Determination of Mesh Stiffness of Gear—Analytical Approach vs. FEM Analysis

This paper focuses on modeling the time-varying stiffness of spur gearings, which in dynamic models of transmission systems acts as an important element of the internal excitation of the dynamic system. Here are introduced ways to approach the modeling of gear stiffness using analytical calculations, which allow to model the course of mesh stiffness depending on its rotation. For verification of used analytical model were created five different gearings, and based on their geometry, the respective stiffness curves were analytically determined. Subsequently, a finite element simulation was performed in the Abaqus CAE software. Due to this software, it was possible to identify and objectively compare the stiffness curves and further determine the suitability of using the analytical model to determine the mesh stiffness of gearing.

Solid-phase excitation-emission matrix spectroscopy for chemical analysis of combustion aerosols

Exposure to ultrafine combustion aerosols such as particulate matter (PM) from residential woodburning, forest fires, cigarette smoke, and traffic emission have been linked to adverse health outcomes. Excitation-emission matrix (EEM) spectroscopy presents a sensitive and cost-effective alternative for analysis of PM organic fraction. However, as with other analytical chemistry methods, the miniaturization is hindered by a solvent extraction step and a need for benchtop instrumentation. We present a methodology for collecting and in-situ analysis of airborne nanoparticles that eliminates labor-intensive sample preparation and miniaturizes the detection platform. Nanoparticles are electrostatically collected onto a transparent substrate coated with solid-phase (SP) solvent—polydimethylsiloxane (PDMS). The PM organic fraction is extracted into PDMS and analyzed in-situ, thus avoiding liquid-phase extraction. In the SP-EEM analysis, we evaluated external and internal excitation schemes. Internal excitation shows the lowest scattering interference but leads to signal masking from PDMS fluorescence for λ<250nm. The external excitation EEM spectra are dependent on the excitation light incident angle; ranges of 30–40° and 55–65° show the best results. SP-EEM spectra of woodsmoke and cigarette smoke samples are in good agreement with the EEM spectra of liquid-phase extracts. The SP-EEM technique can be used to develop wearable sensors for exposure assessments and environmental monitoring.

On the mechanism of three-body adhesive wear in turning

The paper reveals a hypothesis regarding the adhesive mechanism in metal cutting and its mechanical dynamics. One steel grade, 34CrNiMo 6, 285 HB, and one set of coatings on the cutting tool are reviewed. The adhesive mechanism is a transient vibration, including a feedback system limited by the plastic deformation in the chip. The vibration shows as a cluster of waves with stochastic duration in time. It starts up again after a stochastic lapse of silence. The cycle frequency is around 12.5 kHz and the internal excitation is twice that frequency, as the cutting speed and feed are 200 m/min and 0.2 mm, respectively. The adhesive frequency and amplitude are influenced by the cutting speed and the current wear status. The adhesion is monitored by the sound waves emanating from vibrations in the chip, the part still in the workpiece.

Drivability Optimization by Reducing Oscillation of Electric Vehicle Drivetrains

The drivetrain of electric vehicles differs significantly from vehicles with combustion engines. Current concepts of electric vehicle drivetrains usually have a low damping. Typically, there is no clutch to separate the inertial mass of the electric drive machine from the rest of the vehicle drivetrain. External (road unevenness, potholes, etc.) and internal excitation (torque changes of the electric machine, brake interferences, etc.) cause jerk oscillation and sometimes high component stress. These excitations can be reduced by suitable drivability functions, to which a reference filter can also be assigned. A common approach known from conventional drivetrains is to limit the gradient of the demand torque of the drive machine or the driver′s desired torque in order to influence the torque build-up of the drive machine and to reduce the excitation of jerk oscillations. A second approach is the use of a prefilter. The prefilter uses the inverse dynamics of the drivetrain to influence the demand torque of the drive machine. In this paper, the influence of a prefilter based on the inverse dynamics of electric vehicle drivetrains to reduce oscillations is investigated. In addition, an anti-jerk control enhances the drivability function afterwards. All investigations are made on a hardware-in-the-loop test bench to create reproducible results.

