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(a) FIB-milled cross-sectional view of the indented region after unloading of a specimen sintered at 1000°C with an initial porosity of 36.3vol%. The dashed curve indicates the boundary of the densification zone. (b) Contour plot of the porosity distribution from the corresponding FE simulation. (c) High magnification views of the marked zones ① and ② from (a), showing the difference between deformed and un-deformed zones, with arrows marking possible collapse of pores between particles.
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A combined experimental and numerical approach is used to characterise the elastic and plastic deformation of a porous bulk ceramic material (La0.6Sr0.4Co0.2Fe0.8O3, LSCF) with porosities in the range 5–45vol%, undergoing spherical indentation. The Gurson model was used in FEM simulations to describe the densification of the porous material in the...
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... indented specimens were FIB-milled to gain insight into the changes in microstructure in the plastic zone under the inden- ter. Fig. 6 shows the cross-sectional microstructure after a 2.5 m indentation depth for a specimen sintered at 900 • C (with an initial porosity of 44.9 vol%) and Fig. 7 a similar case for a specimen sin- tered at 1000 • C (with an initial porosity of 36.3 vol%). The contour plots of porosities, shown as void volume fraction (VVF), for the cor- responding FEM simulations for the same indentation conditions as the experiments are also displayed in the ...Citations
... The GTN model was originally developed to depict the deformation of porous ductile metallic materials and has been recently extended to encompass ceramics and their composites [22]. In this regard, Chen et al. [23][24][25] conducted a series of studies by utilizing the GTN model in finite element (FE) analysis to simulate the indentation process of porous bulk ceramics which well simulated the densification effect in their experimental observations. ...
... For the plastic characteristics, specifically, an inverse FE analysis was carried out in line with the damped least-square (DLS) technique to identify the most appropriate yield stress ( ) of materials by best matching the FE-derived loading-unloading curve to the measured counterpart. Here, the initial value of was set to be the experimental hardness [23]; and then adjusted to attain the best fit to the experimental load-displacement curves progressively; and the results are presented in the following Section. The coefficients of determination (R 2 ), coefficients of correlation (R) were calculated by using the inverse analysis to quantify the correlation between the FE and the experimental data at different time steps. ...
... This is because the deformation mechanisms involved in plastic behavior are anticipated to bear better correlations with irreversible processes such as localized microcracking, wear, and fatigue, etc. [6]. It is found that the hardness, , is directly related to the yield stress, , because the hardness is defined as the resistance to permanent deformation during the indentation [23,51]. Some researchers attempted to correlate with , and they found that there is a certain proportional relationship, = , where is a fitting constant with an approximate value of 3 for ideal dense plastic materials undergoing a sharp indentation [52]. ...
... Thus, the method is acceptable for studying the localized deformation behavior of porous ceramics. [30] Heat-transfer pertained to the movement of thermal energy and the dispersion of temperatures, along with alterations induced by variations in temperature levels. The process of thermal transport encompassed conduction, convection, and radiation. ...
Dense ultrahigh‐temperature ceramics (UHTCs) carbides are recognized as potential materials for thermal protection systems (TPS) owing to properties beyond existing structural materials’ capabilities. Recent advances in UHTCs have enabled the development of multiscale porous microstructures. Herein, it is highlighted that the porosity in UHTCs are no longer treated as a defect but as a functional property specifically tailored for thermal insulation. It is a promising solution to design and fabricate bulk UHTC foams via a freeze‐drying (FD) approach followed by calibrated pressureless spark plasma sintering. Herein, monolithic TaC and HfC UHTC foams and their composite show the partial solid–solution formation of (Ta, Hf)C with porosity ≥50%. TaC–HfC foam (≈80–92 N) shows an intermediate load‐bearing capability compared to monolithic TaC (≈120–135 N) and HfC (≈28–35 N) foams, with no evident cracking on the sample surface. The thermal conductivity of partial solid‐solution TaC–HfC foam increases up to fivefold compared to parent UHTC foams. In the results, solid solutions’ efficacy and pores’ unidirectionality in providing thermal insulation to TaC–HfC while maintaining its high‐load bearing capability are illustrated. The developed technique establishes a new paradigm shift in UHTCs, expanding their potential for TPS in extreme environments.
