Indentation Depth Research Articles

Multi-functional hybrid sandwich composite structures: Evaluating damage mechanics and tolerance using compression after impacts

Building upon previous researches that introduced an innovative foam core hybrid-sandwich composite structure for radome applications, showcasing promising performance under low-velocity impacts (LVIs), this paper delves into the assessment of damage tolerance and mechanics through Compression After Impact (CAI) testing. The primary objective is to analyze disparities in damage tolerance, damage mechanisms, displacements, deformations, energy absorption, and residual strengths resulting from LVIs followed by CAIs on dissimilar materials on opposite faces of the hybrid structure. The extent of damage is evaluated through Computed Tomography (CT) scans. During LVIs, impacts on the S glass face sheets side demonstrated different energy dispersion and absorption mechanisms, leading to variations in indent damage depths and widths across all impact energy levels, unlike the impact damages observed from the Kevlar side. During CAI testing, this difference becomes more evident, with Kevlar specimens (KS3 & KS5) showing greater indentation depths and narrower widths, and S glass specimens (SK3 & SK5) experiencing buckling. These effects are due to the unique damage absorption and dispersion properties of Kevlar and S glass. These variations prompted an in-depth investigation of the structure using CAI to comprehend damage tolerance and mechanisms under compressive loads. This study, unparalleled in existing literature, proposes hybrid sandwich structures with superior specific impact and residual strength compared to various composite sandwich structures documented in published literature, expanding their utility beyond radomes.

Mapping the composite nature of clay matrix in mudstones: integrated micromechanics profiling by high-throughput nanoindentation and data analysis

AbstractMudstones and shales serve as natural barrier rocks in various geoenergy applications. Although many studies have investigated their mechanical properties, characterizing these parameters at the microscale remains challenging due to their fine-grained nature and susceptibility to microstructural damage introduced during sample preparation. This study aims to investigate the micromechanical properties of clay matrix composite in mudstones by combining high-speed nanoindentation mapping and machine learning data analysis. The nanoindentation approach effectively captured the heterogeneity in high-resolution mechanical property maps. Utilizing machine learning-based k-means clustering, the mechanical characteristics of matrix clay, brittle minerals, as well as measurements on grain boundaries and structural discontinuities (e.g., cracks) were successfully distinguished. The classification results were validated through correlation with broad ion beam-scanning electron microscopy images. The resulting average reduced elastic modulus (Er) and hardness (H) values for the clay matrix were determined to be 16.2 ± 6.2 and 0.5 ± 0.5 GPa, respectively, showing consistency across different test settings and indenter tips. Furthermore, the sensitivity of indentation measurements to various factors was investigated, revealing limited sensitivity to indentation depth and tip geometry (when comparing Cube corner and Berkovich tip in a small range of indentation depth variations), but decreased stability at lower loading rates. Box counting and bootstrapping methods were applied to assess the representativeness of parameters determined for the clay matrix. A relatively small dataset (indentation number = 60) is needed to achieve representativeness, while the main challenges is to cover a representative mapping area for clay matrix characterization. Overall, this study demonstrates the feasibility of high-speed nanoindentation mapping combined with data analysis for micromechanical characterization of the clay matrix in mudstones, paving the way for efficient analysis of similar fine-grained sedimentary rocks.

Meso-level surface modification of Hastelloy C276 by WS2 powder mixed electrical discharge alloying process through micro-EDM setup

The present research provides a rigid, wear-resistant lubricating localized layer on Hastelloy C276 (HC 276) surface at meso level by tungsten disulphide (WS2) powder suspended electrical discharge alloying (EDA) process through micro-electrical discharge machining (μ-EDM) setup. The performance characteristics of the coated surface were evaluated in terms of material deposition rate (MDR), surface morphology, surface roughness (Ra, Rz and Rq), recast layer thickness (RLT), compositional analysis, micro-hardness & indentation depth, wear test and water contact angle analysis. Maximum MDR has been achieved at 15 g/L WS2 concentration and 80 V of gap voltage whereas The RLT varies from 6.87 μm to 18.91 μm and is enhanced with the increase in WS2 concentration. The critical surface characterization confirms higher WS2 concentration reduces the crater dimensions and the presence of micro-cracks and micro-voids on the coated surface. The surface roughness has been increased with the gap voltage and capacitance, whereas higher WS2 concentration provides lower surface roughness. X-Ray diffraction analysis (XRD) confirms the presence of hard and wear resistance phases like WC, WO3, ZnO, and MoO2 on the coated surface. Energy-Dispersive X-Ray Spectroscopy (EDS) analysis along with elemental mapping justifies tool, dielectric materials, and powder particles migration on the coated surface. The micro-hardness of the coated surface (402 HV to 1166 HV) is enhanced by 3–4 times compared to the base material (299 HV) whereas the indentation depth has been reduced with the rise in WS2 concentration and lies within the RLT of the coated surface. The wear rate of the WS2 coated surface is drastically reduced compared to the base material with a lower value of coefficient of friction (COF). The coated surface became hydrophobic in nature with a contact angle of 109.6° compared to the hydrophilic base HC 276.

