra-high-performance mortar (UHPM). Cellulose nanofibers of 0.005%, 0.015%, and 0.030% are combined with 4.8% wollastonite microfiber by weight of binder, which consists of 10% silica fume and 90% cement. Compressive and flexural strengths of the UHPM specimens are measured at 7 days. The microstructure is characterized in terms of SEM/EDX, XRD, FTIR, and nanoindentation. The results show the effectiveness of the fiber hybridization in enhancing the compressive and flexural strength of ultra-high-performance mortar with the improvement in flexural toughness and fracture energy by as much as 10% than control mortar. Moreover, hybrid fiber-reinforcement based on the microstructural analysis provided more synergic effect and uniform distribution of the fibers, thus developing an efficient micro crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carrying capacity. Additionally, the combination of wollastonite microfibers and cellulose nanofibers promoted the hydration reaction products and contributed a denser matrix between the fibers and cement matrix, resulting in an increase of the microstructure and interface area between the fibers and cement matrix. Nano indentation analysis also confirmed the increase of UHD C-S-H from 65% to 84% and lower percentage of anhydrous phase in ultra-high-performance matrix after combining wollastonite microfibers and cellulose nanofibers.

Nanomechanical-ferroelastics behavior, and the low-temperature ferroelectric manifestation of BiMnO3 thin films

Ferroelastic-nanomechanical behavior of BiMnO3 thin films on (100) Nb-doped SrTiO3 substrate is studied at the nanoscale, for the first time using the theories of depth sensing indentation and finite element analysis. This was to understand the redirection of polarization in ferroelastic behavior using piezoelectric direct effect and applying a controlled local force by nanoindentation. The values of the nanomechanical properties Young’s modulus (E), hardness (H), and Stiffness (S) were measured to be E = 142 ± 3 GPa, H = 8 ± 0.2 GPa, and S = 44072 ± 45 N m−1 respectively. Using the experimental mechanical properties, a finite element analysis was carried out to understand the relationship between the irreversible work versus depth curve and plastic-deformation evolution of the thin film-interface-substrate system, associated with the pop-in observed. Von Mises stress maps are presented to clearly illustrate the deformations, mechanical failures, and influences between the BiMnO3 film and the SrTiO3 Substrate. The ferroelastic range for BiMnO3 material was observed between 0 to 12 nm, and the yield strength was Y = 2.6 ± 0.7 GPa. The ferroelectric properties through hysteresis curves were evaluated at two different temperatures of 200 K and 300 K in order to observe the effect of polarization with temperature. Providing better polarization performance at lower temperatures; P s = 9.14 ± 0.01 ( μ C cm–2), P r = 2.23 ± 0.02 ( μ C cm–2) and H c = 0.77 kV cm−1.

A Classical Molecular Dynamics Study of the Effect of the Atomic Force Microscope Tip Shape, Size and Deformation on the Tribological Properties of the Graphene/Au(111) Interface

Atomic force microscopes are used, besides their principal function as surface imaging tools, in the surface manipulation and measurement of interfacial properties. In particular, they can be modified to measure lateral friction forces that occur during the sliding of the tip against the underlying substrate. However, the shape, size, and deformation of the tips profoundly affect the measurements in a manner that is difficult to predict. In this work, we investigate the contribution of these effect to the magnitude of the lateral forces during sliding. The surface substrate is chosen to be a few-layer AB-stacked graphene surface, whereas the tip is initially constructed from face-centered cubic gold. In order to separate the effect of deformation from the shape, the rigid tips of three different shapes were considered first, namely, a cone, a pyramid and a hemisphere. The shape was seen to dictate all aspects of the interface during sliding, from temperature dependence to stick–slip behavior. Deformation was investigated next by comparing a rigid hemispherical tip to one of an identical shape and size but with all but the top three layers of atoms being free to move. The deformation, as also verified by an indentation analysis, occurs by means of the lower layers collapsing on the upper ones, thereby increasing the contact area. This collapse mitigates the friction force and decreases it with respect to the rigid tip for the same vertical distance. Finally, the size effect is studied by means of calculating the friction forces for a much larger hemispherical tip whose atoms are free to move. In this case, the deformation is found to be much smaller, but the stick–slip behavior is much more clearly seen.

Universal contact stiffness of elastic solids covered with tensed membranes and its application in indentation tests of biological materials.

