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Cellulose is the most common polysaccharide that can be obtained from many resources. Plant-based cellulose (PC) is preferable due to its high renewability and availability in nature. This inherent affluence naturally opens the door to new applications for this adaptable material. PC provides various potential applications such as packaging, textile, and biomedical application. Currently, PC shows progress in its feasibility in biomedical applications because it fulfills the requirement of the characteristics of biomaterials such as biocompatible, biodegradable, anti-microbial, and enhancing tissue regeneration. Different morphological forms of PC such as fiber, microfibril/nanofibril cellulose (MFCs/NFCs), and micro/nanocrystalline cellulose (MCCs/NCCs) are adapted for different biomedical applications. This short review provides a general characteristic of plant-based cellulose (PC) and its potential to be applied in biomedical fields such as tissue engineering.

Intervertebral disc degeneration (IDD) is closely related to changes in the intervertebral disc (IVD) composition and the resulting viscoelastic properties. IDD is a severe condition because it decreases the disc's ability to resist mechanical loads. Our research aims to understand IDD at the cellular level, specifically the changes in the viscoelastic properties of the nucleus pulposus (NP), which are poorly understood. This study employed a system integrating nanoindentation with Raman spectrometry to correlate biomechanics with subtle changes in the biochemical makeup of the NP. The characterization was, in turn, correlated with the degenerative severity of IVD as assessed using magnetic resonance imaging (MRI) of different patients with spinal stenosis, degenerative spondylolisthesis, and degenerative scoliosis. It is shown that there is an increase in the crosslinking ratio in collagen, a reduction in proteoglycan, and a build-up of minerals upon the rise in the severity level of the disc damage in the NP. Assessment of mechanical characteristics reveals that the increasing disc degeneration makes the NP lose its elasticity, becoming more viscous. This shows that the tissue undergoes abnormalities in weight-bearing ability, which contributes to spinal instability. The correlation of the individual discs shows that grades III and IV have similarities in the changes of Amide I and III toward the storage modulus. In contrast, grades IV and V correlate with mineralization toward the storage modulus. Reduction of proteoglycan has the highest impact on the changes of the storage modulus in all grades of IDD. Connecting compositional alterations to IVD micromechanics at various degrees of degeneration expands our understanding of tissue behavior and provides critical insight into clinical diagnostics, treatment, and tissue engineering.

An embedded load cell sensor is proposed for the tool life prognosis and thrust force control of a band saw machine. The sensor enables the tool life and surface quality of the machined workpiece to be effectively improved through the use of a single sensing device strategically located in the cutting machine. The feasibility of the proposed sensor is demonstrated experimentally using a double-column horizontal sawing machine with medium carbon steel bars as the workpiece material. An investigation is performed into the effects of the cutting force, feed rate, and machining time on the tool wear and surface roughness of the machined workpiece. It is shown that the thrust force, tool wear and surface roughness of the machined workpiece are strongly correlated and increase over time. Based on the experimental results, a feedback control system is proposed for maintaining a constant thrust force on the band saw during cutting under even the most challenging conditions. Overall, the results confirm that the embedded load cell sensor and force monitoring and control methodology proposed in the present study provide an effective approach for maintaining the optimal cutting conditions in the sawing of medium carbon steel and improving the tool life and machined part quality.

A molecular dynamic (MD) simulation, which is used for estimating mechanical properties of both microscopic and mesoscopic materials during loading/unloading processes. Understanding the deformation mechanisms of material's internal structure, shape and volume is a key step to enhance its strength and rigidity. Novel nanostructures, nanoparticles and nanocomposites, more efficient, selective, and environmental friendly can be developed and suggested. At the moment, few experimental methods can characterize molecular mechanisms due to their time-consuming and cost-intensive. Therefore, MD simulation allows to gain understanding in structure-to-function relationships involved in the low-dimensional materials. Specifically, MD simulation can be performed on the time scale of nanoseconds, and in three dimensions, it is thus sufficient for the study of the mechanical behaviors and deformation mechanisms at a molecular level. This work reviews the progress in MD simulation of the mechanical properties and structure deformations for various tubular nanomaterials including silicon, carbon and III-V compound nanotubes (NTs), respectively. In particular, we have a detailed description and analysis of the impacts of environmental and structural factors on material strength for the present nanostructures. It is hopeful that this review can provide certain reference for the follow-up research.

