Multiple Indentations Research Articles

Multiple concentric indentation marks on the corneal surface due to rigid corneal contact lens usage

Multiple concentric indentation marks on the corneal surface due to rigid corneal contact lens usage

Multi-scale characterization and analysis of cellular viscoelastic mechanical phenotypes by atomic force microscopy.

The viscoelasticity of cells serves as a biomarker that reveals changes induced by malignant transformation, which aids the cytological examinations. However, differences in the measurement methods and parameters have prevented the consistent and effective characterization of the viscoelastic phenotype of cells. To address this issue, nanomechanical indentation experiments were conducted using an atomic force microscope (AFM). Multiple indentation methods were applied, and the indentation parameters were gradually varied to measure the viscoelasticity of normal liver cells and cancerous liver cells to create a database. This database was employed to train machine-learning algorithms in order to analyze the differences in the viscoelasticity of different types of cells and as well as to identify the optimal measurement methods and parameters. These findings indicated that the measurement speed significantly influenced viscoelasticity and that the classification difference between the two cell types was most evident at 5 μm/s. In addition, the precision and the area under the receiver operating characteristic curve were comparatively analyzed for various widely employed machine-learning algorithms. Unlike previous studies, this research validated the effectiveness of measurement parameters and methods with the assistance of machine-learning algorithms. Furthermore, the results confirmed that the viscoelasticity obtained from the multiparameter indentation measurement could be effectively used for cell classification. RESEARCH HIGHLIGHTS: This study aimed to analyze the viscoelasticity of liver cancer cells and liver cells. Different nano-indentation methods and parameters were used to measure the viscoelasticity of the two kinds of cells. The neural network algorithm was used to reverse analyze the dataset, and the methods and parameters for accurate classification and identification of cells are successfully found.

A symplectic analytical wave propagation model for forced vibration of thin plate with acoustic black hole indentation

In recent years, acoustic black holes (ABHs) have been revealed as an effective bending wave control technology and widely used to regulate the vibration and noise reduction performance of plate structure. However, the isolation effect of most traditional ABH plate can only be aroused at frequencies above the cut-off frequency. In order to widen the frequency range of the ABH effect, this paper embedded single and multiple ABH indentations at the end of plate. For the forced vibration response of the ABH indentation plate, an analytical wave propagation model was proposed based on the symplectic method. The governing equations of bending vibration of thin plate was first introduced into the symplectic dual system, then the symplectic analytical solution of wave propagation parameters and waveforms were obtained. A Gaussian-discretization scheme was used to discretize the ABH indentation, whereas the proposed method was used to evaluate the wave amplitude. The vibration response was finally obtained using the superposition principle and wave propagation, reflection, and transmission relationships. The effectiveness of the proposed method was verified using the finite element results. The results showed that the ABH indentation plate, especially the plate with multiple ABH indentations, had significant vibration reduction performance. Considering that embedding ABH indentation can weaken the structural rigidity of the plate, the ABH indentation plate with reinforcing stiffeners was then proposed to alleviate this limitation, and the influence of the width and quantity of reinforcing stiffeners on the vibration response was studied. The results indicated that the increase of width will to some extent weaken the ABH effect, and the quantity of stiffeners had a significant impact on the ABH effect.

