Pyramidal Indenter Research Articles

Accurate Modelling of AFM Force-Indentation Curves with Blunted Indenters at Small Indentation Depths.

When testing biological samples with atomic force microscopy (AFM) nanoindentation using pyramidal indenters, Sneddon's equation is commonly used for data processing, approximating the indenter as a perfect cone. While more accurate models treat the AFM tip as a blunted cone or pyramid, these are complex and lack a direct relationship between applied force and indentation depth, complicating data analysis. This paper proposes a new equation derived from simple mathematical processes and physics-based criteria. It is accurate for small indentation depths and serves as a viable alternative to complex classical approaches. The proposed equation has been validated for ℎ < 3R (where h is the indentation depth and R is the tip radius) and confirmed through simulations with blunted conical and pyramidal indenters, as well as experiments on prostate cancer cells. It is a reliable method for experiments where the tip radius cannot be ignored, such as in shallow indentations on thin samples to avoid substrate effects.

Atomic-scale deformation behavior of SiC polytypes using molecular dynamics simulation

The atomic-scale deformation behavior of the Silicon carbide (SiC) polytypes, including 3 C-SiC and 4 H-SiC, during the nanoindentation with different square-based pyramid indenter angles was investigated by molecular dynamics (MD) simulations. Detailed analyses were conducted on atomic displacement magnitude, atomic structure, radial distribution function and dislocation distribution were analyzed in-depth in both loading and unloading processes. The results show that the indentation deformation phenomenon of ‘‘pile-up’’ occurs with indenter angles below 120°. Maximum load shows a non-linear increase trend as the indenter angles increase. The residual depth of the 3 C polytype has insignificant fluctuations while that of the 4 H polytype generally increases as the angle decreases and fluctuates at the indenter angles of 100° ∼ 110°. The number of amorphous atoms in 4 H is greater than that of 3 C polytype. Most of the amorphous atoms recover to their original structure after the indenter is fully withdrawn. Dislocation analysis indicates that the total length of dislocation lines increases with larger indenter angles. The length of the 3 C dislocation line is greater than that of 4 H. At the same indenter angle, the dislocation slip depth of 3 C polytype is greater than that of 4 H polytype due to the different lattice stacking order of 3 C polytype is greater than that of 4 H polytype due to the different lattice stacking order.

Multi-Pass Laser Polishing of As-Built Directed Energy Deposition Surfaces

Abstract Laser polishing (LP) provides a fast and efficient way of remelting part surfaces manufactured by additive manufacturing to alter both their geometric as well as physical properties. Depending on the laser parameters, remelted surfaces with different properties are achieved, with a majority exhibiting lower surface roughness compared to the original surface. In this study, a high-power continuous fiber laser is used to polish Inconel 718 (IN718) surfaces produced by depositing a single layer of clads on a steel substrate by the powder-blown directed energy deposition (DED) process. Polishing was performed under different sets of parameters, namely, laser power, beam diameter, feed rate or feed, hatch spacing, and the number of polishing passes. Their effects on the surface roughness profiles and the microstructural properties of the sample cross section were analyzed after one and two polishing passes. Optical microscopic images of the sample's cross sections show the presence of supersaturated γ phase particles, γ′+γ″ precipitates, Laves phases, and δ phase needles. The combined effect of high-temperature gradients and lower solidification rates in certain regions within the cross section results in undercooled regions and pseudo-heat treatment of unmelted regions close to the undercooled regions. These results are corroborated by indenting the various regions of the IN718 sample cross section with a pyramidal diamond indenter in the form of a grid, resulting in different micro-hardness values due to different densities of precipitate and phase transformed δ particles.

Determination of Crack Resistance of the Cover and Slide Glass by Indentation Method with the Visualization Using Atomic Force Microscopy

Crack resistance of two types of glass was studied – cover glass (0.17 mm thick) and slide glass (2 mm thick) using an improved technique through the use of the probe methods, which makes it possible to increase the accuracy of determining the crack resistance of glass. Colorless silicate glass was used. Crack resistance was determined by the Vickers pyramid indentation method. Microstructure of glasses surface and deformation region after indentation were studied using an atomic force microscope. Mechanical properties of glasses were determined by nanoindentation. Surface relief of a glass slide is rougher than that one of a cover glass. Roughness Rz for a cover glass is less than for a slide glass. Specific surface energy value of 0.26 N/m is higher for the slide glass compared to the coverslip. One elastic modulus value E of the cover glass is 48 GPa, and that one of the slide glass is 58 GPa. The microhardness value H is almost the same for by the glasses and amounts to 6.7 GPa for a slide glass and 6.4 GPa for a cover glass. Atomic force microscope images of deformation region after indentation with a Vickers pyramid show that the first cracks appear at a load of 1 N on the slide glass, and at 2 N on the cover glass. At a load of 3 N, the cover glass is destroyed. Based on the results of crack resistance calculations it was found that critical stress intensity coefficient KIC values are 1.42 MPa∙m1/2 for a glass slide, and 1.10 MPa∙m1/2 for a cover glass.