The inherent membrane tension of biological materials could vitally affect their responses to contact loading but is generally ignored in existing indentation analysis. In this paper, the authors theoretically investigate the contact stiffness of axisymmetric indentations of elastic solids covered with thin tensed membranes. When the indentation size decreases to the same order as the ratio of membrane tension to elastic modulus, the contact stiffness accounting for the effect of membrane tension becomes much higher than the prediction of conventional contact theory. An explicit expression is derived for the contact stiffness, which is universal for axisymmetric indentations using indenters of arbitrary convex profiles. On this basis, a simple method of analysis is proposed to estimate the membrane tension and elastic modulus of biological materials from the indentation load-depth data, which is successfully applied to analyze the indentation experiments of cells and lungs. This study might be helpful for the comprehensive assessment of the mechanical properties of soft biological systems. STATEMENT OF SIGNIFICANCE: This paper highlights the crucial effect of the inherent membrane tension on the indentation response of soft biomaterials, which has been generally ignored in existing analysis of experiments. For typical indentation tests on cells and organs, the contact stiffness can be twice or higher than the prediction of conventional contact model. A universal expression of the contact stiffness accounting for the membrane tension effect is derived. On this basis, a simple method of analysis is proposed to abstract the membrane tension of biomaterials from the experimentally recorded indentation load-depth data. With this method, the elasticity of soft biomaterials can be characterized more comprehensively.

Hydrophobic electroless nickel phosphorus-graphene carbon nitride coating on AISI 4140 steel with enhanced hardness and scratch resistance

The present article explores the ability of synthesized graphene carbon nitride (g-C3N4) towards the improvement of microstructure, surface energy, surface hardness, and scratch resistance of electroless nickel phosphorus-graphene carbon nitride (NiP/g-C3N4) coated AISI 4140 steel. Comparative studies were conducted to evaluate how the g-C3N4 concentrations affect the physical, mechanical, and surface properties of electroless NiP/g-C3N4 composite coating. Morphology analysis confirmed the nodular formation for the NiP/g-C3N4 composite coating due to the nucleation phenomenon induced by the g-C3N4 particle. Further, the g-C3N4 particle has favoured the growth of the Ni crystal, which is confirmed in the X-ray diffractometer study. In comparison, the higher weight percentage of g-C3N4 particles has increased the hardness, residual stress, surface roughness, and contact angle of the electroless NiP/g-C3N4 composite coating. The maximum tensile residual stress had a positive impact on controlling the formation of slippage cracks for the NiP/g-C3N4 composite coating, which is confirmed in the fractography analysis of the hardness indentation. Furthermore, the detailed failure mechanisms of the coatings during the hardness and scratch test of NiP/g-C3N4 composite coatings were precisely discussed and compared with the particle-free NiP coating.

Indentation analysis on L-Glutamic acid doped ZTS single crystal

The primary aim of the paper is to study the mechanical characteristics of L-Glutamic acid doped ZTS crystal. With sizeable merits in high-power lasers, the growth of L-Glu doped ZTS crystals is grown over 25 days and is mentioned briefly in this paper. Different analysis methods were carried out to describe the mechanical characteristics of the crystal. Though, the methods namely Vickers Pyramid number with applied force, Meyer power law, Hays-Kendall’s approach (HK approach), Proportional Specimen Resistance model (PSR model) and Elastic/Plastic deformation model (EPD model) were utilised, and every method indicated the clear trend of RISE behaviour of the crystal. The EPD model proved that it is best in providing the proper description of the grown crystal.

Simulation and dimensional analysis of instrumented dynamic spherical indentation of ductile metals

Finite element (FE) modeling of instrumented dynamic indentation experiments in a miniature Kolsky bar is undertaken. Geometry, including an output bar with machined spherical indenter tip, and velocity history boundary conditions are extracted directly from experimental diagnostics. The test material (i.e., substrate) is polycrystalline aluminum alloy Al 6061-T6. The constitutive model used in simulations accounts for isotropic elasticity and isotropic plasticity with strain hardening, strain-rate hardening, and thermal softening under adiabatic conditions. The FE model, with representative material parameters culled from the literature, accurately reproduces the curvature of the experimental load versus depth data for three different experimental indentation velocity histories. A framework for dimensional analysis of instrumented dynamic spherical indentation is set forth, improving upon prior work. Parametric FE simulations reveal sensitivity, or lack thereof, of the predicted response to variations in the proposed independent dimensionless variables encompassing material properties. For the indenter size, maximum depth, and maximum strain rate imposed experimentally on the order of 103/s, force-depth predictions are nearly unaffected by realistic variations in mass density, melting temperature, and thermal softening parameters when the sample is initially at room temperature. Predictions are affected by elastic constants (the elastic modulus and to a lesser extent, Poisson’s ratio), initial yield strength, two strain hardening parameters, and strain rate sensitivity. Predictions are also notably affected by initial temperature, with thermal softening prominent at high enough initial temperature or much higher loading rates. Based on the dimensional analysis, static indentation and elevated temperature indentation experiments are proposed for extraction of quasi-static and thermal material properties from previously uncharacterized metals, and dynamic indentation is proposed for extraction of rate sensitivity that cannot be obtained from static tests. Rate sensitivity obtained in this way from the novel instrumented dynamic spherical indentation experiments and FE simulations produces a parameterized stress–strain response for Al 6061-T6 reasonably validated by external studies for strain rates up to the order of 103/s.

