An Experimental Approach for the Determination of the Mechanical Properties of Base-Excited Polymeric Specimens at Higher Frequency Modes

Structures made of the thermoplastic polymer polyether ether ketone (PEEK) are widely used in dynamically-loaded applications due to their high-temperature resistance and high mechanical properties. To design these dynamic applications, in addition to the well-known stiffness and strength properties the vibration-damping properties at the given frequencies are required. Depending on the application, frequencies from a few hertz to the ultrasonic range are of interest here. To characterize the frequency-dependent behavior, an experimental approach was chosen and applied to a sample polymer PEEK. The test setup consists of a piezoelectrically driven base excitation of the polymeric specimen and the non-contact measurement of the velocity as well as the surface temperature. The beam’s bending vibrations were analyzed by means of the Timoshenko theory to determine the polymer’s storage modulus. The mechanical loss factor was calculated using the half-power bandwidth method. For PEEK and a considered frequency range of 1 kHz to 16 kHz, a storage modulus between 3.9 GPa and 4.2 GPa and a loss factor between 9 103 and 17 103 were determined. For the used experimental parameters, the resulting mechanical properties were not essentially influenced by the amplitude of excitation, the duration of excitation, or thermal degrad.ation due to self-heating, but rather slightly by the clamping force within the fixation area

Functional Design Employing Miniaturized Electronics with Wireless Signal Provision to a Smartphone for a Strain-Based Measuring System for Ski Poles

The individual monitoring of cross-country skiers’ technique-related parameters is crucial to identifying possible athlete-individual deficits that need to be corrected in order to optimize the athlete’s performance in competition. To be able to record relevant biomechanical parameters during training in the field, the development of measuring systems exploiting the athlete’s full potential is the key. Known mobile monitoring systems for measuring forces on ski poles use comparably heavy uniaxial load cells mounted on the pole with a data logger also attached to the pole or carried by the athlete. Measurements that are more accurate can be acquired using wire-based systems. However, wire-based systems are highly immobile and only usable when the athletes undergo a stationary test, e.g., on a treadmill. This paper focuses on the functional design of a measuring system using specialized, miniaturized electronics for acquiring data from strain sensors. These data are then used to determine the technique-related parameters pole force and angle of bend. The functional design is also capable of transmitting the acquired data wirelessly via Bluetooth to a smartphone that runs a proprietary app. This approach is advantageous regarding mass, dynamic behavior, analyzing functionality, and signal processing compared to the state of the art

Sound Transmission Loss of a Sandwich Plate with Adjustable Core Layer Thickness

Compressible Constrained Layer Damping (CCLD) is a novel, semi-active, lightweightcompatible solution for vibration mitigation based on the well-known constrained layer damping principle. The sandwich-like CCLD set-up consists of a base structure, a constraining plate, and a compressible open-cell foam core in between, enabling the adjustment of the structure’s vibration behaviour by changing the core compression using different actuation pressures. The aim of the contribution is to show to what degree, and in which frequency range the acoustic behaviour can be tuned using CCLD. Therefore, the sound transmission loss (TL), as an important vibro-acoustic index, is determined in an acoustic window test stand at different actuation pressures covering a frequency range from 0.5 to 5 kHz. The different actuation pressures applied cause a variation of the core layer thickness (from 0.9 d₀ to 0.3 d₀), but the resulting changes of the stiffness and damping of the overall structure have no significant influence on the TL up to approximately 1 kHz for the analysed CCLD design. Between 1 kHz and 5 kHz, however, the TL can be influenced considerably well by the actuation pressure applied, due to a damping-dominated behaviour around the critical frequenc

Material Selection Process for Acoustic and Vibration Applications Using the Example of a Plate Resonator

