Three different processes, Plasma Enhanced CVD (PECVD), Ion Beam (IB), and Cathodic Arc (CA) have been used to deposit highly energetic carbon films in the 2–10 nm thickness range in commercial, high throughput disk manufacturing tools. The deposition conditions used are typical of those required for disk manufacturing. Raman spectroscopy, I-V measurements, nanoindentation, and AFM based scratch testing have been used to characterize the structural, electrical, and mechanical properties of the films. The measured maximum hardness for the PECVD and IBD films are 28 and 25 GPa, respectively, and found to be influenced by the hardness of the softer substrates for the 70–120nm films available for measurement. The scratch resistance of the CAC films is ∼2× the scratch resistance of the IBD films and 25% greater than the PECVD films. Addition of nitrogen to the films produced by both the PECVD and IB techniques reduces the hardness of the films. Both the Raman and I-V data suggest increasing concentrations of sp 2 bonding result from these nitrogen additions.

Nanometer-thick liquid lubricant films are useful for the lubrication of miniaturized mechanical systems, such as hard disk drives or microelectromechanical systems. However, there are no established methods for measuring the mechanical properties of such thin films, which can be an obstacle to the optimal design of lubrication systems. We previously developed a highly sensitive method for measuring shear forces, which we called the fiber-wobbling method (FWM). In the FWM, we used a ball-ended optical fiber to probe shear and we measured the friction force acting on the probe tip by detecting the deflection of the fiber. By this means we succeeded in measuring friction forces in nanometer-thick liquid lubricant films. However, we could not evaluate the mechanical properties of the films quantitatively because the contact area between the probe tip and lubricant film was unknown. Here, we developed a method for measuring the contact area during shearing of nanometer-thick liquid lubricant films in the FWM.

The articular cartilage function is to allow the bones in a joint to move without causing excess friction and damage. When this cartilage becomes damaged, the supportive and lubricating mechanisms break down, leading to injuries which can be permanent or take extended periods of time for recovery. Because of its importance in general health and body mobility, the unique lubricating properties of cartilage have been studied for many decades. Many current theories exist to characterize the biphasic and triphasic nature of cartilage; however, an important reason that cartilage is so effective is its viscoelastic nature, which allows elastic and dissipative mechanisms to exist simultaneously. It is desired to derive the material properties of cartilage in order to better understand its mechanical effectiveness. Utilizing a CETR-UMT-3 Tribometer, stress relaxation experiments will be performed on freshly harvested equine cartilage plugs that remain hydrated in a fluid bath. Viscoelastic models, such as the Prony series and fractional derivative, are applied to the experimental data to determine the storage and loss moduli of the sample explants. The storage and loss information characterizes the mechanical response of cartilage, and provides insight into the effectiveness and longevity of biological joints. A comparison will be made between joints that experience similar loads, but undergo different relative motions, to determine if the mechanical properties of cartilage are tailored to joint function. Osteoarthritic cartilage will also be explored for deviations in viscoelastic behavior compared to healthy cartilage. Ultimately, it is hoped that a viscoelastic characterization of articular cartilage will lead to insight into the precursors of osteoarthritis, more advanced prosthetics, and biomimetric applications such as the integration of flexible surfaces in mechanical systems.

Mechanical rock cutting is a process encountered in different engineering applications including rock excavation, mining and deep oil well drilling. Rock mechanical properties vary with depth in the subsurface and also at different geographical locations due to different environmental conditions. Understanding of fragmentation mechanisms in specific rock materials allows the determination of optimum cutting parameters that improve cutting efficiency and increase tool life during cutting operations. In the present investigation, numerical models that accurately predict the rock fragmentation and stress profiles in the rock slab during cutting were developed using the explicit finite-element method (FEM). In the numerical models, a damage material model was utilized to capture the rock fragmentation process and a rigid steel cutter (at different rake angles) was displaced at different velocities against a stationary rock slab. Rock slabs with significantly different mechanical properties were incorporated with a constant friction factor and a cutting depth of 1 mm. The variation of cutting forces and stresses, and fragmentation of the rock slab were analyzed. The simulation results indicated that the explicit FEM is a powerful tool for simulating rock cutting as the formation of fragments were distinctly observed at different cutting conditions. The rock mechanical properties and tool rake angle were found to have the most significant effect on the rock fragmentation during cutting operations. The cutting forces were also influenced by mechanical properties of the rock and tool rake angle.

