a b s t r a c tEddy current testing is well established for non-destructive testing of electrical conductive materials [1]. The development of radio frequency (RF) eddy current technology with frequency ranges up to 100 MHz made it possible to extend the classical fields of application even towards less conductive materials like CFRP [2][3]( Table 2). It turns out that RF eddy current technology on CFRP generates a growing number of valuable information for comprehensive material diagnostic. Both permittivity and conductivity of CFRP influence the complex impedance measured with RF eddy current devices. The electrical conductivity contains information about fiber texture like orientations, gaps or undulations in a multilayered material. The permittivity characterization influenced by dielectric properties allows the determination of local curing defects on CFRP e.g. hot spots, thermal impacts or polymer degradation. An explanation for that effect is seen in the measurement frequency range and the capacitive structure of the carbon rovings. Using radio wave frequencies for testing, the effect of displacement currents cannot be neglected anymore. The capacitive structures formed by the carbon rovings is supposed to further strengthen the dielectric influences on eddy current measurement signal [3]. This report gives an overview of several realized applications and should be understood as a general introduction of CFRP testing by HF Radio Wave techniques.

No abstract

Coreless filament winding technologies possess the potential to flexibly produce lightweight rigid frame structures at comparably low costs. The key to versatility, geometrical freedom and cost-effectiveness is the avoidance of core elements. Existing research on the filament winding of rigid frames focusses primarily on “isotruss” or “lattice” structures, manufactured by depositing fibers on polygon-shaped mandrels with carved-out gaps. Therefore, an investigation into the performance of coreless wound laminates and their material characteristics under process conditions is performed. Therefore, generic 2D specimens were manufactured on a new fully automated 3D winding equipment and successively exposed to incineration, micro-CT analysis and tensile testing. The benefits of core elements are evaluated by additional reference samples and opposed to coreless winding methods. The research demonstrates the potential of coreless filament winding and inductively quantifies the positive influence of fiber pretension and core/die elements on the material properties at cost of decreased versatility, costs and design degrees of freedom.

No abstract

The most common measuring method to characterise the dynamic yarn path in the ring spinning process is to measure the yarn tension, where the yarn path is almost straight. However, it is much more complex to measure the yarn tension at the other positions, for example, between the yarn guide and traveller (balloon zone) and between the traveller and winding point of the cop (winding zone), as the yarn rotates continuously around the spindle axis. In this paper, two new methods of yarn tension measurement in the balloon zone are proposed. In the first method, the balloon shape was first recorded with a high speed camera. The balloon tension was then calculated by comparing the yarn strain (occurring in the balloon zone) measured by a digital image analysis program with the stress-strain curve of the yarn produced. In the second method, the radial forces of the rotating balloon were measured by using modified measurement techniques for measurement of yarn tension. Moreover a customised sensor was developed to measure the winding tension between the traveller and cop. The values measured were validated with a theoretical model and a good correlation between the measured and theoretical values could be revealed.

An important aspect of soft robotics, next to the different actuation mechanisms, is the monitoring of the robot's position and condition and, thus, the local and global strains via integrated sensors. Currently investigated actuation classes and materials like dielectric elastomer actuators or twisted-coiled polymeric actuators offer large strain potentials, rendering conventional metal or semiconductor strain gauges unsuitable. [3] Apart from their inherent strain limit of less than 5%, the difficult integration into and adhesion to smart materials is preventing their use in novel complex and compact soft robots. [4,5] Additionally, as some of the currently researched actuator mechanisms and principles offer high strain rate actuation, the necessity of not only a quasistatic but also dynamic monitoring and suitable control strategies is conspicuous. One approach to integrate actuators and sensors and to achieve resilient but flexible structures is using fiber-shaped active materials similar to muscles and nerves in biological systems. [6] A popular choice as a sensor material are carbon-based particle-filled highly stretchable elastomers (CPFEs). Such particles can be carbon black (CB), carbon nanotubes (CNT), graphene, or combinations thereof. Until today, there has been a vast amount of studies investigating different polymer materials, fillers, and mixing ratios as well as their applications to monitor soft robots or body posture. [7,8] Additionally, the conducting particles can also be used in order to tailor the electro-thermal response of shape memory polymers. [9] The standard analysis performed to evaluate the different soft sensor systems is a quasistatic tensile test while tracking the resistance. Investigations of dynamic sensor properties with systematically varied strain rates and loading scenarios are scarce. This lack of data also contributes to the poorly understood phenomena occurring during cyclic, dynamic loading of CPFEs. [10] To employ CPFEs as sensors, their linearity, sensitivity, and monotonicity are important features. [11] Unfortunately, the few investigations so far on dynamic mechano-electrical properties show non-monotonic responses, meaning that, apart from the resistance peak at maximum strain, additional peaks occur. [12,13,14] These peaks either appear while releasing or when the imposed strain is fully released and have been called shoulder phenomenon or secondary peaks. The phenomenon appears independently whether the filler material is CB, CNT, or graphene. [11,15,16] To distinguish between the different phenomena described in literature, the nomenclature in Figure 1 Carbon particle-filled polymers are frequently used as stretchable conductors and strain sensors. Many of the proposed resistance-based stretchable strain sensors show non-monotonic strain response, especially under dynamic conditions. This is commonly attributed to the competing destruction and reformation of the conductive network, but the underlying mechanism is still unknown. Therefore, systematic cyclic tens...

Abstract:Wound assessment has become an important issue in the wound treatment procedure. One

No abstract