Indentation Damage Research Articles

A toughening and strengthening technique of hybrid composites with non-woven tissue

The hybrid composite materials with non-woven tissue (NWT) are developed to improve the mechanical properties of conventional fiber reinforced plastic (FRP) composite materials. From the previous works we can see that the interleaving of the non-woven carbon tissue (NWCT) layer largely increases the Mode II interlaminar fracture toughness, while it does not significantly change the Mode I interlaminar fracture toughness. In addition, compared with conventional carbon fiber reinforced plastic (CFRP) composites, the hybrid composites with NWCT have high reliability and high strengthening effect for mechanical properties under tensile static and fatigue loadings. The impact damage mechanism of low-energy range for the hybrid composites with NWCT was also investigated under quasi-static indentation loading. The mechanism of the NWCT interleaving's effect was clarified based on the observation of damage. As the CFRP and hybrid composites with the indentation damage failed by shearing under the compressive fatigue loading, it was effective that the propagation of shear cracks in the hybrid composites were prevented by NWCT located between the CFRP layers. It was found that the Mode II interlaminar fracture is predominant in the delamination by the indentation loads. The purposes of this study of hybrid prepreg with NWT are (i) to increase the interlaminar properties (the fracture toughness and strength), (ii) to improve the mechanical properties (tensile strength and stiffness) and reliability, while maintaining a low cost, (iii) to propose an interlayer hybrid concept with NWT as a “Toughening and Strengthening Technique”. Namely, this concept is designed to introduce a tough and strong interlayer at the positions of typical premature composite failure. A production technique to decrease voids in NWT is exhibited by comparing two types of hybrid laminates. The mechanical properties of the hybrid composites were measured, and then the validity of the present technique was confirmed.

Deformation mechanisms of TiN multilayer coatings alternated by ductile or stiff interlayers

TiN multilayers that alternate with either titanium (ductile) or nanocomposite TiSiN (hard) interlayers were surface coated by filtered arc deposition onto stainless steel substrates. Hardness and deformation mechanisms of these multilayer coatings were investigated using depth-sensing indentation in comparison with traditional monolithic TiN coatings. A dual ion/electron beam microscope was used to analyse subsurface indentation damage. It was found that microstructural layering and the presence of interlayers in TiN multilayers jointly provided resistance to deformation by intercolumnar shear sliding, observed more evidently in the monolithic TiN coatings. This resulted in an increase in hardness, which also increased with both the number of layers and the presence of interlayers. Calculations based upon a mechanistic-based model revealed that the resistance by interlayers played a more important role than an increase in intergranular shear area due to the layered structure in resisting deformation. Compared with the titanium interlayer, the use of a hard nanocomposite interlayer increased the resistance to deformation; however, cracking occurred within both the TiN layers and the nanocomposite interlayers.

Association of Third Body Embedment with Rim Damage in Retrieved Acetabular Liners

Third-body effects are a major cause of the substantial variability of wear in total hip replacements. One potential mechanism by which third-body debris can access wear-critical central regions of closely conforming metal-on-polyethylene bearing couples is by fluid convection during incidents of subluxation accompanying neck-on-liner impingement. To provide evidence for this premise, we determined the association of severity of liner rim indentation damage (indicative of impingement frequency/vigor) and the presence of embedded third-body debris in 194 implants retrieved at revision. Rim damage was graded using the five-point Hospital for Special Surgery scale. Particle embedment was assessed both manually and by means of an image analysis computer program that detected the composition, size, and location of each particle. Sixty-eight percent of the cups showed rim indentation damage. We found an association between severity of rim damage and presence of embedded debris. There was substantial nonuniformity of the spatial distribution of the embedded debris, with the predominance of embedded debris at intermediate latitudes. These findings support the premise of convection of debris-laden joint fluid during lever-out subluxation as a mechanism for wear-consequential third-body particles to gain access to highly loaded regions of the bearing surface, thus potentiating increased wear.

