Indentation Results Research Articles

Quasicontinuum multiscale modeling of the effect of rough surface on nanoindentation behavior

Roughness of surface has as an important influence on identifying the mechanical behavior and performance of crystalline metals. In this study, nanoindentation simulations are conducted by the two dimensional quasicontinuum method to determine the load–penetration response and the critical load associated with the onset of plasticity in rough surfaces of a face-centered cubic single crystal copper. The arithmetic roughness index, ranging between 2 and 13 A, is used to specify the roughness of surface. Results of indentation with different roughnesses are in good agreement with previous studies for the indenter size of 10–140 A. The resultant load–penetration scattering, which stems from the roughness, indicates different dislocation nucleation steps, different subsequent dislocations intervals and varying stiffness values of samples. It can be concluded that the surface roughness has a significant effect on the first dislocation emission because of the indenter position and surface interactions beneath it. Moreover, the critical penetration depth for the first dislocation emission increases by the increase of the contact area between the indenter and surface.

Оценка усилия вдавливания железобетонных свай заводского изготовления в глинистые грунты

The article discusses the pile indentation equipment for dive prefabricated reinforced concrete piles which are used in clay soils in urban environments. It was developed in 2003 and intended for dive reinforced concrete piles of different cross-sectional (square, round, prismatic, ring, etc.) length from 5 to 12 meters. Different modifications (SVU-1, SVU-2 and SVU-3) have been prepared during the period of equipment’s exploitation. They have dived more than 35,000 prefabricated concrete piles in Tomsk, Novosibirsk, Omsk, Kemerovo and other cities of Russia. In 2011 specialists of “FundamentSpetsStroy” (Tomsk) and specialists from the Kuban State Agrarian University (Krasnodar) developed a special device-meter, which provides to get information on efforts of the indentation piles at predetermined elevations. The article describes a structure of device and its operating principle. The principle of device based on the conversion parameters of pressure hydraulic system of pile indentation equipment during the pile diving into an electrical signal that is converted to digital information. The article presents the main results of effort indentation of piles, also tables of received values and graphics. The article performed an analysis and the generalization results of experimental research.

Interstitial magnetic thermotherapy dosimetry based on shear wave magnetomotive optical coherence elastography.

While magnetic thermoseeds are often utilized in interstitial magnetic thermotherapy (iMT) to enable localized tumor ablation, we propose to extend their use as the perturbative source in magnetomotive optical coherence elastography (MM-OCE) so that the heat-induced elasticity alterations can be 'theranostically' probed. MM-OCE measurements were found to agree with indentation results. Tissue stiffening was visualized on iMT-treated porcine liver and canine soft tissue sarcoma specimens, where histology confirmed thermal damages. Additionally, the elasticity was found to increase exponentially and linearly with the conventional thermal dosage metrics and the deposited thermal energy, respectively. Collectively, a physiologically-meaningful, MM-OCE-based iMT dosimetry is feasible.

Determination of mechanical properties of alloy steel 30Cr2CH2MFA according to the instrumented indentation results

Determination of mechanical properties of alloy steel 30Cr2CH2MFA according to the instrumented indentation results

Determining suitable parameters for inverse estimation of plastic properties based on indentation marks

Tensile elastoplastic properties are extensively used in engineering applications; however, sample preparation for tensile tests is time-consuming. Therefore, a technique to estimate the tensile properties from an indentation test, with relatively easy sample preparation, is useful to reduce effort and accelerate the evaluation of advanced materials. Previously proposed techniques for the inverse estimation of elastoplastic properties used plural load-displacement curves. In this study, the authors proposed an estimation technique based on a single indentation involved using three-dimensional information of an indentation mark in addition to a load-displacement curve. To determine the parameter suitable for use in the inverse estimation of elastoplastic properties, the sensitivity and experimental variation in parameters extracted from the indentation results were investigated. The maximum pile-up height normalized by the maximum indentation depth, Zmax/hmax, was determined as the suitable parameter for inverse estimation owing to its high sensitivity compared to experimental variations. Moreover, the stress-strain curve obtained using this technique agreed with that obtained using dual indenters.

