A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Mechanical and thermal properties of ABS/montmorillonite nanocomposites for fused deposition modeling 3D printing

Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

FDM-Based 3D Printing of Polymer and Associated Composite: A Review on Mechanical Properties, Defects and Treatments.

Many different polymers and polymer composites are used for engineering applications in which friction and wear are critical issues. This article briefs (a) the importance of polymer tribology in general, (b) the special design principles of polymer composites for low friction and wear under sliding against smooth metallic counterparts, and (c) synergistic effects of nano-particles and traditional fillers and fibers for an optimal tribological performance. Based on these fundamental aspects, the article reviews traditional applications of polymeric tribo-components in mechanical and automotive engineering, including slide elements in textile machines, filament wound bushings for harsh environments, cages of high-precision ball bearings in dental turbines, and hybrid bushings in Diesel fuel injection pumps. A following chapter on special developments of tribo-components outlines (a) ways to achieve electrical conductivity of polymer bearings, (b) the enhancement of self-lubrication and self-healing potential by the incorporation of micro-capsules into the polymer matrix, (c) modern additive manufacturing methods for friction and wear loaded polymer parts, (d) the application and properties of high temperature polymer coatings, and (e) the composition and use of polymer composites under friction at cryogenic temperature conditions.

Polymer composites for tribological applications

Fused Deposition Modeling (FDM) is a widely used additive manufacturing technology for fabrication of complex geometric parts using thermoplastic polymers. The quality issues and inferior properties of fabricated parts limited this process to manufacture parts for industrial level applications. Reinforcing the polymer with nanoparticles, short fibers or continuous fibers improve mechanical, thermal and electrical properties compared to the neat polymer. Several works have been carried out since last two decades to print quality products through FDM by using composite materials. The success of expanding this technique to industrial applications depends on the preparation of printable composite feedstock filament and printing without defects. This article reviews the challenges involved in the preparation of composite feedstock filaments and printing issues during the printing of nano composites, short and continuous fiber composites. The printing process of various thermoplastic composites ranging from amorphous to crystalline polymers is discussed. Also, detailed explanation is given about the analytical and numerical models used for simulating the FDM printing process and for estimating the mechanical properties of the printed parts. This critical review mainly helps the young researchers working in the area of processing of composite materials via 3D printing.

A critical review on the fused deposition modeling of thermoplastic polymer composites

Mechanical behaviour of ABS: An experimental study using FDM and injection moulding techniques

Strain sensing behaviour of 3D printed carbon black filled ABS

3D printing is nowadays used not only to rapidly produce prototypes, but is further applied for the fabrication of functional parts. Amongst other factors, processing parameters such as scaffolding angle and raster gap greatly affect the behaviour of such printed parts. Little attention has been given so far to the tribological behaviour of such prints. In this study the above mentioned parameters on the friction behaviour, in terms of friction coefficient and wear rate, is investigated. For this purpose the Fused Deposition Modelling is used as one of state of the art 3D printing methods. Graphite flakes were further added to the reference acrylonitrile butadiene styrene (ABS) matrix in an attempt to enhance the properties. Results show that the scaffolding angle only affects the behaviour, if a positive printing gap is applied – when a negative gap is used, the angle has no significant effect on properties. Maximum coefficient of friction at acceptable values of specific wear rates can be attained at a scaffolding angle of 90° with negative gap. The incorporation of graphite further increases the friction coefficient on the expense of reduced wear properties.