“Segment-wise model” for theoretical simulation of barely visible indentation damage in composite sandwich beams: Part I – Formulation

Abstract When localized transverse loading is applied to a sandwich structure, the facesheet locally deflects and the core crushes. A residual dent induced by the core crushing significantly degrades the mechanical properties of the sandwich structure. The authors establish a “segment-wise model” for theoretical simulation of static indentation loading and unloading responses in honeycomb sandwich beams with composite facesheets. The model was developed by modifying a theory developed for an Euler beam on an elastic Winkler foundation. The honeycomb sandwich beam was divided into many segments based on the periodic shape of the honeycomb, and the complicated through-thickness behavior of the core was integrated into each segment. First, compressive stress–strain curves were measured during the crushing–stretching process of the core using uniaxial flatwise compressive-tensile tests. Using the through-thickness properties approximated as a set of lines, the 2D indentation response in an aluminum honeycomb sandwich beam was then theoretically simulated. The obtained load–displacement curve was validated by an experiment, confirming the superiority of the new model over a conventional elastic-perfectly plastic model. Further experiment verification and a discussion are presented in Part II of this study.

“Segment-wise model” for theoretical simulation of barely visible indentation damage in composite sandwich beams: Part II – Experimental verification and discussion

Abstract When localized transverse loading is applied to a sandwich structure, the facesheet locally deflects and the core crushes. A residual dent induced by the core crushing significantly degrades the mechanical properties of the sandwich structure. In a previous paper, the authors established a “segment-wise model” for theoretical simulation of barely visible indentation damage in honeycomb sandwich beams with composite facesheets. Honeycomb sandwich beam was divided into many segments based on the periodic shape of the honeycomb and complicated through-thickness characteristics of the core were integrated into each segment. In this paper, the new model is validated by experiments using specimens with different types of honeycomb cores. In addition, the damage growth mechanism under indentation load was clarified from the viewpoint of the reaction force from the core to the facesheet. The applicability of the model to other types of core materials is also discussed.

Quasi-Plastic Deformation of WC-Co Composites Loaded with a Spherical Indenter

The quasi-plastic deformation behavior of cemented tungsten carbide (WC-Co) materials was studied using Hertzian indentation techniques. The indentation stress-strain curves of three WC-10 wt pct Co alloys with different hardness values demonstrate that WC-Co alloys exhibit “quasi-plasticity” behavior under indentation load and the increase of indentation stress vs indentation strain bears similarity to “strain hardening” in ductile metals. The analysis of the subsurface indentation damage shows that the mechanisms of the quasi-plastic deformation of WC-Co material are the formation of microcracks. Microcracks were found at heavily damaged areas in all three alloys, and the number of microcracks was higher for the sample with the higher apparent quasi-plasticity. The threshold stress values for the onset of quasi-plastic deformation and formation of ring cracks were determined and used to evaluate the brittleness index of these materials. The correlation of the brittleness index with hardness values gives insight with regard to the brittle or quasi-plastic responses of WC-Co materials.

Indentation on YSZ thermal barrier coating layers deposited by electron beam PVD

We have deposited an yttria-stabilized zirconia (YSZ) layer consisting of microsized grains on an alumina substrate using electron beam physical vapour deposition (EBPVD). The effects of Y2O3 concentration and the coating microstructures of YSZ on indentation damage are investigated. Different coating microstructures are prepared by varying the substrate temperature during deposition. Hertzian and nanoindentation are used to characterize the damage responses of the YSZ thermal barrier-coated alumina layered systems. The damage and failure behaviours have been investigated in relation to the effects of microstructures formed at various substrate temperatures as well as indentation loads from indentation tests. Elastic modulus, hardness, and stress–strain behaviours are characterized by results of the indentation tests. With increasing substrate temperature during the EBPVD process, the overall grain sizes became coarser with a smaller fraction of weak interfaces between the columns, and became more faceted. This change in microstructure ultimately influences the indentation behaviour. The results according to the use of smaller and larger scaled indenters during Hertzian/nanoindentations were also analyzed.

Effects of implant design parameters on fluid ingress during THA impingement/subluxation

INTRODUCTION Aseptic loosening from polyethylene wear debris remains the leading cause of failure for metal-on-polyethylene total hip implants. Wear is exacerbated by 3 body debris, leading to femoral head roughening, but the manner by which 3 bodies gain access to the very closely congruent bearing surface is unknown. One possibility is that ingress of 3 body debris is facilitated by fluid transport during subluxation. The high prevalence of indentation damage found on the rim of retrieved acetabular liners from femoral neck impingement (Shon W Yong et al., 2005) suggests that subluxation events are frequent. To study subluxation-induced particle ingress, a computational fluid dynamics (CFD) model has been developed to quantify the ensuing fluid motions. The focus of the present study was on the effects of variations in implant design parameters on fluid velocity.

