Indentation Pressure Research Articles

Surface Defects Vibration Measurements of Automotive Tapered Roller Bearings

The paper investigates vibration testing methodologies for automotive tapered roller bearings. The European Union regulations have indirectly led to improvements in the NVH performance of the bearings that affect both the industrial and automotive markets. The goal of this study was to examine the influence of localized small defects on the vibrations’ magnitudes within tapered roller bearings. A Rockwell indenter was used to create three different surface defects. These three levels, representing different indentation pressures, mimic defects that could occur during manufacturing or bearing installation. Indents were placed on inner raceways, the outer raceways, and the roller bodies. After the assembly of the components, different vibration testing methodologies were applied to quantify those types of defects. This paper presents a new envelope analysis approach to monitoring for defects. The paper presents the current Fast Fourier Transform (FFT) testing approach, whereby the machine sensitivity is representative of a typical quality control bearing thresholds. This paper also presents a new, more robust method and analyzed for its suitability in the detection of localized defects.

Simulation of copper nanoindentation using LAMMPS - atomic to micro-scale

This study explores the mechanical properties of copper at the nanoscale through molecular dynamics simulations of nanoindentation using LAMMPS. Focusing on atomic-scale interactions, the research investigates the relationship between indentation depth and pressure, considering factors like indenter shape and application rate. The simulations reveal complex material behaviors diverging from classical Hertzian contact theory, highlighting the intricacies of nano-scale mechanical responses. The study contributes significantly to the understanding of copper’s mechanical properties and the application of computational simulation in material science.

Optical Elastography for Micropressure Characterization of Zebrafish Embryonic Cardiac Development.

The proper formation of the vertebrate embryonic heart relies on various mechanical forces which determine its form and function. Measuring these forces at the microscale of the embryo is a challenge. We propose a new tool utilizing high-resolution optical elastography and stiffness measurements of surrounding tissues to non-invasively track the changes in the pressure exerted by the heart on the neighboring yolk, as well as changes in contractile patterns during early cardiac growth in-vivo, using the zebrafish embryo as a model system. Cardiac development was characterized every three hours from 24 hours post-fertilization (hpf) to 30 hpf and compared between wildtype fish and those treated with MS-222, a commonly used fish anesthetic that decreases cardiac contractility. Wildtype embryos from 24 to 30 hpf showed an average yolk indentation pressure of 0.32mmHg to 0.41mmHg, respectively. MS-222 treated embryos showed an average yolk indentation pressure of 0.22mmHg to 0.29mmHg. Yolk indentation pressure between control and treated embryos at 24 hpf and 30 hpf showed a significant difference (p < 0.05). Our method allowed for contractility and pressure evaluation at these early developmental stages, which have not been previously reported in published literature, regardless of sample or imaging modality. This research could lead to a better understanding of heart development and improved diagnostic tools for congenital heart disease.

Contact behaviors involving a nanobeam with surface effect by a rigid indenter

In this study, we present a novel surface model that utilizes surface energy density to predict the surface effect in nanobeam contact problems. To address the issue of a finite-length elastic nanobeam being indented by a rigid cylindrical indenter, we propose an equivalent substitution method. This method allows us to formulate analytical relations between the load and contact half-width for two different boundary cases. The explicit expressions of the contact-zone width, the pressure distribution in the contact zone, the deflection outside the contact zone, and the load–displacement relation are obtained for the nanobeam with surface effect and are compared with classical results in detail. The results show that the influence of the surface effect is very significant for nanobeam contact behavior, especially when the half-width of the contact zone increases and the contact zone becomes two independent symmetric strips. It is also found that the length-height ratio of nanobeam and the end support conditions have a fairly obvious effect on the normalized pressure distribution, which deviates significantly from the one predicted by the classical results due to the surface effect. However, for a given beam length and indenter radius, the ratio of the width of the contact zone to the beam thickness is almost constant, independent of the indenter load and beam boundary conditions. Meanwhile, the model predicts that the contact pressure distribution after the normalization of the average indentation pressure is almost independent of the indentation load and beam boundary conditions, but obviously depends on the surface effect parameters. The present method and result should be helpful not only to the measurement of mechanical properties of the indentation nanobeam but also to the design of the nanobeam-based devices.

