Indentation Modulus Research Articles

Facile growth of high-yield and -crystallinity vertically aligned carbon nanotubes via a sublimated ferric chloride catalyst precursor

A facile and effective catalyst deposition process for carbon nanotube (CNT) array growth via chemical vapor deposition using a resistively heated thermal evaporation technique to sublimate FeCl3 onto the substrate is demonstrated. The catalytic activity of the sublimated FeCl3 catalyst precursor is shown to be comparable to the well-studied e-beam evaporated Fe catalyst, and the resulting vertically aligned CNTs (VA-CNTs) have a similar diameter, walls, and defects, as well as improved bulk electrical conductivity. In contrast to standard e-beam-deposited Fe, which yields base-growth CNTs, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy characterizations reveal a tip-growth mechanism for the FeCl3-derived VA-CNT arrays/forests. The FeCl3-derived forests have a lower (∼1/3 less) longitudinal indentation modulus, but higher longitudinal electrical conductivity (greater than twice) than that of the e-beam Fe-grown CNT arrays. The sublimation process to grow high-quality VA-CNTs is a highly facile and scalable process (extensive substrate shape and size, and moderate vacuum and temperatures) that provides a new route to synthesizing aligned CNT forests for numerous applications.

Processing and Mechanical Properties of (Hf-Ta-Zr-Nb-Ti)C

The influence of the processing route on the microstructure characteristics and mechanical properties of high-entropy carbides was investigated. The experimental materials were prepared by a combination of ball milling and spark plasma sintering at the temperature of 2100 °C. The effect of sintering time (5 min, 10 min, and 20 min) on the microstructure development and properties of the investigated systems has been studied. The microstructure analysis was performed using scanning electron microscopy + EDAX analysis on the polished surfaces. Nanoindentation was used for the nano-hardness and Young’s modulus measurements. Micro-hardness was measured using Vickers method and indentation method using a Vickers indenter was used to determine the indentation fracture resistance – fracture toughness. The measured grain size values were in the range from 5 µm to 14 µm. The nano-hardness values changed from 36 GPa to 39 GPa and the indentation modulus of elasticity from 558 GPa to 577 GPa, respectively. The measured micro-hardness values were in the range from 18.93 GPa to 21.95 GPa and the indentation fracture resistance changed from 2.70 MPa.m1/2 to 3.50 MPa.m1/2, respectively.

Measuring elastic parameters of transversely isotropic materials by cylindrical indentation

Based on the cylindrical indentation experiments, a novel model for characterizing the elastic mechanical property of transversely isotropic materials has been established. The cylindrical indentation of transversely isotropic materials was theoretically and dimensionally analyzed. Three-dimensional (3D) indentation experiments that encompass the wide range of transversely isotropic material parameters were simulated by finite element. The effect of each parameter (transversely isotropic Young’s modulus, EP , longitudinal Young’s modulus, EL , longitudinal shear modulus, GL , and loading orientation angle, α) on the normalized indentation modulus was investigated. Then, the dimensionless analytical relationship between indentation moduli and elastic parameters was obtained at three different indentation orientations . Several groups of transversely isotropic materials were selected as input parameters to carry out numerical indentation experiments for the error analysis. The sensitivity of the calculated elastic parameters to the experimental data was analyzed. Simultaneously, the technique was used in the particular case of a Zinc single-crystal material, and the accuracy of these derived formulas was verified. The good agreement shows that the proposed method is reliable and could be applied to characterize the elastic parameters of transversely isotropic materials.

Evaluation of Cross-Linked Polyamide 6 Micro-Indentation Properties: TAIC Concentration and Electron Radiation Intensity

Nowadays, technical practice puts emphasis on improving selected material properties of polymers which could lead to new applications. Material properties can be modified in numerous ways, among which is radiation treatment. This study looks into the influence of beta radiation on several properties of polyamide 6, e.g., indentation hardness, modulus and creep. Main changeable parameters were the concentration of triallyl isocyanurate (TAIC), which promotes cross-linking, and intensity of radiation. The concentration was in the range from 2 to 6 wt.%, while the radiation dose was 0, 66, 99 and 132 kGy. The treated materials were measured for indentation hardness, modulus and creep. Degree of cross-linking was verified by thermo-mechanical analysis (TMA), while degradation processes was investigated by Fourier-transform infrared spectroscopy (FTIR). The results indicate that electron radiation positively affects the tested material properties. The best results were seen in polyamide with 6 wt.% of TAIC, which demonstrated a 38% improvement in mechanical properties after exposure to 132 kGy. This improvement in properties affects the final parts and their application (e.g., in the automotive industry-engine parts; in electrical engineering-insulation of wires and cables; and in industry-pipes for underfloor heating, etc.).