Heute wird die 3-D-Drucktechnologie nicht nur zur schnellen Herstellung von Prototypen eingesetzt, sondern unter anderem auch um Funktionsbauteile zu fertigen. Unter anderem spielen Prozessparameter, wie z. B. Druckwinkel und Rasterspalt eine entscheidende Rolle und beeinflussen das Verhalten der gedruckten Teile. Bislang wird in der Literatur wenig uber das tribologische Verhalten solcher 3D Bauteile berichtet. In dieser Studie wird die Wirkung der oben genannten Parameter auf das Abriebverhalten, anhand von Reibungskoeffizient und Verschleisrate untersucht. Hierzu wird das Fused Deposition Modelling als eines der modernen 3D-Druckverfahren herangezogen. Bei dem Versuch das Reibungsverhalten zu verbessern, wurde dem Ausgangsmaterial Acrylnitril-Butadien-Styrol (ABS) Lammellengraphit zugegeben. Die Ergebnisse zeigen, dass der Druckwinkel nur bei positivem Rasterspalt eine Rolle spielt – bei einem negativen Spalt, scheint der Winkel keinen signifikanten Einfluss zu haben. Maximale Reibwerte bei moderatem Verschleis konnten bei einem Druckwinkel von 90° und negativem Spalt festgestellt werden. Der Zusatz von Graphit erhohte masgeblich den Reibungskoeffizienten, allerdings auf Kosten verringerter Verschleiseigenschaften.

Effect of processing parameters and graphite content on the tribological behaviour of 3D printed acrylonitrile butadiene styrene

In this study, the behavior of greases during oscillating bearing operation with a small oscillation angle and high frequency was investigated. This mode of operation entails demands on the lubrication system that differ significantly from those for continuously rotating bearings. In order to determine the variables influencing the suitability of a lubricating grease for small angle oscillating operation, the grease samples were examined with particular regard to their rheological properties. The focus of this investigation was to find a relationship between the rheological parameters and the real behavior in the bearing. Therefore, rheological and physical parameters, which influence the long-term structural changes and lubrication conditions, were identified. For this purpose, the viscosity was measured over a wide shear-rate range. The storage and loss modulus, the work of deformation, and the adhesion force jump are also determined. Afterward, rotational transient flow measurements were performed. These allowed us to analyze the development of the shear stress over time, at a constant shear rate, and to examine the internal friction behavior by evaluating the energy density. Subsequently, grease-lubricated four-point bearings were used in component tests, while the frictional torque was measured. These bearings operated in oscillating motion. Moreover, the yield point of mechanically aged greases was measured and compared with that of fresh greases to examine the influence of the oscillating operation on the lubricant condition. Finally, correlations between grease composition, rheological measurements, and component tests were investigated. Thereby, parameters influencing the frictional behavior of greases in rolling bearings during oscillating operation at small swivel angles were identified.

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Influence of Rheological Properties of Lithium Greases on Operating Behavior in Oscillating Rolling Bearings at a Small Swivel Angle

Abstract The rolling element slip of an NU215 cylindrical roller bearing fitted with four cage types was studied under various operating conditions. In comparison, a specially designed full complement bearing with the same principal dimensions was also tested as an alternative. Unlike the load zone width, the acceleration zone width was found to be independent of the applied radial force, and when the dynamic force was introduced, the load zone slip was increased. For the full complement bearing, the rollers were found to stall completely in the unloaded zone resulting in a 100% roller slip at the beginning of the acceleration zone. This behavior was also confirmed by using a high-speed camera. For the tested cages, the roller-guidance under a vertically radial force pointing downwards resulted in a secondary load zone where the weight of the cage forces the rollers to contact the rotating inner ring once more leading to decreased overall slip values compared to outer ring guidance while the polyamide introduces higher cage/roller interactions leading to higher load zone slip as well as a wider load zone. 

Michael Dawoud

Papers

Mechanical behaviour of ABS: An experimental study using FDM and injection moulding techniques

Strain sensing behaviour of 3D printed carbon black filled ABS

Effect of processing parameters and graphite content on the tribological behaviour of 3D printed acrylonitrile butadiene styrene

Influence of Rheological Properties of Lithium Greases on Operating Behavior in Oscillating Rolling Bearings at a Small Swivel Angle

Slip Characteristics in Cylindrical Roller Bearings—Part II: Influence of Cage Type on Rolling Element Slip