NANOINDENTATION EXPERIMENTS TO STUDY THE MICROMECHANICAL PROPERTIES OF STRATIFIED SHALE

The micromechanical properties of stratified shale are critical for understanding wellbore stability and hydraulic fracture extension patterns. Based on nanoindentation experiments and data analysis, the mechanical parameters of shale specimens from two laminar directions of the Jimsar Lucaogou Formation in Xinjiang are measured from a microscopic perspective in this paper. The mechanical parameters of multiple indentation points are obtained using grid indentation. The mineral composition of the samples is quantified using field emission scanning electron microscopy (SEM) and XRD ray diffraction. The results show that the shale mechanical parameters have a good linear relationship with each other at the nanoscale. However, the relationship between horizontal bedding and vertical bedding is quite different. The average elastic modulus, average hardness, and average fracture toughness of the parallel laminated specimens are 22.94 GPa, 1.04 GPa, and 1.19 MPa·m<sup>1/2</sup>, respectively. The average elastic modulus, average hardness, and average fracture toughness of the vertical laminated specimens are 35.23 GPa, 3.47 GPa, and 1.32 MPa·m<sup>1/2</sup>, respectively. The shale mechanical parameters in the vertical bedding direction are higher than those in the horizontal laminae. The mechanical parameters at the nanoscale are related to the orientation of the laminae. The shale is anisotropic at the nanoscale and the anisotropy of different mechanical parameters behaves differently. The microscopic elastic modulus, hardness, and fracture toughness of shale conform to Weibull distribution. The dispersion of hardness is the highest. The results can help analyze the relationship between shale mechanical properties and laminar orientation.

LOCAL INDENTATION AS METHOD OF REDUCING FATIGUE CRACK GROWTH RATE

The possibility of a significant decrease in the growth rate of a fatigue crack is studied. The goal can be attained by creating a local field of residual stresses near the crack tip which arises due to the indentation of a spherical indenter. A methodology and program algorithm (in ANSYS) have been developed for numerical simulation of the problem in a three-dimensional formulation of the process of fatigue crack growth in the field of residual stresses. Considering the prospects of developing the technique with regard to the use of dynamic indentation, the ANSYS Explicit STR solver fully integrated into the calculation module was used in the macro. Proceeding from the solution of the elastoplastic problem the program provides determination of the fields of residual stresses (RS) at the first stage of the calculation and numerical simulation of the fatigue crack growth on the second stage. The effect of the indentation parameters (magnitude of the force applied to the indenter and the location of the indentation point, conditions of fixing) on the crack growth rate is considered. Methods for a significant reduction in the crack growth rate based on multiple preliminary indentation are substantiated. Using the developed program, we managed to solve a series of problems regarding the effect of different types of loading and fastenings on the growth rate of a fatigue crack in a plate with a through crack. The use of one-sided indentation of thin-walled objects with cracks, which are installed on the support surface, greatly simplifies the practical application of the technique for creating a residual stress field in the vicinity of the crack tip. It is shown that with multiple indentation along the crack propagation line, the fatigue crack growth rate is significantly lower than that when using a single indenter.

Dynamics of Polymer Nanocapsule Buckling and Collapse Revealed by In Situ Liquid-Phase TEM.

Nanocapsules are hollow nanoscale shells that have applications in drug delivery, batteries, self-healing materials, and as model systems for naturally occurring shell geometries. In many applications, nanocapsules are designed to release their cargo as they buckle and collapse, but the details of this transient buckling process have not been directly observed. Here, we use in situ liquid-phase transmission electron microscopy to record the electron-irradiation-induced buckling in spherical 60-187 nm polymer capsules with ∼3.5 nm walls. We observe in real time the release of aqueous cargo from these nanocapsules and their buckling into morphologies with single or multiple indentations. The in situ buckling of nanoscale capsules is compared to ex situ measurements of collapsed and micrometer-sized capsules and to Monte Carlo (MC) simulations. The shape and dynamics of the collapsing nanocapsules are consistent with MC simulations, which reveal that the excessive wrinkling of nanocapsules with ultrathin walls results from their large Föppl-von Kármán numbers around 105. Our experiments suggest design rules for nanocapsules with the desired buckling response based on parameters such as capsule radius, wall thickness, and collapse rate.

Comparison of hardness and Young’s modulus by single indentation and multiple unloading indentation

Abstract Multiple partial unloading indentation is a useful technique for depth-dependent nanoindentation yielding up to 20 hardness and modulus values of different depth with one single measurement. A comparison between multiple partial unloading indentation and conventional single unloading technique is presented. A representative selection of materials (sapphire, TiN, DLC, tool steel, Ti alloy and aluminium) has been tested and it is found that both methods give comparable results. Soft materials as Al or Ti show certain deviations of about + 11 ± 4% in hardness and + 3.1 ± 1.2% for the modulus. For all other materials, the difference is + 2.2 ± 1.0% for the hardness and –2.1 ± 2.2% for the modulus. Possible reasons for these small systematic deviations will be discussed.