Towards understanding the influence of structured indenters geometry on material deformation behavior of indentation process

Nanoindentation has emerged as a pioneering technique for fabricating array structures at the nanoscale. This research incorporates molecular dynamics simulations to investigate the deformation mechanisms of materials influenced by structured indenters exhibiting diverse geometries. The primary objective of this study is to mitigate interference during the continuous indentation applied by the indenters, diminish the material's elastic recovery, and minimize the occurrence of defects. The simulation results unveil that plastic deformation of the workpiece induced by structured indenters manifests through the nucleation and slip of dislocations. The cylindrical indenter engenders the most pronounced residual indentation morphology, accompanied by substantial pile-up interference and an extensive range of dislocation expansion, surpassing that of other indenters. Conversely, pyramidal indenters exhibit minimal residual indentation morphology, albeit displaying considerable elastic recovery. A comprehensive evaluation that considers factors such as recovery after indentation, ease of processing, system stability, and material transfer against the indentation force is imperative for the determination of the ideally structured indenter. The meticulous analysis supports the efficacy of paraboloidal indenters possessing smaller taper angles in attaining consistent processing results, rendering them highly suitable for continuous indentation processing. The research content bears significant implications for advancing the application of structured indenters.

Scratch performance of natural rubber and natural rubber composites reinforced with nylon, kevlar, and carbon fabrics

The scratch performance of natural rubber (NR) and fibre-reinforced NR was investigated using a scratch test with acoustic emission (AE). Both maximum penetration depth and maximum tangential force were characterised by two procedures. Procedure 1 applied the corner of a steel cube at face leading orientation. Procedure 2 applied a steel pyramid indenter with a spherical tip at the edge leading orientation. AE was adopted in Procedure 2 for evaluation of cutting damage mode that varied from ploughing/tearing the matrix to cutting both the matrix and fabric. The scratched regions of all specimens were observed using an optical microscope to estimate the damage level and examine damage mechanisms. The results show that scratch resistance improved as fibre content and fibre stiffness increased. The maximum tangential force depended on the damage modes. Two or more fabric layers could further increase penetration resistance, but the damage level is more serious in most cases.

Cracking behavior during scratching brittle materials with different-shaped indenters

The cracking behavior greatly influences the material removal and surface integrity during the abrasive machining of brittle materials. The abrasive machining can be simplified as a series of scratching by different-shaped indenters. In this paper, a scratch-induced stress field model is built to analyze the cracking behavior during scratching brittle materials. The model considers conical, pyramidal, and spherical (CPS) indenters and correlates the scratch-induced principal stress with workpiece material properties, indenter geometries, and scratch behavior parameters (e.g., scratch normal load, tangential load, friction coefficient, scratch depth). With the model, the effects of scratch depth and indenter geometries on the scratch behavior and cracking behavior are investigated. The results show that the scratch load decreases when a sharper indenter or a spherical indenter with a smaller radius is used. The larger the scratch depth, the easier it is for radial, median, and lateral (RML) cracks to initiate. There is an optimal indenter half-apex angle at which it is most difficult to initiate radial and median cracks. The lateral crack easily initiates when the indenter becomes sharp. The initiation position of radial crack changes from being in front of the indenter to being behind it as the scratch depth increases or the half-apex angle decreases. The propagation angle of radial crack decreases, while that of median crack increases with an increase in scratch depth. The sizes of RML cracks increase with an increasing scratch depth or half-apex angle. Finally, the model is validated through scratching experiments on fused silica using CPS indenters and by referencing previous research. It demonstrates that the model can accurately determine the sizes of RML cracks, with an average relative error of less than 11%. This research provides guidance on selecting suitable process parameters or indenter geometries to increase the material removal rate and mitigate the crack damage during the abrasive machining of brittle materials.