Experimental and Simulation Studies on Protective Structures in Floating Dock

In this research, two distinct designs of protective structures were developed to address structural damage caused by ships impacting the internal structures of floating docks during maintenance operations. The designed protective structures consist of support sections and load-bearing sections, with the load-bearing section comprising three frame sections. For ease of description, the front frame section, middle frame section, and rear frame section are referred to as Frame A, Frame B, and Frame C, respectively. A drop-weight test was conducted with a stern-shaped indenter impacting the structures at 3.89 m/s. This study also assessed varying impact speeds and positions. The results showed that Specimen 2 had localized indentations on Frame B, while Specimen 1 exhibited overall deformation of Frame B and additional deformations in Frame A. The simulations agreed with the experimental results, confirming the model’s accuracy. At speeds from 2.34 m/s to 5.45 m/s, Specimen 2 consistently showed localized deformations, while Specimen 1 showed comprehensive deformation of Frame B at 3.89 m/s due to lower rigidity. When the indenter impacted the specimens at different locations with a speed of 5.45 m/s, the two specimens exhibited varying degrees of damage. As the impact location shifted from the central area to the end, the maximum indentation depth of Specimen 1 decreased from 52.26 mm to 41.71 mm, while that of Specimen 2 decreased from 43.26 mm to 38.50 mm. The reduction in indentation depth and extent as the impact location approached the support frame can be attributed to the increasing involvement of the web plate beneath the frame in resisting the impact. Additionally, compared to Specimen 1, Specimen 2 exhibited a relatively smaller overall indentation depth, and the impact of location variation on indentation depth was also relatively minor.

Atomistic insight of deformation mechanisms and mechanical characteristics of nano-scale silver (100) using nanoindentation

This work aims to utilize the widely adopted nanoindentation technique to explore the deformation behavior and mechanical characteristics of nanocrystalline silver (Ag) materials. Molecular Dynamics simulations were conducted to understand the material behavior at the nanometer scale. In this simulation, the effect of indentation velocity and indentation depth on defect formation and hardness during nanoindentation of Ag specimens was analyzed and discussed in detail. The results show that the deformation behavior of the Ag specimen was affected by different indentation velocities. These phenomena were confirmed by analyzing the load-displacement curve, which indicates elastic deformation by the appearance of a linear load-displacement at low indentation velocities. In contrast, plastic deformation was found by the presence of intensified serration in the load-displacement relationship at higher indentation velocities. In these cases, the hardness showed little variation when the indenter velocity was increased from 5 m/s to 10 m/s, whereas a significant increase in hardness was observed when the indentation velocity was further increased to 20 m/s. Importantly, the progression of load-displacement curves during nanoindentation demonstrates the occurrence of minor and major load drops, corresponding to an increase in indentation depth from 0.5 nm to 2 nm respectively. These findings were elucidated through dislocation extraction analysis (DXA), which revealed that a minor load drop at low indentation depths is attributed to the nucleation of an amorphous structure, while a major load drop at higher indentation depths is associated with the expansion of dislocation nucleation. Consequently, the hardness increased significantly as the indentation depth increased. This research, provides insight into atomistic investigation and offers guidelines for designing materials with excellent mechanical properties using nanoindentation.