Doping enhances diamond like carbon (DLC) coatings for extreme high-temperature applications. However, understanding the enhancement mechanism is elusive. This study employs a novel system integrating Raman spectroscopy and depth-sensing indentation with a heating chamber to monitor chemical structural, and mechanical properties of doped and un-doped hydrogenated DLC films, with temperature. This in-situ investigation represents extreme working conditions, revealing how doping enhances DLC films thermal stability. It is shown that the thermal stability of the a-C:H:Si films could be maximized by increasing the Si content. The film with the highest Si content was stable until 650 C while the films with lower Si or No–Si content graphitized at lower temperatures. This study presents hardness measurement under high-temperature conditions that were not available before. In-situ observations reveal how Si doping correlates with stability of mechanical properties at elevated temperatures. The correlation of the mechanical properties with WG reveals that the mechanism of thermal stability is that Si doping makes the film resistant to graphitization by promoting sp3 hybridization. Furthermore, our in-situ approach makes it possible to conduct characterization that emulates real service conditions, and therefore, our results show great potential of the industrial application of DLC coatings in extreme thermal conditions.

A general plastic material under plane strain and plane stress is classified by a yield criterion that depends on both the first and second invariants of the stress tensor. The yield criterion together with the stress equilibrium equations forms a statically determinate system. This system is investigated in the principal lines coordinate system (i.e. the coordinate curves of this coordinate system coincide with trajectories of the principal stress directions). It is shown that the scale factors of the principal lines coordinate system satisfy a simple equation. Using this equation, a method for constructing the principal stress trajectories is developed. Therefore, the boundary value problem of plasticity theory reduces to a purely geometric problem. It is believed that the method developed is useful for solving a wide class of boundary value problems in plasticity.

A semi-analytical solution for an elastic/plastic sphere subject to thermo-mechanical loading is given. Material properties are temperature dependent. The solution is valid for any isotropic pressure-independent yield criterion. Even though the general solution in both elastic and plastic regions is rather simple, the solution of the boundary value is cumbersome. The solution is facilitated by using the dimensionless temperature as an independent variable instead of the radial coordinate. A detailed analysis of the solution of the boundary value problem is provided assuming that the pressure and temperature at the inner radius slowly increase whereas the pressure and temperature at the outer radius are kept constant. In particular, qualitative features of the solution are emphasized. Some of these features are useful for the design of spherical vessels subject to thermos-mechanical loading.

A tissue preparation method will inevitably alter the tissue content. This study aims to evaluate how different common sample preparation methods will affect the tissue morphology, biomechanical properties, and chemical composition of samples. The study focuses on intervertebral disc (IVD) tissue; however, it can be applied to other soft tissues. Raman spectroscopy synchronized with nanoindentation instrumentation was employed to investigate the compositional changes of IVD, specifically, nucleus pulposus (NP) and annulus fibrosus (AF), together with their biomechanical properties of IVD. These properties were examined through the following histological specimen types: fresh cryosection (control), fixed cryosection, and paraffin-embedded. The IVD tissue could be located using an optical microscope under three different preparation methods. Paraffin-embedded samples showed the most explicit details where the lamellae structure of AF could be identified. In terms of biomechanical properties, there was no significant difference between the fresh and fixed cryosection ( p > 0.05). In contrast, the fresh cryosection and paraffin-embedded samples showed a significant difference ( p

Variations in the implant thread shape and occlusal load behavior may result in significant changes in the biological and mechanical properties of dental implants and surrounding bone tissue. Most previous studies consider a single implant thread design, an isotropic bone structure, and a static occlusal load. However, the effects of different thread designs, bone material properties, and loading conditions are important concerns in clinical practice. Accordingly, the present study performs Finite Element Analysis (FEA) simulations to investigate the static, quasi-static and dynamic response of the implant and implanted bone material under various thread designs and occlusal loading directions (buccal-lingual, mesiodistal and apical). The simulations focus specifically on the von Mises stress, displacement, shear stress, compressive stress, and tensile stress within the implant and the surrounding bone. The results show that the thread design and occlusal loading rate have a significant effect on the stress distribution and deformation of the implant and bone structure during clinical applications. Overall, the results provide a useful insight into the design of enhanced dental implants for an improved load transfer efficiency and success rate.

