Sign in to use this feature.

Years

Between: -

Subjects

remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline
remove_circle_outline

Journals

Article Types

Countries / Regions

Search Results (22)

Search Parameters:
Keywords = Hertzian indentations

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
19 pages, 2373 KiB  
Article
Simplifying Data Processing in AFM Nanoindentation Experiments on Thin Samples
by Stylianos Vasileios Kontomaris, Anna Malamou and Andreas Stylianou
Eng 2025, 6(2), 32; https://doi.org/10.3390/eng6020032 - 8 Feb 2025
Viewed by 766
Abstract
When testing soft biological samples using the Atomic Force Microscopy (AFM) nanoindentation method, data processing is typically based on equations derived from Hertzian mechanics. To account for the finite thickness of the samples, precise extensions of Hertzian equations have been developed for both [...] Read more.
When testing soft biological samples using the Atomic Force Microscopy (AFM) nanoindentation method, data processing is typically based on equations derived from Hertzian mechanics. To account for the finite thickness of the samples, precise extensions of Hertzian equations have been developed for both conical and parabolic indenters. However, these equations are often avoided due to the complexity of the fitting process. In this paper, the determination of Young’s modulus is significantly simplified when testing soft, thin samples on rigid substrates. Using the weighted mean value theorem for integrals, an ‘average value’ of the correction function (symbolized as g(c)) due to the substrate effect for a specific indentation depth is derived. These values (g(c)) are presented for both conical and parabolic indentations in the domain 0 < r/H ≤ 1, where r is the contact radius between the indenter and the sample, and H is the sample’s thickness. The major advantage of this approach is that it can be applied using only the area under the force–indentation curve (which represents the work performed by the indenter) and the correction factor g(c). Examples from indentation experiments on fibroblasts, along with simulated data processed using the method presented in this paper, are also included. Full article
(This article belongs to the Section Materials Engineering)
Show Figures

Figure 1

17 pages, 8109 KiB  
Article
Angle-Dependent Adhesive Mechanics in Hard–Soft Cylindrical Material Interfaces
by Thao H. Pham, Iakov A. Lyashenko and Valentin L. Popov
Materials 2025, 18(2), 375; https://doi.org/10.3390/ma18020375 - 15 Jan 2025
Viewed by 844
Abstract
In this research, the adhesive contact between a hard steel and a soft elastomer cylinder was experimentally studied. In the experiment, the hard cylinder was indented into the soft one, after which the two cylinders were separated. The contact area between the cylinders [...] Read more.
In this research, the adhesive contact between a hard steel and a soft elastomer cylinder was experimentally studied. In the experiment, the hard cylinder was indented into the soft one, after which the two cylinders were separated. The contact area between the cylinders was elliptical in shape, and the eccentricity of this increased as the angle between the axes of the contacting cylinders decreased. Additionally, the adhesive pull-off force and the contact area increased with a decrease in the angle between the cylinders. The use of a transparent elastomer allowed for observation of the shape of the contact in real time, which facilitated the creation of videos demonstrating the complete process of contact failure and the evolution of the ellipse shape, depending on the distance between the cylinders and normal force. These findings contribute to a better understanding of adhesive interactions in elliptical contacts between cylinders and can be applied to fields such as soft robotics, material design, and bioengineering, where precise control over adhesion and contact mechanics is crucial. Full article
Show Figures

