Instrumented Indentation Technique Research Articles

Assessment of measurement uncertainty associated with fracture toughness calculation based on energy release rate in spherical indentation tests

This work aims to evaluate the uncertainty associated with the fracture toughness of 4130 M steel obtained via instrumented indentation tests and the methodology proposed by Zhang, Wang and Wang (2019). These authors take the energy release rate as a basis to determine fracture toughness. In this study, the uncertainty was assessed using the Guide to the Expression of Uncertainty of Measurement (GUM) and Monte Carlo methods. For uncertainty assessment, all measurands and input variables were identified based on the equations proposed by these authors. Then, the standard uncertainty associated with each input variable was calculated by applying the GUM method. To determine the uncertainty associated with the energy release rate JSIT the Monte Carlo method was applied. The results obtained showed that the expanded uncertainty associated with JSIT considering three tests was 1.486 N.mm−1. This uncertainty represents 7.25 % of the average JSIT value (20.490 N.mm−1). The expanded uncertainty associated with KIC was 7.520 MPa.m0.5. These represent 3.82 % of the average KIC (196.562 MPa.m0.5) value obtained. This paper demonstrates that despite the complexity of the mathematical equation proposed by Zhang, Wang and Wang (2019), to obtain fracture toughness via instrumented indentation tests, the uncertainty associated can be successfully accessed by combining the GUM and Monte Carlo methods. This work showed that the application of the instrumented indentation technique with the methodology proposed by Zhang, Wang and Wang (2019) provided fracture toughness values with excellent quality under the experimental conditions used in this study.

Adapting high-speed indentation mapping for investigating microstructure-property correlations in chromium carbide-nickel alloy coatings: Challenges and solutions

This study investigates the microstructural and mechanical characteristics of chromium carbide‑nickel rich alloy coatings produced through laser cladding, detonation spraying, and plasma spraying techniques. While all three processing techniques used the same feedstock powder, each method yields coatings with unique microstructures encompassing varying compositions and length scales. Employing Field Emission Scanning Electron Microscopy (FE-SEM) in combination with Energy Dispersive Spectroscopy (EDS) and nanoindentation mapping, local microstructure and mechanical properties were assessed at the micrometre length scale. Laser-clad coatings exhibit a typical metal matrix composite microstructure with high carbide content, distinct (MoNb)C2 phases, and Fe in the metallic matrix, while the thermal sprayed coatings showed carbides of varying sizes and metallic matrix with varying degrees of chromium dissolved in it. The instrumented indentation technique helped precisely record the microstructural features in all the coatings. Chromium carbide consistently emerges as the hardest phase across all coatings, with variations in metallic matrix hardness. Higher matrix hardness in thermal sprayed coatings correlates with increased Cr content, attributed to extended solid solubility of Cr and the presence of Mo and Nb. Energy dispersive spectroscopy and transmission electron microscopy provided clearer insight into the microstructure. This study highlights a direct one-to-one correlation between microstructure and mechanical properties mapped using instrumented indentation techniques in chromium carbide‑nickel rich coatings across different deposition methods.

Retracted: Micromechanical properties characterization of 4H–SiC single crystal by indentation and scratch methods

Growth and micromachining of single crystal silicon carbide (SiC) have drawn extensive attention in wide bandgap semiconductors and remained challenging. The micromechanical properties (i.e., hardness, elastic modulus, fracture toughness), which are the key to machinability and machining quality (and therefore the yield of the grown SiC), of 4H–SiC were assessed by nanoindentation, microhardness, and microscratch tests. Consistent values of true indentation hardness of 4H–SiC can be obtained by different approaches without the need for the area function of the indenter. Accurate determination of elastic modulus (i.e., 583.5 GPa) and indentation hardness (i.e., 38 GPa) of 4H–SiC by the instrumented indentation technique requires low loads with slight indentation-induced damage. Consistent values of fracture toughness Kc of 4H–SiC were obtained by different methods such as the Vickers/Berkovich indenter-induced cracking method (2.1 MPa·m1/2), energy-based nanoindentation approaches (the critical void volume fraction of 0.062 should be used for 4H–SiC when the deterioration of indentation hardness is used), and linear elastic fracture mechanics (LEFM)-based scratch approach with a spherical indenter (2.6 MPa·m1/2). This work provides the guidance for the mechanical machining of 4H–SiC wafers and the paradigm of micromechanical characterization of brittle solids by indentation and scratch technologies.

