Indentation Damage Research Articles

Compression-after-indentation study of alumina-based oxide/oxide ceramic matrix composite with variable damage

In this study, the damage tolerance of alumina-based Oxide/Oxide ceramic matrix composite with varying extent of quasi-static indentation damage is evaluated via compression test. Pre-existing damage in the laminates are of different sizes and exist in the form of delaminations, fiber fracture, matrix cracking, and major through-thickness cracks. Digital image correlation is used to monitor the in-test displacements and strain field. When compared to undamaged compressive strength, the strength reduction in the indented specimens range from 52 % to 57 %. This shows that the compression after indentation strength is not significantly affected by variations in the extent of indentation damage. Digital image correlation results showed out-of-plane deformation originating from the indented region that grew stably with increasing load to a critical phase, beyond which they became significantly large. This resulted in the sudden catastrophic failure of the laminate, apparently caused by delamination buckling. This was confirmed by post-test X-ray computed tomography micrographs.

Monitoring of Indentation Damage Propagation and Residual Strength Estimation in Iron Filler-Loaded Glass/Epoxy Composites using Acoustic Emission

Monitoring of Indentation Damage Propagation and Residual Strength Estimation in Iron Filler-Loaded Glass/Epoxy Composites using Acoustic Emission

Detection of indentation damage in carbon fiber/epoxy composites via EIT during the application of bending loads

Electrical impedance tomography (EIT) is a method of spatially mapping the conductivity distribution of a domain and has been studied as a potential embedded sensing or nondestructive evaluation (NDE) tool. An often touted advantage of EIT is that it can be used in-situ; that is, because the method only requires the application of unobtrusive electrodes, it can conceivably be used while the component or structure is in operation. This material-as-the-sensor philosophy strongly aligns with key components of the NDE 4.0 vision such as the realization of intelligent cyber–physical systems (CPS) and digital twins. To date, however, the claim of in-situ sensing via EIT has not been significantly substantiated. This is problematic because operational loads induce strains that often change the conductivity of the material. Establishing that EIT can detect damage-induced conductivity changes through the presence of unrelated strain-induced conductivity changes is therefore important. To that end, we herein study the application of EIT for detecting indentation damage in a carbon fiber/epoxy composite as the composite is loaded in a four-point bend. It was found that the bending load changes the contact impedance of the electrodes, which resulted in poor EIT images when solving the EIT inverse problem with the ℓ2-norm on the error term. Using the ℓ1-norm on the error term, solved via the primal–dual interior point method (PDIPM), significantly improved image quality. Image quality was even further improved through the use of a mixed prior for regularization, and EIT images were compared to thermography with good agreement. These results show that EIT can indeed detect damage through the presence of an applied load, but care must be taken to account for factors such as outlier data arising from electrode degradation and changing contact impedance. Use of the ℓ1-norm on the error term is therefore highly recommended for in-situ imaging via EIT.

The Relationship Between the Extent of Indentation and Impact Damage in Carbon-Fibre Reinforced-Plastic Composites after a Low-Velocity Impact

AbstractThe present paper investigates the low-velocity impact behaviour of carbon-fibre reinforced-plastic (CFRP) composite panels and the damage incurred when they are subjected to a single impact. The relationship between the depth of permanent surface indentation that results and the associated area of interlaminar delamination damage is investigated for two different thicknesses of composite panels. In particular, the delamination damage area increases with impact energy for both thicknesses of composite panel that were studied. Likewise, the indentation depth also increases with increasing impact energy, again for both thicknesses of CFRP panels. It is shown that the indentation depth, at the centre of the indentation, may be used to provide an indication of the extent of delamination damage within the CFRP panel after impact. Indeed, from plotting the indentation depth versus the interlaminar delamination normalised by the thickness of the panel area there is shown to be a unique ‘master’ relationship, with a positive intercept indicating that the indentation damage seems to result before delamination damage initiates. Thus, for both thicknesses of CFRP panels, it is suggested that the indentation process is a precursor to interlaminar delamination damage.