Figure 1

14 pages, 4965 KiB  
Article
Effect of Layer Thickness on the Practical Adhesion of Borided Monel 400 Alloy
by Francisco Javier Alfonso-Reyes, José Martínez-Trinidad, Luis Alfonso Moreno-Pacheco, Osvaldo Quintana-Hernández, Wilbert Wong-Ángel and Ricardo Andrés García-León
Coatings 2024, 14(11), 1414; https://doi.org/10.3390/coatings14111414 - 7 Nov 2024
Cited by 2 | Viewed by 1064
Abstract
This study presents new results on the practical adhesion behavior of a boride layer formed on Monel 400 alloy, developed using the powder-pack boriding (PPBP) at 1223 K for 2, 4, and 6 h of exposure times, obtaining layer thicknesses from approximately 7.9 [...] Read more.
This study presents new results on the practical adhesion behavior of a boride layer formed on Monel 400 alloy, developed using the powder-pack boriding (PPBP) at 1223 K for 2, 4, and 6 h of exposure times, obtaining layer thicknesses from approximately 7.9 to 23.8 µm. The nickel boride layers were characterized using optical microscopy, Berkovich nanoindentation, X-ray diffraction (XRD), and scanning electron microscopy (SEM) to determine microstructure, hardness distribution, and failure mechanisms over the worn tracks. Scratch tests were conducted on the borided Monel 400 alloy according to the ASTM C-1624 standard, applying a progressively increasing normal load from 1 to 85 N using a Rockwell-C diamond indenter, revealing that critical loads (LC1, LC2, and LC3) increased with layer thickness. The tests monitored the coefficient of friction and residual stress in real time. Critical loads were determined based on the correlation between the normal force and visual inspection of the worn surface, identifying cracks (cohesive failure) or detachment (adhesive failure). The results exposed those cohesive failures that appeared as Hertzian cracks, while adhesive failures were chipping and delamination, with critical loads reaching up to 49.0 N for the 6 h borided samples. Also, the results indicated that critical loads increased with greater layer thickness. The boride layer hardness was approximately 12 ± 0.3 GPa, ~4.0 times greater than the substrate, and Young’s modulus reached 268 ± 15 GPa. These findings underscore that PPBP significantly enhances surface mechanical properties, demonstrating the potential for applications demanding high wear resistance and strong layer adhesion. Full article
(This article belongs to the Special Issue Enhanced Mechanical Properties of Metals by Surface Treatments)
Show Figures

Figure 1

17 pages, 5067 KiB  
Article
Unloading Model of Elastic–Plastic Half-Space Contacted by an Elastic Spherical Indenter
by Wenhao Xie, Yuanyuan Guo, Huaiping Ding, Xiaochun Yin and Panpan Weng
Materials 2024, 17(12), 3018; https://doi.org/10.3390/ma17123018 - 20 Jun 2024
Viewed by 1446
Abstract
A new unloading contact model of an elastic–perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully [...] Read more.
A new unloading contact model of an elastic–perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement. Full article
Show Figures

Figure 1

16 pages, 3996 KiB  
Article
Elastic and Elastoplastic Contact Mechanics of Concentrated Coated Contacts
by Patricia M. Johns-Rahnejat, Nader Dolatabadi and Homer Rahnejat
Lubricants 2024, 12(5), 162; https://doi.org/10.3390/lubricants12050162 - 7 May 2024
Cited by 4 | Viewed by 2905
Abstract
Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been [...] Read more.
Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been predicted using classical Hertzian contact mechanics. However, the theory is only applicable when the contact between a pair of ellipsoidal solids of revolution may be considered as a rigid indenter penetrating a semi-infinite elastic half-space. Many coatings act as thin bonded elastic layers that undergo considerably higher pressures than those predicted by the classical theory. Furthermore, inelastic deformation of bonded solids can cause plastic flow, work-hardening, and elastoplastic behaviour. This paper presents a comprehensive, integrated contact mechanics analysis that includes induced sub-surface stresses in concentrated counterformal finite line contacts for all the aforementioned cases. Generated pressures and deformation are predicted for hard coated surfaces, for which there is a dearth of relevant analysis. The contact characteristics, which are of particular practical significance, of many hard, wear-resistant advanced coatings are also studied. The paper clearly demonstrates the importance of using efficient semi-analytical, detailed holistic contact mechanics rather than the classical idealised methods or empirical numerical ones such as FEA. The novel approach presented for the finite line contact of thin-layered bonded solids has not hitherto been reported in the open literature. Full article
Show Figures

Figure 1

15 pages, 1013 KiB  
Article
On Boussinesq’s Problem for a Power-Law Graded Elastic Half-Space on Elliptical and General Contact Domains
by Emanuel Willert
Materials 2023, 16(12), 4364; https://doi.org/10.3390/ma16124364 - 13 Jun 2023
Cited by 4 | Viewed by 1417
Abstract
The indentation of a power-law graded elastic half-space by a rigid counter body is considered in the framework of linear elasticity. Poisson’s ratio is assumed to be constant over the half-space. For indenters with an ellipsoidal power-law shape, an exact contact solution is [...] Read more.
The indentation of a power-law graded elastic half-space by a rigid counter body is considered in the framework of linear elasticity. Poisson’s ratio is assumed to be constant over the half-space. For indenters with an ellipsoidal power-law shape, an exact contact solution is derived, based on the generalizations of Galin’s theorem and Barber’s extremal principle for the inhomogeneous half-space. As a special case, the elliptical Hertzian contact is revisited. Generally, elastic grading with a positive grading exponent reduces the contact eccentricity. Fabrikant’s approximation for the pressure distribution under a flat punch of arbitrary planform is generalized for power-law graded elastic media and compared with rigorous numerical calculations based on the boundary element method (BEM). Very good agreement between the analytical asymptotic solution and the numerical simulation is obtained for the contact stiffness and the contact pressure distribution. A recently published approximate analytic solution for the indentation of a homogeneous half-space by a counter body, whose shape slightly deviates from axial symmetry but is otherwise arbitrary, is generalized for the power-law graded half-space. The approximate procedure for the elliptical Hertzian contact exhibits the same asymptotic behavior as the exact solution. The approximate analytic solution for the indentation by a pyramid with square planform is in very good agreement with a BEM-based numerical solution of the same problem. Full article
Show Figures