Design strategies of the mantis shrimp spike: How the crustacean cuticle became a remarkable biological harpoon

AbstractSpearing mantis shrimps are aggressive crustaceans using specialized appendages with sharp spikes to capture fishes with fast movement. Each spike is a biological tool that has to combine high toughness, as required by the initial impact with the victim, with high stiffness and strength, to ensure sufficient penetration while avoid breaking. We performed a multimodal analysis to uncover the design strategies of this harpoon based on chitin. We found that the spike is a slightly hooked hollow beam with the outer surface decorated by serrations and grooves to enhance cutting and interlocking. The cuticle of the spike resembles a multilayer composite: An outer heavily mineralized, stiff, and hard region (with average indentation modulus and hardness of 68 and 3 GPa), providing high resistance to contact stresses, is combined with a less mineralized region, which occupies a large fraction of the cuticle (up to 50%) and features parallel fibers oriented longitudinally, enhancing stiffness and strength. A central finding of our work is the presence of a tiny interphase (less than 10 μm in width) based on helical fibers and showing a spatial modulation in mechanical properties, which has the critical task to integrate the stiff but brittle outer layer with the more compliant highly anisotropic parallel‐fiber region. We highlighted the remarkable ability of this helicoidal region to stop nanoindentation‐induced cracks. Using three‐dimensional multimaterial printing to prototype spike‐inspired composites, we showed how the observed construction principles can not only hamper damage propagation between highly dissimilar layers (resulting in composites with the helical interphase absorbing 50% more energy than without it) but can also enhance resistance to puncture (25% increase in the force required to penetrate the composites with a blunt tool). Such findings may provide guidelines to design lightweight harpoons relying on environmentally friendly and recyclable building blocks.Key Points The heavily mineralized biological appendages of the mantis shrimp are a constant source of inspiration for developing new engineering materials. We use characterization methods of material science to investigate a biological harpoon based on chitin. Several morphological, compositional, microstructural, and biomechanical features are highlighted, allowing the spikes of the mantis shrimp to be remarkable lightweight, tough, and stiff harpoons.

Nanoindentation and nanotribology behaviors of open-cell metallic glass nanofoams

An in-depth understanding of the mechanical properties of metallic glass nanofoams (MGNFs) is critical to their potential multifunctional applications. In this work, the mechanical properties of Cu50Zr50 open-cell MGNFs are investigated via nanoindentation and nanotribology techniques through virtual molecular dynamics simulations, and the effects of structural parameters (relative density and specific surface area) and loading conditions are studied. The intriguing deformation mechanisms of MGNFs during nanoindentation and nanotribology processes are revealed. It is found that the relationship between indentation modulus and relative density of MGNFs obeys the classical Gibon-Ashby prediction of the bending-dominating porous structure. The hardness of MGNFs monotonously increases with increasing relative density. Differently, as the specific surface area rises, the hardness first increases to its maximum and then decreases. During nanotribology, the MGNFs exhibit relatively steady tribology performance. After being scratched, atoms are pressed into the workpiece surface. In the whole tribology process, no chips or wear debris form. This absence of chips and wear debris effectively avoids the enhancement of frictional force, stabilizing the tribology responses. Von Mises shear strain and Voronoi cluster analysis demonstrate that structural damage is more dramatic for samples having larger relative densities or larger specific surface areas during both indentation and tribology processes. The localized deformation and the surface effect cause more severe damage for larger relative densities and larger specific surface areas, respectively. This study clarifies the essential mechanical properties and deformation mechanisms of MGNFs under nanoindentation and nanotribology loads.