Effectiveness of the analytical models used in standard techniques for mechanical property characterization of 2D materials

Two dimensional (2D) materials are usually assumed to be continuum thin films to study their mechanical behavior. Freestanding indentation testing and pressure bulge testing are two standard techniques for characterizing the mechanical properties of thin films. Compared with the former, the latter is far less often used to characterize the elastic moduli of 2D materials, even though there is no solid evidence to show that the former is more effective than the latter. In the present work, the effectiveness of the analytical models adopted in both approaches on determining the elastic moduli of 2D materials are investigated using numerical analysis, which can be evaluated based upon the accuracy of the determined elastic moduli, and the effects of Poisson’s ratio and the applied loading range are also considered. To account for the effect of the adhesive boundary condition of freestanding 2D materials in the testing, the numerical simulations of the initially unstressed samples, pre-stretched samples and slack samples are all analyzed in the present work. It is found that the bulge testing model is actually more effective than the indentation model on determining the mechanical properties of 2D materials.

Cavity expansion analysis of normal indention of rocks with lateral confinement

Indentation of rocks with lateral confinement is strongly related to rock fragmentation in drilling, mechanized tunnelling, and mining. Yet, the interpretation of the results and its transfer to use in practice is complicated by both the limited specimen size and boundary conditions associated with the application of lateral confinement. In this study, a new semi-analytical solution for the problem of a finite-cavity expansion in rock specimens of finite radial extent is present for the analysis of rock indentation with lateral confinement. To account for possible strain hardening/softening effect, an extended linear strain hardening/softening, i.e. constant plastic tangential modulus, Drucker-Prager model with non-associated flow rule is used to describe the stress-strain behavior of rocks. The model predictions, valid up to crack initiation, agree well with experimental observations that peak indentation pressure increases with lateral confinement, indicating that for a correct interpretation of results, the ratio between specimen size and the tip width of a truncated indenter as well as the boundary conditions shall be considered. The results point to the need for further development of the cavity expansion model by incorporating more features to model the realistic rock behavior and for more experimental studies with lateral confinement using advanced testing technique to monitor the failure process.

Indentation-induced cracking behavior of a Cu(In,Ga)Se2 films on Mo substrate

Abstract Cu(In,Ga)Se2 (CIGS) light absorption films were synthesized by co-sputtering method on Mo/soda-lime glass, and the mechanical behavior of the films was investigated by nanoindentation. The Young's modulus and hardness of the films were approximately 88.5 ± 2.2 and 5.89 ± 0.23 GPa, respectively. The comparison graph of indentation load–displacement curve with the curve based on the theoretical elastic films, while considering the curvature of the indenter tip, revealed that cracks initiated in the CIGS films at approximately 25 mN indentation load. The transmission electron microscopy (TEM) analysis revealed that most of the cracks exhibited intergranular fracture, and the fracture toughness of the films was ~0.22 MPa√m, which is greater than the brittleness of soda-lime glass. Both Palmqvist radial and lateral cracks are observed. Results also reveal that the indentation pressure caused grain subdivision (before cracking initiated), and indentation stress may be absorbed by relatively less dense microstructures of the films.