Unusual indentation depth dependent hardness and creep behaviors in NbMoTaW films at the nanoscale

Herein, nanocrystalline NbMoTaW and (NbMoTaW)N thin films were prepared via magnetron sputtering and investigated using nanoindentation creep tests at various indentation loads (P). The hardness (H) of films increases with P, exhibiting an abnormal indentation size effect (ISE). At the same time, with decreasing indentation depth (h), the creep rate and the creep rate sensitivity (m) both increase. Under a critical h (hc) for each film, m sharply increases. The diffusion between the indenter/film interface dominates the creep mechanism at h lower than hc, whereas the dislocation–grain boundary interaction dominates the creep deformation at h higher than hc. The coble creep and lattice diffusion were both excluded as the main deformation mechanism. The escape of screw dislocations to the surface leads to the softening of the film, whereas the pile-up of screw dislocations leads to hardening, explaining the abnormal ISE on H. The effect of residual stress, grain boundary structures, substrate, and impurities are also discussed.

Nanoindentation Creep Behavior of Additively Manufactured H13 Steel by Utilizing Selective Laser Melting Technology.

Nowadays, H13 hot work steel is a commonly used hot work die material in the industry; however, its creep behavior for additively manufactured H13 steel parts has not been widely investigated. This research paper examines the impact of volumetric energy density (VED), a critical parameter in additive manufacturing (AM), and the effect of post heat-treatment nitrification on the creep behavior of H13 hot work tool steel, which is constructed through selective laser melting (SLM), which is a powder bed fusion process according to ISO/ASTM 52900:2021. The study utilizes nanoindentation tests to investigate the creep response and the associated parameters such as the steady-state creep strain rate. Measurements and observations taken during the holding phase offer a valuable understanding of the behavior of the studied material. The findings of this study highlight a substantial influence of both VED and nitrification on several factors including hardness, modulus of elasticity, indentation depth, and creep displacement. Interestingly, the creep strain rate appears to be largely unaltered by these parameters. The study concludes with the observation that the creep stress exponent (n) shows a decreasing trend with an increase in VED and the application of nitrification treatment.

Assessment of Intraday Variations in Skin Indentation Resistance.

Information about the mechanical properties of skin and their changes with age and other conditions is important to help characterize skin physiology and pathological changes. One method to obtain this information is to measure the force required to indent the skin to a specified indentation depth (FORCE). This process measures the tissue's resistance to indentation or its compressibility and is related to the tissue's elastic modulus. Since such measurements are made in clinical and other settings at various times of day (TOD), it is useful to estimate the extent of intraday variations in FORCE that may be expected. This report focuses on this issue. FORCE was self-measured on the volar forearm, 5 cm distal to the antecubital fossa, every two hours from 08:00 to 24:00 hours on two consecutive days by 12 medical students (six females and six males) who were trained in the measurement process using an indentation device (SkinFibroMeter). Variability in FORCE versus TOD was analyzed using the nonparametric Friedman test and differences between genders by the nonparametric Wilcoxon test. Differences between the first day (day 1) and the second day (day 2) were tested at each TOD. The whole-body fat percentage (FAT%) and water percentage (H2O%) were determined for each participant via bioimpedance measurements at 50 KHz. The age and BMI of the combined group (mean ± SD) were 24.5 ± 1.5 years and 23.2 ± 3.3 kg/m2.The overall average FORCE (mean ± SD) for the day over the 16 hours was 84.1 ± 22.7 mN and for day 2, it was 83.4 ± 28.5 mN with no significant difference between day 1 and day 2. For females, the overall two-day average FORCE (mean ± SD) over the 16 hours was 81.8 ± 20.3 mN and for males, it was 85.7 ± 30.1 mN with no significant difference between them (p = 0.271). Overall, there was no statistically significant difference in FORCE among TOD (p = 0.568). FORCE was not correlated with either FAT%, HTO%, or BMI. The findings indicate no statistically significant variation in indentation force in females, males, or combined concerning the TODof the measurement or differences between consecutive days at corresponding times. This suggests that whether such measurements are done in a research setting or within a clinic, they can be done at various TODwith minimal expected variation for a given subject. However, an extension of these findings to persons with skin conditions or ages not herein evaluated must await further study.

Modeling of Material Removal Rate for the Fixed-Abrasive Double-Sided Planetary Grinding of a Sapphire Substrate.

