Indentation Behavior Research Articles

Atomistic Simulation of the Effect of Twins on the Indentation Behavior of BCC-Fe

Atomistic Simulation of the Effect of Twins on the Indentation Behavior of BCC-Fe

Nanoindentation behaviors of the AlCoCrFeNi2.1 eutectic high-entropy alloy: The effects of crystal structures

The AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA), as a kind of in-situ composite materials, have achieved good match of strength and plasticity due to its typical eutectic lamella structures. Although many previous studies have investigated the indentation behaviors of the AlCoCrFeNi2.1 EHEA, there are still some controversies about the hardness characteristic of different crystal structures, requiring further clarification. Accordingly, in this study, nanoindentation tests were conducted to investigate the indentation behaviors of different crystal structures (primary L12 phase, primary B2 phase, and the eutectic phase region). The residual indentation and the crystallographic orientations were characterized by the laser scanning confocal microscope, scanning electron microscope, and electron backscatter diffraction. The hardness in different crystal structures were comparatively analyzed and the material deformation mechanisms were discussed correspondingly. The statistic results showed that the eutectic phase region had the lowest hardness, and primary B2 phase had the highest hardness. Furthermore, the slip lines in the primary L12 phase were evenly distributed near the residual indentation, but the slip lines in the eutectic phase region were concentrated near the phase boundaries. These findings are expected to deepen the understanding of the microscale deformation behaviors of EHEAs.

Size effect and indenter shape dependence of indentation and scratching behavior for laser melting deposited Ti-6Al-4V alloy

Size effect and indenter shape dependence of indentation and scratching behavior for laser melting deposited Ti-6Al-4V alloy

Evaluation method of dynamic indentation behavior of glass based on electromagnetic induction phenomena

AbstractContact damage of glass is one of the most crucial issues for glass products. To develop strong and tough glass products and to compare damage resistance among glass compositions, a simple method for evaluating the mechanical response of glass during contact is required not only for glass mechanists but also for glass customers and suppliers. Although it is well known that the quasi‐static Vickers indentation test is one of the simplest and most useful methods to evaluate hardness and brittleness in glass, the indentation response of glass under the indenter at higher impact velocities remains to be quantitively understood because of the difficulty of measurement and limited experimental works. In this study, therefore, the dynamic indentation behavior of soda‐lime glass is evaluated by using a lab‐made free‐drop indentation set‐up with the coils for detecting electromotive forces (EMFs). The cono‐spherical indenter made of tungsten carbide attached with a neodymium magnet was employed to generate the EMFs when the indenter passed through the coils located near the glass sample. The impact load versus indentation depth curve during the impact within a few tens of microseconds was successfully obtained both for an elastic contact and for an inelastic contact. Under an elastic condition, where no residual indent nor any cracks were left on the glass surface after the test, it is confirmed that there is almost no hysteresis in the impact load versus indentation depth curve and that the curve can be reproduced by the Hertzian analytical solution. Under an inelastic condition, on the other hand, it is found that the hysteresis in the impact load versus indentation depth curve stems from inelastic phenomena, such as plastic deformation (shear flow and/or permanent densification) and cracking. These results suggest that the dynamic indentation technique based on electromagnetic induction phenomena is a useful and effective tool for evaluating the mechanical responses of glasses during the impact.

Mechanical and Electrochemical Properties of Lithium Aluminoborate Glasses

The elastic moduli and the indentation behavior of glasses from the xLi2O-5Al2O3-(95−x)B2O3 system, with x = 35, 40, and 50 were characterized. Glasses become softer and less resistant to indentation cracking as the lithium content is increased, as a result of increasing the numbers of 3-fold coordinated boron and non-bridging oxygen atoms in this composition range. In parallel, the ionic conductivity at 25 °C is increased from 3.7 10–10 to 5.5 10–8 S∙cm–1, and the activation energy, as measured in the 10 to 90 °C ranges is between 55 (50 % Li2O) and 65 (35 % Li2O) kJ∙mol–1, which shows that the ionic diffusion of lithium is easier in Li-rich compositions. Measurements of the conductivity under a compressive load aligned with the electric field revealed a mechanical-electrical coupling. The change of the activation energy with the stress is associated with an activation volume, and thus a stress sensitivity, that is increased with the lithium content.