Quasi-static indentation responses of FMLs/2.5D woven carbon-fiber honeycomb sandwich structures under different structural parameters

Here, a new type of sandwich structure made of fiber metal laminates (FMLs) as facesheet and 2.5D woven carbon-fiber (CFRP) honeycomb as core was developed. The FMLs/CFRP honeycomb sandwich structures were subjected to quasi-static indentation tests to investigate the mechanical response with the variation of panel structure, honeycomb cell element size, honeycomb core wall thickness, and honeycomb core height. In addition to experiments, a finite element method (FEM) model was also created in ABAQUS/Explicit to analyze the damage mechanisms and failure modes of honeycomb sandwich structures under quasi-static indentation. Both the experimental and FEM simulation results revealed that the honeycomb sandwich structure underwent two different failure modes under quasi-static loading: localized damage dominated by indentation and global damage due to overall bending deformation. The combination of panel strength and honeycomb core strength determined the failure mode of the sandwich structure. Damage analysis of the honeycomb core showed that it mainly underwent fiber compression damage and matrix compression damage under quasi-static indentation. This study provides guidance to optimize the design of honeycomb sandwich structures.

Retracted: Effect of the Reinforcement Phase on Indentation Resistance and Damage Characterization of Glass/Epoxy Laminates Using Acoustic Emission Monitoring

Retracted: Effect of the Reinforcement Phase on Indentation Resistance and Damage Characterization of Glass/Epoxy Laminates Using Acoustic Emission Monitoring

The study on the influence of different damage introduction methods on the damage characteristics of aircraft composites

Composite materials have advantages incomparable to traditional metal materials. However, they are more sensitive to impact damage and their mechanical properties decrease significantly after impact damage. Therefore, it is of great significance to study the energy absorption, mechanical response and damage mechanism of materials in different ways. To study the influence of different punch diameter sizes on the material damage characteristics, three kinds of punch diameters of 12.7 mm, 16 mm and 25.4 mm are selected to carry out the quasistatic indentation test and drop hammer impact damage test on the test pieces respectively. The material damage caused by different punch sizes under two damage introduction methods is analyzed. Damage introduction was carried out on the test piece with the same layering through two methods: quasi-static indentation and drop hammer impact. The damage depth, damage area and residual strength were compared after damage introduction. The difference between quasistatic indentation and drop hammer impact damage introduction was verified by comparing the damage characteristics to each other. The results show that with the increase of punch diameter size, the damage area decreases and the residual strength of the material increases. In addition, the test results of different punch diameter sizes under the two damage introduction methods have the same change trend, which proves that the impact of punch size on the material damage characteristics has no obvious relationship with the damage introduction method. Quasi-static indentation and drop hammer impact damage have no significant difference in the residual strength of materials after damage, which verifies the equivalence of static indentation and damage introduction.

Investigation of the bending and quasi‐static indentation properties of three‐dimensional (3D) textile‐reinforced composites

AbstractThe three‐dimensional (3D) textiles, which are identified as advanced fabric systems, have been under development for decades and are demanded for number of structural or semi‐structural applications. They can be obtained by several production methods. These methods impart distinct, specific properties to the 3D textiles and their composites. However, the discrepancies in the production methods and their effects on the dry structure and composite mechanics need to be elucidated. In this study, the compressibility and bending properties of 3D woven, 3D multiaxis warp knitted, and 3D stitched fabrics were determined. Afterward, their composites were produced and tested under three‐point bending and quasi‐static indentation loads. Therefore, the load bearing capacity of 3D textiles was investigated from the dry structure to the composite. According to the purpose of the end‐uses, significant differences were obtained in their mechanical behaviors. When the indentation properties and damage mechanism are taken into consideration, the 3D woven composite shows the best performance among all composites.Highlights Quadriaxial oriented low crimp carbon yarns gain the best quasi‐static indentation resistance to composites. The stitching process prevents damage progress in composites and restrains smaller areas. Binding warp yarn enables the composite distribute indentation energy more evenly.

The research on the influence mechanism of internal deformation for the performance of Bi-2212

Cable-in-conduit conductor (CICC), one of the most promising conductors for manufacturing magnets in magnetic confinement fusion devices, has attracted lots of attention. In the production of CICC, porosity control is necessary for its stability. The porosity control is usually realized by the diameter-reducing process, which would also lead to indentation damages to the elements of CICC-superconducting wires. In this article, systematic research of indentation damages was carried out on the next generation of high-temperature superconducting materials–Bi-2212 wires. The results indicate that the current carrying capacity of the indentation-damaged wire would first keep steady and then show exponential decline with the increase of indentation depth. The wires subjected to pre-overpressure (pre-OP) treatment exhibit slightly improved resistance against indentation damage at shallow indentation depths. However, their critical current (I c) deteriorates more rapidly at greater indentation depths when compared to wires that have not undergone the per-OP process. The following structural characterization analyzed the reasons for the property changes with the help of scanning electron microscopy, energy dispersive x-ray spectroscopy, computed tomography, and hardness tester. Misalignment between the Bi-2212 grains and shaped filaments was found in the indentation-damaged wires, with which the degradation in I c of the wires and the differences in properties of the two kinds of wires were further discussed.

