Showing papers on "Indentation published in 2023"

Calibration of machine platform nonlinearity in Instrumented Indentation Test in the macro range

Abstract: Instrumented Indentation Test (IIT) is a non-conventional mechanical characterization technique to evaluate hardness, Young modulus, creep and relaxation of materials. In the macro range, it represents a cheaper and faster alternative to conventional tensile-based tests. IIT is a metrological scale; thus, to establish traceability, calibration is essential. Frame compliance calibration is critical because it is a major contribution to the measurement uncertainty. This work discusses the limits of the current state-of-the-art and proposes a novel methodology for frame compliance calibration. The introduced approach demonstrates the source of common systematic errors in the mechanical characterization reported in the literature, i.e. edge effect, while first highlighting a relevant frame compliance nonlinearity. The proposed procedure is cost-effective and relies upon constitutive spring modelling of IIT and calibration of reference block by nanoindentation. Results show that the novel approach corrects systematic trends in the characterization and yields a relative measurement uncertainty of 5%.

Indentation Reverse Algorithm of Mechanical Response for Elastoplastic Coatings Based on LSTM Deep Learning

Abstract: The load-penetration depth (P–h) curves of different metallic coating materials can be determined by nanoindentation experiments, and it is a challenge to obtain stress–strain response and elastoplastic properties directly using P–h curves. These problems can be solved by means of finite element (FE) simulation along with reverse analyses and methods, which, however, typically occupy a lengthy time, in addition to the low generality of FE methodologies for different metallic materials. To eliminate the challenges that exist in conventional FE simulations, a long short-term memory (LSTM) neural network is proposed in this study and implemented to deep learn the time series of P–h curves, which is capable of mapping P–h curves to the corresponding stress–strain responses for elastoplastic materials. Prior to the operation of the neural network, 1000 sets of indentation data of metallic coating materials were generated using the FE method as the training and validating sets. Each dataset contains a set of P–h curves as well as the corresponding stress–strain curves, which are used as input data for the network and as training targets. The proposed LSTM neural networks, with various numbers of hidden layers and hidden units, are evaluated to determine the optimal hyperparameters by comparing their loss curves. Based on the analysis of the prediction results of the network, it is concluded that the relationship between the P–h curves of metallic coating materials and their stress–strain responses is well predicted, and this relationship basically coincides with the power-law equation. Furthermore, the deep learning method based on LSTM is advantageous to interpret the elastoplastic behaviors of coating materials from indentation measurement, making the predictions of stress–strain responses much more efficient than FE analysis. The established LSTM neural network exhibits the prediction accuracy up to 97%, which is proved to reliably satisfy the engineering requirements in practice.

Determining Spatial Variability of Elastic Properties for Biological Samples Using AFM

Abstract: Measuring the mechanical properties (i.e., elasticity in terms of Young’s modulus) of biological samples using Atomic Force Microscopy (AFM) indentation at the nanoscale has opened new horizons in studying and detecting various pathological conditions at early stages, including cancer and osteoarthritis. It is expected that AFM techniques will play a key role in the future in disease diagnosis and modeling using rigorous mathematical criteria (i.e., automated user-independent diagnosis). In this review, AFM techniques and mathematical models for determining the spatial variability of elastic properties of biological materials at the nanoscale are presented and discussed. Significant issues concerning the rationality of the elastic half-space assumption, the possibility of monitoring the depth-dependent mechanical properties, and the construction of 3D Young’s modulus maps are also presented.

Atomic force microscopy-based indentation of cells: modelling the effect of a pericellular coat

Abstract: A simple analytical model is built up to account for the interface deformation effect in a spherical atomic force microscopy (AFM)-based quasi-static indentation of a living cell covered with a pericellular brush. The compression behaviour of the pericellular coat is described using the Alexander–de Gennes model that allows for nonlinear deformation. An approximate second-order relation between contact force and indenter displacement is obtained in implicit form, using the Hertzian solution as a first-order approximation. A method of fitting the indentation brush/cell model to experimental data is suggested based on the non-dimensionalized version of the displacement–force relation in the parametric form and illustrated with a specific example of AFM raw data taken from the literature.

A study on bending deformation behavior induced by shot peening based on the energy equivalence

Abstract: Shot peening is an essential process for forming large thin-walled components in aerospace industries. However, it is challenging to determine directly the mapping relationship between shot peening parameters and deformation response because of the complex elastic–plastic deformation of shot-peened components. In this paper, a computational model of bending deformation of peened plate samples is established by examining the shot peening behavior from the aspect of energy equivalence, in which the deformation energy of the shot-peened plate is determined by the total kinetic energy input due to the shot impacts and a correction factor that takes into account the influences of oblique impact, shot interaction and shot overlap on the peen forming process in practice. It is proven that the square of curvature radius is proportional to the cube of the thickness but inversely proportional to the indentation coverage and the average kinetic energy input of a single shot. For the effect of a single shot impact in peen forming, the average kinetic energy input of a single shot is a power function with the indentation diameter.