Evaluation of nano indentation behavior of TIG, MIG and diffusion bonded Inconel 718 and austenitic Stainless Steel 316L joint interface

The nanomechanical characteristics of Metal Inert Gas (MIG), Tungsten Inert Gas (TIG), and diffusion-bonded Inconel (IN718) and Austenitic Stainless Steel (SS 316L) were investigated. The nano hardness and elastic modulus of different weldments were evaluated using nanoindentation and compared. The results showed that intermetallic compounds (IMCs) and carbides were reduced with diffusion bonding. Moreover, maximum nano hardness and elastic modulus occurred in the welded zone (WZ) of TIG and MIG welded joints while at the bonding interface in diffusion bonding (DB). Lastly, the nano hardness of the bonding interface in diffusion-bonded was 11 % and 7 % lower compared to MIG and TIG welded joints.

Indentation Behavior Assessment of As-Built, Solution, and Artificial Aged Heat-Treated Selective Laser Melting Specimens of AlSi10Mg

This study was conducted to determine the indentation behavior of thin AlSi10Mg specimens manufactured using Selective Laser Melting (SLM) in the as-built condition along with two post-treatments, namely solution heat treatment and artificial aging. Four different thicknesses of 1 mm, 1.5 mm, 2 mm, and 2.5 mm of SLM specimens, with the different post-treatments, underwent standardized Rockwell hardness tests using a spherical indenter to determine their hardness values and assess the impression using a stereo microscope and scanning electron microscope (SEM). The as-built specimens showed a trend of smaller indentation depths with increasing specimen thickness, and finally creased with 0.1547 mm depth at 2.5 mm. However, the post-treatments altered the behavior of the specimens to a certain degree, giving larger experimental indentation depths of 0.2204 mm, 0.1962 mm, and 0.1798 mm at 1.0 mm, 1.5 mm, and 2.5 mm thickness, respectively, after solution heat treatment. Artificial aging showed a general decrease in indentation depth with increasing specimen thickness in contrast to solution treatment, and resulted in depths of 0.1888 mm and 0.1596 mm at 1.0 mm and 2.5 mm thickness. Furthermore, a material numerical model was made using stress–strain data on ANSYS Workbench to develop a predictive model for the indentation behavior of the specimens in contrast to experimentation. Under multi-linear isotropic hardening, the Finite Element Analysis (FEA) simulation produced indentation geometry with an average accuracy of 95.4% for the artificial aging series.

Conical indentation over a transversely isotropic and layered elastic half-space

We propose a novel method for solving the static response of a conical indenter on a transversely isotropic and layered elastic half-space. The newly developed Fourier-Bessel series (FBS) system of vector functions, along with the unconditionally stable dual-variable and position method, is employed to derive the Green's function in the transversely isotropic and layered elastic half-space under a vertical ring load on the surface. To calculate the response at different field points on the surface, we apply discrete love numbers within the FBS vector system. The load densities in the discretized rings within the contact radius of the conical indenter are determined using the integral least-square method, along with a self-adaptive algorithm developed in this study. Finally, the relationship between the indentation depth (vertical displacement) and the applied load is obtained through force balance between the external load and the summed contact traction. The developed scheme is validated using existing exact solutions for the reduced homogeneous half-space case. Selected numerical results clearly demonstrate the effect of anisotropic material and layering on the indentation response. It is observed that, regardless of whether the structure is a stratified half-space or a layered structure with a rigid substrate, the material properties in the top layer have the most significant influence on the indentation behavior. In the case of a layered structure with an underlying elastic half-space, the material properties in the interlayer and bottom layer could also affect the indentation behaviors.

Fracture behaviour of bicrystalline graphene characterized via freestanding indentation

Using molecular mechanics (MM) simulations, the failure stress of bicrystalline graphene with different tilt angles is investigated using their free-standing indentation behaviour, in which two types of grain boundaries, including armchair (ac) and zigzag (zz) grain boundaries, and two types of indenter tip, including cylindrical and spherical tips are considered. For reference purposes, the corresponding results under inplane stretching are also examined. It is found that the failure stress of grain boundary (GB) in bicrystalline graphene decreases with the decrease of the GB tilt angle [Formula: see text], which is similar to that determined in inplane stretching. In indentation, the stress concentration under the indenter tip will decrease the failure stress of graphene; in addition, the out-of-plane deformation of graphene in indentation can partially release the pretension induced by the GB in bicrystalline graphene. For the GB with a small prestress, the effect of the former is larger than that of the latter; but for the GB with a larger prestress, the effect of the latter is larger than that of the former. Consequently, the effect of tilt angle [Formula: see text] on the GB strength of bicrystalline graphene is lower in indentation than that given by inplane stretching.

