Contact Modulus Research Articles

Nanoindentation of carbon microspheres

AbstractThe indentation behavior of carbon microspheres was examined. The indentation load was in the range of 50 μN to 500 μN for the carbon microspheres with a diameter of ∼5 μm, and 15 μN to 100 μN for the carbon microspheres with a diameter of 1 μm. For the same ratio of the maximum indentation depth to the diameter of the carbon microspheres, both the contact modulus and indentation hardness for the carbon microspheres with a diameter of ∼5 μm are larger than the corresponding values for the carbon microspheres with a diameter of ∼1 μm. The carbon microspheres of ∼5 μm in diameter exhibited a larger resistance to the mechanical deformation than the carbon microspheres of ∼1 μm in diameter. The plastic energy dissipated in the nanoindentation increases with the increase of the indentation depth (load) and is a power function of the indentation depth.

Quantifying Cartilage Contact Modulus, Tension Modulus, and Permeability With Hertzian Biphasic Creep.

This paper describes a new method, based on a recent analytical model (Hertzian biphasic theory (HBT)), to simultaneously quantify cartilage contact modulus, tension modulus, and permeability. Standard Hertzian creep measurements were performed on 13 osteochondral samples from three mature bovine stifles. Each creep dataset was fit for material properties using HBT. A subset of the dataset (N = 4) was also fit using Oyen's method and FEBio, an open-source finite element package designed for soft tissue mechanics. The HBT method demonstrated statistically significant sensitivity to differences between cartilage from the tibial plateau and cartilage from the femoral condyle. Based on the four samples used for comparison, no statistically significant differences were detected between properties from the HBT and FEBio methods. While the finite element method is considered the gold standard for analyzing this type of contact, the expertise and time required to setup and solve can be prohibitive, especially for large datasets. The HBT method agreed quantitatively with FEBio but also offers ease of use by nonexperts, rapid solutions, and exceptional fit quality (R2 = 0.999 ± 0.001, N = 13).

Microstructural Evolution and Mechanical Properties in (AuSn)eut-Cu Interconnections

The interfacial reactions between the widely employed solder Au-20wt.%Sn and the common contact metallizations (e.g. Ni, Cu and Pt) are normally complex and not well determined. In order to identify the proper contactor for Au-20wt.%Sn solder, the present study focuses on (1) rationalizing the interfacial reaction mechanisms of Au-20wt.%Sn|Cu as well as (2) measuring the mechanical properties of individual intermetallics formed at the interface. The evolution of interfacial reaction products were rationalized by using the experimental results in combination with the calculated Au-Cu-Sn phase diagram information. It was found that the growth of the AuCu interfacial intermetallic layer was diffusion-controlled. The diffusion path of Au-20wt.%Sn|Cu at 150°C was proposed. The hardness and indentation modulus of the interfacial reaction products were measured using nanoindentation tests. The results revealed a significant influence of the Cu solubility on the mechanical properties of (Au,Cu)Sn and (Au,Cu)5Sn, i.e. their hardness and contact modulus increased with the increase in the amount of Cu. Furthermore, results obtained here for the Au-20wt.%Sn|Cu joints were compared to those from Au-20wt.%Sn|Ni in order to assess the similarities and differences between these widely used interconnection metallization systems.

Protein adsorption capability on polyurethane and modified-polyurethane membrane for periodontal guided tissue regeneration applications

