Institute of Fundamental Technological Research

The long-term stability of alignment precision of microelectromechanical system accelerometers was evaluated. Four commercial biaxial accelerometers (two ADXL 202E and two ADXL 203 accelerometers by Analog Devices Inc.) were tested over a period of 20 and 15 years, respectively. The experimental studies were performed using a custom computer-controlled test rig and employing gravitational acceleration as the reference. Considerable changes in the existing misalignments were observed. It was found that not only misalignments between the sensitive axes changed over time, but due to some micro-movements within the mounting of the printed circuit board with the accelerometer chip, misalignments of the sensitive axes with respect to the mounting datum changed as well. Even though no bigger than 0.6°, the observed misalignments may considerably influence the accelerometer performance, especially in the case of tilt measurements. Some ways of increasing the considered long-term stability of printed circuit board mounting are proposed.

stability, aging, microelectromechanical systems (MEMS), misalignment

graphene, curcuminoids, poly(vinyl chloride), nanocomposites stability, polymer films

In this work, a method to increase the dispersion of graphene (GN) in the matrix of rigid
poly(vinyl chloride) (PVC) by using a natural plant extract from Curcuma longa L. (CE) is proposed. Currently, despite the increasing number of reports on the improvement of GN dispersion in PVC blends, still there is a need to find environmentally friendly and economical dispersion stabilizers. We proposed a stabilizer that can be easily obtained from a plant offering thermal stability and high effectiveness. PVC/GN nanocomposites stabilized with the proposed extract were investigated by SEM, AFM (structure), TGA, and Congo red test (thermal properties). Additionally, static and dynamic mechanical properties and electrical resistivity were measured. The use of CE as a graphene dispersant improved its dispersion in the PVC matrix, influenced tensile properties, increased the storage modulus and glass transition temperature, and extended the thermal stability time of nanocomposites. In this work, a CE extract is proposed as an efficient eco-friendly additive for the production of nanocomposites with an improved homogeneity of a nanofiller in the matrix and promising characteristics.

nanocomposites,graphene,poly(vinyl chloride),curcuma extract

Particulate-reinforced metal matrix composites (PRMMCs) with excellent tribo-mechanical properties are important engineering materials and have attracted constant scientific interest over the years. Among the various fabrication methods used, co-electrodeposition (CED) is valued due to its efficiency, accuracy, and affordability. However, the way this easy-to-perform process is carried out is inconsistent, with researchers using different methods for volume fraction measurement and tribo-mechanical testing, as well as failing to carry out proper interface characterization. The main contribution of this work lies in its determination of the gaps in the tribo-mechanical research of CED PRMMCs. For mechanical properties, hardness is described with respect to measurement methods, models, and experiments concerning CED PRMMCs. The tribology of such composites is described, taking into account the reinforcement volume fraction, size, and composite fabrication route (direct/pulsed current). Interfacial aspects are discussed using experimental direct strength measurements. Each part includes a critical overview, and future prospects are anticipated. This review paper provides an overview of the tribo-mechanical parameters of Ni-based co-electrodeposited particulate-reinforced metal matrix composite coatings with an interfacial viewpoint and a focus on hardness, wear, and friction behavior.

experimental mechanics, tribology, co-electrodeposited composites

In this study, Atomic Force Microscopy-based nanoindentation (AFM-NI) with diamond-like carbon (DLC) coated tip was used to analyze the mechanical response of poly(methyl methacrylate) (PMMA) thin films (thicknesses: 235 and 513 nm) on a silicon substrate. Then, Oliver and Pharr (OP) model was used to calculate hardness and Young’s modulus, while three different Static Linear Solid models were used to fit the creep curve and measure creep compliance, Young’s modulus, and viscosity. Values were compared with each other, and the best-suited method was suggested. The impact of four temperatures below the glass transition temperature and varied indentation depth on the mechanical properties has been analyzed. The results show high sensitivity on experiment parameters and there is a clear difference between thin and thick film. According to the requirements in the nanoimprint lithography (NIL), the ratio of hardness at demolding temperature to viscosity at molding temperature was introduced as a simple parameter for prediction of resist suitability for NIL. Finally, thinner PMMA film was tentatively attributed as more suitable for NIL.

PMMA, atomic force microscopy-based nanoindentation, Young’s modulus, hardness, viscosity, Burger creep model, nanoimprint lithography

This study reports the quantitative, precise and accurate results of nanoscale friction measurements with the use of an Atomic Force Microscope calibrated with a precise nanoforce sensor. For this purpose, three samples of spin-coated thin Polymethylmethacrylate (PMMA) films were prepared with the following thicknesses: 235, 343, and 513 nm. Three different AFM probes were used for the friction measurements: with diamond-like carbon (DLC) tip with a small (15 nm) or big (2 µm) tip radius, and a reference silicon tip with a small (8 nm) radius. The results show that in all of the studied cases, the coefficient of friction strongly depends on the applied load, being much higher for a lower load. Furthermore, a strong relation of the friction force on the cantilever's geometry, the scanning velocity, and the film thickness was observed.

lateral force microscopy, friction, thin PMMA films, atomic force microscope, DLC coatings, adhesion