On understanding the mechanical properties and damage behavior of Cf/SiC composites by indentation method

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have the advantages of high temperature resistance, wear resistance, low density, high hardness as well as specific strength. They have been applied extensively in hot-end components of aerospace and braking systems of trains. Nevertheless, grappling with the anisotropy, non-homogeneity, and weak interlayer bonding of Cf/SiC composites presents a major challenge for achieving efficient and low-damage processing. This paper is primarily intended to investigate comprehensively the mechanical properties and damage behavior of Cf/SiC composites by nanoindentation and Vickers indentation tests. The behaviors of indentation damage on the longitudinal section of fiber (LSF), the cross-section of fiber (CSF) and matrix under different loads and the deflection mechanism of matrix crack were analyzed. The findings reveal a pronounced anisotropy between the radial and axial orientations of the fiber, and plastic deformation exists in the matrix. Furthermore, the matrix has the largest hardness and elastic modulus, while the LSF displays the lowest values among the composites. The main forms of indentation damage on the LSF are fiber crack, fiber peel off, fiber cocked up and squamous crack. The main manifestations of indentation damage on CSF are fiber crushing and fiber debonding, with the total surface damage area being comparatively limited. The fiber orientation and interface are influential factors in the crack propagation path of matrix. Notably, the fibers effectively inhibit the crack propagation of the matrix. This investigation provides valuable theoretical guidance for the formation mechanism and suppression strategy of machining damage in Cf/SiC composites.

Damage and energy absorption behaviour of composite laminates under impact loading using different impactor geometries

The present paper compares the damage and energy absorption behaviour of composites subjected to low-velocity impact using different frontal geometries for the impactor, with the composites possessing a layup of [02/902]2s. In this study, the rigid impactors with either round-nosed or flat-ended frontal geometry are employed to perform drop-weight tests at various impact energies ranging from 10 to 30 J. The measured loading response and energy absorption are analysed and compared. Additionally, the types and extent of impact-induced damage in the composite specimens are assessed via ultrasonic C-scan, optical microscopy (OM) and scanning electron microscopy (SEM) studies. It is shown that the impact energy threshold for damage initiation is greater than 20 J when using the flat-ended impactor but is less than 10 J when using the round-nosed impactor. In both cases, delamination initiates between the plies in the composite laminate. However, for the flat-ended impactor, the damage behaviour of the fibres exhibits kinking fracture, which differs from the pull-out fibre-fracture caused by the round-nosed impactor. These differences in behaviour are attributed to impactor/composite contact geometry effects which leads to different extents of indentation damage, which in turn directly affects the degree of delamination and fibre damage in the composite.

Transverse indentation response and residual axial compressive characteristics of metal-composites hybrid tubes by deep learning-based acoustic emission and micro-CT

This work investigated transverse indentation response and residual axial compressive characteristics of Al-CFRP hybrid tubes with different configurations. The failure mechanism and damage evolution of the hybrid tubes under transverse indentation load were investigated by acoustic emission and micro-CT technologies. To gain an insight into the damage mechanism of CFRP composites, a structural health monitoring system based on image-based acoustic emission waveform and deep learning was developed. It showed that acoustic emission response of internal damage was corresponding to the damage visualization analyses of micro-CT. The proposed damage classification model provided a reliable path for extreme damage mode recognition and damage monitoring of composite structure. Under transverse indentation load, delamination and fiber breakage were the main failure modes of H-I hybrid tube (i.e. the CFRP tube internally filled with aluminum tube). For H-II hybrid tube (i.e. the aluminum tube internally filled with CFRP tube), the interfacial delamination of Al/CFRP tended to aggravate its failure behavior. The quasi-static axial compressive properties of intact and pre-indentation tubes were further compared to evaluate the effects of indentation damage on residual crashworthiness. The transverse indentation resulted in the change of the failure mode. Compared with H-I hybrid tube, H-II hybrid tube showed more significant property degradation.