There are materials whose forward flow curve is practically independent of plastic strain (perfect plasticity) but the Bauschinger effect reduces the elastic range with flow reversal. A new model that is capable of describing such behavior of material under plane stress conditions has been recently proposed. An important class of structures in which the state of stress can often be accurately approximated by plane stress conditions is thin hollow discs. It is therefore of interest to use the new model for determining the distribution of residual stresses in thin discs subject to various loading conditions, followed by unloading. This paper presents a solution for the residual stresses and strains in a hollow hyperbolic disc loading by external pressure, followed by unloading.

In this study, bio-waste catla fish scale (CFS) was used as a reinforcing agent in polypropylene (PP) for the fabrication of biomaterials by using a twin-screw extrusion technique. Tensile strength...

A detailed understanding of surface decoration and interconnecting technologies is essential in realizing high-performance functional devices incorporating metal nanoparticle/graphene nanohybrids. This study employs classical molecular dynamics (MD) simulations to investigate the formation of amorphous copper (Cu) layers on a graphene surface via the collision, coalescence and nucleation of individual Cu nanoparticles (NPs) at temperatures in the range of 300–1300 K. The results indicate that the coalescence and melting temperatures are both sensitive to the particle size and the presence of the substrate. Moreover, an epitaxial interaction is found between the Cu NPs and the graphene substrate, in which mobile Cu atoms are captured and dragged to the graphene surface to produce self-assembled NP layers via a nucleation process. A series of structural evolutions and phase transitions are revealed during the thermalization process of the NPs. Finally, the results show that the presence of the substrate and associated contact epitaxy phenomenon play a key role in governing the structural morphology and thermal behavior of the Cu NP-based thin film.

Herein, we aim to develop a facile method for the fabrication of mechanical metamaterials from templated polymerization of thermosets including phenolic and epoxy resins using self-assembled block copolymer, polystyrene-polydimethylsiloxane with tripod network (gyroid), and tetrapod network (diamond) structures, as templates. Nanoindentation studies on the nanonetwork thermosets fabricated reveal enhanced energy dissipation from intrinsic brittle thermosets due to the deliberate structuring; the calculated energy dissipation for gyroid phenolic resins is 0.23 nJ whereas the one with diamond structure gives a value of 0.33 nJ. Consistently, the gyroid-structured epoxy gives a high energy dissipation value of 0.57 nJ, and the one with diamond structure could reach 0.78 nJ. These enhanced properties are attributed to the isotropic periodicity of the nanonetwork texture with plastic deformation, and the higher number of struts in the tetrapod diamond network in contrast to tripod gyroid, as confirmed by the finite element analysis.

An experimental investigation was performed on the coefficients of friction (COFs) and wear properties of pure water and oil-in-water (O/W) working fluids containing carbon nanocapsules (CNCs) with concentrations ranging from 0 to 1.0 wt.%. For the O/W working fluid, the ratio of oil to water was set as 6%. It was shown that for the water working fluid, the COF decreased by around 20% as the CNC content increased from 0 to 1.0 wt.%. In contrast, the wear volume increased by 50% as the CNC addition increased from 0 to 0.5 wt.%, but it fell to a value slightly lower than that achieved using only pure water (i.e., no CNCs) as the CNC content was further increased to 1.0 wt.%. For the O/W emulsion, the addition of 0.8 wt.% CNCs reduced the COF by around 30% compared to that of the emulsion with no CNCs. Overall, the results showed that while the addition of a small quantity (6%) of oil to the water working fluid had a relatively small effect on the wear performance, the addition of an appropriate quantity of CNCs (i.e., 0.8 wt.%) resulted in a significantly lower COF and an improved wear surface.