The effect of delignification ratio on the PMMA occupation in poplar wood cell wall by the macro and micro comparative study

The polymer/wood functional products may not be true nanocomposites due to the poor permeability of non-polar monomers into the hydrophilic wood cell wall. In this paper, methyl methacrylate (MMA) chosen as the representative non-polar monomer was used to impregnate wood with different lignin removal and then polymerized in situ in delignified wood to obtain polymethyl methacrylate/delignified wood (PMMA/DW). The larger 10 nm mesopores reduction in PMMA/DW-29.9 and the disappearance of the smaller 3 nm mesopores of PMMA/DW-51.7 indicated that the removal of lignin was beneficial for the penetration of MMA in the wood cell wall. When the lignin removal reached between 29.9 and 51.7%, the dimensional stability of PMMA/DW was improved, and it could be speculated that the resin began to enter the wood cell wall at this stage. In addition, the indentation modulus and hardness of the PMMA/DW cell wall were significantly increased when the lignin removal reached 29.9%. This result was consistent with the conclusion of the pore size analysis, which further confirmed that the nanopores of the cell wall were filled with PMMA when the lignin removal was greater than 29.9%. The results of this paper indeed provide a basis for the design of biomass functional nanocomposites.

Superior oxidation resistance of the chemically complex but structurally simple Ti-Al-Ta-Ce-Si-La-B-nitride

Alloying (Ti,Al)N with Ta, CeSi2 or LaB6 is beneficial for both hardness and thermal stability. Here we show that their different mechanisms allow for a cumulative improvement when alloyed together, which is especially pronounced for the oxidation resistance. During isothermal oxidation treatments in ambient air at 900 °C (for up to 25 h), Ti0.44Al0.44Ta0.12N allows for a parabolic scale growth rate constant kp of 6.039 × 10-5 µm2/s. This is reduced to 2.074 × 10-5 and even 0.399 × 10-5 µm2/s when alloying with 2 mol% CeSi2 respectively CeSi2 + LaB6 (1 mol% each). The oxide scale growth kinetics for the latter can be even better described by a logarithmic or cubic law. In the as-deposited state the CeSi2 and CeSi2 + LaB6 alloyed (Ti,Al,Ta)N are single-phase fcc structured providing an indentation hardness of 32.6 ± 1.5 and 37.8 ± 1.5 GPa, combined with an indentation modulus of 496 ± 22 and 496 ± 14 GPa, respectively. After vacuum-annealing at 1000 °C, their hardness is still 33.0 ± 1.6 and 34.8 ± 1.1 GPa, and noticeable formation of hexagonal AlN and TaNx phases can only be detected by X-ray diffraction when annealed at temperatures above 1200 °C.Using CeSi2 and LaB6 instead of their elemental form is furthermore beneficial for the target production itself, as Ce and La are highly reactive.

A multi-technique and multi-scale analysis of the thermal degradation of PEEK in laser heating

The present work studies the thermal degradation of laser-heated poly-ether-ether-ketone (PEEK) as the heating duration increases. Its damage morphology, chemical composition, crystallinity content, and mechanical properties are examined with optical microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, differential scanning calorimetry, Raman spectroscopy, and continuous stiffness measurement nanoindentation. The applicability of those methods in detecting the thermal degradation of laser-heated PEEK and assessing the induced thermal damage is highlighted. Results show that short-time laser heating acts as an annealing process that improves the crystallinity and hardness on the affected surface of PEEK by up to 5.1% and 10.8% respectively. With a further increase in the heating duration, surface carbonisation occurs and a char layer is formed. Surface carbonisation is associated with the thermal limits of PEEK in laser heating decreasing by up to 50% its hardness and by 45% its indentation modulus. Finally, the char layer is found to act as a shielding mechanism that protects the bulk PEEK from the applied thermal load, resulting in mostly superficial thermally induced damage.

An adhesion study in Ni and Cu nanocontacts from a molecular dynamics perspective

In this work, the effects of adhesion in nanoscale indentation tests with copper and nickel samples indented with a spherical diamond tip have been studied. The tests have been simulated by molecular dynamics, initially selecting the appropriate potentials according to the pair of materials put in contact. The force-displacement curves of a complete cycle of loading and unloading have been determined and a procedure for the simultaneously determination of the indentation modulus of elasticity and the adhesion energy of inelastic indentations have been developed. Likewise, a critical evaluation of the contact models available in the literature has been carried out, assessing their suitability for the cases analysed.