Modelling the effects of patch-plug configuration on the impact performance of patch-repaired composite laminates

The patch-plug configuration has been widely used to repair composite structures and restore the structural integrity of damaged composites. In the present research, single-sided CFRP patch-repaired panels, with different patch-plug configurations, are prepared. This is where a circular-shaped damaged area has been removed and a CFRP patch has been adhesively-bonded onto the panel. In some cases, a CFRP plug is inserted into the hole, caused by removal of the damaged area, before the patch is applied. Such patch-repaired panels, and the pristine CFRP panel, are subjected to a low-velocity impact at an energy of 7.5 J. These impacted pristine and repaired panels are then examined using ultrasonic C-scan and optical microscopy to inspect the impact-associated permanent indentation, interlaminar and intralaminar damage. A finite element analysis (FEA) model, which significantly extends a previously validated elastic-plastic (E-P) numerical damage model, has been developed to predict the impact behaviour of the pristine CFRP panel and the various designs of patch-repaired CFRP panels. The comparison between the experimental and numerical results for all the studied cases shows the maximum deviations for the loading response and the damage area are 12% and 15%, respectively. The good agreement between the experimentally-measured impact properties and those predicted using the numerical model demonstrates that the model is a useful design tool.

Quasi-static indentation damage mechanics of PU foam core reinforced with fly ash particulate

The fly ash (FA) particulates are used in this study to reinforce the polyurethane foam (PUF) core. The FA particles inclusion improves the mechanical performance of the PUF core under compression by increasing its modulus of elasticity. Low-velocity impacts have damage dynamics that are pretty similar to quasi-static indentation. Consequently, the indentation resistance capability of the PUF core is investigated for three types of indenter nose tips with varied FA wt. Percentages (flat-circular, hemispherical, and conical). The results reveal that the reinforced foam core’s resistance varies with reinforcement percentage under indentation. However, FA reinforcement to PUF does not necessarily improve indentation resistance. The damage mechanism of the PUF core under indentation has been evaluated for each type of indenter. The interaction of crushing, shear, and tear of the damaged surface with the change in indenter nose tip has been explained with 0–20% variation of FA particles. Scanning electron microscope (SEM) images are taken for the analysis of the damaged PUF core cross-section at the indented location. Earlier mechanical findings of the scatter in deformation behavior with the indenter nose tip geometry are substantiated by the SEM studies.

Experimental Investigation on the Effect of Stacking Sequence on Damage Resistance and Post-indentation Performance of Glass/Epoxy Laminates Under Different Loading Planes Using Acoustic Emission Monitoring

This research work focuses on the experimental investigation of indentation damage resistance and post-indented performance of different stacking sequence of glass/epoxy laminates using mechanical and acoustic responses. The laminates with stacking sequence, namely [0]12, [0/90]6S, [+45/-45]6S and [0/+45/-45/90]3S were subjected to normal and inclined indentation with acoustic emission monitoring. Quasi-static indentation (QSI) test was conducted on the center of the laminates using a hemispherical steel indenter with 12.7 mm diameter. The residual strength of the laminates was computed by conducting flexural after indentation test. Mechanical responses such as peak force, residual dent, linear stiffness and absorbed energy were employed to assess induced damages. The results reveal that the quasi-isotropic (QIS) laminates having better indentation damage resistance under 0o and 10o loading planes, whereas the angle-ply (AP) laminates performed well at 20o. Moreover, the normalised cumulative counts, energy rate, peak frequency, AE hits and sentry function were used to evaluate the damage initiation and propagation. Further, AE results show that the shear induced damage has been reduced in AP as compared with QIS laminates under 20o indentation plane. Finally, this study concluded that the QIS and AP laminates exhibited better indentation resistance under 0o and 10o, and 20o loading planes respectively.

Self-healing of indentation damage in Ti2AlC MAX phase ceramics

Although the crack-healing capacity of Ti2AlC ceramics has been sufficiently studied, the ability of Ti2AlC to self-heal large-scale damage, such as foreign object damage (FOD), remains unknown. This paper investigates the self-healing ability of Ti2AlC ceramics with large-scale damage (∼1000 μm in diameter). Extensive healing was observed even in the plastic damage and radial cracks. The damage and cracks caused by indentations made using a tungsten carbide sphere were filled and covered with newly formed oxides, such as titanium oxide and alumina, by the oxidation of Ti2AlC after heat treatment in air at 1000 °C. The strength, hardness, toughness, and elastic modulus of the Ti2AlC samples were measured before and after healing. The results show that the mechanical properties of Ti2AlC were similar or even slightly higher after the damage had been healed. Thus, Ti2AlC ceramics are attractive healing agents for foreign object damage in high-temperature applications.