Figure 1

13 pages, 13425 KiB  
Article
Comparative Study of Mechanical Performance of AlCrSiN Coating Deposited on WC-Co and cBN Hard Substrates
by Jing Liang, Marc Serra, Sandra Gordon, Jonathan Fernández de Ara, Eluxka Almandoz, Luis Llanes and Emilio Jimenez-Piqué
Ceramics 2023, 6(2), 1238-1250; https://doi.org/10.3390/ceramics6020075 - 9 Jun 2023
Cited by 1 | Viewed by 2491
Abstract
The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for [...] Read more.
The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for observing the contact damage under Hertzian contact with monotonic and cyclic (fatigue) loads. Microscratch and contact damage tests were also used to evaluate the strength of adhesion between the AlCrSiN coatings and the two substrates under progressive and constant loads, respectively. The surface damages induced via different mechanical tests were observed using scanning electron microscopy (SEM). A focused ion beam (FIB) was used to produce a cross-section of the coating–substrate system in order to further detect the mode and extent of failure that was induced. The results show that the AlCrSiN coating deposited on the WC-Co substrate performed better in regard to adhesion strength and contact damage response than the same coating deposited on the cBN substrate; this is attributed to the lower plasticity of the cBN substrate as well as its less powerful adhesion to the coating. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
Show Figures

Graphical abstract

16 pages, 10066 KiB  
Article
Novel Ni-P-Tribaloy Composite Protective Coating
by Ahmed Mabrouk and Zoheir Farhat
Materials 2023, 16(11), 3949; https://doi.org/10.3390/ma16113949 - 25 May 2023
Cited by 4 | Viewed by 1952
Abstract
Oil and gas pipelines are subject to various forms of damage and degradation during their operation. Electroless Nickel (Ni-P) coatings are widely employed as protective coatings due to their ease of application and unique properties, including high wear and corrosion resistance. However, they [...] Read more.
Oil and gas pipelines are subject to various forms of damage and degradation during their operation. Electroless Nickel (Ni-P) coatings are widely employed as protective coatings due to their ease of application and unique properties, including high wear and corrosion resistance. However, they are not ideal for protecting pipelines due to their brittleness and low toughness. Composite coatings of higher toughness can be developed through the co-deposition of second-phase particles into the Ni-P matrix. Tribaloy (CoMoCrSi) alloy possesses excellent mechanical and tribological properties making it a potential candidate for a high-toughness composite coating. In this study, Ni-P-Tribaloy composite coating consisting of 15.7 vol.% Tribaloy was successfully deposited on low-carbon steel substrates. Both the monolithic and the composite coatings were studied to evaluate the effect of the addition of Tribaloy particles. The micro-hardness of the composite coating was measured to be 6.00 GPa, 12% greater than that of the monolithic coating. Hertzian-type indentation testing was carried out to investigate the coating’s fracture toughness and toughening mechanisms. The 15.7 vol.% Tribaloy coating exhibited remarkably less severe cracking and higher toughness. The following toughening mechanisms were observed: micro-cracking, crack bridging, crack arrest, and crack deflection. The addition of the Tribaloy particles was also estimated to quadruple the fracture toughness. Scratch testing was performed to evaluate the sliding wear resistance under a constant load and a varying number of passes. The Ni-P-Tribaloy coating exhibited more ductile behavior and higher toughness, as the dominant wear mechanism was identified as material removal, as opposed to brittle fracture in the Ni-P coating. Full article
Show Figures