Mass sensing by nanomechanical resonators can be routinely performed for analytes of mass ranging from kDa to tens of MDa. Measurement of the heavier analytes (up to hundreds of GDa) that are relevant to viruses, and many biological and chemical complexes, still remains one of the main challenges to be solved. Some studies propose the heavy analyte identification by accounting for its mass, stiffness and binding effects. However, the necessity of using the sophisticated computational tools complicates their widespread use in the nanomechanical mass spectrometry. Here, we report on the heavy analyte mass spectrometry (~GDa) using the multimode nanomechanical resonators, which is directly applicable to analytes of arbitrary mass, stiffness and dimensions. This identification, based on the simultaneous measurement of the multiple by analyte induced resonant frequency shifts, only requires the analyte to resonator mass ratio between 0.001 and 0.02. We show that the analyte stiffness and binding effects must be considered for the lower mass ratios ( 0.02) the inaccuracies in determined mass are independent of both the analyte stiffness and binding effects, and increase with the mass of analyte. Validity of present results have been demonstrated by comparing predictions with the recent experimental measurements performed on the micro-/nanomechanical resonator-based mass spectrometers. Our findings, together with the provided software, which enables an easily accessible determination of the effects of analyte properties on the frequency response, present a novel paradigm in a design of the nanomechanical resonators for mass sensing in GDa range.

In the case of rigid perfectly plastic material, the velocity field is singular in the vicinity of maximum friction surfaces (the equivalent strain rate approaches infinity in the vicinity of such surfaces). This causes significant difficulties with the convergence of finite element solutions. On the other hand, an accurate description of the velocity field near frictional interfaces is crucial for predicting the generation of a narrow fine grain layer that frequently appears near such interfaces. The present paper provides an accurate numerical solution for the singular velocity field in the vicinity of the maximum friction surface in plane strain extrusion. The singularity in the velocity field is represented by means of the strain rate intensity factor. The numerical approach is based on the method of characteristics. The strain rate intensity factor is determined by means of simple formulae once the solution for the radii of curvature of characteristic lines and velocities has been found. It is shown that the distribution of the strain rate intensity factor along the friction surface is discontinuous. Comparison with an analytic solution for material flow through an infinite wedge-shaped die is made and a high accuracy of the numerical solution is demonstrated. On the other hand, it is shown that the analytic solution is not accurate enough to find the strain rate intensity factor even for rather long dies.

A synchronized system integrating Raman spectroscopy and depth-sensing techniques was applied to analyze the microstructure, mechanical properties and surface roughness of amorphous carbon (a-C) films in-situ. This integrated system equipped with a high-temperature chamber coupled with feedback control made it possible to study the temperature effects on the mechanical properties and the microstructure of the films. A series of a-C films with different sp3 content were deposited on Si substrates using a filtered cathodic arc vacuum (FCVA) deposition system. Our study confirms previous results that the thermal stability of the a-C films depends on their sp3 content. The results also show that the structural change is accompanied by a significant increase in the surface roughness. This synchronized characterization technique demonstrates that the film hardness decreases with temperature even before any chemical changes detected using Raman spectroscopy. Moreover, the surface of the films is more sensitive to the temperature compared to the bulk as evidenced by the surface roughness characterization, showing that the surface roughness starts to rise at temperatures lower than for the onset of structural transition in the bulk. Nanoscratch and nanowear tests further support the conclusion that the surface sensitivity to temperature is greater than for the bulk.