Influence of multiple load indentation on the mechanical and material behaviour of steel cone-cylinder under axial compression

The first set of test data on axial collapse of cone-cylinder assembly having multiple load indentation (MLI) and its accompanying numerical studies is presented in this paper. Two perfect and two imperfect steel cone-cylinders were prepared in pairs. The cone-cylinder models have the following geometric parameters: cone radius of 40 mm, cylinder radius of 70 mm,wall thickness of 0.5 mm and cone angle of 16.7°. Cone and cylinder part were combined using Metal Inert Gas (MIG) welding technique. Results show that the repeatability of the experiment was good (3% for the perfect and 7% for the imperfect). Also, numerical prediction tends to reproduce the test data with good accuracy. The error between both approches ranges from 1% to −8%. Furthermore, the influence of geometric parameters are also significant in determining the collapse load of this type of structure. Finally, the worst multiple load indentation (WMLI) was explored for steel cone-cylinders assembly using different number of load indentations. Results indicate that as the number of indents increases, the sensitivity of the cone-cylinder models to imperfection also increases. However, at different imperfection amplitude, A, two regions were observed; (i) the region where cone-cylinder with N = 8 is more sensitive (A < 1.5), and (ii) the region where N = 4 produce the worst imperfection (1.5 < A ≤ 1.68).

Diagnosis of Mechanical Properties with Instrumented Indentation Technique Using Multiple Pyramid Indenters

Abstract This paper presents a semi-nondestructive method for diagnosing mechanical properties through an instrumented indentation technique using multiple pyramid indenters with different dihedral angles. In the developed method, an approximated true stress–true strain curve can be obtained from the plots of the representative stress–representative strain relation estimated for each of the four different pyramid indenters. A functional relation between the representative stress and the indentation load–depth curve was derived from dimension analysis using the π theorem. Then, specific values of constants in the functional equation were determined for each of the pyramid indenters using experimentally validated finite element analysis of the instrumented indentation test. Meanwhile, the representative strain levels were quantified according to the dihedral angle of the pyramid indenters. The developed method was applied to estimate the true stress–true strain curve of non- and prestrained steels. As a result, a small difference could be seen only in non-strained steel with Lüders strain, but the estimated results are nearly in agreement with those obtained by tensile tests. The approximated curves were also used to estimate yield stress and prestrain. The results showed that estimation accuracy of yield stress was better than that based on an empirical correlation with Vickers hardness, and the estimated values of prestrain were in good agreement with those actually introduced by tensile tests. It is expected that the developed multi-indenter method will become useful for semi-nondestructively diagnosing mechanical properties for steel.

Experimental investigation of multiple rock indentations on hard rock using a conical cutter at different cutting depths

To apply roadheaders to deep hard rock mines, one must investigate the influence of multiple rock indentations and cutting depths on rock breakage. In this study, multiple rock indentations using a conical cutter were performed on hard rock samples at different cutting depths. The relationship between the cutting depth and the parameters reflecting the rock cuttability was regressed. The experimental results of the single and multiple rock indentations were compared. They showed that the failure pattern affects the cutting parameters. In the case of partial splitting, the cutting parameters increase with the increase of the cutting depth. Meanwhile, in the case of complete splitting, the force and the work required to break the rock did not show any obvious relationship with the cutting depth, but were directly proportional to the area of the formed fracture surface. Moreover, the free and fracture surfaces formed by multiple rock indentations facilitated the subsequent rock breakage.

