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Scaling laws are used to scale-up calculation or measurement results from a prototype structure to those of an original structure or vice versa. The scaling laws of mechanical structures are usually obtained from their equations of motion or from a dimensional analysis. This paper proposes scaling laws that are represented by a power law. The power law is directly deduced from the Π -theorem of similitude theory and the coefficients of the power law are obtained from first order sensitivities (sensitivity-based scaling laws). Among existing similitude analysis methods such as dimensional analysis the sensitivity-based scaling laws can be directly obtained from a model without a priori knowledge of its scaling behavior, e.g., from a finite element (FE) model. The applicability of the sensitivity-based scaling laws is demonstrated in three case studies. A simply supported rectangular plate subject to mechanical vibrations is modeled by an analytical approach based on the Kirchhoff plate theory and by an FE model based on the Mindlin-Reissner theory. The plate’s dimensions are considered as design parameters for the sensitivity-based scaling laws. It is found in the first case study that the sensitivity-based scaling laws exactly predict the natural frequencies and the mean squared transfer admittances of scaled models from those of the original plate. This is in agreement with current literature and, thus, the method proposed in this paper can be considered verified. In the second case study the sensitivity-based scaling laws are directly obtained from the FE model. A good accuracy of the predicted vibration responses of the scaled models is found since (1) the scaled model and the original one are in similitude, i.e., the mode shape order and the damping are kept, and (2) the scaled plate can still be considered thin. The latter is assessed by the length (or width) to thickness ratios of the investigated plates and a lower bound is proposed. The third case study comprises a simplified car undercarriage to demonstrate the applicability of the method in practical design engineering. Besides the geometry parameters the material properties are incorporated in the sensitivity-based scaling laws as well. It is found that the natural frequencies as well as the vibration velocities at an arbitrarily chosen receiver point of the scaled models can be accurately predicted from those of the original one for complete similitude conditions.

The active approach is nowadays well developed and widely used for various kinds of structures for vibration control or compensation. However, it makes the structure more complex than a passive structure. In this study, active and passive beam structures with the same designed size are compared with regard to uncertainty analysis of the system. The purpose of the comparison is to find a comprehensive way to decide whether an active or a passive approach should be used in the structural design phase. An active beam structure used in this study is a beam structure with one sensor, one actuator, and one controller. The controller is designed to reduce the structural vibration. An active beam structure with a properly designed controller can reduce the structural vibration without changing the structure’s physical dimensions. In contrast, a passive approach can also reduce the structural vibration without additional electric energy for active components, e.g., by changing the material. The comparison of the active and the passive beam structure is based on a beam structure with the same boundary conditions. It is well known that after manufacture and assembly the input parameters of the structure do not exactly correspond to the designed values. Therefore, the input parameters are assumed to be normally or uniformly distributed according to the manufacture tolerance class. They are varied according to the Monte Carlo method to compare the vibration reduction ability of the active and the passive approaches. Finally, uncertainty analysis supports the decision if an active or a passive approach should be used in the structural design phase.

In the present work the bubble diameter, heater surface temperature distribution, and local heat flux during different stages of single bubble cycles during pool boiling of PF-5060 at a pressure of p = 600 mbar have been investigated in several stable low g levels during the 1st Joint European Partial-g Parabolic Flight (JEPPF) Campaign. In previous parabolic flight campaigns, microgravity conditions were achieved by following a parabolic trajectory with the specially equipped A-300-Zero-G Aircraft. In this recent JEPPF campaign, the parabolic trajectories were slightly shifted, to establish—apart from microgravity conditions—also stable gravity levels of 0.16 g (lunar gravity) and 0.38 g (Martian gravity). High-resolution measurements of the heater surface temperature were performed using high-speed infrared thermography. An infrared (IR)-transparent sputtered heater design was employed in order to allow temperature measurements by IR thermography at a distance of approximately 800 nm to the heater/fluid...

The present study reports on nucleate boiling tests performed with specifically textured chromium nitride (CrN) coatings exhibiting either predominant (1 1 1), (2 0 0) or (2 2 0) crystal lattice orientations. Those tests reveal promising results concerning thin film applications in the field of heat transfer enhancement during nucleate boiling. High power impulse magnetron sputtering (HiPIMS) in combination with direct current magnetron sputtering (DCMS) was applied to deposit CrN coatings of 4.5 μm thickness on average. A thin coating of pure chromium (Cr) was used as adhesive interlayer between substrate and CrN coating. The crystallographic phases and orientations of the coatings were determined by X-ray diffraction (XRD) in θ/2θ mode and texture coefficients T c (h k l) were calculated. High resolution scanning electron microscope (SEM) visualizes the shapes, sizes and orientations of the grains. Different Cr|CrN coating systems were deposited on pure copper heater samples and boiling curves were measured in nucleate boiling experiments in order to determine heat transfer coefficients (HTC) and critical heat flux (CHF) at dry out of the heater surface. Final comparison among the coatings' heat transfer properties reveals differences in CHF and HTC of a factor of 1.8, respectively 1.6, according to the applied microstructure.