Double-sided planetary grinding (DSPG) with a fixed abrasive is widely used in sapphire substrate processing. Compared with conventional free abrasive grinding, it has the advantages of high precision, high efficiency, and environmental protection. In this study, we propose a material removal rate (MRR) model specific to the fixed-abrasive DSPG process for sapphire substrates, grounded in the trajectory length of abrasive particles. In this paper, the material removal rate model is obtained after focusing on the theoretical analysis of the effective number of abrasive grains, the indentation depth of a single abrasive grain, the length of the abrasive grain trajectory, and the groove repetition rate. To validate this model, experiments were conducted on sapphire substrates using a DSPG machine. Theoretical predictions of the material removal rate were then juxtaposed with experimental outcomes across varying grinding pressures and rotational speeds. The trends between theoretical and experimental values showed remarkable consistency, with deviations ranging between 0.2% and 39.2%, thereby substantiating the model's validity. Moreover, leveraging the insights from this model, we optimized the disparity in the material removal rate between two surfaces of the substrate, thereby enhancing the uniformity of the machining process across both surfaces.

The adjustable adhesion strength of multiferroic composite materials via electromagnetic loadings and shape effect of punch

Tunable and reversible dry adhesion possess great potential in a wide range of applications including transfer printing, climbing robots, wearable devices/electronics, and gripping in pick-and-place operations. Multiferroic composite materials offer new routines and approaches to achieve tunable adhesion due to their multi-field coupling effects. In this paper, the classical Johnson-Kendall-Roberts (JKR) adhesion model is extended to investigate the adhesive contact problem of a multiferroic composite half-space indented by an axisymmetric power-law shaped punch, whose shape index is denoted by n. The JKR-n adhesion models under the action of the power-law shaped punches with four different electromagnetic properties are set up by means of the total energy method. The explicit analytical expressions relating the indentation load and indentation depth to the contact radius are obtained, which can include the existing results in open literature as special cases. The generalized Tabor parameter and the interfacial adhesion strength applicable to multiferroic composite materials are defined. The effects of the shape index and the electromagnetic loadings on adhesion behaviors are revealed. It is found that both of them have prominent influences on the relationships among the indentation load, indentation depth and contact radius, the contact radius and indentation depth at self-equilibrium state, and the critical contact radius and indentation depth at pull-off moment. The pull-off force under the action of the conducting spherical punch subjected to non-zero electromagnetic loadings is dependent on material properties, which is different from the classical JKR result. More importantly, our analysis indicates that the pull-off force and the interfacial adhesion strength can be adjusted via altering the electromagnetic loadings and the shape index of the punch, which provides new approaches to achieve tunable adhesion.

Empirical and numerical analysis of damage tolerance in multifunctional hybrid sandwich fiber reinforced polymers composite structures for aerospace applications using compression after impact (CAI) testing

AbstractThis study presents a novel hybrid‐sandwich composite structure, customized for nose radomes applications, incorporating a foam core and distinct opposite face sheets composed of Kevlar and S‐Glass materials. Addressing in‐phase electromagnetic properties, UV protection and low velocity impact responses in our previously published work, this paper empirically and numerically investigates the damage tolerance response of the proposed structures through compression after impact (CAI) testing. The low velocity impacts (LVIs) on S‐Glass face sheets exhibited unique energy dispersion and absorption mechanisms, resulting in variations in indent damage depths and widths across all impact energy levels as compared with LVIs on Kevlar face sheets. After experimentally assessing the CAI behavior, a FE model is developed to predict CAI behavior, which closely aligned with experimental findings. This study, unprecedented in existing literature, proposes hybrid sandwich structures for nose radome aerospace applications, with superior specific impact and residual strength compared to various composite sandwich structures documented in the published literature expanding its utility beyond radomes.Highlights Innovative composites with superior low velocity impact response, tested for compression after impact performance. Designed for nose radomes found suitable for other impact prone applications. Experimental and numerical modeling showed comparable results. Major differences observed in damage mechanics, resistance, and tolerances.

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.

Numerical simulation of single-pass selective laser melting of Mg-Y-Sm-Zn-Zr alloy

A three-dimensional finite volume method (FVM) thermal-fluid coupling model was developed to simulate the temperature field distribution and dimensions of the melt pool in selective laser melting (SLM) of Mg-Y-Sm-Zn-Zr alloy powder. This model aims to accurately determine the temperature field and surface morphology of the melt pool by considering the laser's impact on powder particles, free surface dynamics, convection, and multiphase heat transfer. The study explores how laser power and scanning speed influence temperature distribution, melt pool size, and flow dynamics. The findings show that increasing laser power or reducing scanning speed consistently affects the melt pool size, peak temperature, and cooling rate. During the evaporation of the alloy in the melt pool, fluid flow is primarily governed by recoil pressure and Marangoni convection. Notably, increasing the laser power from 40 W to 100 W and the scanning speed at 0.3 m/s enhances the depth of the melt pool indentation from 13.86 µm to 23.35 µm. Furthermore, the indentation depth correlates positively with the laser line energy density.