Periodontal disease if left untreated can result in creation of defects within the alveolar ridge. Barrier membranes are frequently used with or without bone replacement graft materials for achieving periodontal guided tissue regeneration (GTR). Surface properties of barrier membranes play a vital role in their functionality and clinical success. In this study polyetherurethane (PEU) membranes were synthesized by using 4,4'-methylene-diphenyl diisocyanate (MDI), polytetramethylene oxide (PTMO) and 1,4-butane diol (BDO) as a chain extender via solution polymerization. Hydroxyl terminated polydimethylsiloxane (PDMS) due to having inherent surface orientation towards air was used for surface modification of PEU on one side of the membranes. This resulting membranes had one surface being PEU and the other being PDMS coated PEU. The prepared membranes were treated with solutions of bovine serum albumin (BSA) in de-ionized water at 37°C at a pH of 7.2. The surface protein adsorptive potential of PEU membranes was observed using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Raman spectroscopy and Confocal Raman spectroscopy. The contact angle measurement, tensile strength and modulus of prepared membranes were also evaluated. PEU membrane (89.86±1.62°) exhibited less hydrophobic behavior than PEU-PDMS (105.87±3.16°). The ultimate tensile strength and elastic modulus of PEU (27±1MPa and 14±2MPa) and PEU-PDMS (8±1MPa and 26±1MPa) membranes was in required range. The spectral analysis revealed adsorption of BSA proteins on the surface of non PDMS coated PEU surface. The PDMS modified PEU membranes demonstrated a lack of BSA adsorption. The non PDMS coated side of the membrane which adsorbs proteins could potentially be used facing towards the defect attracting growth factors for periodontal tissue regeneration. Whereas, the PDMS coated side could serve as an occlusive barrier for preventing gingival epithelial cells from proliferating and migrating into the defect space by facing the soft tissue flaps. This study demonstrates the potential of a dual natured PEU barrier membrane for use in periodontal tissue engineering applications and further investigations are required.

Current-induced strength degradation of activated carbon spheres in carbon supercapacitors

Activated carbon microspheres (ACSs), which are prepared using hydrothermal synthesis and ammonia activation, are used as the active materials in the anode and cathode of electric double layer capacitors (EDLCs). The ACS-based EDLCs of symmetrical electrodes exhibit good stability and a high degree of reversibility over 2000 charge-discharge cycles for electric current up to 10 A g−1. The ACSs maintain a nongraphitized carbon structure after over 2000 charge-discharge cycles. Nanoindentation experiments are performed on the ACSs, which are electrochemically cycled in a voltage window of 0–1 V at three electric currents of 0.5, 5, and 10 A g−1. For the same indentation load, both the contact modulus and indentation hardness of the ACSs decrease with the increase of the electric current used in the electrical charging and discharging. These results suggest that there exists strength degradation introduced by the electric current. A larger electric current will cause more strength degradation than a smaller electric current.

The effect of storage pressure on the mechanical properties of paddy grains

Abstract To investigate the effect of storage pressure and storage time on the mechanical properties of paddy grains, an experimental study was carried out to determine the mechanical properties of paddy grains compressed at minor axis orientation using the Texture Analyzer. The paddy grains were stored under different pressures and for different time. The results showed that as the storage pressure increased from 0 to 300 kPa, the rupture force of paddy grains stored for 60 days decreased from 81.58 to 73.78 N, the rupture energy from 8.10 to 6.27 mJ, the rupture strain from 0.1392 to 0.1168, the apparent contact modulus of elasticity from 171.32 to 57.68 MPa and the maximum contact stress from 40.84 to 19.11 MPa. All of the mechanical properties of the paddy grains exhibited a linear relationship with storage pressure. As for the paddy grains stored under the pressures of 77, 100, 139, 200 kPa, as the storage time increased from 0 to 60 days, the rupture force of the paddy grains decreased from 81.58 to 79.58 N, 81.58 to 79.12 N, 81.58 to 78.21 N and 81.58 to 76.96 N; the rupture energy decreased from 8.10 to 7.55 mJ, 8.10 to 7.35 mJ, 8.10 to 7.08 mJ and 8.10 to 6.85 mJ; the rupture strain decreased from 0.1392 to 0.1309, 0.1392 to 0.1283, 0.1392 to 0.1257 and 0.1392 to 0.1213. The apparent contact modulus of elasticity decreased from 171.32 to 135.97 MPa, 171.32 to 121.77 MPa, 171.32 to 110.59 MPa and 171.32 to 83.32 MPa; the maximum contact stress decreased from 41.16 to 35.00 MPa, 41.16 to 32.45 MPa, 41.16 to 30.32 MPa and 41.16 to 14.97 MPa, respectively. The results revealed that both storage pressure and storage time have a significant effect on the mechanical properties of paddy grains.