... The cutting process has been qualitatively and quantitatively analyzed using the finite element analysis (FEA) to understand chip morphologies, stresses, strains, cutting forces, temperatures, and other exogenous variables. A number of analyses are used in the FEA machining investigations, including machining parameters and conditions [223,[246][247][248][249][250][251][252], tool geometry [253][254][255][256][257], workpiece orientation [258,259], tool wear measurements [255,260,261], chip separation criteria [262][263][264][265], and meshing and remeshing techniques [266][267][268][269]. Finite element approaches have been utilized in several studies to model the formation of radial cracks in cutting tool inserts due to Vickers [270][271][272], Berkovich [273], or Brinell [274] indentations in cutting tool inserts. ...
... Spherical indentation is a method for determining the hardness of cutting tool inserts. Zhangwei Chen et al. [274] developed a mixed experimental and numerical technique for assessing elastic and plastic deformation of porous bulk ceramic material under spherical indentation. After sintering at high temperatures between 900 and 1200 • C, tests of indentation were carried out on porous bulk ceramic specimens. ...
Cermet materials exhibit advanced mechanical and tribological properties, and are widely used for tribology, elevated temperature, and machining applications due to their unique amalgamation of hardness, strength, and toughness. This paper presents a comprehensive overview of various cermet systems and recent advances in high-temperature tribology and cutting performance of cermet and ceramic tool materials. It outlines microstructural properties, such as lessening grain sizes, obtaining extended grains, lowering grain boundary phase content, amorphous grain boundary phases crystallizing, inter-granular phase strengthening, and managing crack propagation path. Additionally, surface processing or surface modifications, such as surface texturing, appropriate roughness, or coating technique, can optimize the ceramic and cermet tribological performances. The purpose of this study is to present some guidelines for the design of ceramics and cermets with reduced friction and wear and increased cutting performance. The current research progress concerning tribological properties and surface texturing of cutting tool inserts is critically identified. Lubrication techniques are required in commercial applications to increase the lifetime of cutting tools used in harsh conditions. Liquid lubricants are still commonly utilized in relative motion; however, they have the limitations of not working in extreme settings, such as high-temperature environments. As a result, global research is presently underway to produce new solid lubricants for use in a variety of such conditions. This review also provides a quick outline of current research on this topic.
... ∼8 v% water which is confined inside porous regions between the rods and nanofibers. When enamel is loaded, especially in the highly localized compressive hydrostatic stress state with a spherical tipped indenter, the crystallites may slide against each other [29] and the porous structure may densify, as observed for porous ceramics [30] , which is facilitated by water (up to 8 v%) and will narrow the pore channels, displacing the contained water. The data presented in the supplementary information for the synthetic HAP shows a similar effect of the water content on the HAP sample. ...
... It is interesting to compare the present indentation results with those of He et al. [34] investigating the indentation response of porous HAP and the study by Chen et al. [30] investigating the spherical indentation of porous ceramics. In both studies the indentation response showed elastic like initial behavior that exhibited a plastic like response above a critical contact pressure. ...
... Chen et al. analyzed their observations based upon a model by Gurson, developed for porous metallic materials, whereby the nominal plastic deformation is accommodated by the densification of the porous material beneath the indenter. That is the energy loss during indentation, especially for the lowest loading rate, is associated with densification [30] . He et al. in the case of HAP found the energy loss during indentation increased as the porosity increased which is similar to what is evident in the results of Chen et al. [34] . ...
The creep behavior of untreated and deproteinized dental enamel in dry and wet state was analyzed by nanoindentation with a spherical tip. Additionally, the influence of the loading rate was investigated. Dry untreated and deproteinized dental enamel only showed minor creep over 100 s and deproteinization did not affect the dry enamel's behavior significantly. With slower loading rates some creep already occurs during the loading period, such that the creep displacement during load hold is less than with faster loading rates. Wet untreated and deproteinized enamel showed significantly more creep compared to the dry samples. The differences between the untreated and deproteinized enamel were only minor but significant, revealing that water affects the creep behavior of biological materials such as enamel significantly. The proposed deformation mechanism of naturally porous enamel under compression is compaction of the HAP crystallites and fluid displacement within material underneath the indented area. STATEMENT OF SIGNIFICANCE: This study investigates the creep behavior of untreated and deproteinized dental enamel in dry and wet conditions. It is shown that while the protein content does not affect enamel's behavior significantly, the wet conditions lead to an increased creep in enamel. The proposed deformation mechanism of naturally porous enamel under compression is compaction of the HAP crystallites and fluid displacement within material underneath the indented area. Based on this observation a simple analytical model has been developed, aiming to deepen our understanding of the deformation behavior of biological materials.