Diamond-like-carbon (DLC) is a promising material for tribological applications such as hard disk, automotive, machine tool, and aerospace coatings. We performed in-situ transmission electron microscopy (TEM) and molecular dynamics (MD) studies of nanoscale single-asperities made of tetrahedral amorphous carbon (ta-C, a type of DLC with high strength) contacting single-crystal diamond, to understand the factors controlling adhesion. Visualization of the contacts in TEM enabled us to correlate the asperity's geometry and the adhesion measurements. MD simulations allowed the atomic-scale mechanisms of adhesion to be elucidated and correlated with the TEM observations. Experimentally-determined pull-in forces show less scatter than pull-off forces. The magnitude of the pull-in forces is consistent with adhesion arising from van der Waals (VDW) interactions, allowing us to estimate the ta-C/diamond Hamaker constant. MD simulations with the AIREBO potential confirmed that including VDW interactions leads to less scatter in adhesive forces in approach than in separation. MD simulations with the REBO+S potential demonstrate that the large scatter in pull-off forces observed experimentally arises from the complex nature of covalent bonding between substrate and tip, influenced by the local energy landscape, hydrogen coverage, and the number of repeated contact events. The scatter in pull-off force also tends to decrease with increasing roughness.

This work reveals the initial stages of Inconel 718 (IN718) oxidation manufactured by selective laser melting (SLM). In-situ and ex-situ investigations were conducted on SLM-IN718 and a commercially obtained Inconel 718 sample (Comm-IN718) to compare their oxidation behavior. In-situ and ex-situ testing was performed using a unique synchronized system integrating precise thermal control with Raman spectroscopy, optical microscopy and scanning probe techniques. X-Ray diffractometry (XRD) and Scanning Electron Microscopy (SEM) were used for microstructure analyses before and after heating. Raman spectroscopy indicated that, in both samples, there is a threshold temperature for oxidation at around 300 °C. The highest rate of oxidation was observed up to 550 °C as different oxides form. After 550 °C, there was no noticeable formation of new compounds up to 650 °C. Extended heating at 650 °C resulted in further changes in the Comm-IN718 sample, however the SLM-IN718 sample was unchanged by longer heating times. XRD of cooled samples did not detect any oxides because of the structurally disordered nature of the oxides. After being cooled, Comm-IN718 showed undesirable oxides like iron oxides in an inhomogeneous crystalline oxide layer. For SLM-IN718 the continuous unbroken oxide layer on the cooled SLM-IN718 sample imparted more effective protection of the alloy.

Due to their small sizes, compactness, low cost, high sensitivity, high resolution and extraordinary physical properties, nanoresonators have attracted a widespread attention from the scientific community. It is required that the nanoresonators can operate at desired but adjustable resonant frequencies. In this work, we present a novel active frequency tuning method utilizing a large change of the Young’s modulus (more than 50 %) and generated interlayer stress (up a few hundred of MPa) during a phase transformation of NiTi thin film deposited on an elastic substrate. We show that this tuning mechanism can allow one to achieve the extraordinary high fundamental resonant frequency tunability (~30 %). The impact of NiTi film thickness and dimensions on the first three consecutive resonant frequencies of the cantilever nanobeam is examined. In addition, developed theoretical model can be used as a simple guide for further design of novel tunable cantilever nanoresonators with thin films that cover only partially the entire cantilever length.

Using nanoindentation and energy dispersive X-ray spectrometry (EDS), we have conducted an investigation into corner failures to elucidate not only the nanomechanical properties of Sn 37Pb solder balls but also the effects of temperature cycling tests (TCTs). We found that the hardness of Sn 37Pb solder balls was greater in central locations [1.18 ± 0.05 GPa for room-temperature (RT) sample; 1.3 ± 0.05 GPa for TCT sample], but had standard values in corner locations (> 0.2 ± 0.02 GPa). The modulus increased after the TCTs. Nevertheless, the mechanical properties were closely related to the average area of the α-Pb phase. The average area of the Pb-rich region was more stable after the TCTs than that of the RT sample, due to the enhanced mechanical properties of the Sn 37Pb solder, suggesting good reliability. From an analysis of average areas in the RT sample, it appears that the Pb-rich solid solution that formed led to weak Sn Pb bonds near the corner locations. Electron back-scattered diffraction measurements revealed that grains with grain boundaries formed as a result of accelerated TCT cycling. We conclude that Sn Pb recrystallization was initiated and propagated after the TCTs, followed by propagation to the interfacial region.