Stress-induced martensitic transformation in metastable austenite grains during nanoindentation investigation

ABSTRACT In general, the formation of martensite in the metastable austenite grains in steels during nanoindentation investigations is believed to be induced by strain as the plastic deformation of austenite takes place prior to the martensitic transformation. However, it is not clear whether the formation of martensite occurs without the prior initiation of plasticity (stress-induced martensitic transformation) during nanoindentation measurement. The present work demonstrates that the martensitic transformation can be triggered during elastic deformation of austenite under an ultralow load when the indenter is close to the annealing twin boundaries. The indentation pressure interacts with the martensite transformation strain, providing the mechanical interaction energy to overcome the nucleation barrier of the martensite embryo. The present work suggests that the annealing twin boundaries can also serve as the nucleation sites of martensite and the stress-induced martensitic transformation is possible during nanoindentation investigation.

Pressure-Induced Formation and Mechanical Properties of 2D Diamond Boron Nitride.

Understanding phase transformations in 2D materials can unlock unprecedented developments in nanotechnology, since their unique properties can be dramatically modified by external fields that control the phase change. Here, experiments and simulations are used to investigate the mechanical properties of a 2D diamond boron nitride (BN) phase induced by applying local pressure on atomically thin h‐BN on a SiO2 substrate, at room temperature, and without chemical functionalization. Molecular dynamics (MD) simulations show a metastable local rearrangement of the h‐BN atoms into diamond crystal clusters when increasing the indentation pressure. Raman spectroscopy experiments confirm the presence of a pressure‐induced cubic BN phase, and its metastability upon release of pressure. Å‐indentation experiments and simulations show that at pressures of 2–4 GPa, the indentation stiffness of monolayer h‐BN on SiO2 is the same of bare SiO2, whereas for two‐ and three‐layer‐thick h‐BN on SiO2 the stiffness increases of up to 50% compared to bare SiO2, and then it decreases when increasing the number of layers. Up to 4 GPa, the reduced strain in the layers closer to the substrate decreases the probability of the sp2‐to‐sp3 phase transition, explaining the lower stiffness observed in thicker h‐BN.

Quantifying stent-induced damage in coronary arteries by investigating mechanical and structural alterations

Vascular damage develops with diverging severity during and after percutaneous coronary intervention with stent placement and is the prevailing stimulus for in-stent restenosis. Previous work has failed to link mechanical data obtained in a realistic in vivo or in vitro environment with data collected during imaging processes. We investigated whether specimens of porcine right coronary arteries soften when indented with a stent strut shaped structure, and if the softening results from damage mechanisms inside the fibrillar collagen structure. To simulate the multiaxial loading scenario of a stented coronary artery, we developed the testing device ‘LAESIO’ that can measure differences in the stress-stretch behavior of the arterial wall before and after the indentation of a strut-like stamp. The testing protocol was optimized according to preliminary experiments, more specifically equilibrium and relaxation tests. After chemical fixation of the specimens and subsequent tissue clearing, we performed three-dimensional surface and second-harmonic generation scans on the deformed specimens. We analyzed and correlated the mechanical response with structural parameters of high-affected tissue located next to the stamp indentation and low-affected tissue beyond the injured area. The results reveal that damage mechanisms, like tissue compression as well as softening, fiber dispersion, and the lesion extent, are direction-dependent, and the severity of them is linked to the strut orientation, indentation pressure, and position. The findings highlight the need for further investigations by applying the proposed methods to human coronary arteries. Additional data and insights might help to incorporate the observed damage mechanisms into material models for finite element analyses to perform more accurate simulations of stent-implantations.

Normal and Superconducting Properties of Bi1.7Pb0.30Sr2Ca1−xLaxCu2Oy Superconductor with 0.00 ≤ x ≤ 0.30