Numerical investigation of indentation tests on a transversely isotropic elastic material by power-law shaped axisymmetric indenters

Nowadays, there exist many well-known classical models of frictionless adhesive contact including the Johnson–Kendall–Roberts (JKR) model, the Derjaguin–Muller–Toporov (DMT) model, and the Maugis solution for the JKR-type-to-DMT-type transition regimes. These models are very helpful for studying molecular adhesion between two contacting linearly elastic isotropic spherical bodies. However, in experimental studies, such as nanoindentation tests, the shapes of the indenters are often more general than the spherical or flat ones. Moreover, very often, the materials to be tested are anisotropic. A special case of anisotropy is transverse isotropy, which contains a plane of isotropy, implying that the material can be rotated with respect to the loading direction about one axis without measurable effect on the material’s response. In this paper, numerical studies on JKR-type frictionless adhesive contact between power-law shaped indenters and transversely isotropic materials are presented. It shows that the formulae for numerical simulations of JKR-type frictionless adhesive contact for transversely isotropic materials have the same mathematical form as the corresponding formulae for isotropic materials, except that the effective elastic contact modulus has different expression for different materials. The DMT-type and JKR-type-to-DMT-type transition regimes have been explored by conducting the simulations using smaller values of Tabor parameters. The good agreement between numerical simulation results and existing analytical solutions shows that this numerical simulation method can be extended to simulate indentation tests using indenters of arbitrary shapes.

Simulation of the elastic deformation of laser-welded joints of an austenitic corrosion-resistant steel and a titanium alloy with an intermediate copper insert

The macro- and microstructures and the distribution of elements and of the values of the microhardness and contact modulus of elasticity along the height and width of the weld metal and heat-affected zone of austenitic corrosion-resistant 12Kh18N10T steel (Russian analog of AISI 321) and titanium alloy VT1-0 (Grade 2) with an intermediate copper insert have been studied after laser welding under different conditions. The structural inhomogeneity of the joint obtained according to one of the regimes selected has been shown: the material of the welded joint represents a supersaturated solid solution of Fe, Ni, Cr, and Ti in the crystal lattice of copper with a uniformly distributed particles of intermetallic compounds Ti(Fe,Cr) and TiCu3. At the boundaries with steel and with the titanium alloy, diffusion zones with thicknesses of 0.1–0.2 mm are formed that represent supersaturated solid solutions based on iron and titanium. The strength of such a joint was 474 MPa, which corresponds to the level of strength of the titanium alloy. A numerical simulation of the mechanical behavior of welded joints upon the elastic tension–compression has been performed taking into account their structural state, which makes it possible to determine the amplitude values of the deformations of the material of the weld.

Correlative Nanomechanical Measurements for Complex Engineered Systems

ABSTRACTMultilayered film stacks, with length scales less than 10 nm are commonly used in a variety of devices, but present significant challenges to mechanical testing and evaluation. This is due to property convolution of the different layers. Both the properties of the individual layers and the combined response of the film stack are important input for design optimization. Here, we present ex-situ nanoindentation of a film stack representative of a perpendicular magnetic recording (PMR) hard disc drive (HDD), with more than 10 layers. We then compare this with in-situ transmission electron microscopy indentation to visualize deformation of individual layers of the stack. The ex-situ testing reveals early plastic deformation, with an initially high contact pressure (13 GPa) and modulus ( >160 GPa), followed by significant softening (8 GPa contact pressure and 140 GPa modulus), then slight hardening to 9 GPa. From in-situ testing, it is revealed that the metallic layer directly under the diamond like carbon (DLC) contributes the majority of the deformation and plastic flow, which is in turn constrained by a metallic oxide.