Disease surveillance in England and Wales, April 2021

Disease surveillance in England and Wales, April 2021

Influence of eccentric nanoindentation on top surface of silicon micropillar arrays

In this paper we present an investigation of the influence of nanoindentation location on the top surface of silicon micro-pillar. This silicon micro-pillar array which will be employed as a micro force sensor array based on three-dimension silicon (3D Si) structures, is fabricated by near UV nanoimprint lithography (NIL) technique and etched by Cryogenic Inductively Coupled Plasma (ICP) sequentially. To determine its mechanical properties, those micropillars are measured by instrument indentation testing (IIT) to obtain its hardness and reduced modulus. For the measurement, a Berkovich diamond indenter is utilized to penetrate a single and also multiple point indentations on a micro-pillar surface. Afterwards, these results are compared to the indentation at the central point of the tested pillar and Si bulk as its reference to examine the influence of different probing locations on the measured reduced modulus and hardness.

High-Throughput Characterization of Composition and Performance of Titanium Alloys Based on Nanoindentation Technology and EPMA

Traditional high-throughput experiments increase the test efficiency by designing component gradient tests and other methods. This article intends to improve the traditional high-throughput experiments and proposes an experimental scheme combining nanoindentation technology and electron probe microanalysis (EPMA). Based on a new Ti-Mo-Al-Zr-Cr-Sn alloy, micro-region composition and corresponding performance at multiple indentations are directly characterized, including a series of different alloy compositions composed of 8 elements such as Mo, Al and the corresponding hardness (H) and elastic modulus (E). Then the principal analysis method in statistics, the theory of molybdenum equivalent and aluminum equivalent are used to process the obtained data, and a series of atlases such as "E-H-component characteristic parameters" and "E-H-alloy equivalents" are constructed, which has achieved high-throughput characterization of the relationship between composition and performance of titanium alloy. Related work can not only quickly determine the alloy composition range corresponding to high E and high H values, but also provide guidance for further optimization of titanium alloy composition design.

STUDY ON FRACTURE TOUGHNESS OF SEMICONDUCTOR MATERIAL USING VICKERS AND BERKOVICH INDENTERS

The indentation method is one of the commonly used methods to determine fracture toughness ($K_{\rm IC})$ of brittle materials. One of the challenges is to obtain a suitable equation of the materials from various equations according to different materials and indenters. Therefore, fracture toughness tests with pyramid indenters (Vickers indenter and Berkovich indenter) were conducted on Si (111) and 4H-SiC (0001) under various loads. The crack length $c$ generated in the Vickers indentation experiments were statistically analyzed, and thirteen equations were selected to calculate the fracture toughness of semiconductor materials at room temperature. The applicability of the indentation test was evaluated, based on a comparative analysis with the results of the scratch test. The results show that to eliminate the inherent discreteness of crack length $c$ generated in the Vickers indentation experiment, multiple indentation tests (at least thirty tests) need to be conducted. The ratio of crack length $c$ over the indentation diagonal length $a$ increases with an increase in the applied load $P$. The crack types of the materials depend on $P$: Palmqvist crack system appears for low loads and Median crack system appears for high loads. Compared with the average fracture toughness (0.96~MPa,$\cdot$,$\sqrt{\rm m}$ and 2.89~MPa,$\cdot$,$\sqrt{\rm m}$, respectively) of Si (111) and 4H-SiC (0001) obtained by micro scratch test, based on linear elastic fracture mechanics (LEFM), the appropriate equations was obtained for both Vickers and Berkovich indenters for the same as material, but which can not be obtained for both Si (111) and 4H-SiC (0001) under the same as indenter from thirteen equations. The fracture toughness of semiconductor materials are best calculated by an expression develope from the Median crack system, and the relationship between fracture toughness being obtained with Vickers indenter and that of with Berkovich indenter is not theoretically 1.073 times, which should be 1.13$\pm $0.01.