In this work, a new method for selecting suitable materials is presented. This method has a high potential for a variety of engineering applications, such as the design of sound-absorbing and vibration-loaded structures, where a large number of different requirements have to be met. The method is based on the derivation of functional dependencies of selected material parameters. These dependencies can be used in parameter studies to consider parameter combinations that lie in the range of real existing and targeted material groups. This allows the parameter space to be reduced, the calculation to be accelerated, and suitable materials to be (pre-)selected for the respective application, which contributes to a more target-oriented design. The method is applied to the example of a plate resonator. For this purpose, a semi-analytical model is implemented to calculate the transmission loss as well as the reflected and dissipated sound power of plate silencers, taking into account the influence of flow velocity and fluid temperature on the performance of plate silencers.DFG, 416814415, Bauweisenentwicklung und Technologiesynthese zur Fertigung zellularer Kunststoffhybridstrukturen für den Einsatz in SchalldämpfernDFG, 416728326, Modellierung und Berechnung von Plattenresonator-SchalldämpfernBMWK, 20E1915B, Modellierung und Optimierung der akustischen Wirksamkeit von Linern mit flexiblen StrukturenBMWK, 20E1915C, Untersuchung von neuartigen geometrieangepassten Schallabsorbern aus neuartigen Kunststoffen für Luftfahrtapplikatione

Modeling Electrical Conductivity of Metal Meshes for Predicting Shielding Effectiveness in Magnetic Fields of Wireless Power Transfer Systems

The dimensioning of wireless power transfer systems requires compliance with safety standards for human exposure and electromagnetic compatibility. For this reason, shielding is conventionally carried out with heavy and costly plates. In order to evaluate a lightweight and low-cost alternative, this paper presents a comprehensive investigation of the shielding effectiveness of metal meshes in magnetic fields of wireless power transfer systems, including analytical modeling and experimental validation. Special emphasis is laid on the validation of novel analytical approximation approaches to model the anisotropic electrical conductivity of metal meshes. The proposed approaches show good consistency of the mean value taking into account warp and weft direction, whereas the modeling of the anisotropic behavior is not sufficiently accurately represented. Using the calculated electrical conductivity, the analytical modeling of the maximum shielding effectiveness based on a literature-known approach is very consistent for the experimental validation. Thus, the performed studies provide a significant contribution to the dimensioning of metal meshes as shielding for wireless power transfer systems

Optical thermal model for LED heating in thermoset-automated fiber placement

Control of material temperature distribution and governing phenomena during automated fiber placement is an important factor. Numerical modeling of the radiative heat transfer for a newly presented LED-based heating unit is developed and analyzed in theory. An optical model allows taking into account the radiative energy output of every individual LED. By adjusting the electrical input to the multiple LED arrays on the heating unit, the irradiance distribution on the substrate’s surface can be controlled. To investigate the capability to adjust the surface temperature distribution resulting from this feature, thermal models for two and three dimensions are developed and employed for the calculated irradiance distributions. The resulting temperature distributions show that temperature gradients can be avoided or created, depending on the input to the heating unit. The results from the two models are compared and a method to select an appropriate model in general is proposed

Vibration damping of lift masts of rack service cranes using composite materials with fibrous or textile reinforcement

Die hohen Leistungsansprüche an moderne Lagersysteme führen zu immer kürzeren Taktzeiten beim Warenumschlag, die auch von Regalbediengeräten (RBG) realisiert werden müssen. Um trotz der kurzen Umschlagzeiten eine schnelle und sichere Gutübergabe zu gewährleisten, muss innerhalb der Ausschwingzeit die Amplitude der Schwingungen des Lastaufnahmemittels vor dem Ein- beziehungsweise Auslagerungsvorgang weitgehend abgeklungen sein. Diese Wartezeiten beeinflussen die Taktzeit und damit die Umschlagleistung des RBG negativ. Ein möglicher Ansatz, die Ausschwingzeiten zu verkürzen, ist der Einsatz hochdämpfender Materialien, wie etwa Verbundwerkstoffe. Durch die erreichte Reduzierung der Schwingungsamplituden bei gleichzeitiger Erhöhung des Leichtbaugrades ist eine deutliche Effizienzsteigerung von RBG zu erwarten.High performance requirements for modern storage systems cause shorter cycle times during cargo handling. Especially rack servicing cranes have to realize those requirements. The amplitude of oscillation of the lifting device should be largely subsided before storage and retrieval operation, to ensure a quick and safe delivery of the material despite .Such delays raise the cycle time and influence the storage performance of rack servicing cranes negatively. One option to reduce the oscillation time is the use of highly damped materials such as composite materials. A significant improvement in efficiency of rack servicing cranes is be expected, trough the reduction in vibration amplitudes by simultaneously increasing the lightweight design level