Damage tolerance assessment of composite sandwich panels with localised damage

The work described herein is part of a larger context in which the effect of damage in sandwich composite structures for marine applications has been investigated. The overall aim of this effort has been twofold: to develop and verify existing damage assessment models to be used to assess the effect of damage on marine sandwich structures, and to develop a damage assessment scheme to be used by shipyards, ship owners and navies. More specifically, this paper presents a sub-set of this overall effort looking at impact and indentation damage and its effect on the load carrying capacity of state-of-the-art carbon composite sandwich panels for marine applications. Damage types are modelled based on physical observations from tests. Testing is then performed on different scales in order to validate the models. The overall aim is to use such models to produce information that can be used for decision-making at two levels. The first is to evaluate the damage tolerance of ship structural components and thus to calculate the size and extent of damage that a component can have without risk of growth or failure at ultimate local or global loads on the entire ship. The second is to have information at hand to decide if, and when, a structural part needs to be repaired if damage has been detected. A scheme developed for this purpose is presented herein. Finally the paper will briefly describe a common framework for damage assessment in composite sandwich structures. Herein, models are used in conjunction with the design specifics and functional requirements to create a scheme for repair decisions.

In-Vitro Hertzian Fatigue Properties of Glass Infiltrated Ceramic Composites for Dental Crowns

Hertzian cyclic fatigue properties of the glass-infiltrated alumina and spinel were evaluated using a WC sphere of radius of 3.18 mm in exact in vitro environment (artificial saliva) at contact loads from 200 N to 1000 N to investigate indentation damage and strength degradation. At 200 N, no strength degradation was observed up to 106 contact cycles. As the load increased from 200 N to 1000 N, the reduction in strength was found when the transition from ring to radial cracking occurred. The degree of strength degradation after critical cycling was more pronounced probably owing to the chemical reaction of the artificial saliva with the glass phase along the radial cracks introduced during the large numbers of contact cycles.

Atomistic mechanisms of amorphization during nanoindentation of SiC: A molecular dynamics study

Atomistic mechanisms underlying the nanoindentation-induced amorphization in SiC crystal has been studied by molecular dynamics simulations on parallel computers. The calculated load-displacement curve consists of a series of load drops, corresponding to plastic deformation, in addition to a shoulder at a smaller displacement, which is fully reversible upon unloading. The peaks in the load-displacement curve are shown to reflect the crystalline structure and dislocation activities under the surface. The evolution of indentation damage and defect accumulation are also discussed in terms of bond angles, local pressure, local shear stress, and spatial rearrangements of atoms. These structural analyses reveal that the defect-stimulated growth and coalescence of dislocation loops are responsible for the crystalline-to-amorphous transition. The shortest-path-ring analysis is effectively employed to characterize nanoindentation-induced structural transformations and dislocation activities.

Numerical Study of Creep Damage Behavior of Thin Film/Substrate Systems under Indentation

A numerical study has been performed on the creep damage development of the thin film/substrate systems by the Kachanov-Rabothov damage law. The emphasis was to study the influence of the modulus ratio of the substrate to the thin film, the size of the indenter and the indentation stress. Results show that two obvious damage zones are found ahead of the indenter. One is at the edge of the indenter, the other is at the interface ahead of the indenter edge. The influence of the modulus ratio of the substrate to the thin film on the indentation damage is not obvious before a certain creep time, and later, the greater modulus ratio of the substrate to the thin film has the smaller damage rate. And the indentation depth rate and the damage rate are also affected by the size of the indenter and indentation stress.

Fatigue sensitivity of Y‐TZP to microscale sharp‐contact flaws

The strength degrading effects of sharp-contact damage are examined for Y-TZP ceramic plates bonded to a plastic substrate. Contacts are made with Vickers and Berkovich diamond indenters at low loads (0.1 N to 100 N) in the ceramic lower surfaces prior to bonding to the substrates. The indentations remain in the subthreshold region, that is, without visible corner radial cracks, over the lower region (< 10 N) of the load range. A concentrated load is then applied sinusoidally to the ceramic upper surface, with the loading axis centered on the subsurface indentation flaw, thereby subjecting the flaw to cyclic tension. Relative to polished surfaces, the indentations diminish the single-cycle strength by an amount that increases with increasing indentation load. The critical number of cycles required to cause failure from the indentation flaws is then measured at specified maximum lower surface tensile stresses. At each indentation load, the strength of the ceramic plates diminishes with increased cycling. The scale of degradation is compared with that from previous studies on Y-TZP surfaces containing larger-scale surface damage: sandblast damage, as used in dental crown preparation; and blunt-contact trauma from a spherical indenter at 3000 N. These other damage modes are shown to be equivalent in their strength-degrading capacity to diamond pyramid indentations in the microscale load range 0.1 N to 1 N, attesting to the highly deleterious nature of sharp particulate contacts. The mechanism of fatigue is considered in terms of microcrack evolution within the indentation damage zone.