Figure 1

15 pages, 5140 KiB  
Article
Hardness Measurements and Interface Behavior of SiC-B4C-Si Multiple Phase Particulate Composites Made with Melt Infiltration and Additive Manufacturing
by Corson L. Cramer, Ercan Cakmak and Kinga A. Unocic
J. Compos. Sci. 2023, 7(4), 172; https://doi.org/10.3390/jcs7040172 - 20 Apr 2023
Cited by 7 | Viewed by 2829
Abstract
Reaction-bonded SiC-B4C-Si ceramic composites were binder jet 3D-printed and subsequently pressureless-melt-infiltrated with molten Si. The addition of B4C aided the Si infiltration to produce a highly dense composite. The microstructures and phases of these composites were examined. The measured [...] Read more.
Reaction-bonded SiC-B4C-Si ceramic composites were binder jet 3D-printed and subsequently pressureless-melt-infiltrated with molten Si. The addition of B4C aided the Si infiltration to produce a highly dense composite. The microstructures and phases of these composites were examined. The measured hardness values of each constituent with Vickers and nanoindentation matched the bulk values, and the macro-hardness values with Knoop and spherical indentation represented the bulk, composite hardness values of all three phases together, which was close to a rule of mixtures value. For particulate-based composites, this is a significant finding. The interfacial bonds of SiC and Si were imaged using scanning transmission electron microscopy to view intimacy, whereas the crack propagation was examined with carefully placed indents. This work demonstrated that pressureless melt infiltration with a reactive particle provides a method to shape non-wetting reaction-bonded ceramic composites with limited shrinkage and high density and provides insights into the mechanical behavior with numerous indentation techniques. Full article
(This article belongs to the Topic Progress in Si-Based Ceramic and Composites)
Show Figures

Graphical abstract

16 pages, 2544 KiB  
Article
AFM Indentation on Highly Heterogeneous Materials Using Different Indenter Geometries
by Stylianos Vasileios Kontomaris, Andreas Stylianou, Georgios Chliveros and Anna Malamou
Appl. Mech. 2023, 4(2), 460-475; https://doi.org/10.3390/applmech4020026 - 18 Apr 2023
Cited by 10 | Viewed by 3196
Abstract
Hertzian mechanics is the most frequently used theory for data processing in Atomic Force Microscopy (AFM) indentation experiments on soft biological samples, due to its simplicity and significant scientific results previously published. For instance, using the Hertz model, it has been proven that [...] Read more.
Hertzian mechanics is the most frequently used theory for data processing in Atomic Force Microscopy (AFM) indentation experiments on soft biological samples, due to its simplicity and significant scientific results previously published. For instance, using the Hertz model, it has been proven that there are significant differences in the mechanical properties of normal and cancerous tissues and that cancer cells’ invasive properties are correlated with their nanomechanical properties. However, many scientists are skeptical regarding the applicability of the Hertz theory to biological materials, as they are highly heterogeneous. The main critical question to be addressed is “what do we calculate” when fitting the force-indentation data to Hertz equations. Previous studies have shown that when using cylindrical, parabolic, or conical indenters, the fitting parameter is the average Young’s modulus. In this paper, it is demonstrated that it is also valid to fit equations derived from Hertzian mechanics to force-indentation data when testing soft, heterogeneous samples for any indenter geometry. The fitting factor calculated through this approach always represents the average Young’s modulus for a specific indentation depth. Therefore, Hertzian mechanics can be extended to soft heterogeneous materials, regardless of the indenter’s shape. Full article
(This article belongs to the Special Issue Feature Papers in Material Mechanics)
Show Figures

Figure 1

9 pages, 1506 KiB  
Communication
Prediction of Work Hardening in Bearing Steels Undergoing Rolling Contact Loading with a Dislocation-Based Model
by Hongxiang Yin, Xue Bai and Hanwei Fu
Metals 2022, 12(4), 555; https://doi.org/10.3390/met12040555 - 25 Mar 2022
Cited by 5 | Viewed by 3453
Abstract
The work hardening behaviour of GCr15 bearing steel during rolling contact fatigue (RCF) is investigated. Ball-on-rod RCF tests and micro-indentation tests are performed to obtain various subsurface hardness profiles in rod specimens. It is found that orthogonal shear stress is responsible for work [...] Read more.
The work hardening behaviour of GCr15 bearing steel during rolling contact fatigue (RCF) is investigated. Ball-on-rod RCF tests and micro-indentation tests are performed to obtain various subsurface hardness profiles in rod specimens. It is found that orthogonal shear stress is responsible for work hardening under Hertzian contact and that the extent of hardness increase is positively associated with the stress level and number of cycles. A dislocation-based work hardening model is established by combining the Kocks–Mecking theory, the bearing steel plasticity equation and the Taylor relation. The proposed model is capable of predicting hardness changes with any given rolling contact stress state and number of cycles. The modelling results are compared against the experimental results, with good agreement obtained. This research also provides a methodology for studying the work hardening of different types of bearing steels undergoing RCF, from experiment to modelling. Full article
Show Figures