Wear efficiency of oil-well casings exposed to rotating tooljoints

Wall loss due to adhesive wear between a rotating drillstring tooljoint and the softer inner surface of a steel casing is often encountered while drilling deviated oil and gas wellbores. Despite the significance of the problem in the drilling industry, there is little data on casing wear efficiencies in the public domain. A large body of data collected during a joint industry project was deemed proprietary to participants who sponsored the private project (DEA-42). In this paper, we outline an approach to determine the wear efficiency of unlubricated surfaces by using the roughness parameters and material properties of the wearing surface. Our method combines the classic Greenwood & Williamson (1966) approach with the Archard-Rabinowicz (1953) interpretation of wear efficiency. The Greenwood & Williamson study models surface morphology as an ensemble of randomly distributed asperities. Archard (1953) interprets wear efficiency as the probability of a wear particle being created during an encounter of asperities between sliding surfaces. By using these notions we derive a formula for wear efficiency of an unlubricated surface as a function of the standard deviation of its summit height distribution, the summit radius, the hardness and contact modulus. Our predicted wear efficiencies are in the range of 1.5 - 5 ×10-3. These values agree well with published results for similar metals sliding on each other without lubrication. Future work along these lines will consider the effect of lubricants on adhesive wear efficiency.

Numerical Analysis of Indentation of an Elastic Hemispherical Shell

AbstractNanoindentation technique has been used to measure the elastic modulus of virus capsids, capsules, vesicles, and tubules. The principle of the nanoindentation technique is based on the elastic solution of an isotropic, homogeneous, semi-infinite material, which limits the use of nanoindentation in measuring the mechanical properties of materials of small scales. To address this limitation, Reissner's thin shell model, which is based on the point indentation on a thin shell, has been used in analyzing the indentation of thin shells. In this work, the indentation of elastic hemispherical shells of various thicknesses by a rigid, spherical indenter is analyzed, using the finite element method. The simulation results reveal the limitation of the Reissner's thin shell model. A semi-analytical relationship between the indentation depth and the indentation load is proposed, which consists of the contributions of the Hertz's local deformation, the Reissner's local flattening, and the Pogorelov's deflection of the shell. This relationship provides an analytical basis of using nanoindentation to determine the nominal contact modulus of spherical shells. The comparison between the numerical results and the experimental results in literature supports the proposed semi-analytical relationship and reveals the effect of viscoelastic characteristic of shell structures on the indentation deformation.

Effect of electric current on nanoindentation of superelastic NiTi alloy

NiTi alloys have many engineering applications in microelectromechanical systems due to their super-elasticity and shape memory effect. Using nanoindentation technique, the effect of DC electric current on the nanoindentation behavior of superelastic NiTi wires with a composition of Ni: 55.8 wt%, Ti: balance, O2: ≤0.05 wt%, C: ≤0.05 wt% was studied for the current density in a range of 0 to 2.74 kA/cm2 and the indentation load in a range of 100 to 1500 μN. The reduced contact modulus increased with increasing electric current density for the current density larger than or equal to 1.32 kA/cm2. For the indentation load larger than or equal to 200 μN, the indentation hardness slightly increased with increasing electric current density. The indentation hardness decreased with increasing indentation load, showing the normal indentation size effect. A simple linear relation was derived between the indentation hardness and the square root of the ratio of indentation hardness to indentation load, which is supported by experimental results.

Amino acid mediated synthesis of silver nanoparticles and preparation of antimicrobial agar/silver nanoparticles composite films

Silver nanoparticles (AgNPs) were synthesized using amino acids (tyrosine and tryptophan) as reducing and capping agents, and they were incorporated into the agar to prepare antimicrobial composite films. The AgNPs solutions exhibited characteristic absorption peak at 420 nm that showed a red shift to ∼434 nm after forming composite with agar. XRD data demonstrated the crystalline structure of AgNPs with dominant (111) facet. Apparent surface color and transmittance of agar films were greatly influenced by the AgNPs. The incorporation of AgNPs into agar did not exhibit any change in chemical structure, thermal stability, moisture content, and water vapor permeability. The water contact angle, tensile strength, and modulus decreased slightly, but elongation at break increased after AgNPs incorporation. The agar/AgNPs nanocomposite films possessed strong antibacterial activity against Listeria monocytogenes and Escherichia coli. The agar/AgNPs film could be applied to the active food packaging by controlling the food-borne pathogens.