Influence of dry micro abrasive blasting on the physical and mechanical characteristics of hybrid PVD-AlTiN coated tools

The current study investigates the effect of the micro abrasive blasting (MAB) on the physical and mechanical characteristics of the cutting tools before and after coating deposition. Cutting tools were subjected to micro blasting by alumina (Al2O3) grains at varying pressure so as to improve the efficacy of the coating process. AlTiN coating of thickness 1.45 μm was deposited onto the tool surface by arc enhanced high power impulse magnetron sputtering (HiPIMS) hybrid deposition technique. The coatings were characterized using nano indentation, atomic force microscopy and micro scratch test. The results of nano indentations on the coated surface revealed the influence of the micro abrasive blasting technique and pressure on the superficial hardness. Surface morphology results showed better-adhered surface in case of cutting tools subjected to micro abrasive blasting before the deposition due to an increase in density of the nucleation sites for growth of aluminum which can be judged with the help of higher aluminum content in the energy dispersive x-ray analysis. The film adhesion of the coating onto the tool substrate is observed to be improved significantly with an increase in blasting pressure in the case of the samples subjected to micro abrasive blasting before coating. Additionally, X-ray diffraction analysis was performed to investigate crystallographic phases. The attained results provide insight concerning the optimum selection of micro abrasive blasting technique along with the pressure, for enhancing the cutting performance of coated tools during the machining of nickel-based superalloy Nimonic C 263.

Method for highly spatially resolved determination of residual stress by using nanoindentation

Measurement of highly spatially resolved residual stresses is a crucial task for tailoring the stress state during manufacturing to improve mechanical performance of metallic objects. Especially in sheet metal forming or blanking with sheet thicknesses down to 0.1 mm, a highly resolved pattern of the stress distribution over the sheet thickness is required for optimisation. For this purpose, a method which uses an extended Hertzian theory for calculating residual stresses from the results of nanoindentation is used to measure the stress profile in metallic cylinders. For verification of the indentation results, hole drilling is utilised to determine residual stresses in the near-surface area. This method provides similar assumptions about the stress state (biaxial). The measuring principle is also based on correlations between mechanical behaviour of the material and the residual stress distribution. The results yield a good accordance of the measured values despite the different scales of measurement. Therefore, a highly spatially resolved measurement of residual stresses with nanoindentation is possible and shows comparable values to the classic hole drilling technique.

An elastoplastic energy model for predicting the deformation behaviors of various structural components

• An elastoplastic energy model about energy, load, displacement and materials properties is proposed. • For thirteen SCs, the model predictions agree well with the FEA results under linear elastic, fully plastic and elastoplastic conditions. • For cracked SCs, the J - integral vs. load relation is derived and verified based on the EEM. • The model has been applied into materials testing like indentation, small punch test and ring compression etc. Elastoplastic load-displacement relation is widely concerned in material testing. For isotropic-homogeneous and power-law hardening ductile materials, an elastoplastic energy model (EEM) correlating energy, load, displacement and uniaxial constitutive parameters is derived based on equivalent energy principle. An elastoplastic factor λ for engineering superposition of elastic displacement and plastic displacement is introduced and discussed, which makes the model applicable with more structural components (SCs). The model is verified with thirteen SCs used in materials testing and the results show a good agreement between model predictions and calculations from finite element analysis (FEA) under linear elastic, fully plastic and elastoplastic conditions. Some experimental results for ring-compression, spherical indentation and funnel tension are conducted to verify the model and a valid accordance is presented. Additionally, an explicit J -integral – load relation for classic cracked SCs is also derived based on the EEM and a good coincidence is observed during a comparison with results directly from FEA.

Material Characterisation with New Indentation Technique Based on Laser-Induced Shockwaves

Conventional material development of new compositions is expensive and time consuming. Thus, for material characterisation there is a demand to enable high through-put experimentation to analyse and develop new materials in a short time. In this context, a new experimentation method is presented, which is based on TEA CO2 laser-induced shockwaves. First, plasma is created with a nanosecond pulsed TEA CO2 laser on top of a spherical indenter. Further interactions of the plasma with the high intensity laser beam result in a shockwave. The pressure of the shockwave is used to force the indenter penetrate inside the test material. Indentations are created on different aluminium alloys and correlated with hardness. The influence of environmental conditions, indenter material and diameter are investigated. Additionally, an energy model is introduced, which describes the possible indentation strain energy in dependence of the indenter diameter and the shockwave energy transferred to the indenter. The experiments reveal that smaller indenter diameters are recommendable for higher impact efficiencies. Best indentation results are achieved in terms of reproducibility and depth with a 3 mm indenter.

Structure and tribological behavior of (AlCrNbSiTiV)N film deposited using direct current magnetron sputtering and high power impulse magnetron sputtering

Multi-element nitride films of AlCrNbSiTiV high-entropy alloy (HEAs) are deposited on a cermet cutter (T1200A) and glass substrates using reactive direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) with a single equimolar AlCrNbSiTiV HEA target. This study determines the effect of the ratio of the nitrogen flow (varying from 0 to 40%) on the chemical composition, microstructure, mechanical properties and cutting tool performance of the (AlCrNbSiTiV)N film. The films are found to have increased hardness and elastic recovery when the nitrogen flow ratio is increased. The (AlCrNbSiTiV)N film adheres well to the substrate and the Rockwell indentation results are HF1. (AlCrNbSiTiV)N films that are grown using DCMS and HIPIMS feature only a simple face-center-cubic structure. The samples that are deposited using HIPIMS exhibit a higher film density, a smoother surface and excellent hardness and elastic recovery, compared to coatings that are deposited using DCMS. The (AlCrNbSiTiV)N films are coated onto cutters for the dry turning of a SCM440 steel work-piece. The machining surface of a coated tool that is deposited using a HIPIMS system exhibits fewer surface defects and the tool flank wear is decreased.