Synergistic fractural features observed in Ti-B-Si-C hard coatings on enhancing the sharpness of nano indenters

The multicomponent Ti-B-Si-C hard coatings consisting of different hard phases have varied uses in tool, heavy duty as well as microelectronic industries, The fractural features related to the toughness of Ti-B-Si-C coatings by pyramidal indenters of two different geometry (Berkovich and cube corner) were investigated. The differences in stress distribution beneath the indentation region were studied by means of Finite Element Analysis. The dislocation distribution in front of a growing crack obtained through high-resolution microscopy was related to the fractographic aspects.

Indentation of living cells by AFM tips may not be what we thought!

The models used to calculate Young's moduli from atomic force microscopy (AFM) force curves consider the shape of the indentation. It is then assumed that the geometry of the indentation is identical to the geometry of the indenter, which has been verified for hard materials (E > 1 MPa). Based on this assumption, the force curves calculated by these models, for the same object with a given Young's modulus, are different if the indenter geometry is different. On the contrary, we observe experimentally that the force curves recorded on soft living cells, with pyramidal, spherical, or tipless indenters, are almost similar. This indicates that this basic assumption on the indentation geometry does not work for soft materials (E of the order of 5 kPa or less). This means that, in this case, the shape of the indentation is therefore different from the shape of the indenter. Indentation of living cells by AFM is not what we thought!

Multiscale wood micromechanics and size effects study via nanoindentation

Wood as a material is a natural composite with a complex hierarchically arranged structure. All scale levels of wood structure contribute to its macroscopic mechanical properties. The nature of such characteristics and deformation modes differs radically at different scale levels. Wood macroscopic properties are well studied, and the relevant information can be easily found in the literature. However, the knowledge of the deformation mechanisms at the mesoscopic level corresponding to the cellular structure of early and late wood layers of annual growth rings is insufficient. It hinders building the comprehensive multiscale model of how wood mechanical properties are formed. This paper described the results of scanning of mechanical properties of softwood and hardwood samples, such as common pine, small-leaf lime, and pedunculate oak, by means of nanoindentation (NI). The NI technique allows varying the size of deformed region within a wide range by altering maximal load (Pmax) applied to the indenter so that one can repeatedly and non-destructively test wood structural components at different scale levels on the same sample without changing the technique or equipment. It was discovered that the effective microhardness (Heff) and Young's modulus (Eeff) decreased manifold with Pmax growing from 0.2 to 2 000 mN. This drop in Heff was observed when the locally deformed region grew, and resulting from Pmax increase generally follows the rule similar to the Hall-Petch relation for yield stress, strength, and hardness initially established for metals and alloys, though obviously in those cases the underlying internal mechanisms are quite different. The nature and micromechanisms of such size effect (SE) in wood revealed using NI were discussed in this study. At Pmax < 0.2 mN, the deformed area under the pyramidal Berckovich indenter was much smaller than the cell wall width. Hence, in this case, NI measured the internal mechanical properties of the cell wall material as long as free boundaries impact could be neglected. At Pmax > 200 mN, the indentation encompassed several cells. The measured mechanical properties were significantly affected by bending deformation and buckling collapse of cell walls, reducing Heff and Eeff substantially. At Pmax ≈ 1–100 mN, an indenter interacted with different elements of the cell structure and capillary network, resulting in intermediate values of Heff and Eeff. Abrupt changes in Heff and Eeff at annual growth ring boundaries allow accurate measuring of rings width, while smoother and less pronounced changes within the rings allow identification of earlywood and latewood layers as well as any finer changes during vegetation season. The values of ring width measured using NI and standard optical method coincide with 2%−3% accuracy. The approaches and results presented in this study could improve the understanding of nature and mechanisms lying behind the micromechanical properties of wood, help to optimize the technologies of wood farming, subsequent reinforcement, and utilization, as well as to develop new highly informative techniques in dendrochronology and dendroclimatology.

No-Cap Flowable Bulk-Fill Composite: Physico-Mechanical Assessment.

(1) Background: A newer class of flowable bulk-fill resin-based composite (BF-RBC) materials requires no capping layer (Palfique Bulk flow, PaBF, Tokuyama Dental, Tokyo, Japan). The objective of this study was to assess the flexural strength, microhardness, surface roughness, and color stability of PaBF compared to two BF-RBCs with different consistencies. (2) Methods: PaBF, SDR Flow composite (SDRf: Charlotte, NC, USA) and One Bulk fill (OneBF: 3M, St. Paul, MN, USA) were evaluated for flexural strength with a universal testing machine, surface microhardness using a pyramidal Vickers indenter, and surface roughness using a high-resolution three-dimensional non-contact optical profiler, a and clinical spectrophotometer to measure the color stability of each BF-RBC material. (3) Results: OneBF presented statistically higher flexural strength and microhardness than PaBF or SDRf. Both PaBF and SDRf presented significantly less surface roughness compared with OneBF. Water storage significantly reduced the flexural strength and increased the surface roughness of all tested materials. Only SDRf showed significant color change after water storage. (4) Conclusions: The physico-mechanical properties of PaBF do not support its use without a capping layer in the stress bearing areas. PaBF showed less flexural strength compared with OneBF. Therefore, its use should be limited to a small restoration with minimal occlusal stresses.