... However, these analytical models do not provide plasticity characteristics of the coating from indentation experiments. The most suitable tool for this is the Finite Element Method (FEM), which has been widely applied to indentation testing with the objective of obtaining information about the plastic properties of the coating [18][19][20]. In this case, numerous other studies proposed mechanical characterization models for the coated systems based on both the Dimensional Analysis Method (DAM) and the FEM [1,5,[21][22][23][24][25]. ...
This paper proposes an identification methodology based on nanoindentation analysis of coating/substrate system to extract the elastic-plastic properties of coating materials on elastic-plastic substrate when the indenter penetration depth is greater than the film thickness. In order to accurately predict the elastic-plastic properties of the coating materials, a trust-region reflective optimization algorithm is integrated with the finite element analysis, in cooperation with the Jönsson and Hogmark model. The proposed reverse analysis algorithm modifies a predicted load-displacement (P-h) curve by changing the elastic-plastic properties of the coating and the substrate until it fits the experimental nanoindentation (P-h) curve. Numerical and instrumental indentations tests were carried out on a CrN film/Martensitic stainless steel substrate system to verify the proposed reverse method, by which Young's modulus (E), yield stress (σy), and work hardening exponent of the film were obtained. A sensitivity analysis is conducted to study the effect of the elastic-plastic properties of the CrN film/substrate on the (P-h) curve. The results showed a high impact to the loading and unloading part of the (P-h) curve due to variations in (E) and (σy) of the steel substrate compared to those of the CrN coating.
... Additional experimental studies are required to characterize the underlying mechanisms of the newly fabricated silica aerogel and guide enhancing the multiphase mixture model. For instance, the stress-strain measurements, including loading and unloading, indentation experiments, e.g., [10,19] , and microstructure imaging before and after compression testing can provide more insights on the micro-mechanical responses and the effect of fluid pressure on the silica aerogel deformation. Additionally, a higher fidelity simulation of the hierarchical porous structure and pore size on the silica aerogel properties may be achieved by gradient-enhanced nonlocal models, such as those in [20,21]. ...
This work develops a systematic uncertainty quantification framework to assess the reliability of prediction delivered by physics-based material models in the presence of incomplete measurement data and modeling error. The framework consists of global sensitivity analysis, Bayesian inference, and forward propagation of uncertainty through the computational model. The implementation of this framework on a new multiphase model of novel porous silica aerogel materials is demonstrated to predict the thermomechanical performances of a building envelope insulation component. The uncertainty analyses rely on sampling methods, including Markov-chain Monte Carlo and a mixed finite element solution of the multiphase model. Notable features of this work are investigating a new noise model within the Bayesian inversion to prevent biased estimations and characterizing various sources of uncertainty, such as measurements variabilities, model inadequacy in capturing microstructural randomness, and modeling errors incurred by the theoretical model and numerical solutions.
... It can be observed that the continuous contact stiffness of investigated CAD/CAM restorative materials increases nonlinearly with the increasing depth (Figure 4), which is characteristic of polymer-based composite materials [22]. the local and respectively intrinsic mechanical properties of materials. ...
... It can be observed that the continuous contact stiffness of investigated CAD/CAM restorative materials increases nonlinearly with the increasing depth (Figure 4), which is characteristic of polymer-based composite materials [22]. According to the literature, the contact stiffness is proportional to the root square of the contact area [23]. ...
