In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise absorption for HR liners is presented. By replacing rigid cell walls in the liner’s honeycomb core structure by flexible polymer films, additional acoustic energy is dissipated. A manufacturing technology for square honeycomb cores with partially flexible walls is described. Samples with different flexible wall materials were fabricated and tested. The acoustic measurements show more broadband sound absorption compared to a reference liner with rigid walls due to acoustic-structural interaction. Manufacturing-related parameters are found to have a strong influence on the resulting vibration behaviour of the polymer films, and therefore on the acoustic performance. For future use, detailed investigations to ensure the liner segments compliance with technical, environmental, and life-cycle requirements are needed. However, the results of this study show the potential of this novel liner concept for noise reduction in future aero-engines.

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It was found that the ultrasonic spot welding may serve as an efficient method to join relative large thin-walled parts made of fiber-reinforced thermoplastics. In this study, a new control method for the ultrasonic spot-welding process was investigated. It was found that, when welding fiber-reinforced thermoplastic laminates without energy directors, overheating and decomposition of the polymer at the weld spot occurred. The occurrence of the overheating took place at unpredictable times during welding. It was observed that the time trace of the consumed power curve by the welder follows a similar pattern as the time trace of the temperature in the weld spot center. Based on this observation, a control system was developed. The time derivative of the welder power was monitored in real time and, as soon as it exceeded a critical value, the ultrasonic vibration amplitude was actively adjusted through a microcontroller. The controlling of the ultrasonic welding process forced the temperature in the weld spot to remain in an adequate range throughout the welding duration for the polymer diffusion to occur. The results of the controlled welding process were evaluated by means of weld temperature measurements, computed tomography scans, and microscopic analysis of the weld spot fracture surfaces.

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Fibre reinforced plastics feature versatile function‐integrative capabilities, e.g. the possibility to realise embedded Structural Health Monitoring (SHM) systems. Material‐compatible sensors are a prerequisite for a robust and reliable function of such systems. Among others, sensors based on carbon fibres are in the focal point of research due to their high material compatibility. The contribution proposes a novel continuous strain sensor based on embedded carbon fibres. In opposition to typical carbon fibre sensors, the presented measurement principle is based on the reversible opening and closing of aligned carbon fibre fragments. The phenomenological effects are investigated by a combined electrical, mechanical and optical analysis. The sensor features a strain sensitivity that is up to four orders of magnitude higher than the one of current carbon fibre sensors. For the first time, the application of the electrical time domain reflectometry for a spatially resolved strain measurement with carbon fibre sensors is presented here. In addition a damage localisation capability with an observed spatial resolution in the lower mm‐range is possible.

The ultrasonic spot welding of fiber-reinforced thermoplastic laminates received a wide interest from researchers mainly in the fields of aerospace and automotive industries. This study investigated a new technique for focusing the ultrasonic vibration energy at the desired spot between two mating thermoplastic composite laminates. In this investigated method, no additional energy directing protrusions between the mating laminates were required to focus the vibration energy. It was found that by welding the laminates amid an ultrasonic horn and an anvil in which the prior had a larger contact surface with the laminate as the latter, it was possible to generate a localized friction heating. In the initial phase of the welding, the friction heating softened the interfacial layers and thus caused the focusing of the majority of the cyclic ultrasonic strain energy in the weld spot center. The assumption for the presence of the friction and its influence on the heat generation was investigated by means of finite element method (FEM) mechanical dynamic analysis. Microscopic analysis of the weld spot eventually delivered the proof for the melt initiation by friction at a ring around the weld spot and subsequent spot growth by viscoelastic heating.

Function-integrative lightweight engineering represents an essential element in modern design methods. Currently, there is a great need for the incorporation of sensors, actuators and electronics in novel, demand-oriented components. In contrast to a subsequent, mostly adhesive bonding, structural integration offers numerous advantages, for example in terms of space requirements and robustness. This paper demonstrates the potential of integrated sensors for various industrial sectors based on selected examples from mechanical engineering, aviation, mobility, sports, and medical technology.