Simulations of the effect of shot peening backstress on nanoindentation

Shot peening is a mechanical surface treatment that can introduce compressive residual stress and work hardening simultaneously. This work hardening, considered as a modification of the elastic region with plastic strain, can be modeled with two types of contributions: isotropic hardening and kinematic hardening. In order to characterize the mechanical properties of the treated surface using the instrumented indentation technique, the effect of the backstress associated with kinematic hardening should be studied, especially for works related to fatigue loading. In this paper, the distribution of three backstress components is obtained by shot peening simulations on a nickel-based alloy, Inconel 718, commonly used in the aerospace industry, and a series of indentation simulations are carried out using a spherical tip with different equivalent backstress levels. For Inconel 718, the third backstress component, which has the slowest evolution rate, is found to have the most significant influence on the response. However, compared to the effect of residual stress and cumulated plastic strain, the effect of backstress can be neglected.

Модуль упругости и твердость титанового сплава, сформировавшегося в условиях электронного лучевого сплавления при 3D-печати проволокой

Introduction. The development and application of additive manufacturing depends on many factors, including the printing process performance and buy-to-fly ratio. Wire-feed electron-beam additive manufacturing (EBAM) is attracting more and more attention from research teams. Moreover, the use of electron beams is the most effective and competitive for additive manufacturing of parts from alloys possessing high oxidation characteristics, e.g., titanium, stainless steels, since selective laser melting occurs in vacuum. Welding titanium wire VT6sv is the most preferable choice due to its availability and a wide range of thickness. This alloy, however, has fewer alloying elements than VT6 (Ti–6Al–4V) alloys. The high performance of wire-feed 3D printing and the VT6sv alloy composition affect the structure, phase composition, and properties of the fabricated alloy. As is known, the elastic modulus and hardness of alloys are important parameters, which can be measured rapidly also using non-destructive testing. The purpose of this work is to study the application of different approaches to measuring the elastic modulus and hardness of products obtained by wire-feed EBAM using the equipment of the Institute of Strength Physics and Materials Science SB RAS. Research methods. The structure of VT6sv titanium alloys fabricated by 3D printing and VT1-0 (Grade 2), VT6 (Ti–6Al–4V) alloys, was investigated by different methods such as metallography, ultrasonic gauging, instrumented indentation technique, macro- and micro-indentation, indentation hardness testing. Results and Discussion. Titanium alloy fabricated from VT6sv titanium wire under different thermal conditions has a typical columnar structure throughout the forging height. The structure formation determines the elastic modulus and hardness at various points of the forging. It is found that the elastic modulus is higher than that of as-delivered Ti–6Al–4V alloys, while the hardness is lower. Micro-indentation shows lower values of the elastic modulus than macro-indentation, which approach to values obtained by ultrasonic gauging and in other works. Different values of the elastic modulus at different points of the 3D printed forging indicate its sensitivity to the structure and phase composition of the material and demonstrate capabilities of measuring techniques used in this work.

Study on correlation and scaling protocol between indentation stress-strain and uniaxial stress-strain

Most important mechanical structures produce complex local material changes during the moulding and servicing process. Obtaining the specific local mechanical properties of materials and conducting field tests are problems in structural integrity evaluation. The instrumented indentation technique (IIT) is a solution to these problems. However, the core challenge with the IIT is the quantitative correlation between indentation response and uniaxial stress-strain (USS) response. In this study, we investigate the scaling relationship between indentation stress-strain (ISS) and uniaxial stress-strain (USS). A new protocol for obtaining the mechanical properties of alloy steels using ISS curves is proposed, which can directly obtain the plastic stage of the USS curves from the ISS curves. We used a finite element inversion method based on existing theories. Models with different mechanical properties (USS curves) were established using the ABAQUS software to obtain the corresponding ISS curves. We then explored the relationship between the two; the strain-scaling factor and stress-scaling function were specifically identified. Our work proposes an ISS protocol for power-law-hardening materials. Two alloy steels (SA508 and 42CrMo) were experimentally verifieds. The predicted results are approximately consistent with the practical curves and the error was within ± 10%. Because of the universality and reliability of the protocols, it is expected to provide a theoretical reference and technical approach for the development of IITs and structural integrity evaluation of important mechanical structures.

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.

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.