The imperfection sensitivity of axially compressed steel conical shells – Lower bound curve

This paper presents the numerical results centered on the buckling behavior of axially compressed imperfect conical shells. It was assumed that the cone model was made from mild steel. The perfect cone will be subjected to multiple imperfection approaches such as (i) eigenmode imperfection, (ii) single and multiple load indentation approaches, (iii) crack imperfection, and (iv) uneven axial length imperfection to study the reduction of buckling strength of the structure. As predicted, imperfection severely affected the buckling strength of conical shells, and the decrease in buckling strength could be seen to be heavily reliant on the imperfection approach. It is apparent that for axially compressed cones with radius-to-thickness ratio, r1/t = 25, uneven axial length imperfection was seen to produce the lowest buckling load, followed by eigenmode imperfection, crack imperfection, and load indentation for imperfection amplitude 0 < A < 1.68. Increasing the imperfection amplitude, A, beyond this level, i.e., A ≥ 1.68, the highest reduction in buckling load was found to be eigenmode imperfection, followed by the uneven axial length, crack and load indentation. Furthermore, based on ECCS 2008 recommendation for imperfection tolerance, the lower bound curve, which can be used for design recommendation purposes, has been proposed for the worst imperfection approach case, i.e., uneven axial length and eigenmode imperfection for different conical shell geometry configurations. Finally, the proposed lower bound curve was compared with the plot of NASA SP-8019 recommended imperfection correlation factor for axially compressed cone. Results showed that the proposed lower bound curve for axially compressed conical shells with uneven axial length imperfection is notably higher than the NASA SP-8019 KDF by 7%, thus confirms the conservativeness of NASA SP-8019 KDF. However, axially compressed conical shells with eigenmode imperfection were seen to underestimate NASA's KDF by 55%, particularly for elastic buckling.

New Insights into the Antimicrobial Properties of Hydrolysates and Peptide Fractions Derived from Chia Seed (Salvia hispanica L.).

Bioactive peptides derived from chia (Salvia hispanica) seed with antioxidant, antihypertensive, and anti-inflammatory activities have been well documented; however, few studies describe the antimicrobial properties of these peptides, which is of great interest not only in the prevention of food-borne diseases but also food spoilage. The aim of this study was to generate chia seed peptides using microwave-assisted hydrolysis with sequential (alcalase + flavourzyme) enzymes (AF-MW), fractionate them into 3-10 and < 3kDa fractions, and evaluate their potential antimicrobial activity towards Escherichia coli, Salmonella enterica, and Listeria monocytogenes. Overall, the peptide fraction < 3kDa showed higher antimicrobial activity than both chia seed hydrolysate and peptide fraction 3-10kDa. Furthermore, the < 3kDa fraction showed remarkable increase in membrane permeability of E. coli (71.49% crystal violet uptake) and L. monocytogenes (80.10% crystal violet uptake). These peptides caused a significant extension in the lag phase, decreases in the maximum growth, and growth rate in the bacteria and promoted multiple indentations (transmembrane tunnels), membrane wrinkling, and pronounced deformations in the integrity of the bacterial cell membranes. Finally, a select group of peptides in the AF-MW < 3kDa fraction contained 16 sequences with cationic and hydrophobic character, with seven of them sharing the exact same sequence (GDVIAIR) and eight of them having the amino acid K as either N- or C-terminal or both. In conclusion, our results indicate that bioactive peptides obtained from chia seed proteins by microwave and enzymatic hydrolysis could be employed as antimicrobial agents in foods and therapeutic applications.

Extraction of mechanical properties of materials through deep learning from instrumented indentation

Instrumented indentation has been developed and widely utilized as one of the most versatile and practical means of extracting mechanical properties of materials. This method is particularly desirable for those applications where it is difficult to experimentally determine the mechanical properties using stress-strain data obtained from coupon specimens. Such applications include material processing and manufacturing of small and large engineering components and structures involving the following: three-dimensional (3D) printing, thin-film and multilayered structures, and integrated manufacturing of materials for coupled mechanical and functional properties. Here, we utilize the latest developments in neural networks, including a multifidelity approach whereby deep-learning algorithms are trained to extract elastoplastic properties of metals and alloys from instrumented indentation results using multiple datasets for desired levels of improved accuracy. We have established algorithms for solving inverse problems by recourse to single, dual, and multiple indentation and demonstrate that these algorithms significantly outperform traditional brute force computations and function-fitting methods. Moreover, we present several multifidelity approaches specifically for solving the inverse indentation problem which 1) significantly reduce the number of high-fidelity datasets required to achieve a given level of accuracy, 2) utilize known physical and scaling laws to improve training efficiency and accuracy, and 3) integrate simulation and experimental data for training disparate datasets to learn and minimize systematic errors. The predictive capabilities and advantages of these multifidelity methods have been assessed by direct comparisons with experimental results for indentation for different commercial alloys, including two wrought aluminum alloys and several 3D printed titanium alloys.