A smart structure is a structure that can reduce a structural vibration by means of the integration of one or more sensor, actuator, and controller. A sensor detects a vibration in the structure and transfers a signal to a controller. The controller, designed to compensate the structural vibration, then computes the desired control signal and sends it to an actuator. A piezoelectric ceramic patch is often used, as in the present study, as a sensor or an actuator in a smart structure. A smart structure with a properly designed controller can reduce the structural vibration without changing the structure’s physical dimensions. Since a smart structure contains more uncertainty factors, not least due to the additional interfaces in comparison to a passive structure, the smart structure should be well analyzed to ensure its reliability and robustness. This paper focuses on how to set up a numerical model for a smart beam structure, how to design its control concept, and how to investigate the controller’s robustness by means of the Design of Experiments (DoE) method (In this paper experiment refers to numerical simulation.). A full factorial design is used, in which the parameters of the smart structure are either varied in their distributed range or held constant, so that several structures are designed with slight variations. This study aims at determining, which controller is the most robust by comparing the performance for different structural variations of the smart structure. Only if a smart structure is connected to a robust controller, its reliability can be analyzed, which is the aim of further research.

In the present work the behavior of single vapor bubbles of FC-72, generated on a thermal capacitive heater element, has been investigated during microgravity. A newly developed heater design allows temperature measurements by highspeed infrared thermography on the backside of the heater surface at a distance of approx. 800 nm from the fluid/heater-interface. The employed heater was manufactured by Physical Vapor Deposition (PVD) of a chromium based layer for better emissivity (Slomski et al., Mater Sci Technol 41:161–165, 2010) and a pure chromium heating layer supplying the energy required for bubble generation and sustainment by electrical heating. The thermal diffusivity of the employed Calcium Flouride (CaF) heater substrate is comparable to the thermal diffusivity of stainless steel, which makes this heater design very close to technical applications. The acquired transient temperature fields of the heater surface allow numerical determination of the local heat flux from the heater surface to the fluid. A local temperature drop and high heat fluxes have been observed in the vicinity of the 3-phase contact line. This effect has already been reported by former publications for thin stainless steel foil heaters (Stephan and Hammer, Int J Heat Mass Transfer 30:119–125, 1994; Wagner et al., Int J Heat Mass Transfer 42:875–883, 2006) and is also confirmed for heaters with significantly higher thermal capacities.

Imperfection on substrate surfaces commonly causes growth defects in hard coatings prepared by magnetron sputtering, leading to local loss of adhesion, higher friction, voids and corrosion at coating defects. CrN coatings are known for their high hardness and good wear resistance. The structure and the mechanical properties of those coatings can be influenced varying bias voltage and gas flow during film growth. Due to variation of those parameters CrN coatings were deposited with preferred crystallized lattice orientations (111) and (200). The main objective of investigation is the potential to cover imperfections to increase robustness, especially under superimposed corrosive loads. With the intent to generate comparable surface defects, Vickers indentations were applied as artificial imperfections. With X-ray diffraction analysis and cross-sectional SEM micrographs film orientation and texture around those artificial imperfections was studied, aiming to examine coating microstructure and grain growths. In this context the potential of specified crystallized lattice orientation to cover imperfections is of particular interest.