We report here normal and superconducting properties of Bi1.7Pb0.30Sr2Ca1−xLaxCu2Oy superconductor with various x values (0.00 ≤ x ≤ 0.30). It is found that the replacement of Ca2+ by La3+ does not influence the phase purity of the samples, while the orthorhombic distortion, excess oxygen, effective Cu valance, and hole carriers/Cu ions are affected. Further, the doping distance and crystal geometry factor are decreased by La, but the distance between neighboring Cu atoms and the density of excess doping are increased. Furthermore, the DTA graphs show strong endothermic peaks at a temperature of 844.1, 848.03, 850.10, and 857.41 °C for pure and La-doped samples, respectively. The thermogravimetric analysis diagrams displayed a sharp mass loss started at about 800 °C and extended up to 1000 °C for all samples. Although the critical temperature Tc of the samples is decreased by La from 94 K to 83, 63, and 51 K, the critical concentration for quenching superconductivity can be extended above 0.30. Moreover, an inverse linear relation between Tm and Tc, given by Tc (K) = − 2.544 Tm (°C) + 2272.1, is also estimated. On the other hand, the Vickers hardness Hv is increased by La up to 0.30 (Hv α Tm, Hv α (1/Tc)), but it is decreased by the applied load F. The Hv-F characters are divided according to the applied load into two parts: the first at lower loads (0.00–1.962 N) and the second at higher loads (2.942–4.904 N). It is noted that the surface energy, elastic indentation, and resistance pressure are increased by La, but their values at higher loads are generally more than that of lower loads. Our results are discussed in terms of the balance between the hole carriers lost by La3+ with that introduced by excess oxygen in the Cu-O2 planes, which alters the quenching of superconductivity by La3+ and highlights the present work.

Pressure response and life assessment of filament-wound composite pipes after impact

This paper presents the results of drop-weight impact (5 J–150 J), quasi-static indentation, and post-impact internal pressure testing of a ±55°, filament-wound, glass fibre reinforced epoxy (GRE) pipe. The void content in the tested pipes was quantified by optical and stereo microscopy image analysis and ranged from 5% to approximately 13%. The void content was found not to influence the damage area, or the observed damage mechanisms, following impact loading. However, the void content was found to greatly affect the damage tolerance of the pipe during the pressure testing following an impact. It is established that impact damage area alone is not enough to determine the reduction in pipe failure performance under internal pressure. After impacts at low energies, a number of the tested pipes surpassed the operating pressure of the pipe during pressurisation (no leakage occurred). In these instances, an industry accepted regression gradient was used to determine the pipe's residual life, which estimated the reduction in service life from 20 years to less than two years. The quasi-static indentation testing confirmed that low energy impact behaviour (<20J) is largely equivalent to a quasi-static event under the tested constraints. Fabrication induced voids and their interaction with impact damage, are currently not considered by the existing testing standards (BS EN ISO 14692), but according to this investigation may influence the safe continued use of a GRE pipe subjected to internal pressure.

Effect of probe pressure on skin tissue optical properties measurement using multi-diameter single fiber reflectance spectroscopy

Multi-Diameter Single Fiber Reflectance spectroscopy (MDSFR) allows rapid and noninvasive extraction of tissue optical properties that requires the fiberoptic to be placed in contact with the tissue. To ensure a good optical contact, the application of probe pressure is inevitable and usually not well controlled. In this study, we investigated the effect of probe pressure by performing in vivo MDSFR measurements (400–1600 nm) on human inner forearm skin with controlled probe indentation and continuous pressure monitoring. For the probe pressures up to 28.4 s mm−2 (213 mmHg), the reduced scattering coefficient pivoted around 800 nm (increasing scattering slope) while the phase function related parameter decreased (up to 20%, depending on the wavelength). A significant decrease of hemoglobin concentration (∼81%), oxygen saturation (∼86%), apparent vessel diameter (∼100%) as well as the displacement of extracellular water (∼24%) was observed with increasing probe pressure. A correlation was observed between the changes in water volume fraction and phase function related parameter gamma . We theorize that the latter changes in phase function may be due to the induced deformation of the tissue structure and the displacement of extracellular water. The extensive analysis of the pressure induced changes in the measured MDSFR spectra and the related changes in optical properties demonstrate that the effects of probe pressure must be minimized to avoid bias in the results.