The actual contact between solid surfaces is generally rough and time dependent. The stresses induced by the rough contact can only be correctly described using a detailed 3D model. Even finer details are required in the case of surface coatings. Consequently, the rough coated contact problem is strongly multi-scale: the characteristic dimensions of the contact, the coating and the roughness range from the millimeter to the nanometer. A straightforward discretisation of this multi-scale problem would exceed the memory and CPU capacity of current (and next generation) computers. This paper proposes an efficient numerical model that can handle this multi-scale problem: using 10 9 points and locally refined grids. The proposed model is based on multigrid techniques within a finite difference frame work. Localised refinement is implemented to optimize memory requirement and computing time. Validation of the solver is performed through a comparison with analytical results for simple cases. The algorithm performance is analyzed through a parametric study describing the influence of layer thickness (0.01 < t/a < 10) and mechanical properties (0.005 < E c /E s < 10) of the coating on the contact parameters (P h , a). A linear graded coating, used as a solution to avoid interfacial problems, is then compared to a coating with constant properties. A quantitative analysis of the evolution of the maximum tensile stress with depth is conducted in both cases.

Nanoindentation measurements on TiAlN, CrN, a-C:H:Me, and TiN, deposited on steel substrates have been performed. It was found that the resulting surface roughness/morphology after deposition significantly affects the measurements of nanomechanical properties, while measurements of these properties on the surface may be significantly different than the bulk portion of the coating, exhibiting a lower nanohardness due to the existence of a surface contamination layer. A simple method is proposed for accurately measuring the nanomechanical properties of coatings alleviating the need for excessive statistical analysis and the issues that arise from surface topography and the presence of surface and contamination layers on thin films.

The mechanical behavior of eukaryotic cell components is critical to cell mobility, division, signaling, and proliferation. Cell components are in such harmony with each other that often mechanical testing of individual components produces less meaningful results than testing performed within living cells. Moreover, cell components are constantly undergoing growth and remodeling, normally through polymerization and depolymerization. An appropriate experimental and modeling framework is therefore essential for cell mechanics. In this study, a special atomic force microscope (AFM) with controlled adhesion area of the cell to a substrate was used to probe the mechanical response of cells to an external force. This experimental set up enables direct control of the applied force and precise measurement of the cell penetration by the AFM tip. A modeling framework that combines the displacement field with the applied force/stress obtained with the AFM is developed to estimate the mechanical properties of each cell component. The tribological relevance of this research is the viscoelastic deformation of cell components under different contact loads.

An ultrathin (<4 nm) film of amorphous carbon ( a -C) is used in contemporary disk drives to protect the magnetic medium of the hard disk from corrosion and mechanical wear due to intermittent impact of the low-flying magnetic head. Because of increasing demands for much higher magnetic storage densities (i.e., >10 Tbits/in 2 ), the a -C film thickness must be decreased to <2 nm. However, the tribological and mechanical properties of such thin a -C films are not well understood and, moreover, are extremely difficult to determine experimentally. The objective of this study was to obtain insight into the tribological behavior of ultrathin a -C films by performing molecular dynamics (MD) simulations. MD results of the hardness and friction properties of nanometer-thick a -C films are interpreted in terms of the ratio of tetrahedral-to-trigonal carbon atom hybridization. A critical thickness for the effective protection of the magnetic medium by the a -C film is estimated from MD results. The results of this study elucidate the nanomechanical and nanotribological properties of ultrathin a -C films used as protective overcoats in extremely-high-density magnetic recording.

Skin is the largest organ of the human body. Its main role is to ensure cohesion and protection of the internal body structures, acting as a physical and social interface to the external environment. The geometry and biophysics of this multi-layered biological structure are key elements in determining the nature and characteristics of these interactions [1]. Skin wrinkles [2], of particular relevance for skin care and shaving products, are the result of a complex interplay between material and structural properties, boundary and loading conditions the exact nature of which remains to be elucidated [3]. The variability of these properties/conditions according to the anatomical site, gender, race, from individuals to individuals or from experimental measurement techniques call for stochastic computational models [4]. The objective of this study was therefore to quantify the relative dependence of the wrinkling behavior of skin on these mechanical and geometrical factors by performing a stochastic finite element study accounting for 14 random variables. An integrated methodology combining design of experiment, solid modeling, finite element analysis and Bayesian meta-modeling was developed for this purpose. A three-layer finite element skin model including epidermis, dermis and hypodermis was designed. The sensitivity of the eigenvalues of the skin structure, number of wrinkles, amplitude of wrinkles, average roughness of the skin surface to the 14 probabilistic variables were calculated. It was found that the first four eigenvalues of the three-layer skin structure are mostly sensitive to the stiffness of the epidermis whilst this is no longer the case from the fifth eigenvalue. The thickness of the epidermis has the most significant effect on the number of wrinkles whilst the sensitivity of the average roughness to the length of the skin sample is maximum.