Assessment of phenomenological models for Indentation Size Effect (ISE) through physically based dislocation density evolution

The depth dependent hardness, referred to as indentation size effect (ISE) has gained considerable attention. ISE is attributed to the strain gradient caused by the inhomogeneous strain distribution beneath the indenter tip. The depth dependence of hardness is phenomenologically accounted using an appropriate length scale parameter. The Unified model is one such model that is built on Nix–Gao’s model and focuses on integrating various length scale parameters resulting from both microstructural and geometrical effects. One aspect of the current work is to assess the applicability of the Unified model to a material like bulk Nickel with a history of cold work. Also, the physics of ISE in metals can be related to the dislocation mean free path influenced by strengthening mechanisms. Past attempts are scarce to quantify the ISE through the microstructure variables. In the present work, an attempt has been made to simulate the nanoindentation test using a dislocation density based constitutive model. The objective of this study is to establish a correlation between the equivalent plastic strain resulting from deep depth indentation (which does not exhibit a size effect) and an equivalent dislocation density. The dislocation density here serves as a state variable that describes the microstructure-dependent mechanical behaviour. The modified KME, a dislocation density-based model, is incorporated as a user subroutine in a commercial finite element solver. It has been proven to accurately predict the indentation behaviour at substantially large depths, which aligns well with the predictions of the Unified model or experimental observations. The good correlation between the value of effective dislocation density and equivalent plastic strain in the plastic zone underneath the indenter assures to extend the use of dislocation density as a state variable to predict ISE.

Indentation behavior of a semi-infinite piezoelectric semiconductor under a rigid flat-ended cylindrical indenter

Indentation behavior of a semi-infinite piezoelectric semiconductor under a rigid flat-ended cylindrical indenter

Experimental study on resin pin-reinforced marine sandwich composites under quasi-static indentation load

This study aims to experimentally examine the indentation behaviour of marine sandwich composites with pin-reinforced polyvinyl chloride foam core and E-glass face sheets. The effects of indenter diameter, resin pin diameter, and arrangement on force-displacement, maximum contact force, and absorbed energy values of sandwich panels were evaluated by the indentation tests. Throughout the experiments, the contact forces increased as the pin diameter increased. The contact forces reduced as the distance between pin diameters increased. Additionally, the values of absorbed energy increased as the diameters of the resin pin and indenter increased. Placing the pins more closely together additionally allows the material to absorb more energy in the event of indentation. A visual inspection took place on the post-indentation cross-sections of the sandwich specimens to detect any damage modes. Damage modes varied depending on the size of the indenter and the hole pattern in the foam core.

Indentation of sandwich beams: Comparison of Vlasov, Winkler, and shear theories with composite surfaces reinforced by CNTs and ANN model

The use of sandwich structures has spread to a wide range of fields today. As a result of their thin top and low stiffness, sandwich beams are very susceptible to local loads. One practical solution to increase the sandwich structure's indentation resistance is to add bending strength to the top. The structural properties of carbon nanotubes make them well-suited for use in polymer matrixes; their addition improves the attributes of polymers. Experimental and theoretical investigations of the sandwich structure's indentation behavior are presented in this article. As well, simulations of sandwich structures are conducted using Abaqus software. A tensile test of composite samples and Mori Tanaka's theory were used to determine the elastic modulus of epoxy resin reinforced with carbon nanotubes at different mass percentages. The elastic modulus of composites can be improved by adding carbon nanotubes up to 0.3 % by mass while the mechanical properties are reduced when more than 0.3 % of carbon nanotubes were added. Finally, the analytical solution and Abaqus modeling results for the indentation of the sandwich structure were compared with the results obtained from the experimental tests. A machine learning model is proposed for prediction of sandwich beams deflection. The results of the predictions were phenomenal, with MAE of less than 2 %. The computational costs have been compared with the experimental results, and the machine learning method is very efficient.