Experimental investigation on mechanical behavior of 3D integrated woven spacer composites under quasi-static indentation and compression after indentation: Effect of indenter shapes

This paper presents an experimental study on the mechanical response of 3D integrated woven spacer carbon fiber composites under quasi-static indentation (QSI) and the failure behavior under compression after indentation (CAI). The test specimens are divided into weft direction ones (X-type) and warp direction ones (Y-type). The quasi-static indentation process is conducted using four types of indenters: the hemispherical indenter, the flat indenter, the conical indenter, and the pyramid indenter. A C-scan ultrasonic imaging system and a digital microscope are used to evaluate the damage visibility and penetration resistance of 3D integrated woven spacer composites during the QSI test. The digital image correlation (DIC) is used to perform the CAI analysis. The results indicate that the flat indenter has the largest indentation damage area (395 mm2 for X-type specimens, 398 mm2 for Y-type specimens), and the average indentation damage area caused by the four indenters is less than twice of the maximum cross-sectional area of each indenter. The maximum absorbed energy of two types of 3D integrated woven spacer composites is very similar in QSI tests under the same indenter. It is found that the residual strength of the X-type specimen decreases by 51.7% and that of the Y-type specimen decreases by 35.8% after the flat indenter penetrates the specimen.

Study of self-healing capability of composite material with phase changing paraffin wax and graphene

The main aim of this research work was to conduct an experimental study of self-healing capability of the composite material by using phase changing material. The phase changing material utilized was “paraffin wax” for healing the material made up of the carbon fiber and epoxy. Three combinations of carbon fiber reinforced epoxy with phase changing materials were prepared i.e., plain carbon fiber epoxy without any phase changing material, carbon fiber epoxy with paraffin wax and carbon fiber epoxy with paraffin wax nano graphene. The fabrication of the carbon fiber composite material inside the capsulation has been done by keeping the 3d model. To identify the structural properties of the material some tests were done i.e., the tensile test and flexural test at normal room temperature and pressure. Damage was produced at the center of each specimen with the help of a Barcol hardness test machine. The Specimens were tested without indentation damage, immediately after indentation damage and after 48 hours of producing damage.

Fracture behaviour of microwave-heated granite under indentation: Experimental and numerical investigation

Microwave-assisted rock breakage is a promising solution for drilling and crushing hard-rock formations. The fundamental mechanical and thermophysical properties of microwave-treated granite were obtained, and the factors affecting the fracture behaviour under indentation were investigated using experimental and numerical methods. The results show that the uniaxial compressive strength, tensile strength, brittleness index, thermal conductivity, and thermal diffusivity of microwave-heated granite are negatively correlated with temperature, whereas the specific heat capacity of treated granite is positively correlated with temperature. The fracture process of microwave-heated granite under indentation can be divided into three stages: elastic deformation, fluctuating penetration, and post-peak. The indentation damage zone near the indenter consists mainly of tensile cracks. Meanwhile, regression analysis shows that the peak indentation force, penetration depth, and consumed energy of the microwave-heated sample are linearly correlated with the brittleness index. In addition, microwave treatment can weaken the inhibitory effect of a high confining stress on the damage zone and is conducive to reducing the indentation force and penetration depth of rock fragmentation. The specific energy is more sensitive to temperature under high confining stress conditions, and the relationship between the specific energy, temperature, and confining stress can be described by a 2D poly function.

Indentation and abrasion in glass products: Lessons learned and yet to be learned

AbstractGlass has provided many life‐changing products over the past millennia to improve the quality of human living. In this “International Year of Glass 2022” paper, we review the applied science and technology of indentation and abrasion damage in glass, highlighting its practical importance for commercial products. We briefly review what has already been learned from the several hundred high‐quality publications on this topic. Though glass products have hard surfaces, indents, and abrasion arise upon contact with other glass and materials during manufacturing, transportation, subsequent user handling, and vandalism. The mechanical response of glass to impact is elastic–plastic, which generates several modes of cracks upon indentation. The science of deformations and stress generation is discussed in terms of theories by Hertz, Boussinesq, and Yoffe. The hydrostatic and shear yield strengths of the glass are suggested to be the more important parameters that govern hardness. Commercial opportunities for repairing or reducing damage from indents, particularly using diamond‐like carbon coatings, are briefly discussed. Finally, challenges that lie ahead for a sustainable future of the Earth with increased commercial utility of beautiful glass products from increased damage resistance are outlined with emphasis on network topological principles and hard coatings.