Nonlinear impact and damping investigations of viscoporoelastic functionally graded plates with in-plane diffusion and partial supports

Fluid seepage and viscoelasticity play important roles in the dissipation of the undesired vibration and impact energies of the poroelastic structures. In the present article, the impact behavior of viscoporoelastic functionally graded plates with bending-induced fluid-flow is analyzed, for the first time. Moreover, the effects of partial support are investigated. Biot’s poroelasticity and Zener’s viscoelasticity models are combined, for the first time and then, the governing equations of the impact of the plate are derived based on the non-linear Hertz law. The nonlinear finite element form of the governing integrodifferential equations of the solid skeleton and the fluid pressure is obtained based on Galerkin’s method and solved using a special accumulation-based time-marching procedure. Treating the adopted quadratic through-thickness distribution of the fluid pressure is another superiority of the present research. The second-order Runge-Kutta numerical time-integration, trapezoidal discretization, and Picard’s iterative updating techniques are employed to deal with the time-dependency of the resulting equations. The effects of the poroelastic, viscoelastic, and support parameters on the time variations of the contact force, indentation, lateral deflection, and pore pressure moment are investigated. Results reveal that the viscoporoelastic plates may exhibit some behaviors that are in contradiction to those of the traditional plates.

PREPARATION OF TUFF IN THE DUMPS OF BASALT QUARRIES FOR VIBRATION SCREENING

The article presents the current development of an integrated technology for the processing of tuff in the dumps of basalt pits to highlight the valuable metal fraction and silicate masses. In order to prepare tuff for processing, it is proposed to use the effect of moisture absorption and reduce the strength of tuff when moistened with water, since it has a porous structure and is relatively easy to absorb moisture. This operation, followed by vibratory screening in a small class of -2.5 + 2.0 mm, is promising for the selective extraction of tuff from dumps of basalt quarries, where, unlike other rocks, tuff is a water-absorbing mineral. The article presents the results of experimental studies and the development of mathematical models of the process of softening tuff with water. The objective of the research was to determine the degree of change in the strength of tuff under the influence of moisture and to establish the dependence of humidity and strength to predict the process of softening of tuff when wet. Experimental studies were carried out on various samples of tuffs of the Rafalovsky basalt quarry, while the exposure time of the sample in water was recorded, humidity, indenter indentation pressure on the press or contact load and compressive strength or contact stress during indenter penetration were determined. It was found that when moistening tuff during the day, humidity increases on average by 9%, strength decreases from 120.5 to 10.6 MPa and is 9.2% of the strength of the feedstock. Humidity of tuff in time increases according to the law of a quadratic parabola with a complex argument, the force of indentation of the indenter from moisture and wetting time changes according to the logarithmic law, strength from humidity and time - according to the law of the quadratic parabola. Also, the article proposes an algorithm for calculating humidity and strength characteristics during wetting during the day. It is advisable to use this technology of softening tuff with water as an ore preparation operation with the integrated technology of tuff processing.

PIEZO1-Mediated Currents Are Modulated by Substrate Mechanics.

PIEZO1 is a bona fide mammalian mechanically activated channel that has recently been shown to provide instructive cues during neuronal specification, texture sensing, and cell migration where mechanical inputs arise at the interface between the cells and their substrate. Here, we have investigated whether the mechanical properties of the substrate alone can modulate PIEZO1 activity, in response to exogenously applied stimuli, using elastomeric pillar arrays as force transducers. This methodology enables application of mechanical stimuli at cell-substrate contact points by deflecting individual pili. We found that PIEZO1 is more sensitive to substrate deflections with increased spacing between pili (reducing surface roughness) but not on more stiff substrates. Cellular contractility was required for the sensitization of PIEZO1 but was not essential for PIEZO1 activation. Computational modeling suggested that the membrane tension changes generated by pillar deflections were below the membrane tension changes that arise from cellular indentation or high-speed pressure clamp assays. We conclude that the mechanics of the microenvironment can modulate PIEZO1 signaling, highlighting the importance of studying channel activation directly at the cell-substrate interface. We propose that forces arising from actin-mediated contractility and within the lipid bilayer act synergistically to regulate PIEZO1 activation by stimuli applied at contacts between cells and their surroundings.