Towards a better understanding of wood cell wall characterisation with contact resonance atomic force microscopy

Nowadays, the multi-scale modelling of wood has a great need for measurements of structural, chemical and mechanical properties at the lowest level. In this paper, the viscoelastic properties in the layers of a wood cell wall are investigated using the contact resonance mode of an atomic force microscope (CR-AFM). A detailed experimental protocol suitable for obtaining reproducible and quantifiable data is proposed. It is based on three main steps: sample preparation to obtain a good surface state, calibration of the contact modulus using reference samples, and image processing to produce the viscoelastic images. This protocol is applied on chestnut tension wood. The obtained topography and semi-quantitative viscoelastic maps are discussed with respect to the cell wall structure, sample preparation effects, and AFM measurement specificity compared with nanoindentation.

A numerical test method of California bearing ratio on graded crushed rocks using particle flow modeling

In order to better understand the mechanical properties of graded crushed rocks (GCRs) and to optimize the relevant design, a numerical test method based on the particle flow modeling technique PFC2D is developed for the California bearing ratio (CBR) test on GCRs. The effects of different testing conditions and micro-mechanical parameters used in the model on the CBR numerical results have been systematically studied. The reliability of the numerical technique is verified. The numerical results suggest that the influences of the loading rate and Poisson's ratio on the CBR numerical test results are not significant. As such, a loading rate of 1.0–3.0 mm/min, a piston diameter of 5 cm, a specimen height of 15 cm and a specimen diameter of 15 cm are adopted for the CBR numerical test. The numerical results reveal that the CBR values increase with the friction coefficient at the contact and shear modulus of the rocks, while the influence of Poisson's ratio on the CBR values is insignificant. The close agreement between the CBR numerical results and experimental results suggests that the numerical simulation of the CBR values is promising to help assess the mechanical properties of GCRs and to optimize the grading design. Besides, the numerical study can provide useful insights on the mesoscopic mechanism.

Evaluation of elastic modulus and hardness of highly inhomogeneous materials by nanoindentation

The experimental and numerical techniques for evaluation of mechanical properties of highly inhomogeneous materials are discussed. The techniques are applied to coal as an example of such a material. Characterization of coals is a very difficult task because they are composed of a number of distinct organic entities called macerals and some amount of inorganic substances along with internal pores and cracks. It is argued that to avoid the influence of the pores and cracks, the samples of the materials have to be prepared as very thin and very smooth sections, and the depth-sensing nanoindentation (DSNI) techniques has to be employed rather than the conventional microindentation. It is shown that the use of the modern nanoindentation techniques integrated with transmitted light microscopy is very effective for evaluation of elastic modulus and hardness of coal macerals. However, because the thin sections are glued to the substrate and the glue thickness is approximately equal to the thickness of the section, the conventional DSNI techniques show the effective properties of the section/substrate system rather than the properties of the material. As the first approximation, it is proposed to describe the sample/substrate system using the classic exponential weight function for the dependence of the equivalent elastic contact modulus on the depth of indentation. This simple approach allows us to extract the contact modulus of the material constitutes from the data measured on a region occupied by a specific component of the material. The proposed approach is demonstrated on application to the experimental data obtained by Berkovich nanoindentation with varying maximum depth of indentation.

Simulation of triaxial response of granular materials by modified DEM

A modified discrete element method (DEM) with rolling effect taken into consideration is developed to examine macroscopic behavior of granular materials in this study. Dimensional analysis is firstly performed to establish the relationship between macroscopic mechanical behavior, mesoscale contact parameters at particle level and external loading rate. It is found that only four dimensionless parameters may govern the macroscopic mechanical behavior in bulk. The numerical triaxial apparatus was used to study their influence on the mechanical behavior of granular materials. The parametric study indicates that Poisson’s ratio only varies with stiffness ratio, while Young’s modulus is proportional to contact modulus and grows with stiffness ratio, both of which agree with the micromechanical model. The peak friction angle is dependent on both inter-particle friction angle and rolling resistance. The dilatancy angle relies on inter-particle friction angle if rolling stiffness coefficient is sufficiently large. Finally, we have recommended a calibration procedure for cohesionless soil, which was at once applied to the simulation of Chende sand using a series of triaxial compression tests. The responses of DEM model are shown in quantitative agreement with experiments. In addition, stress-strain response of triaxial extension was also obtained by numerical triaxial extension tests.