This article presents a mathematical model for the meshing of involute spur gears in mixed lubrication. The model is formulated by integrating a gear meshing model with a thermal tribofilm mixed lubrication model. The resulting model can produce a number of important meshing variables from which the gear meshing performance and the tooth surface damage may be assessed. The model is used to analyze the performance of a high-load and high-speed gear system under various degrees of mixed lubrication. The results show a stronger desire to use low-module and high-pressure-angle gears than that suggested in earlier studies under good lubrication conditions. The results also show the high importance of enhanced heat transfer design of the system to prevent or reduce the possibility of the gear system migrating into temperature-induced unfavorable lubrication conditions. Although the model is developed for spur gears and results are obtained around a nominal system, the relations of the gear meshing tribo...

Carbon nanotube reinforced copper alloy (CNT/Cu) composites with high strength and good wear resistance have been developed using acid treatment, sintering processes and consolidation techniques. The effects of CNT reinforcement and grain size refinement on the mechanical properties and surface deformations of CNT/Cu composite coatings are investigated by means of nanoindentation and block-on-ring wear tests, respectively. High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses reveal that the CNTs are firmly implanted in the Cu alloy due to the formation of Cu-oxides at the CNT-Cu interface. The effect of CNT addition on the CNT/Cu coating strength is significantly greater than that of grain size reinforcement. Finally, the present results indicate that the addition of CNTs to the Cu matrix reduces the surface deformations of the CNT/Cu composite coatings due to the formation of a carbonaceous solid-lubricant film at the contact interface during sliding.

We decorate Zn-doped TiO2 ¬nanoparticle-based photoanodes with carbon nanotube (CNT)-derived TiO2 nanotubes (i.e., TNs) in order to enhance the power conversion efficiency of dye-sensitized solar cells (DSCs). X-Ray photoelectron spectroscopy (XPS) analysis verifies that Zn ions, in the range of 0-1 at.%, are successfully doped into TiO2 lattice. Field emission scanning electron microscopy (FE-SSEM) and transmission electron microscopy (TEM) images of sol-gel template-assisted derived TNs reveal that a uniform TiO2 coating with the thickness of 60-120 nm is deposited on the surface of the template through the non-covalent route. We observed that the cell efficiency improves from 6.80% for pure TiO2 to 7.52% for 0.75 at.% Zn-doped TiO2 nanoparticles due to reduction of charge recombination and enhancement of electron injection, as confirmed by photoluminescence spectroscopy (PL). Further improvement of the efficiency up to 8.47% is achieved by incorporation of 5 wt.% TNs into Zn-doped TiO2 photoanodes as a result of electron transport and light scattering enhancements, as verified by diffuse reflectance spectroscopy (DRS).

We performed cathodoluminescence (CL) investigations on GaN NCs grown using molecular beam epitaxy. Bundled GaN was used to form NCs that were deposited onto commercial sapphire templates. The structures of the bundled NCs were analyzed using nanoindentation. The samples were grown with a T G of 700, 800, and 850 °C, and the H values were 7.4 ± 0.2 and 6.4 ± 0.2 GPa; the E values were 308.4 ± 4.3, 296.4 ± 3.8, and 75.5 ± 1.4 GPa, respectively. It is suspected that the discrepancies of the mechanical parameters obtained by various indentation methods are partially a result of the stress distribution inherent in the different orientations on the sapphire substrate. A scanning electron microscopy (SEM) system equipped with CL allows the direct comparison of SEM images and CL maps, captured from exactly the same area of the samples. In addition to the SEM and CL images, photoluminescence spectroscopy (PL) profiling was obtained by collecting the 20 K PL spectra at the samples. The PL profiling enables the distinguishing of the emissions by the 5 meV of the blueshift from 3.440 to 3.445 eV due to localization effects. The bundled GaN NCs resulted from the (0002) reflection at 34.6° for a wurtzite structure and a raised intensity difference when the T G was increased from 700 to 850 °C. The crystal texture of the GaN can influence the mechanical properties at different T G stages.