Bonding mechanisms and micro-mechanical properties of the interfacial transition zone (ITZ) between biochar and paste in carbon-sink cement-based composites

Abstract: A better understanding of the interfacial transition zone (ITZ) in biochar-augmented carbon-negative cementitious materials can facilitate their potential applications. This study illustrated the key chemical and mechanical features of such a region in Portland cement using backscattered electron microscopy-energy dispersive X-ray analysis (BSEM-EDX), nano-indentation, and X-ray computed tomography (X-CT). It was found that a significant ‘wall effect’ was identified at the side-edge of biochar, where the degree of hydration and the porosity significantly increased. The biochar was integrated into the hardened cement matrix via a layer of Ca-rich hydration products mainly composed of AFm phases, CH and C–S–H gels. Regarding the mechanical behaviour, the biochar showed a typical viscous-elastic (VE) deformation mode at the nano/micro scale, whereas the hardened cement was a typical plastic-elastic (PE) material. Therefore, the value of the hardness of biochar was not accurate under limited plastic deformation. The distinct differences in deformation resulted in the largest residual deformation (i.e., plasticity) of the hardened cement after indentation when compared to ITZ and biochar regions, whereas the ITZ maintained a lower value due to well connection with biochar. These microstructural characteristics partially explained the higher compressive strength of biochar-cement composites than previously expected.

Mechanical Properties of Structural Components in Hastelloy X Joints Brazed with Ni-Pd-Cr-B-Si Alloy

Abstract: The brazing of structural high-temperature-resistant nickel alloys is a predominant method in manufacturing jet engines in the aircraft industry. Ni-Cr-base brazing filler metals (BFMs) containing B and Si as the melting point depressants are used for this purpose. The presence of the latter can lead to the formation of brittle constituents in the joints, decreasing their strength, toughness and creep resistance. The structures of Hastelloy X nickel superalloy joints brazed with Palnicro 36M BFM are presented in this paper along with the mechanical properties of their particular phases as a function of brazing time. Indentation hardness, Martens hardness, reduced modulus and creep coefficient were measured using the instrumented indentation method. The elastic part of the indentation work was also calculated. Pd forms an unlimited solution with Ni, but its high content in BFM does not fundamentally change the general joint structure known from other Ni-superalloy–Ni-BFM systems. However, new Pd-containing phases are emerging. The hardest components were Ni-B and Cr-B boride phases and Pd-Ni-Si phase in MZ and the boundary of DAZ and BM. MZ reduces the plasticity of a joint to the highest extent. The hardness of particular parts in the joints and the elastic portion of the indentation work decreased with the increase in brazing time, while the reduced modulus of the indentation contact and indentation creep increased. The results of indentation creep measurements indicate that all structural components of the joints were less susceptible to creep than the parent material at room temperature.

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

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

Acquisition of heterogeneous constitutive relationship of Ni60 laser cladding layer based on nano-indentation experiment

Abstract: Laser cladding technology has broad application prospects in the field of parts repair. The acquisition of heterogeneous constitutive relationship of laser cladding layer is an important aspect in the study of laser cladding mechanism. This paper studied the acquisition method of heterogeneous constitutive relationship of Ni60 laser cladding layer. Single and multi-channel lap Ni60 laser cladding layers were prepared using a synchronous powder delivery laser cladding system on a Cr12MoV substrate, which were observed by electron microscopy, and the hardness was measured by a Vickers hardness meter. According to the distribution characteristics of metallographic structure and the magnitude and stability of Vickers hardness, the cladding layer was divided into surface zone, middle zone, bonding zone and heat affected zone. The elastic modulus of different zones were obtained by the nano-indentation experiment. A finite element model was established to simulate the experimental process of nano-indentation. The mechanical property parameters of different zones of cladding layer were inversely calculated, and the heterogeneous constitutive relationship of cladding layer was established. The comparison of over simulation results and experimental results verifies the effectiveness of the established constitutive model. The results show that the heterogeneous constitutive model of cladding layer can be effectively obtained by the proposed method. The experiment is simple and only less experiment is needed.