A new hardness formula incorporating the effect of source density on indentation response: A discrete dislocation plasticity analysis

Planar discrete dislocation plasticity (DDP) calculations that simulate thin single crystal films bonded to a rigid substrate indented by a rigid wedge are performed for different values of film thickness and dislocation source density. As in prior studies, an indentation size effect (ISE) is observed when indentation depth is sufficiently small relative to the film thickness. The dependence of the ISE on dislocation source density is quantified in this study, and a modified form of the scaling law for the dependence of hardness on indentation depth, first derived by Nix and Gao, is proposed, which is valid over the entire range of indentation depths and correlates the length scale parameter with the average dislocation source spacing. Nano-indentation experimental data from the literature are fitted using this formula, which further verifies the proposed scaling of indentation pressure on dislocation source density.

An analytical model for the flat punch indentation size effect

An analytical approximation for the indentation size effect (ISE) due to plane strain flat punch nanoindentation is derived. The flat punch ISE differs from that observed for self-similar (pointed) and spherical indenters in a number of ways: (1) the contact area does not change; (2) the contact pressure depends on two length scales not just one (the punch width and the indentation depth); (3) the profile of the punch is not differentially continuous, resulting in singular plastic strain gradients at the sharp edges, such that (4) the shape and connectivity of the plastic zones change with indentation depth and punch width, resulting in (5) changes in the proportion of the deformation accommodated by elasticity and plasticity are important, meaning that a fully elastoplastic model is required. Complete loading-unloading curves are modelled, with the calibration of geometrical parameters from finite element strain gradient plasticity simulations. As the punch width decreases, it is observed that there are increases in the indentation pressure, the relative size of the plastic zone(s) and the elastic component of the deformation. These predictions are found to compare favourably with experimental measurements in the literature. The model is extended to incorporate the consequence of imposing natural limitations on the maximum dislocation density at the edges. It is suggested that observable changes in the plastic zone morphology with the ISE make this an experimentally interesting area for the validation of size effects in plasticity.

Ice edge failure process and modelling ice pressure.

Ice action on ships and offshore structures is commonly determined by calculating the contact ice pressure. The aim of this paper is to describe the empirical background for determining the ice pressure. This review article describes six different test series where ice edge indentation and contact ice pressure have been investigated. These test series are ice pressure measurements onboard IB Sisu in the Baltic in 1977, pendulum tests carried out at Arctec in Ottawa, Canada, in 1979, laboratory and full scale ice crushing tests at WARC in 1988 and onboard IB Sampo 1989, medium scale indentation tests on Hobson's Choice Ice Island 1990, ice crushing tests at NRC, Ottawa 1992 and the JOIA tests in Hokkaido 1996–1999. These tests were selected as at each series a new phenomenon was observed. The aim of the paper is to introduce the main features for ice–structure contact empirically through the description of tests. The paper is concluded with a short description of the existing models for ice pressure, especially to gain an insight and highlight the main observations in each test series and how the models for ice pressure have developed based on the observations.This article is part of the theme issue ‘Modelling of sea-ice phenomena’.

Bridging Length Scales in the Analysis of Transient Tests for Metallic Materials

The transient data obtained during stress relaxation test of polycrystalline materials has broader implications. The test is influenced by the material length scale. Efforts to mathematically bridge data at different length scales is scarce. In the present work, it is attempted to modify a recently proposed stress relaxation model with additional coefficients to accommodate the mechanical behavior at different length scales. The macroscale stress relaxation test was performed using a tensile testing machine, whereas the micro- and nanoscale specimens were tested using indentation technique. Assuming power law rate behavior, a scaling relation is derived initially to correlate the indentation pressure and flow stress.