Graphical abstract

12 pages, 894 KiB  
Article
An Approximate Solution for the Contact Problem of Profiles Slightly Deviating from Axial Symmetry
by Valentin L. Popov
Symmetry 2022, 14(2), 390; https://doi.org/10.3390/sym14020390 - 15 Feb 2022
Cited by 9 | Viewed by 2471 | Correction
Abstract
An approximate solution for a contact problem of profiles which are not axially symmetrical but deviate only slightly from the axial symmetry is found in a closed explicit analytical form. The solution is based on Betti’s reciprocity theorem, first applied to contact problems [...] Read more.
An approximate solution for a contact problem of profiles which are not axially symmetrical but deviate only slightly from the axial symmetry is found in a closed explicit analytical form. The solution is based on Betti’s reciprocity theorem, first applied to contact problems by R.T. Shield in 1967, in connection with the extremal principle for the contact force found by J.R. Barber in 1974 and Fabrikant’s approximation (1986) for the pressure distribution under a flat punch with arbitrary cross-section. The general solution is validated by comparison with the Hertzian solution for the contact of ellipsoids with small eccentricity and with numerical solutions for conical shapes with polygonal cross-sections. The solution provides the dependencies of the force on the indentation, the size and the shape of the contact area as well as the pressure distribution in the contact area. The approach is illustrated by linear (conical) and quadratic profiles with arbitrary cross-sections as well as for “separable” shapes, which can be represented as a product of a power-law function of the radius with an arbitrary exponent and an arbitrary function of the polar angle. A generalization of the Method of Dimensionality Reduction to non-axisymmetric profiles is formulated. Full article
(This article belongs to the Special Issue Axisymmetry in Mechanical Engineering)
Show Figures

Figure 1

22 pages, 3973 KiB  
Article
Effect of Artificial Aging on Mechanical and Tribological Properties of CAD/CAM Composite Materials Used in Dentistry
by Marcel Firlej, Daniel Pieniak, Agata M. Niewczas, Agata Walczak, Ivo Domagała, Anna Borucka, Krzysztof Przystupa, Joanna Igielska-Kalwat, Wojciech Jarosz and Barbara Biedziak
Materials 2021, 14(16), 4678; https://doi.org/10.3390/ma14164678 - 20 Aug 2021
Cited by 19 | Viewed by 4861
Abstract
With easy-to-process 3D printing materials and fast production, the quality of dental services can be improved. In the conventional procedure, the dentist makes temporary crowns directly in the patient’s mouth, e.g., from the most commonly used bis-acrylic composites. Temporary crowns made directly in [...] Read more.
With easy-to-process 3D printing materials and fast production, the quality of dental services can be improved. In the conventional procedure, the dentist makes temporary crowns directly in the patient’s mouth, e.g., from the most commonly used bis-acrylic composites. Temporary crowns made directly in the office without the use of CAD/CAM are often of inferior quality, which directly results in impaired hygiene, poorer masticatory mechanics, greater deposition of plaque, calculus and sediment, and may adversely affect periodontal and gum health. The mechanical strength, resistance to aging and abrasion of 3D printing materials are higher than those of the soft materials used in conventional methods. This translates into durability. The patient leaves the surgery with a restoration of higher utility quality compared to the conventional method. The objective of the paper was to determine the influence of aging in artificial saliva of AM (additive manufacturing) orthodontic composites on their functional properties. For the purpose of the study, fillings well-known worldwide were selected. These were traditional UV-curable resins (M I, M II, M III, M V) and a hybrid material based on a UV-curable resin (M VI). Samples were stored in artificial saliva at 37 ± 1 °C in a thermal chamber for 6 months. Indentation hardness, frictional tests and sliding wear measurements were conducted. A comparison between various materials was made. Descriptive statistics, degradation coefficients, H2E, Archard wear and specific wear rate were calculated. The Weibull statistical test for indentation hardness was performed and Hertzian contact stresses for the frictional association were calculated for unaged (M I, M II, M III, M V, M VI) and aged (M I AS, M II AS, M III AS, M V AS, M VI AS) samples. M I exhibited the lowest average hardness among the unaged materials, while M III AS had the lowest average hardness among the aged materials. Comparably low hardness was demonstrated by the M I AS material. The coefficient of friction values for the aged samples were found to be higher. The lowest wear value was demonstrated by the M I material. The wear resistance of most of the tested materials deteriorated after aging. The M VI AS material had the highest increase in wear. According to the results provided, not only the chemical composition and structure, but also aging have a great impact on the indentation hardness and wear resistance of the tested orthodontic materials. Full article
(This article belongs to the Special Issue Properties of Dental Restorative Materials)
Show Figures