Experimental and numerical investigation on low‐velocity impact response of sandwich structure with functionally graded core

AbstractThe present research investigates optimizing the impact resistance of functionally graded sandwich structures using experimental and numerical approaches. The low‐velocity impact (LVI) responses of functionally graded sandwich composite (FGSC) with different configurations with skin material jute/rubber/jute (JRJ) and core material having epoxy and sea sand by volume fraction of sea sand at 0%, 10%, 20%, and 30%. Sandwich structures were impacted with LVI (5.89, 10.92, and 15.18 m/s), with the impactor dropped from heights of 0.5, 1, and 1.5 m with precompressed spring loads. FGSC samples are considered a deformable body, and the impactor is modeled as a rigid body using commercially accessible dynamic explicit software. The burn‐out test and weight method were used to test the core's gradience; both methods' results substantially matched, and the variance in gradation could be observed. The proposed sandwich structure characteristics are examined by energy absorption, peak force, energy loss percentage, and coefficient of restitution. Results showed that SC30S provides greater energy absorption and superior damage resistance when tested on LVI. To evaluate the accuracy of experimental findings in predicting the indentation behavior of the sandwich structure, the finite element analysis was used to compare with the experimental results. According to the examination of these proposed FGSC overall performance, they could potentially be employed as sacrificial materials for LVI applications like claddings to shield major structural components. The systematic approach used in this work serves as a standard for choosing and using FGSC effectively for LVI applications.Highlights Low‐velocity impact behavior of sandwich structures was investigated. Combining flexible skin and epoxy core enhances energy absorption. Based on impact energy levels, impact damage areas were determined. Examined sandwich structure advantages in structural and aerospace uses. In terms of time and cost, the numerical analysis method would be useful.

Non-equibiaxial residual stress evaluation methodology using simulated indentation behavior and machine learning

Measuring the residual stress in the components in nuclear power plants is crucial to their safety evaluation. The instrumented indentation technique is a minimally invasive approach that can be conveniently used to determine the residual stress in structural materials in service. Because the indentation behavior of a structure with residual stresses is closely related to the elastic-plastic behavior of the indented material, an accurate understanding of the elastic-plastic behavior of the material is essential for evaluation of the residual stresses in the structures. However, due to the analytical problems associated with solving the elastic-plastic behavior, empirical equations with limited applicability have been used. In the present study, the impact of the non-equibiaxial residual stress state on indentation behavior was investigated using finite element analysis. In addition, a new nonequibiaxial residual-stress prediction methodology is proposed using a convolutional neural network, and the performance was validated. A more accurate residual-stress measurement will be possible by applying the proposed residual-stress prediction methodology in the future.

Indentation behavior of multiferroic composite materials under an axisymmetric power-law shaped indenter

Nanoindentation technique has been widely employed to characterize various material properties of multiferroic composite medium, where the indenter tip may have more general profile rather than just three common simple shapes (flat, cone and sphere). In this paper, the frictionless indentation problem of a transversely isotropic multiferroic half-space punched by an axisymmetric power-law shaped indenter is investigated. By virtue of the Hankel integral transform, the stated mixed boundary value problem is reduced to dual integral equations, which are then solved analytically. Closed-form solutions for the coupled physical fields at the surface of multiferroic half-space under the action of the power-law shaped indenters with four different electromagnetic properties are obtained, which can include the existing results in literature as special cases. The explicit analytical expressions of load-displacement relationship for the power-law shaped indenter are derived for the first time, which provide the theoretical foundation for characterizing material properties of multiferroic composite medium. The effects of the shape index and electromagnetic properties of the indenter on indentation behaviors are discussed in detail. It is found that the shape index has a significant effect on both the load-displacement relationship and the distribution of the generalized stress fields. The analytical solutions derived from this work can serve as benchmarks for experimental test and characterization of multiferroic composite materials.

Influence of micro-segregation on the microstructure, and microhardness of MoNbTaxTi(1-x)W refractory high entropy alloys: Experimental and DFT approach