The tremendous technological and dental material progress led to a progressive advancement of treatment technologies and materials in restorative dentistry and prosthodontics. In this approach, CAD/CAM restorations have proven to be valuable restorative dental materials in both provisional and definitive restoration, owing to multifarious design, improved and highly tunable mechanical, physical and morphological properties. Thus far, the dentistry market offers a wide range of CAD/CAM restorative dental materials with highly sophisticated design and proper characteristics for a particular clinical problem or multiple dentistry purposes. The main goal of this research study was to comparatively investigate the micro-mechanical properties of various CAD/CAM restorations, which are presented on the market and used in clinical dentistry. Among the investigated dental specimens, hybrid ceramic-based CAD/CAM presented the highest micro-mechanical properties, followed by CAD/CAM PMMA-graphene, while the lowest micro-mechanical features were registered for CAD/CAM multilayered PMMA.
... Additional experimental studies are required to characterize the underlying mechanisms of the newly fabricated silica aerogel and guide enhancing the multiphase mixture model. For instance, the stress-strain measurements, including loading and unloading, e.g., [124] and indentation experiments, e.g., [31,19] can provide more insights on the hysteresis mechanical responses, the effect of fluid pressure, and micromechanical contributions. Additionally, a higher fidelity simulation of the hierarchical porous structure and pore size on the silica aerogel properties may be achieved by gradient-enhanced nonlocal models, such as those in [117,33,116,32]. ...
This work develops a multiphase thermomechanical model of porous silica aerogel and implements an uncertainty analysis framework consisting of the Sobol methods for global sensitivity analyses and Bayesian inference using a set of experimental data of silica aerogel. A notable feature of this work is implementing a new noise model within the Bayesian inversion to account for data uncertainty and modeling error. The hyper-parameters in the likelihood balance data misfit and prior contribution to the parameter posteriors and prevent their biased estimation. The results indicate that the uncertainty in solid conductivity and elasticity are the most influential parameters affecting the model output variance. Also, the Bayesian inference shows that despite the microstructural randomness in the thermal measurements, the model captures the data with 2% error. However, the model is inadequate in simulating the stress-strain measurements resulting in significant uncertainty in the computational prediction of a building insulation component.
... The exact yield strength of the silica glass under the given stress condition is not known. But, based on the general relationship between strength and hardness [49][50][51] , the yield strength of silica glasses can be estimated to be around 3 GPa. During the ramp-load nanoscratch, the tip is constantly moving and thus the critical load for the onset of plastic deformation is likely to be higher than the value measured in the static condition. ...
Surface defects or flaws on materials made by physical contacts with foreign objects can deteriorate their mechanical properties and limit technical applications. Thus, understanding the contact-induced subsurface damage is of great importance. Using nanoscale infrared spectroscopy and reactive molecular dynamics simulations, the subsurface structural changes of silica upon nanoindentation and nanoscratch are investigated. The results reveal an elongation of the Si-O bond length distribution even after the topographically-elastic contact, indicating a “chemical plasticity” at the sub-Angstrom level. In the plastic region with subsurface densification, the Si-O bond is found to be slightly longer than the pristine region, indicating the decrease in molar volume is accompanied with the elongation, not shortening, of the Si-O bond. These results elucidate the structural damage of a material upon physical contact cannot be delineated based on the topographic deformation of the surface.
... The main local mechanical properties of the medium, such as hardness and elasticity, are up to several tens of MPa. Such values of hardness are typical for soft polymers [6]; they are well below ones reported for even highly porous ceramics [7]. The same is true for the elastic modulus [8]. ...
Mats of yttria-stabilized tetragonal zirconia nanofibers were prepared in the present research. The effect of the mats calcination temperatures (600, 900, and 1200 °C) on their structure and morphology was investigated. It was found that phase composition of the fibers did not change in all range of the calcination temperatures, while the average grain size in fiber increased from 8 to 39 nm. Multi-cyclic and single loading-unloading nanoindentation testing of the ceramic mats showed that the hysteresis loop energy in samples decreases with higher calcination temperature. Hardness and the elastic modulus measured by spherical (with 10 and 250 μm radii) and sharp Berkovich indenters were the highest in the mats calcined at 900 °C. This calcination temperature can be considered an optimal one for preparation of nanofibers mats which mechanical properties are of importance for their application.