Cluster and MMS Simultaneous Observations of Magnetosheath High Speed Jets and Their Impact on the Magnetopause

Discontinuities in the solar wind, bow shock ripples or ionized dust clouds carried by the solar wind, high speed jets (HSJs) are observed in the magnetosheath. These HSJs have typically a Vx component larger than 200 km s-1 and their dynamic pressure can be a few times the solar wind dynamic pressure. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these HSJs and their impact on the magnetopause. Over one hour-fifteen minutes interval in the magnetosheath, Cluster observed 21 HSJs. During the same period, MMS observed 12 HSJs and entered the magnetosphere several times. A jet was observed simultaneously by both MMS and Cluster and it is very likely that they were two distinct HSJs. TDuring this period, two and six magnetopause crossings were observed respectively on Cluster and MMS with a significant angle between the observation and the expected normal deduced from models. The angles observed range between from 11° up to 114°. One inbound magnetopause crossing observed by Cluster (magnetopause moving out at 142 km s-1) was observed simultaneous to an outbound magnetopause crossing observed by MMS (magnetopause moving in at -83 km s-1), showing that the magnetopause can have multiple local indentation places, most likely independent from each other. Under the continuous impacts of HSJs, the magnetopause is deformed significantly and can even move in opposite directions at different places. It can therefore not be considered as a smooth surface anymore but more as surface full of local indents. Four dust impacts were observed on MMS, although not at the time when HSJs are observed, showing that dust clouds would have been present during the observations. No dust cloud in the form of Interplanetary Field Enhancements was however observed in the solar wind which may exclude large clouds of dust as a cause of HSJs. Radial IMF and Alfven Mach number above 10 would fulfil the criteria for the creation of bow shock ripples and the subsequent crossing of HSJs in the magnetosheath.

Gaussian expansion for the vibration analysis of plates with multiple acoustic black holes indentations

Abstract The acoustic black hole (ABH) effect can be achieved embedding cuneate indentations with power-law profile in plates. That results in remarkable properties like the reduction of plate vibrations, the potential for energy harvesting thanks to the focalization of energy, or the design of new metamaterials to manipulate acoustics waves. The analysis of such phenomena demands simulating the modal shapes and response to external excitations of ABH plates. This is usually done by means of numerical approaches, like the finite element method (FEM). However, if one is interested in performing long parametric analyses and in capturing the ABH plate behavior at high frequencies, the computational cost associated to numerical methods may become too demanding. In this work, a semi-analytical approach is suggested to circumvent the situation. The Rayleigh-Ritz method is applied using two-dimensional Gaussian functions to expand the flexural motion of a plate with non-uniform thickness. Then, a matrix-replacing strategy is proposed to embed the multiple ABHs in the plate. That results in low dimensional matrix systems, which yet provide very accurate solutions. After presenting all theoretical developments, the semi-analytical method is first applied to analyze the performance of a single ABH when varying several of its parameters. Then, various configurations involving multiple ABHs are considered. Those range from long strips exhibiting frequency attenuation bands, to plates containing ABH indentations in many shapes and sizes.

Energy dissipation studies of SMA reinforced composites under multiple quasi-static indentation loading

The aim of this paper is to find out the increase in energy dissipation by adding pseudoelastic shape memory alloy (PE-SMA) in glass fibers reinforced (GFRP) composites. Nature of loading is quasi-static, performed multiple times until material fails completely and indenter goes inside the sample. This is done to find out the alteration in the ultimate failure load due to the addition of SMA. It also gives the pattern of degradation in energy dissipation and stiffness over the number of cycles in both GFRP and SMA/GFRP samples. Reduction in the effective properties exhibits the advantages of embedding SMA.