Nonlinear dynamic analysis of spur gear system based on fractional-order calculus

In this paper, nonlinear dynamic model of spur gear pairs with fractional-order damping under the condition of time-varying stiffness, backlash and static transmission error is established. The general formula of fractional-order damping term is derived by using the incremental harmonic balance method (IHBM), and the approximate analytical solution of the system is obtained by use of the iterative formula. The correctness of the results is verified by comparing with the numerical solutions in the existing literature. The effects of mesh stiffness, internal excitation amplitude and fractional order on the dynamic behavior of the system are analyzed. The results show that changing the fractional order can effectively control the resonance position and amplitude in the meshing process. Both the mesh stiffness and internal excitation can control the collision state and the stability.

Testing of the heating element integrated into the honeycomb sandwich structure for active thermography inspection

The honeycomb sandwich structures with carbon composite face sheets combined with aluminium or Nomex® honeycomb core are extensively used in the aircraft airframe structure. They provide some key benefits over conventional structures such as increased bending strength and stiffness combined with low weight. However, they show high sensitivity to a certain type of damage, such as object impact, mishandling, etc. Non-destructive inspection methods are needed for a structural health examination. Active infrared thermography is one of them. The quality of the inspection and defect detection depends heavily on the proper application of the external thermal excitation. This paper presents a concept of the sandwich structure with internal excitation by means of an integrated thin-film resistive heating element.

A Robust Optimization Method on the Transmission System of the Cutting Unit of Shearer

The transmission system of the cutting unit of shearer is divided into three basic components: planetary reduction form, one gear on one shaft form and a double gears on one shaft. The dynamic differential equations of three basic components are established respectively, and the volume functions of each structure are obtained. The characteristics of the internal excitation of the transmission system are analyzed, and the solution methods of the motion parameters of each component are obtained based on the harmonic balance method. Taking the parameters such as tooth number, modulus and tooth width as optimized variables, and a robust optimization method with the minimum value of multi-parameter evaluation function weighted linearly by dimensionless volume and vibration for the transmission system of the cutting unit of shearer is presented. Taking a certain type of shearer as an example, the transmission system of the cutting unit is optimized by using the presented method. After the design, the size is reduced by 5.4%, the maximum torsional acceleration of the drum is reduced by 17.8%, and the maximum torsional acceleration of the first gear is reduced by 9.6%. The results show that the design method can reduce the manufacturing cost of shearer and reduce the failure rate of the cutting unit.

Solid Phase Excitation-Emission Matrix Spectroscopy for In-Situ Chemical Analysis of Combustion Aerosols

<p>Exposure to combustion generated aerosols such as PM from residential woodburning, forest fires, cigarette smoke, and traffic emission have been linked to adverse health outcomes. It is important to assess the chemical composition of PM to examine personal exposure. Excitation-emission matrix (EEM) spectroscopy has been shown as a sensitive and cost-effective technique for evaluation of combustion PM composition and as a source apportionment tool. However, EEM measurements are hindered by a solvent extraction step and a need for benchtop instrumentation. Here, we present a methodology that eliminates this labor-intensive sample preparation and allows to automate and miniaturize the detection platform. A miniature electrostatic collector deposits PM sample onto transparent polydimethylsiloxane (PDMS) coated substrate, where PAH components are extracted into solid-phase (SP) solvent and analyzed using EEM spectroscopy in-situ. We evaluated external and internal excitation schemes to optimized signal to noise ratio. Analysis of woodsmoke and cigarette smoke samples showed good agreement with liquid extraction EEM spectra. Internal excitation is hindered by fluorescent interference from PDMS at λ<250nm. The external excitation EEM spectra are dependent on the incident angle; ranges of 30-40⁰ and 55-65⁰ showed the best results. The proposed SP-EEM technique can be used for development of miniaturized sensors for chemical analysis of combustion generated PM. </p>