Figure 1

30 pages, 2517 KiB  
Article
Modeling Adhesive Hysteresis
by Anle Wang, Yunong Zhou and Martin H. Müser
Lubricants 2021, 9(2), 17; https://doi.org/10.3390/lubricants9020017 - 8 Feb 2021
Cited by 18 | Viewed by 3769
Abstract
When an elastomer approaches or retracts from an adhesive indenter, the elastomer’s surface can suddenly become unstable and reshape itself quasi-discontinuously, e.g., when small-scale asperities jump into or snap out of contact. Such dynamics lead to a hysteresis between approach and retraction. In [...] Read more.
When an elastomer approaches or retracts from an adhesive indenter, the elastomer’s surface can suddenly become unstable and reshape itself quasi-discontinuously, e.g., when small-scale asperities jump into or snap out of contact. Such dynamics lead to a hysteresis between approach and retraction. In this study, we quantify numerically and analytically the ensuing unavoidable energy loss for rigid indenters with flat, Hertzian and randomly rough profiles. The range of adhesion turns out to be central, in particular during the rarely modeled approach to contact. For example, negligible traction on approach but quite noticeable adhesion for nominal plane contacts hinges on the use of short-range adhesion. Central attention is paid to the design of cohesive-zone models for the efficient simulation of dynamical processes. Our study includes a Griffith’s type analysis for the energy lost during fracture and regeneration of a flat interface. It reveals that the leading-order corrections of the energy loss are due to the finite-range adhesion scale at best, with the third root of the linear mesh size, while leading-order errors in the pull-off force disappear linearly. Full article
(This article belongs to the Special Issue Friction Mechanisms)
Show Figures

Figure 1

9 pages, 3142 KiB  
Article
Dislocation Reaction Mechanism for Enhanced Strain Hardening in Crystal Nano-Indentations
by Ronald W. Armstrong and Wayne L. Elban
Crystals 2020, 10(1), 9; https://doi.org/10.3390/cryst10010009 - 23 Dec 2019
Cited by 6 | Viewed by 3489
Abstract
Stress–strain calculations are presented for nano-indentations made in: (1) an ammonium perchlorate (AP), NH4ClO4, {210} crystal surface; (2) an α-iron (111) crystal surface; (3) a simulated test on an α-iron (100) crystal surface. In each case, the calculation of [...] Read more.
Stress–strain calculations are presented for nano-indentations made in: (1) an ammonium perchlorate (AP), NH4ClO4, {210} crystal surface; (2) an α-iron (111) crystal surface; (3) a simulated test on an α-iron (100) crystal surface. In each case, the calculation of an exceptionally-enhanced plastic strain hardening, beyond that coming from the significant effect of small dislocation separations in the indentation deformation zone, is attributed to the formation of dislocation reaction obstacles hindering further dislocation movement. For the AP crystal, the exceptionally-high dislocation reaction-based strain hardening, relative to the elastic shear modulus, leads to (001) cleavage cracking in nano-, micro- and macro-indentations. For α-iron, the reaction of (a/2) <111> dislocations to form a [010] Burgers vector dislocation obstacles at designated {110} slip system intersections accounts for a higher strain hardening in both experimental and simulated nano-indentation test results. The α-iron stress–strain calculations are compared, both for the elastic deformation and plastic strain hardening of nano-indented (100) versus (111) crystal surfaces and include important observations derived from internally-tracked (a/2) <010> Burgers vector dislocation structures obtained in simulation studies. Additional comparisons are made between the α-iron calculations and other related strength properties reported either for bulk, micro-pillar, or additional simulated nano-crystal or heavily-drawn polycrystalline wire materials. Full article
Show Figures

Figure 1

Back to TopTop