Tribological and material properties for cartilage of and throughout the bovine stifle: support for the altered joint kinematics hypothesis of osteoarthritis

Prior studies suggest that ligament and meniscus tears cause osteoarthritis (OA) when changes in joint kinematics bring underused and underprepared regions of cartilage into contact. This study aims to test the hypothesis that material and tribological properties vary throughout the joint according to the local mechanical environment. The local tribological and material properties of bovine stifle cartilage (N=10 joints with 20 samples per joint) were characterized under physiologically consistent contact stress and fluid pressure conditions. Overall, cartilage from the bovine stifle had an equilibrium contact modulus of Ec0=0.62±0.10MPa, a tensile modulus of Et=4.3±0.7MPa, and a permeability of k=2.8±0.9×10(-3)mm(4)/Ns. During sliding, the cartilage had an effective friction coefficient of μeff=0.024±0.004, an effective contact modulus of Ec=3.9±0.7MPa and a fluid load fraction of F'=0.81±0.03. Tibial cartilage exhibited significantly poorer material and tribological properties than femoral cartilage. Statistically significant differences were also detected across the femoral condyle and tibial plateau. The central femoral condyle exhibited the most favorable properties while the uncovered tibial plateau exhibited the least favorable properties. Our findings support a previous hypothesis that altered loading patterns can cause OA by overloading underprepared regions. They also help explain why damage to the tibial plateau often precedes damage to the mating femoral condyle following joint injury in animal models. Because the variations are driven by fundamental biological processes, we anticipate similar variations in the human knee, which could explain the OA risk associated with ligament and meniscus tears.

Experimental assessment of the elastic properties of thin TiN/AlN superlattice and nano-multilayer coatings

Nanoindentation is widely used for the mechanical assessment of coatings and thin films . Whereas this can lead to reliable assessments for coating-only properties for short range properties like plasticity the longer range of elastic interactions means that measured data always contains a contribution from the substrate. This paper describes a simple model which can be used to assess the extent of these interactions and predict how changing the elastic properties of individual layers in a complex multilayer or superlattice coating may influence the contact modulus measured by nanoindentation. The model highlights the effect of the transition from hexagonal to cubic AlN as the bilayer period is reduced in TiN/AlN nano-multilayer coatings and how the elastic anisotropy of the layer materials can also be significant in textured coatings. These effects may be masked by the effects of tip bluntness on nanoindentation data from very thin (submicron) films and a coating thickness of at least 3 μm is required for reliable coating data to be obtained for hard coatings on a stiff substrate tested with a typical used Berkovich indenter. • A model has been developed to determine the variation of elastic properties with contact depth for superlattice coatings. • The model has been used to understand the changes in TiN/AlN superlattices as the superlattice period is reduced. • The importance of phase and crystallographic texture has been demonstrated.

Anisotropic Behavior of the Nanoindentation of Single Carbon Fibers

The mechanical behavior of carbon fibers determines the applications of carbon fiber reinforced composites in automotive and aerospace. The indentation behavior of single carbon fibers has been investigated in the indentation load range of 0.5 mN to 2.5 mN on two different cross-sections; one is a longitudinal section with the surface normal perpendicular to the fiber axis and the other is a transverse section with the surface normal parallel to the fiber axis. The indentation results reveal the anisotropic characteristics of the mechanical behavior of the carbon fibers. The contact modulus of the transverse section of the carbon fibers is about twice of that of the longitudinal section of the carbon fibers, while the indentation hardness of the transverse section of the carbon fibers is slightly larger than that of the longitudinal section. The plastic energy dissipated in the nanoindentation for both of the sections increases with the increase of the indentation load and is a power function of the indentation load with a power index of about 1.9.