On the promotion of serrated flows and shear band behaviors in a Zr-based metallic glass during ultrasonic vibration nanoindentation

Initiation and evolution of flow units and their correlation with mechanical behaviors of metallic glasses (MGs) are well known significant for understanding the rheological behavior of glassy substances. Here, the evolution of plastic deformation behavior of a typical Zr-based MG induced by ultrasonic vibration is investigated by means of nanoindentation, especially focusing on studying structural evolution through analysis of load-displacement curves. Furthermore, the micro-morphologies of residual indentations are characterized by using the scanning electron microscope (SEM) and atomic force microscope (AFM). Compared to quasi-static nanoindentation tests, a significant reduction in the hardness and elastic modulus of the MG by about 15 % and 30 %, respectively, is observed when subjected to ultrasonic vibration nanoindentation with an amplitude of 0.4 μm, accompanied by a pronounced indentation size effect. In addition, higher ultrasonic vibration amplitude induces larger indentation depth, more pronounced serrated flows in the load-displacement curves and more remarkable shear bands around the residual indentations, indicating ultrasonic vibration-promoted plastic flows in MG. This study provides an insight into the structural origin of plastic flows in MG systems under ultrasonic vibration, which will help to facilitate their application in the fields such as ultrasonic vibration assisted forming.

Mechanical characterization of Xenopus laevis oocytes using atomic force microscopy

Mechanical properties are essential for the biological activities of cells, and they have been shown to be affected by diseases. Therefore, accurate mechanical characterization is important for studying the cell lifecycle, cell-cell interactions, and disease diagnosis. While the cytoskeleton and actin cortex are typically the primary structural stiffness contributors in most live cells, oocytes possess an additional extracellular layer known as the vitelline membrane (VM), or envelope, which can significantly impact their overall mechanical properties. In this study, we utilized nanoindentation via an atomic force microscope to measure the Young's modulus of Xenopus laevis oocytes at different force setpoints and explored the influence of the VM by conducting measurements on oocytes with the membrane removed. The findings revealed that the removal of VM led to a significant decrease in the apparent Young's modulus of the oocytes, highlighting the pivotal role of the VM as the main structural component responsible for the oocyte's shape and stiffness. Furthermore, the mechanical behavior of VM was investigated through finite element (FE) simulations of the nanoindentation process. FE simulations with the VM Young's modulus in the range 20–60 MPa resulted in force-displacement curves that closely resemble experimental in terms of shape and maximum force for a given indentation depth.

Experimental and Numerical Analysis of the Damage Mechanism of an Aramid Fabric Panel Engaged in a Medium-Velocity Impact.

The aim of this study is to analyze the ballistic impact behavior of a panel made of Twaron CT736 fabric with a 9 mm Full Metal Jacket (FMJ) projectile. Three shots are fired at different velocities at this panel. The ballistic impact test procedure was carried out in accordance with NIJ 010106. The NIJ-010106 standard is a document that specifies the minimum performance requirements that protection systems must meet to ensure performance. The 9 mm FMJ projectile is, according to NIJ 010106, in threat level II, but the impact velocity is in threat level IIIA. Analysis of macro-photographs of the impact of the Twaron CT736 laminated fabric panel with a 9 mm FMJ projectile involves a detailed examination of the images to gather information about the material performance and failure mechanisms at the macro- or even meso-level (fabric/layer, thread). In this paper, we analyze numerically and experimentally a panel consisting of 32 layers, made of a single material, on impact with a 9 mm FMJ projectile. The experimental results show that following impact of the panel with three projectiles, with velocities between 414 m/s and 428 m/s, partial penetration occurs, with a different number of layers destroyed, i.e., 15 layers in the case of the projectile velocity of 414 m/s, 20 layers of material in the case of the panel velocity of 422 m/s and 22 layers destroyed in the case of the projectile velocity of 428 m/s. Validation of the simulated model is achieved by two important criteria: the number of broken layers and the qualitative appearance. Four numerical models were simulated, of which three models validated the impact results of the three projectiles that impacted the panel. Partial penetration occurs in all four models, breaking the panel in the impact area, with only one exception, i.e., the number of layers destroyed, in which case the simulation did not validate the validation criterion. The performance of Twaron CT736 fabric is also given by the indentation depth values by two methods: according to NIJ 0101.06 and by 3D scanning. The NIJ 010106 standard specifies that a panel provides protection when the indentation depth values are less than 0.44 mm.