Storstellen in Bauteiloberflachen wirken sich haufig ungunstig auf die Schichtnukleation bei PVD-Beschichtungen aus. Sie konnen beim Schichtwachstum zu defekten in der Schichtstruktur fuhren. Die Konsequenz ist eine Minderung der lokalen Haftfestigkeit, hohere Reibwerte und Fehlstellen in der Schicht. Diese begunstigen in korrosiven Medien die Entstehung von lokalen Korrosionselementen an Defekten. CrN-Schichten sind fur ihre hohe Harte und ihre guten Verschleiseigenschaften bekannt. Zudem weisen sie eine bessere Korrosionsbestandigkeit als Ti basierte Nitride auf. Die strukturellen und mechanischen Eigenschaften dieser Schichtsysteme konnen unter anderem durch die Veranderung der Biasspannung und des Stickstoffgehalts wahrend des Schichtwachstums beeinflusst werden. Durch gezielte Variation dieser Parameter beim reaktiven Magnetronsputtern wurden CrN-Schichten mit den bevorzugten Kristallgitterstrukturen (111) und (200) abgeschieden, mit dem Ziel, deren Fahigkeit zur Abdeckung von Storstellen zu untersuchen. Effect of PVD process parameters on structural properties of CrN layers Commonly, imperfections on substrate surfaces influence layer nucleation unfavorably. They cause growth defects in the coating structures prepared by physical vapor deposition. In consequence this leads to local loss of adhesion, higher friction, voids and thus favoring pitting corrosion. CrN-coatings are known for their high hardness and good wear resistance. Further they have a better resistance to corrosion than Ti-based nitrides. Among other parameters, the structure and the mechanical properties of those coatings can be influenced by varying bias voltage and gas flow during film growth. Due to variation of those parameters during reactive magnetron sputtering CrN-coatings were deposited with preferred crystallized lattice orientation (111) and (200). The main objective of investigation is the potential to cover imperfections.

Storstellen in Bauteiloberflachen wirken sich negativ auf die Schichtnukleation bei PVD-Schichtsystemen aus. Sie konnen im anschliesenden Schichtwachstum zu Defekten in der Schichtstruktur fuhren. Die Konsequenz ist eine Minderung der lokalen Haftfestigkeit, hohere Reibwerte und Fehlstellen in der Schicht. Diese begunstigen in korrosiven Medien die Entstehung von Korrosion. CrN-Schichten sind fur ihre hohe Harte und ihre guten Verschleiseigenschaften bekannt. Zudem weisen sie eine bessere Korrosionsbestandigkeit als Titan basierte Nitride auf. Die strukturellen und mechanischen Eigenschaften dieser Schichtsysteme konnen unter anderem durch die Veranderung der Biasspannung und des Stickstoffgehalts wahrend des Schichtwachstums beeinflusst werden. Durch gezielte Variation dieser Beschichtungsparameter wurden CrN-Schichten mit den bevorzugten Kristallgitterstrukturen (111) und (200) abgeschieden, mit dem Ziel deren Abdeckungsfahigkeit von Storstellen zu untersuchen. Fur die gezielte Untersuchung und Vergleichbarkeit der Ergebnisse wurden Vickerseindrucke HV 0,5 als bewusst gestaltete Storstellen auf der Grundwerkstoffoberflache aufgebracht. Als Grundwerkstoff diente niedriglegierter Stahl (100Cr6). Die Kristallgitterorientierungen der abgeschiedenen Schichten wurden zunachst anhand von rontgenographischen Messungen (XRD) identifiziert. Anhand weiterer rasterelektronenmikroskopischer Aufnahmen (REM) wurden die bewusst erzeugten Storstellen in Form von Vickerseindrucken und Ritzspuren sichtbar gemacht, mit dem Ziel die Schichtqualitat und die Mikrostruktur um Fehlstellen zu beschreiben. Imperfections on substrate surfaces can cause growth defects in hard coatings prepared by magnetron sputtering, leading to local loss of adhesion, higher friction, voids and corrosion at coating defects. CrN-coatings are known for their high hardness and good wear resistance. In addition CrN-coatings are better corrosion resistant than Ti based nitrides. The structure and the mechanical properties of those coatings can be influenced by varying bias voltage and gas flow during film growth. Due to variation of those parameters CrN-coatings were deposited with preferred crystallized lattice orientations (111) and (200). The main objective of investigation is the potential to cover imperfections. Vickers indentations (HV 0.5) were applied as designed imperfections. As base material low alloyed steel was used (100Cr6). At first crystallized lattice orientations were identified by X-ray diffraction (XRD). Further scanning electron microscope analysis (SEM) was applied to identify and study crystallized lattice orientations near those imperfections.

In the present work, the influence of micro-structured chromium nitride (CrN) surfaces on boiling heat transfer during nucleate boiling of FC-72 at saturation temperature was investigated. The CrN thin coatings of 4.5 μm thickness in average were deposited by Physical Vapor Deposition (PVD) as a combination of High Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (DCMS) on polished copper surfaces. Due to variation of the applied bias voltage to the substrates different sizes and orientations of the CrN crystals were realized. The typical dimensions of the hereby generated surface structures are in the order of a few hundred nm to a few μm. It was found that all employed micro-structured CrN surfaces yield an increase of the critical heat flux (CHF) compared to an uncoated reference surface. The maximum ratio of the CHF of a CrN structured surface to the CHF of the uncoated copper surface reached within this study was CHFmax/CHFref = 2.5.