Synthesis and characterization of metal carbides for nanoindentation tip applications

Instrumented indentation experiments at elevated temperatures require careful attention to a myriad of experimental details. Not the least of these is the choice of the indenter tip material. Traditional room-temperature indenters, e.g., diamond and sapphire, can break down, react, and wear excessively at elevated temperatures. In this work, rf-induction heating float-zone and high-temperature solution single-crystal growth techniques have been used to prepare a suite of bulk refractory carbide specimens (i.e., ZrC, VC0.86, NbC, TiC0.95, WC). These potential indenter tip materials were subsequently characterized using nanoindentation testing techniques to determine their single-crystal elastic modulus, hardness, and fracture toughness in order to evaluate their potential for use as elevated-temperature nanoindentation tips. Additionally, subject carbide crystal characteristics were compared to those of single-crystal sapphire and polycrystalline WC-Co. The cumulative results show that single-crystal WC is a promising candidate for indenter tip material based on a combination of its high elastic modulus, hardness, and resistance to cracking—in addition to being crystallographically favorable for fabrication in the frequently used three-sided pyramidal indenter tip geometries.

Indenting glasses with indenters of varying stiffness and sharpness

In this study, the effects of both indenter sharpness and stiffness on the indentation response of oxide glasses have been investigated. Using five different indenters, the indentation response in terms of glass deformation mechanism, cracking behavior, and hardness has been examined for three glasses (sodium silicate, sodium borate, and sodium borosilicate). For right square-based pyramidal diamond indenters with varying tip angle, increased indenter sharpness reduces the magnitude of the indentation size effect. Additionally, increased indenter sharpness lowers the crack initiation resistance, which is linked to a reduction of densification. For indenters with the same geometry but made of different materials, the effect of the indenter material is insignificant when the indenter is substantially stiffer than the specimen. When the stiffness of the indenter is only slightly higher or similar to that of the sample, substantial deformation of the indenter occurs, reducing the effective indenter sharpness and hence affecting the indentation response.

Microstructure and mechanical analyses of Ti6Al4V/B4C composites on Ti6Al4V substrate: Effect of laser power on multiple track laser metal deposition

Components used in many manufacturing applications especially in the defence, automotive and aerospace are required to meet certain properties, such as elastic modulus, toughness, resistance to wear and corrosion. Additive manufacturing (AM) is a technique used for the fabrication of layer-by-layer geometries via three dimensional (3D) mechanisms at a certain process parameter. Titanium alloy and boron carbide (Ti6Al4V/B4C) composites coatings have been successfully fabricated on titanium alloy (Ti6Al4V, grade 5) by laser metal deposition (LMD) of additive manufacturing (AM) process. Microstructure analysis of the fabricated multiple clad is characterized by optical and scanning electron microscopy. The obtained multiple tracks show that the coatings are profound with TiC and TiB phases with dendrites of TiC particles in the coatings. The evolving microstructures of the deposited coatings at a laser power of 1000 W and 1200 W with a scanning speed of 1 m/min exhibit some lateral cracks which is associated to the brittle nature of ceramic boron carbide in the clad zone. The atomic level characterization of the coatings is determined through the surface roughness obtained by atomic force microscope (AFM). Microhardness analysis is performed at the cross-section surface of the coatings by Vickers pyramid indentation at 300 gf load with dwell time of 10 s on Zwick Roell microhardness tester. From the samples investigated, sample at a laser power of 1200 W has the highest hardness value of 548 HV0.3/10s.

Influence of Corrosion-Induced Damage on Mechanical Integrity and Load-Bearing Capability of Cemented Carbides

Tungsten carbide based cemented carbides, often simply termed hardmetals, are established forefront materials for tools, structural components, and wear parts with stringent requirements. Several of the technological applications in which they are used include exposure to chemically aggressive media. Under these conditions, failure induced under applied load may be accelerated; and consequently, the service life may be decreased. Within this context, this work addresses the influence of corrosion-induced damage on the mechanical integrity and load-bearing capability of hardmetals at different length scales, i.e., from 100s nanometers to 1000s microns. Experimental data acquired by means of nanoindentation, pyramidal, and spherical indentation, as well as sliding contact (micro- and nanoscratch) techniques, are presented. The attained results allow for identifying guidelines for the microstructural design of these materials under combined consideration of corrosion and mechanical contact as service-like conditions. Discussion of the reported findings includes a critical analysis of corrosion effects on the evolution of microstructure-property-performance interrelations for the materials under consideration.