Solid‐State Field‐Assisted Ion Exchange (Ag → Na) in Soda–Lime Float Glass: Tin Versus Air Side

The application of a DC current allows fast (few minutes) Ag+ → Na+ ion exchange in soda–lime–silicate (SLS) glass. The effect of processing parameters, electric current, and treating time is studied on both air and tin sides of SLS float glass, and non‐Fickian diffusion is revealed. It is shown that ion exchange kinetics are similar on both sides and the tempering process results in similar mechanical properties (crack formation probability after Vickers indentation, hardness, and Young's modulus). However, the structure/microstructure of the tin and air sides is hugely different. In particular, clear silver nanoclustering takes place on the tin side, resulting in ≈8 nm metallic particles in the vicinity of the surface. The formation of nanoparticles is also coupled with a deep structural reorganization of the amorphous network and the Q n units. The nanoparticles’ size decreases moving from the surface to the interior of the glass. Silver nanoparticles are also detected on the air side, although their density and size are largely reduced. Whereas the mechanical properties measured on the air and tin side are similar, significative differences are observed in terms of optical properties.

Multiscale study of the effect of fly ash geopolymer on the fatigue cracking of cement stabilized macadam

Understanding of the correlation between the micro-composition and macro-mechanics of cement stabilized macadam (CSM) is crucial to an optimized design of cement-treated base (CTB) with improved crack resistance. In this study, acoustic emission (AE) technique was used to monitor the crack propagation of plain cement stabilized macadam (P-CSM) and fly ash geopolymer cement stabilized macadam (FAG-CSM) under cyclic loading. Experimental tests and characterizations, including such as nanoindentation, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), were further performed. The test results show that FAG-CSM has better fatigue performance than that of P-CSM; the AE counts, risetime/AE amplitude values (RA) and b-value can be used to assess the damage degree, cracking mode as well as the bulk modulus of cement composites. Interfacial transition zone (ITZ) is the weakest modulus area in CSM and the incorporation of fly FAG can effectively increase the indentation modulus of ITZ. The volcanic ash reaction of fly ash leads to the hydration of cement to produce more hydration products, which reduce the voidance within ITZ and thus improve the bonding between the aggregate and mortar, which supports the findings of the macro-mechanical analysis and AE monitoring of CSM.

Characterization of the structural and mechanical properties of pinecone fish (Monocentris japonica) scales.

In this paper, the microstructure characteristics and mechanical properties (including nano-indentation, tensile, and penetration behaviors) of the scales from pinecone fish (Monocentris japonica) were investigated. The M. japonica scales display a unique hierarchical structure and consist of three layers: an outer bone layer with high mineralization, an intermediate bone layer with obvious pore structures, and an inner collagen layer composed of multiple plies of collagen fibers. The hardness and indentation modulus of the three structural layers exhibit gradient changes, and decrease gradually from the outer layer to the inner layer. Tensile tests show that the tensile response and failure modes of the scales are different under dry and hydrated conditions. The dry scales have higher tensile strength (46.35 MPa) and Young's modulus (0.74 GPa), while the hydrated scales exhibit higher ultimate strain (20.18%) and toughness (4.57 MPa). Penetration tests indicate that the scales have a significantly high resistance to penetration, and increase the penetration force by more than six times compared with the descaled skin. Furthermore, the structure-property relationship of the M. japonica scales was discussed. It is found that the hard outer layer and the porous intermediate layer help to disperse the stress, and the soft inner layer containing collagen fiber plies helps to deflect the crack propagation, which are responsible for the excellent mechanical properties of the scales. The outcome of this study can provide a valuable biomimetic design inspiration for lightweight and high-strength composite materials in engineering fields. RESEARCH HIGHLIGHTS: Microstructure characteristics and mechanical properties of the Monocentris japonica scales were investigated. The M. japonica scales can be divided into three layers rather than two layers. The M. japonica scales exhibited high tensile strength and penetration resistance.