Effect of poisson's ratio on the indentation of open cell foam

Abstract: We tested whether conventional and auxetic (negative Poisson's ratio) foam indentation response fits with classical indentation theory. We first made foam cubes with 20–25 mm sides, and Poisson's ratios spanning negative and positive values (−0.35 to 0.3). These foam cubes were compression tested, and indented by the curved face of two cylinders (10 and 50 mm diameters) and a stud (12 mm diameter), to 20% of their thickness. Full-field true strains were measured by digital image correlation, to obtain Poisson's ratios and to study foam deformation during indentation. Indentation force vs. displacement was measured and calculated using incremental Poisson's ratios and tangent moduli. Normalised root mean square errors between measured and calculated indentation forces were ∼5% of measured values. Foam densification during indentation, and compression towards sample edges, increased with the magnitude of negative Poisson's ratio; these may both increase indentation resistance beyond predictions from indentation theory.

Experimental Verification of the Boundary Element Method for Adhesive Contacts of a Coated Elastic Half-Space

Abstract: We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical approximation of the dependence of contact stiffness on the indenter diameter was used to verify the results of BEM simulations. Adhesive contacts of hard indenters of different shapes with soft rubber layers have been experimentally studied using specially designed laboratory equipment. The comparison of the results from all three implemented methods shows good agreement of the obtained data, thus supporting the generalized BEM simulation technique developed for the JKR limit of very small range of action of adhesive forces. It was shown that the half-space approximation is asymptotical at high ratios of layer thickness h to cylindrical indenter diameter D; however, it is very slowly. Thus, at the ratio h/D = 3.22, the half-space approximation leads to 20% lower contact stiffness compared with that obtained for finite thickness using both an experiment and simulation.

Nanoindentation size effects of mechanical and creep performance in Ni-based superalloy

Abstract: ABSTRACT Nanoindentation technique was adopted to study indentation size effects of physical-mechanical and creep performance with various depths (200–2000 nm) in GH901 utilising sharp and spherical tip. Residual impressions of both indenters with pile-up patterns are discussed. Nanohardness, reduced modulus and elastic recovery rates curves versus maximum displacement of two tips are obtained and nanohardness size effects are discussed with different models for Berkovich tip. The data obtained with spherical indentation are analysed separately by establishing stress–strain diagram. The creep results using Berkovich tip indicate that creep strain rate declines while creep stress exponent first decreases and then increases with the increasing depth; the creep stress exponent (n) values, 2.39–7.35, imply the dominant creep deformation mechanism is dislocation control.

Effect of twist on indentation resistance

Abstract: With mechanical metamaterials that display force-torque coupling receiving recent attention, we tested the effect of twist on indentation resistance. We hypothesised that the force required to indent a twisting lattice to a set depth would increase with the amount of transverse deformation caused by twist. Based on previous work, various chiral lattices were designed to twist by up to 1.3° per 1 % compression. These lattice designs were 3D-printed in Nylon-12, then tested, with the experiments replicated in finite element simulations. Indentation resistance increased with twist; the lattice with maximum twist required ∼70 % higher indentation force (when normalised to compressive stiffness) than the non-twisting (antichiral) one during spherical indentations to 1 % of sample thickness. Further, we calculate the expected effects of twist on indentation resistance by combining the established micropolar and Willis’ plane stress moduli with classical Hertzian indentation equations. We found reasonable agreement (within 10 %) between 2D calculation methods use here and previous 3D calculation methods. The indentation resistance calculated using the micropolar plane stress modulus followed the same trends as the simulations and experiments. The calculated indentation force was within 10 % of the simulations and experiments.

Probing interlayer van der Waals strengths of two-dimensional surfaces and defects, through STM tip-induced elastic deformations

Abstract: A methodology to test the interlayer bonding strength of two-dimensional (2D) surfaces and associated one (1D)- and two (2D)- dimensional surface defects using scanning tunneling microscope tip-induced deformation, is demonstrated. Surface elastic deformation characteristics of soft 2D monatomic sheets of graphene and graphite in contrast to NbSe2 indicates related association with the underlying local bonding configurations. Surface deformation of 2D graphitic moiré patterns reveal the inter-layer van der Waals strength varying across its domains. These results help in the understanding of the comparable interlayer bonding strength of 1D grain boundary as well as the grains. Anomalous phenomena related to probing 2D materials at small gap distances as a function of strain is discussed.