Subsurface Indentation Damage and Mechanical Characterization of α‐Sialon Ceramics

Two hot‐pressed sintered α‐sialon samples of differing microstructures, but identical chemical composition, were evaluated first, in terms of indentation hardness and modulus, by depth‐sensing indentation (DSI) tests on planes parallel and normal to the hot‐pressed surface. The surface and subsurface cracks created under the DSI tests have also been investigated in relation to the effect of microstructure. Subsequently, Vickers indentation tests were conducted to explore the deformation and fracture characteristics in the two samples. The effect of microstructure and grain orientation on the development of different types of cracks, in particular subsurface cracks, was revealed and analyzed. Additionally, it suggested that the focused ion beam (FIB) miller is a preferred tool, in comparison to the conventional cross‐sectioning techniques, for examining subsurface crack formation and structural characteristics.

Residual Compressive Failure Characteristics of Hybrid Composites with Nonwoven Carbon Tissue after Indentation Damage

The purpose of this study is to investigate the relationship between the low-energy impact damages under static indentation loadings and the residual compressive static and fatigue strengths after damage in hybrid composites with nonwoven carbon tissue (NWCT). The hybrid laminates are made by interleaving the NWCT layer between the CFRP layer interfaces. The indentation damages were discussed by investigating the delamination areas and the indentation energies of four kinds of angle-ply laminates ([455/ 455/455] and [453/ 453/453/ 453/453] CFRP laminates, and [455// 455//455] and [453// 453//453// 453//453] hybrid laminates; the symbol “//” means that the NWCT layer is located at an interface between the CFRP layers. The delamination areas of the hybrid laminates were reduced to about half of the CFRP’s by the indentation loading (Lee, S.H., Aono, Y., Noguchi, H. and Cheong, S.K. (2003). Damage Mechanism of Hybrid Composites with Non-Woven Carbon Tissue Subjected to Quasi-Static Indentation Loads, Journal of Composite Materials, 37: 333–349). After the indentation damage, compressive static and fatigue tests are carried out using an anti-buckling guide for the angle-ply laminates. The failure modes of the angle-ply CFRP and hybrid specimens are caused by global buckling under the compressive static loading. However, the failure modes of the angle-ply CFRP and hybrid specimens at Nf &lt;10 6cycles are caused by shearing the damaged part under the compression–compression fatigue loading. Compared with CFRP laminates, compressive fatigue lives of the hybrid laminates were significantly extended in all the stress ranges. The NWCT interleaving effect is examined based on the observations of the damage in the hybrid specimens after the indentation damage. Also, the compressive static and fatigue failure processes are discussed from the observation of the fracture surfaces of damaged parts and failed appearance of specimens when subjected to the compressive loadings after the indentation damage.

Indentation study of foam core sandwich composite panels

Due to their high stiffness and strength to weight ratios, composite sandwich structures have proven their usefulness in a large number of applications in various technical fields, especially in aeronautics, automotive and civil engineering. One of the main drawbacks of sandwich structures is the loss of load caring capacity due to indentation damages. The purpose of the present work is the evaluation of the response of foam core sandwich composite panels to indentation. Experimental tests were performed by a spherical indentor using an Instron universal test machine under displacement control at cross-head speed of 2 mm/min. The test specimens were manufactured by using rigid foam Rohacell WF51 with a thickness of 50 mm and glass-fiber reinforced composite face sheets with a thickness of 2.4 mm. The load–displacement response for both loading and unloading steps was recorded during the testing. The diameter of the damaged zone on the face sheet was measured after the unloading. A numerical modeling of the indentation response in axisymmetrical conditions was performed using the ABAQUS finite element computer code. The plastic response of the core material was described by the *CRUSHABLE FOAM HARDENING option. The geometrical nonlinearity was taken into account by using the *NLGEOM option. The main goal of the analysis was to predict the residual stresses and strains, and especially the magnitude of the residual dent. A good match between the finite element modeling and the experimental data was obtained. The present work should be considered as a step towards developing a more sophisticated numerical model capable of describing indentation as well as post-indentation mechanical behavior of sandwich structures.