Scratch-related magnetic signal degradation can occur during magnetic storage hard disk drive operation when the read-write heads contact the spinning multilayer disks. To investigate this phenomenon controlled nanoscratch experiments were performed on perpendicular magnetic recording media using various indenters of different radii of curvature. Various loading conditions were used to cause permanent scratches that were measured using atomic force microscopy. The nanoscratch experiments were simulated using finite element analysis (FEA) that included the detailed nanometer scale thin-film multilayer mechanical properties. The permanently deformed field in the sub-surface magnetic recording layer was extracted from the FEA results. The residual scratch widths measured on the surface of the magnetic storage disk were directly compared with the residual sub-surface widths of the region on the magnetic recording layer where extensive permanent lateral deformation was present. It was found that the sub-surface widths of the deformed regions were significantly larger than the surface scratch widths. Thus, sub-surface thin-film layers, such as the magnetic recording layer could be damaged without observable damage to the protective top surface carbon overcoat. The exact location and extent of damage to the magnetic recording layer depends on the scratch load, size of scratch tip, and the friction at the interface. Such permanent deformation in magnetic recording layer could lead to demagnetization, which has been reported in the literature.

Cr-N and Cu-Cr-N coatings with Cu content between 3–65 at.%, Cu/Cr ratios in the 0.04–4.5 range and 21–27 at.% N, synthesized by twin e-beam Physical Vapor Deposition (EBPVD) at 450°C, were investigated. Using X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GAXRD) and scanning electron microscopy (SEM), in combination with nanoindentation mechanical property measurements and laboratory controlled ball-on-disc sliding experiments, it is shown that Cu-Cr-N coatings with low Cu content (3 at.%) possess sufficient wear resistance for high temperature demanding tribological applications.

Wear reduction by Carbon Nanotube (CNT) addition in composites with Ultra-High Molecular Weight Polyethylene (UHMWPE), Polyimide (PI), Polytetrafluoroethylene (PTFE), and epoxy resins have been reported separately. We studied Polypropylene (PP) and Polyamide (PA) composites and showed that with the addition of Multi-wall Carbon Nanotube (VGCF: Vapor Grown Carbon Fiber), wear decreased for PA composites but increased for PP composites. Differences in tribological characteristics of CNT composites with different resins were not well understood. In this paper, we compared tribological and mechanical characteristics of VGCF composites with PE, PP, and Polyacetal (POM) resins. Ball-on-Disk wear tests and mechanical strength measurements were performed. It was found that with the increase in VGCF content, specific wear amount (SWA) of VGCF-PE composite decreased while SWA of VGCF-POM composite stayed almost constant and SWA of VGCF-PP composite increased. On the other hand, with the increase in VGCF content, the tensile strength of VGCF-PE composite was increased but those of VGCF-PP and VGCF-POM composite were decreased. Decrease in SWA of VGCF-PE composite corresponded to the increase in tensile strength with VGCF content. We considered that the intermolecular force between side wall of VGCF and PE was strong enough to make both the SWA small and the tensile strength large.

The friction characteristics of lubricated contacts are usually determined by the shearing of three interfacial structural elements; namely lubricant fluid film, tribochemical reaction films and the near-surface materials. The shear behavior of the fluid film components of lubrication can be adequately described by either the hydrodynamic, or elastohydrodynamic theories and calculations. The shear behavior of the near surface materials can also be approximated by contact mechanics. However, due to the complexity and lack of adequate information, description and analysis of the tribochemical film contributions to frictional behavior is more challenging. In this study we present evaluation of the friction behavior of a lubricated contact as a function of tribological test duration, as the tribochemical surface films were being formed. Tests were conducted with two different formulated lubricants, in addition to an unformulated PAO basestock lubricant. One of the formulated lubricants consists of PAO synthetic basestock with 2.5% each of ZDDP and MoDTC additives. The other formulated lubricant is a fully formulated commercial gear oil with similar viscosity. During the friction tests in a fully flooded reciprocating sliding roller-on-flat contact configuration, the friction coefficient decreased exponentially as the tribochemical films were formed; highlighting the impact of boundary films on friction. In the test with the basestock fluid, the friction remained constant for the duration of the test; although an oxide layer was formed. Nanoindentation hardness and modulus measurements were conducted on two of the tribochemical films to measure their mechanical properties and the consequent impact on measured friction during testing.

In this study the tribological analysis of Al 2 O 3 nanocomposites/Al 2 O 3 pair; proposed as a candidate material to fabricate hip prostheses was carried out. Nanopowders of Al 2 O 3 (AKP 50, 300 nm), TiO 2 (PS-25, 50 nm) and Co metallic powder (Nilaco, 28 nm) were mixed and hot pressed. Wear test was carried out in a pin-on-plate tribometer, with a frequency of 1 Hz, a load of 49 N, for 4h; the counterface used was Al 2 O 3 . Mechanical properties as Vickers hardness, fracture toughness and Young’s modulus were estimated using the indentation method. Distilled water and fetal bovine serum solution (FBSS) were used as environment. It was found that the specific wear rate of Al 2 O 3 nanocomposites was about 10 −8 mm 3 /N*m and the coefficients of friction were around 0.3–0.5 for FBSS. Worn surfaces were observed using SEM.