An indentation method for measuring welding residual stress: Estimation of stress-free indentation curve using BP neural network prediction model

The measurement of welding residual stress (WRS) is necessary to formulate the stress control strategies, in order to ensure the reliability of engineering structures during their service life. The instrumented indentation technique can detect surface residual stress nondestructively with an acceptable accuracy, making it a desirable option for in-situ applications. However, it is difficult to meet the requirement for stress-free samples, particularly in the case of welded joints with non-uniform mechanical properties. In this work, the impact of stress-free indentation curves on determining WRS is furtherly studied based on the previously proposed indentation energy difference method. The WRS in a mismatched welded plate is measured using single reference method and distributed reference method, respectively. The study suggests that using the single reference method can lead to significant errors in determining the sign and magnitude of WRS in the weld zone. A prediction model combining the continuous spherical indentation (CSI) method and Back Propagation (BP) neural network is proposed to obtain the stress-free indentation curves of local positions nondestructively. And the CSI-BP method is verified through reverse finite element analysis and experiments.

Fracture mechanism of 316L/BNi-2 brazed joints using experiment and microstructure-based model

Compact components are prone to failure at brazed joints. To ensure the reliability of brazed joints, it is vital to have a comprehensive understanding of the fracture mechanism of brazed joints which can be attributed to highly inhomogeneous microstructures and individual phase mechanical properties. This study measured the stress-strain curve of brazed joint micro-zone of 316L austenitic stainless steel with the BNi-2 filler alloy by a tensile testing machine equipped with a CCD camera. The instrumented indentation technique was used to determine the flow properties of individual phases in joints considering the size effect. Representative volume element (RVE) technology was applied to simulate the mechanical behavior of brazed joints, which was in good agreement with the tested. The fracture of brazed joints can be divided into ductile fracture and brittle fracture which includes the decohesion of the interface between the boride and the austenite matrix and the fragmentation of the boride in terms of the analysis of the morphology of cross-section and fracture surface in brazed joints. According to the stress and strain distribution in the brazing micro-zone, the plastic strain localization cause decohesion, and the stress concentration along the loading direction cause boride fragmentation.

Application of spherical macro-indentation for determination of plastic anisotropy and residual stresses using indentation geometry and inverse analysis

The simultaneous determination of mechanical properties and residual stresses using the instrumented indentation technique is more challenging when the anisotropic behaviour of a material is considered. If ignored, it may lead to inaccurate estimation of residual stresses and mechanical properties of materials. In this paper, the existence of in-plane anisotropic plasticity and the equi-biaxial residual stresses were considered in materials simultaneously. These anisotropic plastic properties and residual stresses were extracted for two materials, an aluminium alloy and a stainless steel, using an inverse analysis method and macro-spherical indentation test. The considered anisotropic materials have different yield stresses in both the longitudinal and transverse directions of the part. The inverse analysis method was based on a wide range of finite element (FE) simulations, which included a large number of models covering the properties of different steel and aluminium materials. In this method, the parameters extracted from the load-displacement (P-h) curve for indentation, along with the pile-up around the indentation area after unloading, were considered as the input parameters of the inverse analysis method. The outputs were the mechanical properties of the anisotropic material and the equi-biaxial tensile and compressive residual stresses. The proposed inverse method was based on the analysis of the artificial neural network (ANN). The effectiveness of the inverse method was examined and verified using experimental data which were found to be reliable. The method employed the P-h curve parameters and unloading morphology and was successful to determine the anisotropic plastic properties and residual stresses.

Micromechanical characterization of microwave dielectric ceramic BaO–Sm 2O 3–5TiO 2 by indentation and scratch methods

Mechanical characterization of dielectric ceramics, which have drawn extensive attention in wireless communication, remains challenging. Micromechanical properties with microstructures of dielectric ceramic BaO-Sm₂O₃-5TiO₂ (BST) were assessed by nanoindentation, microhardness, and microscratch tests under different indenters, along with X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Accurate determination of elastic modulus (i.e., 260 GPa) and indentation hardness (i.e., 16.2 GPa) of brittle BST ceramic by instrumented indentation technique requires low loads with little indentation-induced damage. Elastic modulus and indentation hardness were analyzed by different methodologies such as energy-based and displacement-based approaches, and elastic recovery of Knoop imprint. Consistent values (about 3.1 MPa·m^1/2) of fracture toughness of BST ceramic were obtained by different methods such as Vickers indenter-induced cracking method, energy-based nanoindentation approaches, and linear elastic fracture mechanics-based scratch approach with a spherical indenter, demonstrating successful applications of indentation and scratch methods in characterizing fracture properties of brittle solids. The deterioration of elastic modulus or indentation hardness with the increase in indentation load is caused by indentation-induced damage, and can be used to determine fracture toughness of material by energy-based nanoindentation approaches, and the critical void volume fraction is 0.27 (or 0.18) if elastic modulus (or indentation hardness) of the brittle BST ceramic is used. The fracture work at the critical load corresponding to the initial decrease in elastic modulus or indentation hardness can also be used to assess fracture toughness of brittle solids, opening new venues of application of nanoindentation test as a means to characterize fracture toughness of brittle ceramics.