Characterization of power-law constitutive relationship of nickel-based single crystal superalloys under different loading rates by nanoindentation with different types of indenters

This work attempts to explore a method to characterize the effect of loading rate on the power-law constitutive parameters of nickel-based single crystal superalloys (NBSX) by nanoindentation, which avoids the influence of indentation sinking-in or piling-up and indentation size effects. Specifically, combing the reduced modulus obtained from a cylindrical flat punch indentation test with the indentation contact stiffness obtained from two pyramidal indentation tests with different equivalent half cone angles, the actual indentation projected contact area of two pyramidal indenters can be acquired. Based on the actual projected contact area and the intrinsic hardness results calculated by Nix-Gao model, the corrected indentation load-depth curves from two pyramidal indenters are constructed. The elastic modulus can be known from the reduced modulus in advance, and then according to the equivalent half cone angle of the pyramidal indenters and the corrected indentation load-depth curves, the representative strain and stress of two pyramidal indenters are obtained, respectively. The power-law constitutive parameters of NBSX along [001] orientation under different loading rates are accomplished by inverse analyses of the representative stress and strain of two pyramidal indenters, and verified by the test results of a pyramidal indenter with another equivalent half cone angle. Results demonstrate the effectiveness of the explored method.

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.

Determination of plastic properties of surface modification layer of metallic materials from scratch tests

A new test method was proposed to extract plastic parameters, i.e., yield stress and strain hardening index, and interfacial coefficient of friction of metallic materials via scratch tests with a pyramid indenter based on dimensional analysis and finite element analysis. Yield stress and strain hardening index of scratched materials can be calculated with scratch width, residual scratch depth and normal force obtained from the scratch tests. Interfacial coefficient of friction between the scratched materials and scratch tip can be determined by the ratio of tangential force and normal force. The accuracies of the proposed formulas were verified by comparing the results of uncarburized and carburized 18CrNiMo7-6 alloy steel obtained by conventional methods with those by scratch tests. This work provides a convenient method to determine plastic parameters and interfacial coefficient of friction of metallic materials simultaneously, which is important for the mechanical analysis, design and safety evaluation of mechanical parts.

Measurement of aluminum alloys plasticity under their dynamic and static loading by the Vickers pyramid

The paper considers the possibility of assessing the plasticity of aluminum alloys and aluminum matrix composites by the method of quasi‑static and micro‑impact indentation at pre‑impact velocities in the range of 1–3 m/s. It is proposed to use a pyramidal Vickers indenter for testing, which allows creating a constant amount of deformation. The characteristic plasticity values for industrial aluminum alloys and aluminum matrix composites of the Al‑Fe‑Cr system δ=0.83–0.98 are established. The influence of the deformation rate on the dynamicity coefficient Kd, which is the ratio of dynamic and static hardness, is shown. It was found that the increase in Kd for aluminum matrix composites is more significant than for other materials. At the same time, the well‑known expression linking plasticity with other mechanical characteristics: hardness HV and modulus of elasticity E, is not fulfilled for the studied aluminum matrix composites. The difference in the values of δ, calculated based on the parameters of the print and as a function of E/HV, can serve as an additional sign of the atypical behavior of materials during deformation.

Study of some thermo-mechanical parameters in Se70Te30-xMx (x = 0, 2; M = Cd, Ag, and Zn) alloys

Vickers microhardness has been determined by performing micro-indentation experiments on Chalcogenide glasses (ChGs) of Se70Te30, and Se70Te28M2 (M = Cd, Ag, and Zn) alloys using micro-indentation and optical microscopic techniques. Vickers micro-hardness is directly observed by the diagonal lengths of the indentation marks of a pyramidal diamond indenter. Thermally-induced glass transition was noticed by the DSC technique. Mechanical property such as modulus of elasticity (E), is calculated by well-known empirical relations. The minimal energy of micro-void (Eh), micro void volume (Vh), and covalence character of the glassy system are discussed in terms of microhardness (Hv). Physical parameters i.e., overall mean bond energy, density, molar volume, and compactness have been also carried out.