This study aims to contribute to better understand the antiwear action of zinc dialkyldithiophosphate (ZDTP) additives used in car engine lubrication. The antiwear action of ZDTP is associated to the formation of a protective tribofilm onto the rubbing surface. On a mechanical point of view, the efficiency of ZDTP tribofilms results from equilibrium between film formation and wear rates, associated with appropriate rheological properties. In this work, the mechanical properties of a ZDTP tribofilm have been measured by nanoindentation in different test conditions in order to investigate the effect of temperature and strain rate. A Nanoindenter XP® entirely set into a climatic chamber was used to perform the nanoindentation tests. For all tests, an increase of the elastic modulus was observed from a threshold contact pressure value. This effect is similar to the anvil effect observed on polymers: in confined geometry, the elastic modulus increases versus hydrostatic pressure. For the tribofilm, in the studied range, this effect is enhanced at high temperature and low strain rate. Furthermore, when the temperature increases, a change in the rheological behavior of the tribofilm is observed. Up to about 50°C, the tribofilm exhibits viscoplastic behavior — the hardness increases versus strain rate — and above 50°C, the hardness decreases versus strain rate (“shear thinning-like” behavior).

A significant component of our understanding of cartilage mechanical behaviour is the ability to model its response to various types of mechanical loading, for which we require detailed knowledge of cartilage material properties. The Finite Element Analysis software ABAQUS is renowned for the ability to model poroelastic materials using the soil consolidation theory . In this research, ABAQUS has been used to model and investigate the mechanical behaviour of articular cartilage, mainly using indentation and unconfined compression techniques. A biphasic model of articular cartilage was first created and subsequently modified to incorporate more detailed material descriptions. Various material constitutive laws (and mechanical properties), accounting for the strain dependent permeability of the porous matrix, solid viscoelasticity and transverse isotropy, have been adopted to produce increasingly sophisticated models. The presence of collagen fibril networks embedded in the solid has been also considered and Fibril Reinforced Elastic and Viscoelastic models produced. A salient feature of these models is their ability to simulate fibril stiffening by replicating the nonlinear fibrillar response. In this paper, we provide an overview of the state-of-art modelling techniques adopted to simulate cartilage behaviour. The comparative study performed by the authors provides a critical assessment of the effectiveness of such techniques.

The tribological behavior of CrN and Al-Cr-N coatings prepared by twin electron-beam evaporation at 450°C was investigated. The composition, structure, mechanical and tribological properties of the coatings were determined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) in combination with nanoindentation mechanical property measurements, scanning electron microscopy (SEM), and laboratory controlled ball-on-disc sliding experiments. It was found that all of the Al-Cr-N coatings exhibit higher hardness compared to CrN coatings. Also, the compositions of Al-Cr-N coatings with the lower Al content and lower Al/Cr ratios showed better tribological performance than the rest of the coatings.

Recent improvements in growth methodologies have decreased the grain sizes and thicknesses of polycrystalline diamond films to the nanometer range, while also increasing the film uniformity and growth rate and preserving the outstanding mechanical properties of diamond. This is rendering such films more technologically and commercially viable. Ultrananocrystalline diamond (UNCD) are the thinnest (<200 nm) and smoothest (Rq < 10 nm) diamond films available.[1] These films demonstrated self-mated friction coefficients as low as near frictionless carbon (μ < 0.007) in environments with sufficient humidity, and the corresponding wear rates could not be measured using scanning white-light interferometry. However, their response to environmental conditions (e.g. relative humidity, ambient species, velocity, and temperature) had not been systematically explored in the past. This study focused on identifying conditions that contribute to favorable tribological performance. We find low friction performance at humidity levels below 1.5% in both nitrogen and argon environments.

Experimental comparison of common nano and micro scales for hardness evaluation has been performed on metal samples and discussed in details. Instrumented indentation was found advantageous in both repeatability and a number of measured parameters over classical hardness methods for metals, while sclerometry was advantageous for ultra-thin films.

Chemical mechanical polishing (CMP) is a critical nanomanufacturing process used to remove or planarize ultrathin metallic, dielectric, or barrier layers on silicon wafers. The CMP process is a vital interim fabrication step for integrated circuits and data storage devices. One of the major shortcomings of existing CMP models is that they do not account for crystallographic effects of the thin film metal materials when predicting material removal rates. This work investigates the effect of the microstructure on the CMP of copper and metal thin films on silicon wafer. Nanoindentation tests were conducted to measure the hardness variations across a wafer surface due to the crystallography of the metal films. Spatial variation of mechanical properties was also input into an existing multi-scale CMP model. Nano-characterization and CMP experimental results are presented and compared to an existing CMP wear model.