Impact characterisation of low fibre-volume glass reinforced polyester circular laminated plates

Drop-weight impact tests have been carried out for low fibre-volume glass-polyester laminates for a range of diameter to thickness ratios. Three damage stages were defined, ‘un-delaminated’, ‘delaminated’ and ‘fibre damage’. Analysis of the impact response using a mainly graphical methodology allowed further characterisation of the behaviour. Impact damage occurs in two stages: hidden internal delamination damage at low incident energy, and then finally perforation failure. Bending and membrane effects are significant for thin laminates. For thick laminates shear deflection, delamination and indentation damage are more important. Some form of strain-rate stiffening effects appear to be significant for bending, but not for shear-controlled deflections or when damage is present. Indentation follows the Hertzian contact law at low contact forces, but a linear contact stiffness is seen at higher forces. A fracture mechanics model describes well the onset of delamination, and gives good scaling between specimen sizes. An energy balance approach gives good correlation between impact force and incident energy. Fibre failure leading to penetration is back-face tension controlled. The complex behaviour observed shows that the impact response must be characterised before mathematical modelling might be attempted. Modelling of the un-delaminated behaviour should consider bending, shear, indentation and membrane effects.

Effect of laminate thickness and of matrix resin on the impact of low fibre-volume, woven roving E-glass composites

Instrumented falling weight tests led to the definition of three behaviour `regimes'; `undamaged', `internal delamination' and `severe' (at low, medium and high incident energies, respectively). The reduction in stiffness due to the internal delamination gave a bi-linear force–deflection relationship. A shear-dominated theory and an energy balance approach gave the relationship between incident energy and maximum force. By considering deviations from this model the complex impact behaviour seen was related to the damage modes observed. At low incident energies bending was significant for all except for the thickest polyester laminates. Delaminated behaviour was shear-dominated for all except the thinnest laminates. At higher incident energies back-face fibre damage controlled behaviour before membrane effects became significant for thinner laminates, and indentation damage of thicker laminates became influential. Subtle differences between the damage modes of the epoxy and polyester laminates were seen; the epoxy laminates suffered more back-face fibre damage, but less internal delamination.

Organosilicate Spin-on Glasses: I. Effect of Chemical Modification on Mechanical Properties

Methylsilsesquioxane (MSSQ) films were chemically modified by (i) the bulk incorporation of a short-chain polymer or surface treatment by an plasma, and the effects of these modifications on elastic, plastic, and fracture properties were investigated. In (i), a copolymer of 10 mol % 1,2-bis(trimethoxysilyl)ethane (BTMSE) and methyltrimethoxysilane was synthesized and cured to form an MSSQ:BTMSE copolymer film. In an plasma treatment was applied to cured MSSQ films for 5, 15, 30, or 60 min. Films were characterized using scanning electron microscopy (SEM), IR spectroscopy, and ellipsometry. Depth-sensing indentation was used to determine plane strain modulus, and hardness, H. Indentation traces and SEM images of residual indentation damage were used to determine the threshold load for cracking, The addition of BTMSE to MSSQ doubled H, and relative to MSSQ with a slight increase in relative dielectric constant, k, from 2.70 to 2.86. Apparent and H at the surface of plasma-treated films increased with plasma treatment time. IR spectroscopy indicated that improved properties resulted in (i) from increased organic and inorganic networking and in from the formation of a dense, largely inorganic, surface layer. Such chemical modifications may be used to improve the performance of organosilicates as low-k dielectrics in microelectronic interconnection structures. © 2004 The Electrochemical Society. All rights reserved.

Indentation Damage of Porous Alumina Ceramice

The Hertzian indentation contact damage behavior of porous alumina with controlled pore shape was investigated by experiments. Porous alumina ceramics containing well-defined pore shape, size and distribution were prepared by incorporation of fugitive spherical starch. Porous alumina with isolated pore structure was prepared with porosity range up to 30%. The indentation stress-strain curves of porous alumina were constructed. Elastic modulus and yield stress can be obtained from the stress-strain relationship. Impulse excitation method for the measurement of elastic modulus was also conducted as well as Hertzian indentation and was confirmed as a useful tool to evaluate the elasticity of highly porous ceramics. Elastic modulus of the inter-connected pore structure is more sensitive to porosity than that of the isolated pore structure. When the specimen had isolated pore structure, higher yield point was obtained than it had inter-connected pore structure. This study proposed that the elastic modulus of porous ceramics is strongly related to not only porosity , but also the structure of pore.