Detection of early stage of ductile and fatigue damage presented in Inconel 718 alloy using instrumented indentation technique

Abstract Structural materials under various mechanical loads are damaged as a result of their plastic deformation and subsequent nucleation and propagation of cracks. Detection of damage in its initial phase is crucial to ensure safety and durability of construction elements. In this work, we proposed contact stiffness ( S S ) determined using the instrumented indentation technique as the damage indicator. New procedure for deformation-induced damage investigation is proposed and the indentation tests were performed in the specially designed specimens made from Inconel 718 alloy, which was previously subjected to mechanical loads. Damage parameter ( D ε {D}_{\varepsilon } ) determined on the basis of Johnson–Cook damage model was used as a reference measure of damage degree. Fracture analysis was carried out to investigate the early stage of damage development in the tested specimens. The value of contact stiffness determined from the instrumented indentation shows linear correlation with the value of damage parameter. This innovative approach was used in the presented investigation.

Evaluation of Residual Stress and Tensile Properties of Railway Axle Using Instrumented Indentation Method

Abstract This paper deals with the characterization of residual stresses of the railway axle made of EA4T steel using the instrumented indentation technique (IIT). Additionally, tensile properties were also evaluated by using IIT. Moreover, the hole drilling method was carried out to measure the residual stress. Multiple comparison tests between conventional methods and IIT were carried out. The obtained results were also discussed against the literature data. Results of the residual stress assessed by IIT and the hole drilling follow the same trend and are in acceptable agreement. The tensile data obtained by IIT were as follows: YS ≥ 420 MPa and UTS ∈ ❬650-800❭MPa which is in satisfactory agreement with the results of standardized tensile tests.

Instrumented indentation for determining stress and strain levels of pre-strained DC01 sheets

In classical mechanical testing, determining the stress and strain states of complex shape specimens turns out to be very challenging, especially in the most deformed regions. In the latter case, when not enough material is present, non-destructive testing is needed for determining the corresponding mechanical state. In this study, a novel approach, based on the local quasi-non-destructive instrumented indentation technique (IIT) coupled with the inverse analysis technique (IAT), is used to determine the stress and strain levels of pre-strained DC01 specimens using monotonic and non-monotonic loading paths. Monotonic and cyclic shear tests as well as Marciniak tests, in both plane and equi-biaxial strain states, are used to apply different pre-strain levels. For monotonic loading paths, i.e. monotonic shearing and Marcianiak tests, the applied methodology showed very satisfying results in determining the stress and strain states of the pre-strained specimens, especially for pre-strain values close to the representative indentation strain values. A maximum stress error of less than 15% was obtained in the case of the highest applied pre-strain value (29.04%). The purely isotropic Voce hardening law was adopted for determining the hardening behavior of the studied specimens in both cases: as-received and pre-strained. In the case of cyclic shear, a mixed isotropic-kinematic hardening law is to be used to determine the stress and strain states of the pre-strained specimens. Adopting a mixed isotropic-kinematic Chaboche hardening law led to satisfying results where the estimation errors of the applied pre-strain value and corresponding yield stress didn't exceed 6% and 1.3%, respectively. The obtained results show that the proposed indentation-based method can be very useful in estimating the work-hardening level and corresponding plastic deformation of pre-strained parts under various loading paths

Instrumented indentation based methods to assess fracture toughness (KIC) of self-compacting concrete: Influence of water to binder (w/b) ratio and type of concrete

The main objective of this paper is to compare the fracture toughness determined by instrumented indentation tests of a variety of self-compacting concretes (SCCs) and normal vibrated concretes (NVCs). For this purpose, five mixing compositions of self-compacting concrete (SCC) with different water/binder ratios of 0.33 to 0.41 (water/cement ratio = 0.44 to 0.56) and two mixing compositions of normal vibrated concrete (NVC) were prepared. The fracture behaviors of both (SCCs) and (NVCs) with laboratory-size specimens under the instrumented indentation test (IIT) were investigated. It was found that the fracture toughness values of the self-compacting concrete increased with the decreasing w/b ratio. The largest values of the stress intensity factor (KIC) were showed on the concretes with the lowest (w/b) ratio (w/b = 0.33, the case of SCC5). Moreover, it is confirmed that the self-compacting concretes exhibit larger fracture toughness than those of the normal vibrated concretes at the same compressive strength. The obtained results indicated that there existed a remarkable relationship between the water/binder (water/cement) ratio, fracture behavior and mechanical properties of these materials. It is shown that the instrumented indentation technique can be very useful for determination of the fracture parameters.