Microfluidic device using metallic nanostructure arrays for the isolation, detection, and purification of exosomes

Microfluidic devices are widely used in disease detection and specimen separation due to their low cost, rapid processing, and the ability to use even minuscule samples. This study reports on the embedding of metallic nanostructure arrays (MeNTAs) with tube-like features in microfluidic devices for the immunoaffinity-based detection and efficient isolation of exosomes. We assessed MeNTA candidates in terms of their ability to withstand the mechanical stress of microfluidic operations (indentation analysis) as well as X-ray diffraction, zeta potential, and electrostatic interactions involving antibody coatings. Note that Zr60Cu25Al10Ni5 thin film metallic glass (Zr-TFMG) features outstanding mechanical properties and a negative zeta potential exceeding those of other common materials (e.g., Cu, Bronze, Ag, 7075Al, Ti64, 718Ni, SS316, Cu-TFMG, W-TFMG, and Al-TFMG). The resulting microfluidic device featured Zr-based MeNTAs with an interdigital electrode embedded in a microchannel. When applied to MCF-7 derived exosomes using a liquid biopsy of only 500 μL, the proposed device (∼6.25 million nanostructures/cm2) achieved an exosome recovery rate of 95.3% within 1 h, while resisting nonspecific binding to HeLa-derived exosomes (recovery rate of<0.1%). The device enabled the isolation of 1 × 108 exosome particles per mL–1 for detection via electrochemical impedance spectroscopy. It also enabled the efficient release of captured exosomes via cyclic voltammetry (CV) operations over a potential range of –0.8 to +0.8 V. The proposed Zr-MeNTA microfluidic device has considerable potential for the isolation, detection, and purification of exosomes in liquid biopsy samples for cancer diagnosis.

Determination of process window for laser peening of thin metal sheets by localized indentation analysis

Determination of process window for laser peening of thin metal sheets by localized indentation analysis

Three-dimensional analytical solutions to the half infinite thermo-elastic body pressed by a rigid cylindrical structure in thermal environment

The novelty of this paper is to propose exact three-dimensional analytical solutions to the half infinite thermo-elastic body pressed by a rigid cylindrical structure for the first time, in which uniform heat flux flowing from rigid structure into the half infinite body is considered. Using recent general solutions expressed by four harmonic functions and extending potential theory method to consider heat effect, the governing integral equations are first derived. Then, the equations are analytically solved and displacement, stress, and temperature field components expressed by elementary functions are obtained. To validate the presented solutions, the correctness of the solutions is exactly examined, and normal contact displacement and stress without heat effect are compared with those in literatures. Furthermore, a numerical example which is the stainless steel thermo-elastic body pressed by a displacement restrictor is studied. Displacement, stress, and temperature distributions are analyzed, and the influence of heat flux on the pressed depth is also discussed in detail. The analytical solutions presented in this paper are rather important in engineering practice and can provide a basis for indentation analysis, displacement restrictor design, foundation settlement calculation, and so on.

Microhardness, Indentation Size Effect and Real Hardness of Plastically Deformed Austenitic Hadfield Steel.

Microhardness testing is a widely used method for measuring the hardness property of small-scale materials. However, pronounced indentation size effect (ISE) causes uncertainties when the method is used to estimate the real hardness. In this paper, three austenitic Hadfield steel samples of different plastic straining conditions were subjected to Vickers microhardness testing, using a range of loads from 10 to 1000 g. The obtained results reveal that the origin of ISE is derived from the fact, that the indentation load P and the resultant indent diagonal d do not obey Kick's law (P = A · d2). Instead, the P and d parameters obey Meyer's power law (P = A · dn) with n < 2. The plastically strained samples showed not only significant work hardening, but also different ISE significance, as compared to the non-deformed bulk steel. After extensive assessment of several theoretical models, including the Hays-Kendall model, Li-Bradt model, Bull model and Nix-Gao model, it was found that the real hardness can be determined by Vickers microhardness indentation and subsequent analysis using the Nix-Gao model. The newly developed method was subsequently utilised in two case studies to determine the real hardness properties of sliding worn surfaces and the subsurface hardness profile.

Indentation analysis of coating structure based on parabolic concave indenter contact

Indentation analysis of coating structure based on parabolic concave indenter contact

Effect of Ti as co-sputtering target on microstructure and mechanical properties of FeCoNi(CuAl)0.2 high-entropy alloy thin films

Three different FeCoNi(CuAl)0.2 alloy films sputtered with Ti were prepared using magnetron sputtering: single sputtering films of FeCoNi(CuAl)0.2 target, co-sputtering films of FeCoNi(CuAl)0.2/Ti targets, and alternating sputtering composite films of FeCoNi(CuAl)0.2/Ti targets. SEM, XRD, AFM and nano indentation analysis showed that with the increase in Ti content and change in sputtering mode, the main phase structure of the film changed from FCC to BCC. The hardness and elastic modulus of FeCoNi(CuAl)0.2/Ti target co-sputtered films reached 7.33 GPa and 145 GPa, respectively. This can be attributed to the large atomic radius of Ti dissolved in the FeCoNi(CuAl)0.2 system that caused phase transformation and significant lattice distortion.