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[Display omitted] Contact angle and sliding angle measurements are widely used to characterize superhydrophobic surfaces because of the simplicity and accessibility of the technique. We hypothesize that dynamic friction measurements, with increasing pre-loads, between a water drop and a superhydrophobic surface is more accurate because this technique is less influenced by local surface inhomogeneities and temporal surface changes. A water drop, held by a ring probe which is connected to a dual-axis force sensor, is sheared against a superhydrophobic surface while maintaining a constant preload. From this force-based technique, static and kinetic friction forces measurements are used to characterize the wetting properties of the superhydrophobic surfaces. Furthermore, by applying increased pre-loads to the water drop while shearing, the critical load at which the drop transitions from the Cassie-Baxter to Wenzel state is also measured. The force-based technique predicts sliding angles with reduced standard deviations (between 56 and 64%) compared to conventional optical-based measurements. Kinetic friction force measurements show a higher accuracy (between 35 and 80%) compared to static friction force measurements in characterizing the wetting properties of superhydrophobic surfaces. The critical loads for the Cassie-Baxter to Wenzel state transition allows for stability characterization between seemingly similar superhydrophobic surfaces. [ABSTRACT FROM AUTHOR]

[Display omitted] Popular deep eutectic solvents (DESs) typically lack amphiphilic molecules and ions and therefore do not have the useful self-assembled nanostructures prevalent in many ionic liquids. We hypothesise that nanostructure in DESs can be induced via an amphiphilic hydrogen bond donor (HBD), and that nanostructure becomes better defined with HBD chain length. The structure of DESs formed from choline chloride mixed with either butyric acid (ChCl/BuOOH) or hexanoic acid (ChCl/HeOOH) in a 1:4 M ratio were studied using atomic force microscopy (AFM) imaging, force curves, and friction measurements combined with bulk rheology. DESs formed with both the C 4 and C 6 acids are nanostructured. As the length of the acid group is increased from C 4 to C 6 , AFM images reveal the nanostructure becomes larger and better defined due to the longer acid chain, and AFM force curves show the interfacial nanostructure extends further from the surface. Self-assembled nanostructure in these systems is a consequence of choline cations, chloride anions, and acid alcohol groups clustering together due to electrostatic attractions and hydrogen bonding to form polar domains. Acid alkyl chains are solvophobically excluded from the polar domains and aggregate into apolar domains. [ABSTRACT FROM AUTHOR]

• The proposed method uses a simpler setup and allows the test to be done in the application condition. • Instrumentation of a connecting rod with a tee-rosette strain gauge is detailed. • Signal processing is presented in a straightforward manner. • Experimental results are compared with results from the literature. • Connecting rod strain offers important information about forces which act on the piston. The design of slider-crank mechanisms is usually done using numerical simulation supported by experiments to validate the results of both the individual parts and whole assembly. The largest challenge in this process is to establish parameters to evaluate the simulation using experimental results. The dynamic measurement of the connecting rod strain can provide important information about the forces which act on the piston, such as the ones caused by friction and pressure. However, this measurement is challenging, since it is done in an adverse environment where oil, high temperature variation and vibration are present. This work aims to solve this problem by proposing a concept of connecting rod instrumented with a strain gauge tee-rosette bridge and the proper signal conditioning method to measure the friction forces between the piston and the cylinder. To work with the worst-case scenario, a small-sized sintered connecting rod was used to verify if the proposed method is applicable to a wide range of equipment. The obtained results are at least equivalent to the ones presented in the literature, but the proposed method uses a simpler setup and allows the test to be done using the motor in its application condition. In addition, the proposed method allows the observation of high-frequency phenomena, such as impacts during a cycle, which cannot be characterized using the methods proposed in the literature. [ABSTRACT FROM AUTHOR]

• Measurements of friction noise coming from the sliding contact in a dedicated tribometer. • Characterization of squeal propensity for brake lining materials. • Parametrical analysis and effect of the main system parameters on the friction noise. • Strong correlation between measured friction noise and squeal propensity on a full brake system. Disc brake systems are a technology widely adopted within the automotive and rail industry, especially when high performance is needed. The interaction between the disc and the pads is responsible for friction-induced vibrations, leading often to squeal noise emission. Squeal vibrations are generated by the onset of an unstable mode, which is triggered by an external excitation. Local phenomena occurring at the contact interface, and resulting in friction noise, can be responsible of the dynamic excitation triggering the squeal instability. This work proposes a new approach for characterizing friction lining materials, by measuring the friction noise coming from the contact between different pad materials and a disc rotor, in order to quantify and compare the attitude of materials to trigger squeal. Then, a parametrical analysis has been carried out with the aim of highlighting the influence of the main parameters on the friction noise. When testing the same set of materials on a full brake disc system, the measured friction noise indexes resulted to be strongly correlated with the squeal occurrence, validating the proposed characterization method for the squeal propensity of lining materials. [ABSTRACT FROM AUTHOR]

Robust and accurate measurement techniques are essential to studying the piston-assembly friction of Internal Combustion (IC) engines. Based on the instantaneous Indicated Mean Effective Pressure (IMEP) method, this paper develops an improved measurement technique to evaluate the piston-assembly friction in engines. Wireless telemetry technology is employed in the measurement of connecting rod axial force, which greatly minimizes the engine modifications and enhances the measurement stability compared to the conventional wired way. The measurement system, which is composed of computer, data acquisition system, sampling trigger apparatus and sensors, is exploited with special attention given to the sampling synchronization of signal channels including cylinder pressure, connecting rod force and crank angle position. Engineering implementations are carried out on a four-stroke gasoline engine under motored condition. The measurement results are compared with numerical results from a newly developed numerical coupling model system, and it shows that the two agree well. In addition, the piston-assembly friction under different engine speeds and inlet lubricant temperatures are also measured, and analyses indicate that these results are in good correlation with the well-known Stribeck curve. This improved measurement technique provides an accurate and reliable option for the friction evaluation of piston-assembly components in engine designs. [ABSTRACT FROM AUTHOR]

This work wants to provide insights on the coupling between contact behaviour (local scale) and vibrational response (global scale) which brings to different contact scenarios arising in dry frictional systems. A newer setup, named TriboWave, has been developed in order to reproduce and investigate the system response to frictional contact, under well-controlled boundary conditions. The experimental results highlighted how a simple frictional system can switch from stable friction-induced vibrations to unstable vibrations, i.e. either macroscopic stick–slip instabilities or mode coupling instabilities. The effect of the contact surface roughness on the reproduced frictional scenario has been investigated too. [ABSTRACT FROM AUTHOR]

The solution approach of an asymmetric spinning disk under stationary friction loads requires the mode shape function fixed in the disk in the assumed mode method when the equations of motion is described in the space-fixed frame. This model description will be termed the 'moving mode shape function approach' and it allows us to formulate the stationary contact load problem in both the axisymmetric and asymmetric disk cases. Numerical results show that the eigenvalues of the time-periodic axisymmetric disk system are time-invariant. When the axisymmetry of the disk is broken, the positive real parts of the eigenvalues highly vary with the rotation of the disk in the slow speeds in such application as disc brake squeal. By using the Floquet stability analysis, it is also shown that breaking the axisymmetry of the disc alters the stability boundaries of the system. [ABSTRACT FROM AUTHOR]