An exact dual-integral formulation of the indentation of finite, free-standing, end-supported adhesive elastic layers

We study indentation by a rigid cylindrical punch of finite, free-standing, adhesive elastic layers that are supported only at their ends. The adhesion is considered through an adhesive-zone model. Formulating the boundary-value problem, we obtain two coupled Fredholm integral equations of the first kind, which are solved by a collocation method. Results for non-adhesive contact are obtained when adhesion is zero, and they match well with our own finite element computations and earlier approximate analyses. Additionally, we obtain new results for deeper indentation of non-adhesive contact. In the limit of very adhesive and/or very soft solids, we formulate an approximate model similar to the well-known Johnson–Kendall–Roberts (JKR) model for half-spaces. Our results for adhesive contact match well with preliminary indentation experiments on adhesive layers. Finally, we demonstrate the utility of our approach in modelling structural adhesives through a specific example.

DETERMINATION OF PARAMETERS FOR THE PLASTICITY MODEL OF VT-22 ALLOY POWDER PARTICLES

A computational and experimental method is proposed to determine the medium model for describing the mechanical properties of powder particles of a high-strength VT-22 titanium alloy obtained by plasma spraying in an inert gas jet. The method is based on the indirect determination of the σs ~ ε strain hardening diagram (yield stress dependence on plastic deformation). A specimen for fullscale tests was prepared as a section of powder particles filled into a special resin. The paper provides the results of Vickers indentation into VT-22 powder particles and the results of computer simulation of this process by the finite element method. The average value of the maximum indentation depth was hmax = 6,56 μm with a maximum loading value of 2 N. The Johnson-Cook elasto-plastic model of a material with nonlinear hardening was used for the volume element considered during the computer simulation. An algorithm for searching coefficients by computational experiment multistage planning was proposed to identify the parameters of the equation sought. Estimated maximum coincidences of experimental and calculated data were chosen as selection criteria, in particular, based on maximum indentation depth. As a result of the study, material model coefficient values that meet search conditions best were chosen from a possible set of such values. According to the algorithm proposed, the result was achieved in 4 calculation cycles. Powder metallographic study was carried out. It was found that particles have a coarse intragranular structure with the dominating b phase formed during plasma spraying. This probably led to a decrease in VT-22 alloy deformation resistance in the powder particles.

Influence of strain rate on indentation response of porcine brain.

Knowledge of brain tissue mechanical properties may be critical for formulating hypotheses about some specific diseases mechanisms and its accurate simulations such as traumatic brain injury (TBI) and tumor growth. Compared to traditional tests (e.g. tensile and compression), indentation shows superiority by virtue of its pinpoint and nondestructive/quasi-nondestructive. As a viscoelastic material, the properties of brain tissue depend on the strain rate by definition. However most efforts focus on the aspect of velocity in the field of brain indentation, rather than strain rate. The influence of strain rate on indentation response of brain tissue is taken little attention. Further, by comparing different results from literatures, it is also obvious that strain rate rather than velocity is more appropriate to characterize mechanical properties of brain. In this paper, to systematically characterize the influence of strain rate, a series of indentation-relaxation tests n = 210) are performed on the cortex of porcine brain using a custom-designed indentation device. The mechanical response that correlates with indenter diameters, depths of indentation and velocities, is revealed for the indentation portion, and elastic behavior of brain tissue is analyzed as the function of strain rate. Similarly, a linear viscoelastic model with a Prony series is employed for the indentation-relaxation portion, wherein the brain tissue shows more viscous and responds more quickly with increasing strain rate. Understanding the effect of strain rate on mechanical properties of brain indentation may be far-reaching for brain injury biomechanics and accurate simulations, but be important for bridging between indentation results of different literatures.

Determination of mechanical properties of steel 15Kh2NMFA using instrumented indentation results

Розроблено алгоритм відтворення діаграми деформування зразків на розтяг за параметрами діаграми контактного деформування. Визначено механічні характеристики сталі 15Х2НМФА за діаграмою одновісного розтягу, отриманої методом інструментованого індентування. Показано, що відхилення між значеннями характеристик міцності, визначеними при індентуванні й випробуванні на розтяг, не перевищує 1%.