Indentation, Finite Element Modeling and Artificial Neural Network Studies on Mechanical Behavior of GFRP Composites in an Acidic Environment

Abstract: In this study, the indentation tests are performed with various forces using the Vickers indenter to investigate the mechanical properties, including the elastic modulus, hardness, and the plasticity index of pure, and incorporated glass fiber reinforced polymer (GFRP) composites with nanosilica and nanoclay. To study the effect of adding different nanoparticles on reducing the mechanical properties of immersed specimens in acid for 0, 1 and 3 months, incorporated composite specimens with 3 wt percent (wt. %) of nanoparticles were fabricated using hand lay-up method. Accordingly, the reduction in mechanical properties and increase in plasticity index was attributed to the penetration of acid into composite specimens during the immersion period, which resulted in the failure of matrix and fiber following increased moisture penetration. Adding the nanoparticles especially nanoclay, has alleviated the trend of drop in mechanical properties. In fact, for the incorporated composite specimen with nanoclay, the hardness and elastic modulus of the immersed samples in acid for 0 and 3 months indicated a decrease of 10.55 and 7.88%, respectively on grounds of hydrophobic nature of nanoclay. Conversely, incorporating nanosilica increased the plasticity index leading to higher rate of degradation, which was even more than pure sample, yet the pure sample had the lowest mechanical properties after 3 months of immersion. In addition, Finite element modeling (FEM) and artificial neural network (ANN) were used to respectively predict the indentation behavior of fabricated composite specimens and study the effects of immersion time in an acidic environment.

Integrating MR imaging with full-surface indentation mapping of femoral cartilage in an ex vivo porcine stifle.

Abstract: The potential of MRI to predict cartilage mechanical properties across an entire cartilage surface in an ex vivo model would enable novel perspectives in modeling cartilage tolerance and predicting disease progression. The purpose of this study was to integrate MR imaging with full-surface indentation mapping to determine the relationship between femoral cartilage thickness and T2 relaxation change following loading, and cartilage mechanical properties in an ex vivo porcine stifle model. Matched-pairs of stifle joints from the same pig were randomized into either 1) an imaging protocol where stifles were imaged at baseline and after 35 min of static axial loading; and 2) full surface mapping of the instantaneous modulus (IM) and an electromechanical property named quantitative parameter (QP). The femur and femoral cartilage were segmented from baseline and post-intervention scans, then meshes were generated. Coordinate locations of the indentation mapping points were rigidly registered to the femur. Multiple linear regressions were performed at each voxel testing the relationship between cartilage outcomes (thickness change, T2 change) and mechanical properties (IM, QP) after accounting for covariates. Statistical Parametric Mapping was used to determine significance of clusters. No significant clusters were identified; however, this integrative method shows promise for future work in ex vivo modeling by identifying spatial relationships among variables.

Surface Deformation Recovery by Thermal Annealing of Thermal Plasma Sprayed Shape Memory NiTi Alloys

Abstract: The shape memory effect is the most important attribute of shape memory alloys where material can recover to its initial shape after deformation by heating above its transformation temperature. In this article, the thermally induced recovery of well-defined microscopic deformation in a NiTi shape memory alloy was investigated. Surface deformation was performed by indenting the plasma sprayed NiTi shape memory alloy in a martensitic phase at room temperature using spherical indenters. In this article, a series of indentations, scratch lines and wear lines were made on the surface of two different NiTi shape memory alloys at the micrometre scale using two spherical indenters with different radii. Three-dimensional imaging of indentation topography using scanning confocal microscopy provided direct evidence of the thermally induced martensitic transformation of these plasma sprayed thick films allowing for partial recovery on the micro-scale. The partial recovery is achieved at various indentation depths and for different scratches and wear volumes.

Profilometry‐Based Indentation Plastometry for Evaluating Bulk Tensile Properties of Aluminum‐Silicon Carbide Composites

Abstract: The need for large samples with specific geometries and the destructive nature of conventional tensile testing pose a challenge in the rapid mechanical characterization of metal matrix composites (MMCs). Herein, the efficacy of a high‐throughput profilometry‐based indentation plastometry (PIP) technique for evaluating bulk tensile properties of SiC‐reinforced aluminum MMC with minimum sample volume and preparation is investigated. Plastic properties, namely yield strength (YS), ultimate tensile strength (UTS), and elongation up to necking (εn) in aluminum composites reinforced with 0, 17.5, and 25 vol% of SiC from PIP, are compared with uniaxial tensile tests. While PIP estimations of YS for all composites and UTS for Al‐17.5 vol% SiC are accurate within 3–6%, those of UTS in 25 vol% and εn in all composites show significant deviation from tensile test data. These deviations are attributed to the PIP overestimation of strength due to local SiC crowding beneath the indenter and the limitation of the Voce plasticity‐based FEM simulation in capturing brittle behavior of high vol% reinforcement. Herein, the high‐throughput PIP technique that can be reliably extended to MMCs with low volume (≈17.5%) of SiC reinforcements is established, thus harboring potential for advancement in the nondestructive testing of MMCs.