Characterization of the hierarchical architecture and micromechanical properties of walnut shell (Juglans regia L.)

In the present work a comprehensive characterization of the hierarchical architecture of the walnut shell (Juglans regia L.) was carried out using scanning electron microscopy (SEM), atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). Furthermore, micromechanical properties (hardness, HIT and elastic modulus, EIT) of plant tissues were evaluated at cell wall level by applying the instrumented indentation technique (IIT). The complex architecture of the material was described in terms of four hierarchical levels (HL): endocarp (H1), plant tissues (H2), plant cells (H3) and cell wall (H4). Our findings revealed that the walnut shell consists of a multilayer structure (sclerenchyma tissue, ST; interface tissue, IT; porous tissue, PT; and flattened parenchyma tissue, FPT), where differences in the microstructure and composition of plant tissues generate parallel gradients along the cross-section. The indentation tests showed a functional gradient with a sandwich-like configuration, i.e., a lightweight and soft layer (PT, HIT = 0.04 GPa) is located between two dense and hard layers (ST, HIT = 0.33 GPa; FPT, HIT = 0.28 GPa); where additionally there is an interface between ST and PT (IT, HIT = 0.16 GPa). This configuration is a successful strategy designed by nature to improve the protection of the kernel by increasing the strength of the shell. Therefore, the walnut shell can be considered as a functionally graded material (FGM), which can be used as bioinspiration for the design of new functional synthetic materials. In addition, we proposed some structure-property-function relationships in the whole walnut shell and in each of the plant tissues.

Correlation between microstructure and nanomechanical properties of 9Cr– 1Mo ferritic martensitic steel through instrumented indentation technique

Instrumented indentation technique (IIT) has been used to probe the phase-specific nanomechanical properties of heat treated 9Cr 1Mo ferritic martensitic (P9) steel. P9 steel was subjected to austenitization treatment, followed by water quenching, normalizing, furnace cooling, and subsequently tempering. Quantitative TEM analysis showed systematic changes in microstructure with variation in cooling rate in aforementioned heat treatments. Instrumented indentation tests were carried out at room temperature with a spherical indenter for evaluating hardness and elastic modulus. The yield strength of the steel from the load-displacement curves of cyclic indentation tests has been derived using neural networking method and yield parameter calculations. The properties derived from IIT using these methods were also validated with tensile test results. This work aims at correlating the local mechanical response measured by IIT with microstructural changes due to different heat treatments, which would be useful to extract mechanical properties of materials with heterogeneous microstructure.

Degradation of Dental Methacrylate-Based Composites in Simulated Clinical Immersion Media.

The selection of restorative materials with regard to the longevity and durability of a restoration is of crucial importance for daily dental practice and requires that the degradation of the material in the oral environment can be assessed. The aim of this study was to investigate the extent to which the mechanical properties of four (Esthet X, Ceram X, Filtek Supreme XT, and Filtek Supreme XT flow) resin-based composites (RBCs) alter during storage in saliva substitutes (artificial saliva) for 24 h and 28 days and in the context of simulated, more aggressive clinical conditions, including cycles exposure to de- and remineralization, alcohol, or salivary enzymes. For this purpose, flexural strength and modulus were determined in a three-point bending test (n = 20) followed by Weibull analysis, while quasi-static behavior was evaluated by instrumented indentation techniques. Degradation occurred in all RBCs and all aging protocols and was quantifiable at both macroscopic and microscopic levels. The postulated stabilizing effect on degradation through the incorporation of urethane-based co-monomers into the organic matrix or a higher filler loading is refuted. Even though modern RBCs show high clinical survival rates, biodegradation remains an issue that needs to be addressed.

Revealing the surface structural cause of scratch formation on soda-lime-silica glass

Scratch formation on glass surfaces is a ubiquitous phenomenon induced by plastic deformation, often accompanied by radial, lateral or median cracks with consequent chipping and brittle fracture caused during and after the event of dynamic abrasion instigated by shear stress by a harder material. This paper addresses the fundamental aspect of scratch formation on soda-lime-silica (SLS) glass surfaces. A constructive combination of surface-sensitive characterization tools, including field emission scanning electron microscopy (FESEM), laser scanning microscopy (LSM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and instrumented indentation technique (IIT), helped to investigate the structural cause of generation of visible scratches on SLS glass surfaces. The experimental results indicate that a silicate network possessing a mechanically weakening structural characteristic in terms of network connectivity confined to the region between 5 and 100 nm below the glass surface is likely to cause a destructive surface scratch eminently visible to the naked eye.