has been significantly improved and used to measure the stiffness of a cantilever. The facility is based on a disc pendulum with electrostatic reduction of its deflection and stiffness. In this paper, we will demonstrate that the facility is able to measure horizontal forces in the range below 1 μN with a resolution below 5 pN and an uncertainty below 2.7% for a measured force of 1 nN at a measurement duration of about 20 s. We will demonstrate the possibility of using this facility as a calibration device that can accurately determine spring constants of soft cantilevers (K < 0.1 N m −1 ) with traceability to the SI units. The method and the results of measuring the spring constant of a soft cantilever (K = 0.125 N m −1 ) in air, in a medium vacuum, in a high vacuum and in nitrogen are presented. We will show that a relative standard uncertainty of the spring constant calibration of better than 0.3% (measurement in a medium vacuum) and a repeatability of better than 0.04% are achieved.

In recent works, a novel light-induced attractive force was predicted between two metal plates. This force arises by the interaction of surface plasmons which are excited at the metal when a transverse magnetic mode propagates through a subwavelength slit between two metal bodies. In this paper, the analytical and numerical calculations of this magnetic field are presented for the perfect metal and for gold. The amplitude and the phase transient curves between the known limiting cases of narrow and wide slits compared to the wavelength are found. The curve is shown to oscillate due to the emergence of new waveguide modes. The analytic solution for the perfect metal is in agreement with the computation for gold by means of the finite element method. The simple asymptotic formula for the light-induced attractive force is found in the limit of a narrow slit.

The improvement of land-, sea-, or air-based turbines is driven by the goal of higher efficiency and lower fuel burn. One way to achieve this goal is to increase the operating temperatures. This was very successfully done in the past few years by improvements in the fabrication of the components, but has now become limited due to the melting temperature of the traditional materials like nickel base superalloys used for turbine blades. To overcome this problem thermal barrier coatings (TBCs) can be applied onto turbine parts. First TBCs were used in the mid 1970s, but the concept has become increasingly interesting in the past few years. [1][2][3] The idea behind TBCs is to apply additional thin layers on the turbine parts that act as insulation without adding too much weight to the part itself. By the insulation of the coating, the component is exposed to a lower surface temperature than the gas temperature at the coating surface. This allows reducing the maintenance intervals while maintaining the operating temperature due to lower degradation or increasing the operating temperatures beyond the melting temperature of the metallic component. As failure of the coating in the latter case may result in serious damage of the turbine, reliable estimation of the lifetime is essential to estimate maintenance intervals with good balance between safety and cost-efficiency.The TBC itself consists mainly of a ceramic material of low heat conductivity and a thinner layer (bond coat) between the metallic substrate and the ceramic top coat for better adhesion. The layers are applied onto the components by different techniques. Mostly used are physical vapor deposition methods or plasma spraying methods. Different ceramic materials were studied but the best results yet were achieved with yttria stabilized zirconia (YSZ) and therefore it is the most commonly used coating. [4] The optimal ceramic material for the top coat needs a low thermal conductivity and a comparable thermal expansion as the underlying substrate and bond coat. A high thermal shock resistance is also desirable as thermally induced stresses due to thermal cycling and thermal shock are the main load during operation. The mismatch of the thermal expansion coefficients of the metallic substrate and the coating as well as the temperature gradient during heating and cooling are the main reasons for failures of TBCs. COMMUNICATION [*] Dr. [**] We would like to thank the group of Prof. Vaßen of the Forschungszentrum Jülich for providing us with samples of thermal barrier coatings.Thermal barrier coatings (TBCs) are used to increase the operating temperature of land-, sea-, or air-based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of the lifetime is essential. Most experiments to assess the lifetime or to determine parameters for simulations of the behavior of TBCs are done by burner-rig-tests, where the operating conditions are simulated by cyclic heating of the surface and cooling of the backside of a coated sam...

Thermal barrier coatings allow increasing the operating temperature and efficiency of land‐, sea‐, or air‐based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of its lifetime is essential. To assess the lifetime, cyclic tests are conceived to combine thermal loading by heating the surface of the coating with laser irradiation and nondestructive methods for damage determination. Using laser irradiation allows a high reproducibility of the thermal load. The temperature of the sample surface during thermal loading is determined by an infrared‐camera which also enables the possibility to detect damage in the coating via thermography. Additionally, four acoustic sensors, attached to the experimental setup, are used to detect damage in the sample and determine the source of acoustic events. Results of acoustic emission correlate well with thermographic images that visualize the formation and evolution of damage through delaminations in the samples.

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