Nanomechanical characterization of 3D printed cement pastes

Cement-based 3D printing (additive manufacturing) has drawn significant attention in recent years as an emerging construction technology because of its potential environmental and economic benefits over the traditional cast-in-place concrete construction. Most research to date has focused on the macroscale properties of the printed structure. However, the performance of the printed materials depends on the properties of the individual filaments. In this study, grid nanoindentation coupled with scanning electron microscopy and energy dispersive X-ray spectroscopy was used to determine the effects of the printing process through extrusion on the local elastic indentation modulus and hardness of filaments in 3D printed cement paste structures. Dynamic changes in the water-to-cement ratio during the extrusion process combined with stress-induced dissolution of the cement particles led to variation in the median modulus of the printed filaments, with filaments having values greater than 23 GPa or lower than 20 GPa. Extrusion through a small diameter nozzle affected the mesoscale assemblage of the primary hydrate phases and led to printed filaments having a more uniform mesoscale packing of calcium silicate hydrates (C–S–H) with the disappearance of loosely packed C–S–H compared to their traditionally cast counterparts.

Gradient characterization of steel-concrete interface at early ages

Steel-Concrete Interface (SCI) refers to the porous weak area at the interface between steel bar and cement matrix. This study proposes sophisticated methods for quantifying gradient properties and their evolution of SCI using back-scattered electron (BSE) imaging and nano-indentation. The gradient of SCI is identified through a robust statistical analysis. Distinct stratification structure of SCI is discovered, which can be demonstrated from the grayscale of BSE as well as the indentation modulus and hardness. The thickness of SCI increases with age and the increasing rates roughly decline with the increase of w/c. SCI can be divided into highly porous layer I and transition layer II according to the hierarchically porosity. The layer II is subdivided into II(a) and II(b) based on the gradient of mechanical properties, which is mainly caused by the spatial distribution of cement particles within SCI.

Reactive HiTUS TiNbVTaZrHf-Nx Coatings: Structure, Composition and Mechanical Properties.

High entropy metal sub-lattice stabilized nitride coatings based on multicomponent refractory transition metals (TM = Ti, Nb, V, Ta, Zr, Hf) are promising candidates for extreme conditions due to their high thermal, mechanical, and corrosion properties. The aims of the current work included the investigations of the possibilities of the novel High Target Utilization Sputtering (HiTUS) technique applied to reactive sputtering of TiNbVTaZrHf-xN coatings from the viewpoints of hysteresis behavior during reactive sputtering as well as the structure, composition, stoichiometry, and mechanical properties of the resulting coatings. With increasing nitrogen content, coating structures varied from amorphous in metallic alloy coatings to textured nano-columnar fcc structures. Despite certain deviations of TM from equiatomic concentrations, homogeneous solid solutions corresponding to single-phase multicomponent nitride analogous to high entropy stabilized compounds were obtained. Mechanical properties were found to be proportional to nitrogen content. The highest hardness HIT ~ 33 GPa and indentation modulus EIT ~ 400 GPa were found in a slightly sub-stoichiometric (~42 at% nitrogen) composition. HIT/EIT and limited pillar split measurements suggested that these coatings exhibit low fracture toughness (around 1 MPa.m1/2). The work confirmed that reactive HiTUS is suitable for the preparation of multicomponent nitrides with the control of their stoichiometry and mechanical properties only via nitrogen additions.

Structure and Properties of Composite Materials Sintered at High Pressure and Reinforced with Amorphous Boron Particles

Metal matrix composite materials (CMs) reinforced with boron particles are synthesized from powders of amorphous boron and metal (Ni, Ti) at a pressure of 8 GPa and temperatures of 500–1000°C. It is established that amorphous boron crystallizes during synthesis at temperatures above 800°С. Amorphous boron particles are characterized by a hardness of ~30 GPa, an indentation modulus of elasticity of up to 270 GPa, and an elastic recovery of more than 60%. The patterns of boride formation during high-pressure synthesis are studied. It is shown that the wear resistance of a Ni–B CM synthesized at 600°С grows by more than 30 times, relative to the wear resistance of pure nickel. Reinforcing titanium with 30% amorphous boron increases wear resistance by more than two orders of magnitude, but the coefficient of friction of CMs is reduced slightly.