A Methodology for Inverse Determination of Stress-strain Curves Based on Spherical Indentation

Instrumented indentation testing is widely used for the mechanical characterization of materials and phases. Among important mechanical parameters such as hardness and Young’s modulus the determination of yield stress and hardening behavior of metallic materials calculated from indentation results is a particular topical subject. This paper presents a methodology which allows for the reconstruction of the stress-strain curve from a single load-displacement curve measured by a spherical indenter. The method is based on the depth-dependent strain field induced by a spherical indenter. The loading part of the curve is discretised in single tuples of indentation depth and force. Since the mean strain induced by the spherical indenter is dependent on indentation depth, every depth can be assigned to a mean uniaxial strain value. The force is then used to calculate the associated uniaxial stress. The method was exemplarily applied to the carbon steel C45 in different heat treatment conditions. It could be shown that after a calibration procedure the stress-strain curves of the carbon steel can be calculated without the requirement of assuming a mathematical description of the curve (e.g. power-law material behavior). The method and its framework can easily be expanded and adjusted in order to be used as an easy and quick method for inverse determination of material parameters.

Effect of Processing on Nix-Gao Bilinear Indentation Results Obtained for High Purity Iron

Instrumented indentation of a high purity Fe surface with unresolved surface deformation due to mechanical polishing is compared to the same grain surface annealed at increasing time and temperature. The differences in indentation size effect behavior with annealing are correlated with hardness and electron backscatter diffraction measurements as independent measures of surface layer deformation. It is found that the Nix Gao plot evolves from non-linear (bilinear) towards the predicted linear relationship as the surface deformation is removed. The experimental observations are rationalized by inclusion of a depth dependent, polishing induced forest dislocation density within the Nix-Gao model.

A Review of Indentation Theory

Indentation hardness testing has been used for many years to assess the quality of materials. Recently, with the advent of computers and sophisticated instruments, the hardness test and result analysis has been automated. Thus, it has become a ubiquitous tool among scientific and engineering community and in industry as well. Consequently, now it is possible to extract the more fundamental properties like young’s modulus, yield stress, creep, fatigue and fracture properties using the correlations developed between indentation and conventional full-scale test results. This paper reviews the evolution of different hardness testing methods and mechanisms of indentation. The information provided the mechanisms of indentation like nature and extent of deformation zone beneath the indenter provides a basis for setting the limits on the variables on hardness testing practice. In addition the influence of indentation parameters like strain hardening exponent, friction, residual stress etc. on the nature of deformation of the specimen is explained

Hardening Curve Plotting and Determination of the Coating Limiting State Criterion based on the Continuous Indentation Method and Computational Modelling

The article describes the method of determining the parameters of the hardening curve of homogeneous and structured coatings (modulus of elasticity, tangential modulus of elasticity and yield strength) required for the strength analysis of parts with coatings that determine their basic performance and strength characteristics. The dependence for determination of tangential (tangential) modulus of elasticity using the results of nanoindentation is proposed. An algorithm for determining the yield strength of the coating material is developed based on solving the problem of elastic-plastic deformation of the coating during the introduction of the indenter by the finite element method. According to the proposed method, the parameters of the TiN/AlN in coating hardening curve were determined based on the results of indentation of the sample of tool high-speed steel with the appropriate coating.

Comparing damage from low-velocity impact and quasi-static indentation in automotive carbon/epoxy and glass/polyamide-6 laminates

The results of a low-velocity impact programme on both carbon/epoxy and glass/polyamide-6 composite laminates are compared to the results of quasi-static indentation. Cross-ply and quasi-isotropic stacking sequences are impacted and quasi-static indentation tests are performed up to the same maximum displacement. The response of the laminates to both test methods is compared in terms of force-displacement behaviour, dissipated energy and resulting damage. Significant differences between low-velocity impact and quasi-static indentation are found for both material systems. It is therefore concluded that the test methods cannot be interchanged for material characterisation.

A Simulation of the Viscoelastic Behaviour of Heel Pad During Weight-Bearing Activities of Daily Living.

Internal strain is known to be one of the contributors to plantar soft tissue damage. However, due to challenges related to measurement techniques, there is a paucity of research investigating the strain within the plantar soft tissue during daily weight-bearing activities. Therefore, the main aim of this study was to develop a non-invasive method for predicting heel pad strain during loading. An ultrasound indentation technique along with a mathematical model was employed to calculate visco-hyperelastic structural coefficients from the results of cyclic-dynamic indentation and stress-relaxation tests. Subject-specific structural coefficients of heel pads were calculated from twenty participants along with the assessment of plantar pressure. The average difference betweenthe predicted and the measured force during the cyclic-dynamic indentation test was only 5.8%. Moreover, the average difference between the predicted and the in vivo strain during walking was 14%. No statistically significant correlation was observed between maximum strain and peak plantar pressure during walking; indicating that the measurement of strain along with plantar pressure can improve our understanding of the mechanical behaviour of the plantar soft tissue.