In recent times, MoNbTaW Refractory High Entropy Alloys (RHEAs) have drawn attention due to their exciting high-temperature applications and efforts are being made to improve their properties further. Alloying addition is an effective and practical approach to enhancing material properties. Ti is well known for its strength, low density, and corrosion resistance and its role in the properties of MoNbTaW-based RHEAs is required to be understood. RHEAs are commonly synthesized by vacuum arc melting (VAR) process and micro-segregation of the elements is reported. However, the effect of micro-segregation on MoNbTaW RHEAs is not well understood. Hence, the present work deals with the addition of Ti and micro-segregation on the structure, microstructure, and indentation behavior of MoNbTaW RHEAs. A novel non-equiatomic MoNbTaxTi1-xW (x = 0, 1, and 0.5) RHEAs were prepared by vacuum arc melting (VAR) process. The structure and microstructure of these RHEAs were ascertained through X-ray diffraction (XRD) and transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with EDS for ascertaining the nominal chemical composition. The as-cast MoNbTaxTi1-xW (x = 0, 1, and 0.5) RHEAs contains two BCC phase having slightly different lattice parameter i.e., BCC1 (a = 0.324 nm) and BCC2 (a = 0.323 nm) close to Ti and W respectively. These as-cast RHEAs having dendritic and inter-dendritic regions were found to be enriched in W and Ta, and Mo, Nb and Ti respectively. The microhardness of these RHEAs was investigated through instrumented indentation techniques. The microhardness of the BCC1 and BCC2 phases was found to be ∼4.5 GPa and 5.7 GPa. Further, the influence of Ti addition on the structure, elastic constant, and microhardness were estimated from the perspective of the first principle approximation. The special quasi-random structure (SQS) was used for first-principle calculations. The strengthening mechanisms influencing the mechanical properties in these BCC RHEAs were discussed in details. The experimental results were in good agreement with the results pertaining to theoretical modelling, demonstrating the effectiveness of these methods in predicting the structure and mechanical properties of RHEAs.

Water-enhanced plasticity of calcium fluoride

Calcium fluoride (CaF2) ionic crystals have been observed to be sensitive to humid environments during ultra-precision machining, but further discussion about detailed mechanisms of the corresponding water-induced mechanical behaviors is still lacking. This work aims to perform a systematic investigation to understand the effect of water on the deformation and correlated plastic enhancement of CaF2 under indentation. Micro-indentation experiments were employed to observe different mechanical responses including the pop-in behavior and surface pile-up to identify the water-enhanced plasticity of CaF2 preliminarily. Then, atomic simulations were performed to reproduce the indentation process and confirm the close relationship between the indentation behaviors and water. The dislocation activities and crystal slip of both simulations with and without water were captured to analyze the plastic flow induced by hydration. Furthermore, Raman spectroscopy measurement was also adopted in this study to explain the corresponding enhancing mechanisms of plastic behaviors from the perspective of surface effect.

Characterizing dynamic load propagation in cohesionless granular packing using force chain

When dynamic load is applied on a granular assembly, the time-dependent dynamic load and initial static load (such as gravity stress) act together on individual particles. In order to better understand how dynamic load triggers the micro-structure's evolution and furtherly the ensemble behavior of a granular assembly, we propose a criterion to recognize the major propagation path of dynamic load in 2D granular materials, called the “dynamic force chain”. Two steps are involved in recognizing dynamic force chains: (1) pick out particles with dynamic load larger than the threshold stress, where the attenuation of dynamic stress with distance is considered; (2) among which quasi-linear arrangement of three or more particles are identified as a force chain. The spatial distribution of dynamic force chains in indentation of granular materials provides a direct measure of dynamic load diffusion. The statistical evolution of dynamic force chains shows strong correlation with the indentation behaviors.

Finite element modeling of spherical indentation behavior of 3D mesh fabric at the yarn level

This paper reports an experimental and numerical study on the spherical indentation behavior of three-dimensional (3D) warp-knitted mesh fabrics. A full-size finite element (FE) model of a typical 3D mesh fabric is established at the yarn level based on the realistic monofilament architecture from micro-computed tomography (μCT) scanning and verified with experiments. The structural change of the fabric in the spherical indentation process is quantitatively analyzed in terms of fabric global deformation, local deformation, mesh deformation, and spacer monofilament deformation from the FE simulation. The numerical results show that the fabric shrinks walewise and expands coursewise from the spherical indentation of the continuous intermeshed monofilament architecture, showing counterintuitive partial auxeticity. The coursewise symmetry and walewise asymmetry of the 3D mesh fabric produce relatively symmetrical coursewise deformation and asymmetrical walewise deformation under spherical indentation. The symmetrical coursewise deformation includes even widening, good fitting of the indenter, and almost identical mesh sizes in the coursewise direction. Walewise asymmetry leads to uneven shortening, inferior fitting of the indenter, and considerably varied mesh sizes in the walewise direction. Spacer monofilaments in different positions relative to the spherical indenter have different deformations. The closer to the indenter, the greater bending and twisting of the spacer monofilament. The spacer monofilament knitted earlier of the tested fabric has smaller deformation than that knitted later due to the walewise asymmetry. The coursewise symmetry and walewise asymmetry of the inhomogeneous 3D mesh fabric structure result in a highly nonlinear spherical indentation behavior.