Investigation on mechanical properties deterioration of concrete subjected to freeze–thaw cycles

Concrete structures in cold regions are usually suffer from froze and thaw action. A combined investigation of nanoindentation technique and X-ray diffraction were adopted to demonstrate the microstructure change and micromechanical properties deterioration of concrete subjected to freeze–thaw (F-T) cycles in this study. The results showed that the indentation modulus and hardness of the main compositions in mortar, such as calcium-silicate-hydrates and calcium hydroxide, both gradually decreases as the F–T cycles increase, with the greatest reduction approximate 38% after 1500 F–T cycles, while the corresponding greatest reduction of the main compositions in interfacial transition zone (ITZ) is close to 50%. In addition, the micropores in mortar and ITZ both gradually converge and connect to form larger diameter pores, and the thickness of ITZ increased rapidly from 25 to 50 μm after 1500 F–T cycles. On this basis, the effective modulus of elasticity under different F–T cycles are analyzed through Mori–Tanaka scheme with consistent variation tendency of dynamic modulus of elasticity test. Subsequently, the mechanical properties deterioration of concrete under F–T cycles is mainly attributed to the decrease of mechanical properties (such as modulus and hardness) of microscopic components, and the increase and propagation of the internal micropores especially for micropores in ITZ.

Hardness and indentation modulus of human enamel and dentin

Information on mechanical properties of human enamel and dentin and effect of load on their deformation and damage tolerance is very important in the development of successful dental materials. In this study, the hardness, indentation modulus and deformation characteristics of tooth have been investigated across the lingual–buccal enamel and dentin cross‐section by instrumented indentation up to 1500‐nm indentation depth. We realized and examined the distribution of hardness and modulus at different areas of enamel and dentin with the aim to understand deformation behaviour at these different locations. Scanning electron microscopy was used for the microstructure characterization of the enamel and dentin and their deformation behaviour. Raman spectroscopy analyses were carried out for determination of the enamel and dentin composition as well. The average values of hardness and modulus for enamel in the occlusal area are 5.35 ± 0.19 and 98.1 ± 1.5 GPa, in the inner area 3.68 ± 0.5 and 81.8 ± 5 GPa and in the area close to the dentin–enamel junction 2.83 ± 0.27 and 71.4 ± 4.1 GPa, respectively. The average values of hardness and modulus of dentin in the area close to the dentin–enamel junction are 0.71 ± 0.05 and 21.27 ± 0.76 GPa and in the inner area 0.65 ± 0.06 and 19.79 ± 0.93 GPa, respectively. The effect of the indentation location on deformation and mechanical properties was clarified.

Probing the effect of glycosaminoglycan depletion on integrin interactions with collagen I fibrils in the native extracellular matrix environment.

Fibrillar collagen-integrin interactions in the extracellular matrix (ECM) regulate a multitude of cellular processes and cell signalling. Collagen I fibrils serve as the molecular scaffolding for connective tissues throughout the human body and are the most abundant protein building blocks in the ECM. The ECM environment is diverse, made up of several ECM proteins, enzymes, and proteoglycans. In particular, glycosaminoglycans (GAGs), anionic polysaccharides that decorate proteoglycans, become depleted in the ECM with natural aging and their mis-regulation has been linked to cancers and other diseases. The impact of GAG depletion in the ECM environment on collagen I protein interactions and on mechanical properties is not well understood. Here, we integrate ELISA protein binding assays with liquid high-resolution atomic force microscopy (AFM) to assess the effects of GAG depletion on the interaction of collagen I fibrils with the integrin α2I domain using separate rat tails. ELISA binding assays demonstrate that α2I preferentially binds to GAG-depleted collagen I fibrils in comparison to native fibrils. By amplitude modulated AFM in air and in solution, we find that GAG-depleted collagen I fibrils retain structural features of the native fibrils, including their characteristic D-banding pattern, a key structural motif. AFM fast force mapping in solution shows that GAG depletion reduces the stiffness of individual fibrils, lowering the indentation modulus by half compared to native fibrils. Together these results shed new light on how GAGs influence collagen I fibril-integrin interactions and may aid in strategies to treat diseases that result from GAG mis-regulation.