Optimization study on airfoil aerodynamic performance with local indentation treatment based on drainage characteristics of dolphin fluke

Enhancing the aerodynamic performance of airfoils is the key to optimizing the energy harvesting efficiency of rotating machinery such as wind turbines. Motivated by the bowl-shaped outline of the dolphin's fluke during the propulsion process, this paper proposes a local indentation method that generates a concave region on the pressure surface of the airfoil. The NACA 0018 airfoil is selected as the reference airfoil, and two types of treatments are applied near the trailing edge point: rigid deformation and flexible deformation. Based on the grid quantity independence and experimental results validation, the results demonstrate that compared with the original airfoil, the local indentation method can modify the pressure distribution of the indentation section itself and optimize the airfoil's overall aerodynamic performance. The lift coefficient of the whole airfoil increases gradually with the rise in the indentation depth and reaches a stable value eventually. Quantitative results reveal that when the indentation depth D = 0.020c, the lift coefficient of the whole airfoil can increase by up to 26.27%; when the indentation depth D = 0.010c, the airfoil's lift-to-drag ratio reaches the maximum, which is 16.39% higher than that of the original airfoil. When replacing the rigid indentation section with a flexible medium, the fluid flowing over the pressure surface interacts with the flexible medium. The method of local indentation proposed in this paper can provide valuable reference for optimizing the aerodynamic profile of airfoils and improving the energy harvesting efficiency of wind turbines.

Exploring the impact of pre-existing helium bubbles on nanoindentation in tungsten through molecular dynamics simulation

Gaining insight into the underlying mechanisms driving nanoindentation-induced behavior in tungsten is essential for comprehending its mechanical properties. Although the plasticity of conventional pure tungsten under nanocontact conditions is well understood, these theoretical constructs may become inadequate when applied to irradiated tungsten due to the interplay between helium bubbles and dislocations. Here, we employed an integrated approach, combining crystal defect theories, molecular dynamics simulations, and machine learning, to explore the initiation and progression of dislocations in tungsten containing helium bubbles during nanoindentation, focusing on elucidating the impact of helium bubbles. In contrast to the typical dislocation nucleation in pure tungsten, the presence of helium bubbles mitigates local shear strain, thereby hindering dislocation nucleation and propagation, leading to a reduction of indentation force. Additionally, we conducted a comparative analysis between samples with and without helium bubbles, examining factors such as atomic displacement, strain localization parameters, dislocation line length, and stress component distribution. More importantly, a significant outcome of our study is the establishment of a relationship between the consistent alteration in the shape of helium bubbles and their size during micro-scale nanoindentation, achieved through machine learning techniques. Our findings reveal that the area occupied by helium bubbles post-nanoindentation is inversely correlated with indentation depth and directly linked to helium bubble size. These discoveries represent a notable advancement in understanding the effects of irradiation to a certain degree.

A Correction Function to Improve the Accuracy of Measuring Elastic Modulus by Instrumented Spherical Indentation

Abstract Instrumented indentation combined with the classic Oliver–Pharr method has been widely utilized to measure elastic modulus of various materials. However, the elastic modulus measured by instrumented spherical indentation (ISI) is not as accurate as that measured by instrumented sharp indentation, especially at large indentation depth. In this work, the effect of the maximum indentation depth on measurement of elastic modulus by ISI was deeply investigated through finite element simulations and experiments. It was found that errors in measured elastic moduli increase significantly due to the inaccurate estimation of contact radius and excessive increase in initial unloading stiffness as maximum indentation depth increases. A correction function was then proposed to correct the measured elastic modulus. After correction, the errors were effectively reduced to within ±5 % for most cases. This work contributes to discovery of the error source in the measurement of elastic modulus by ISI, thereby improving the measurement accuracy.

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.