The local viscoelastic properties of soft polishing pads with different usage durations are measured by a micro-scale mechanical analysis testing platform. The testing reveals stimulus-adaptive local viscoelasticity of soft pads under the activation of asperity contact. This phenomenon suggests asperity-dependent local modulus. Such an increase of local modulus induced by higher asperity provides a further enhancement effect to the planarization of surface asperity. Furthermore, the measurement outcomes suggest that the reaction of local micro-scale viscoelastic properties of the soft pad surface to the workpiece asperity will decay with usage time. The current study provides a detailed understanding of the aging effects for the soft pad and explains the performance decay during soft pad polishing from a local micro-scale interfacial perspective.

This tech brief presents some basic theory and calculations to help assess the feasibility of surface-film lubricated dry skin pass of metal strips to enhance surface finish after cold-rolling operations. Results are presented of the required rate of heat removal from the rolling apparatus and the maximum rise of roll surface temperature for steel and aluminum strips under various parametric conditions of practical interest. The theory and the calculation tool may be used to perform analyses with other material, geometry, and operating parameters and to assist the design and development of surface-film lubricated dry skin-pass processes.

A triboelectric generator (TEG) is a simple coupling combined with triboelectrification and electrostatic induction, which can convert mechanical energy into electrical energy and have the potential for self-powered device application. In this study, TEGs are fabricated consisting of a conductive textile (CT) layer (a fabric woven with polyester and stainless steel) and a polydimethylsiloxane (PDMS) layer. The CT friction layer is also used as a conductive electrode and designed with various surface morphologies, including unpatterned, dots, and lines with 1 and 2 cm spacings. Experimental results show that the TEG with an unpatterned CT layer produces an output voltage of 54.6 V and an output current of 5.46 µA. The patterned surfaces increase the effective contact area and friction effect between the CT and PDMS layers and hence enhance the output voltage and current to 94.4 V and 9.44 µA. Compared to the unpatterned CT layer, the pattern use of 1 cm spaced lines, 2 cm spaced lines, and dots improves the output voltage and current by 1.73, 1.68, and 1.24 times, respectively. Moreover, the TEG with 1 cm spaced lines generates a high output power density of 181.9 mW/m2.

Temperature-induced evolution of Si-doped hydrogenated amorphous carbon films on Silicon was monitored using Raman, X-ray photoelectron spectroscopy (XPS) with depth profiling, and electron microscopy. XPS showed that carbon on the surface of as-deposited films is present as sp2 > SiC > SiCxOy > sp3 > C O > C O > COOR. sp2 and sp3 carbon decrease with depth and are stable until 600 °C when they evaporate. Carbon rich SiOxCy is higher deeper in the sample and is stable up to 450 °C, after which SiO2 and intermediate oxidation states of Si start to form. SiC is present evenly throughout the film and is stable until 600 °C. After 600 °C nearly all carbon in the film evaporates from the surface to a depth of 63 nm. The ratio of sp2 to sp3 is lower on the surface and is constant with temperature until 600 °C. Other carbon oxygen species form as the temperature is increased to 400 °C, above which they evaporate. Carbon atoms leave the surface by gasification between 600 and 750 °C. Raman data strongly supports the XPS conclusions. Optical and electron microscopy shows that at 750 °C the surface of the film is optically different and cracked. The fact that the films were stable up to 600 °C demonstrates the great potential of Si-doped coatings for high-temperature applications.

Thermal instability has been considered by pioneer researchers to be one of the most promising lines for a fundamental investigation into the failure mechanisms of rolling–sliding contacts. This article uses a recently developed mixed lubrication model that integrates interrelated topographical, mechanical, thermal, and tribochemical aspects to study the thermal instability of high-performance rolling–sliding contacts. The effects of various system parameters on the relation between the system bulk temperature and the heat generation in the contact are analyzed. The parameters include surface roughness; contact component size; surface and lubricant mechanical, thermal, and tribochemical properties; and operating conditions. Key results and their implications to system design and operation considerations are summarized in the Conclusion section of the article in relation to enhancing the thermal stability of the contact, particularly under adverse lubrication conditions.