Filtern
Erscheinungsjahr
- 2011 (194) (entfernen)
Dokumenttyp
- Beitrag zu einem Tagungsband (194) (entfernen)
Sprache
- Englisch (194) (entfernen)
Schlagworte
- CCS (7)
- Corrosion (7)
- Steel (7)
- Concrete (6)
- Strain sensor (6)
- Computed tomography (5)
- Structural health monitoring (5)
- CO2-storage (4)
- Emission (4)
- Fibre optic sensors (4)
The paper presents numerical methods to detect and classify defects and inhomogeneities by means of active thermography. The objective is to determine the wall thickness of structure elements with an inaccessible back wall, for example, of pipes or Containers. As test specimens we used approximately 2 cm thick PVC samples with spatial variations in the back wall geometry. Flash lamps provided the heating. To know the thickness of the wall, we used two inversion methods and compared the results achieved. One is an iterative echo defect shape method and already tested on Steel test specimens with good reconstruction results. The second one is the Levenberg-Marquardt method, applied here to thermographic data for non-destructive testing. Since data capturing using active thermography and the presented numerical methods can easily be automated, the combination of these two procedures is a promising approach providing a broad area of application.
Reinforced concrete piles are used in case of structures that are constructed on soft ground to transfer the loads into deeper strata with sufficient bearing capacity. In order to determine the pile’s behavior and possible damage, static and dynamic pile tests are carried out. Dynamic measurements taken from the pile head can show the bearing behavior and structural integrity by using the theory of wave propagation. In order to receive more precise information about the pile features, now, a string of sensors is embedded at different levels of the pile. A fiber optic strain wave sensor, based on the extrinsic Fabry-Perot interferometer (EFPI), has already been developed and tested in full-scale field tests by Schallert (2010). It was possible to detect the introduced deformation caused by the static load and the dilatational wave during dynamic loading. Although the full-scale tests were successful, the engineering design of the sensor body left room - from the economical point of view - to be optimized. After laboratory tests with the optimized sensor, a cast-in-situ bored pile has been built at the BAM Test Site Technical Safety in Horstwalde, South of Berlin. Additionally to the EFPI sensors, fiber Bragg grating (FBG) sensors, temperature sensors and resistance strain gauge (RSG) sensors are embedded in order to compare the signals with each other. In this paper, the modified sensor and the Setup of the cast-in-situ bored pile along with results of dynamic tests are shown.
Structural health monitoring of wind turbine blades by strain measurement and vibration analysis
(2011)
Wind turbine blades have to withstand a high number of load cycles in mostly hard weather conditions over 20 years. In a research project BAM and several partners have designed, evaluated and tested a condition monitoring system for all parts of a wind turbine. At a rotorblade with a length of 58 m fibre bragg grating sensors were applied for in-service strain measurement. Additionally a complex test rig was designed to enable real biaxial loading conditions at a representative test rotor blade to simulate the mechanical loading conditions in the lab. In this test blade with a length of 8 m also fibre bragg grating sensors were implemented to determine their influences for the structure and the condition monitoring system. Vibration measurements were carried out at different test phases. The results were compared with finite element strain and modal analysis.
Integration of magnetic functional components in LTCC Circuit boards calls for co-firing of dielectric and ferrite tapes. Ni-Cu-Zn ferrites with permeability of p=900 were developed which can be fully densified at the Standard LTCC sintering temperature of 900 °C. Successful co-firing of this ferrite with dielectric tapes requires the adaptation of the shrinkage behavior of the materials as well as the thermal expansion during the cooling period - especially in the temperature range below the transformation point of the glassy phase of the dielectric tape. To match these preconditions, a new dielectric LTCC material with steep sintering curve and high thermal expansion coefficient was designed. Sintered multilayer composed of Ni-Cu-Zn ferrite and tailored dielectric tapes are free of cracks and possess no open porosity. No significant interdiffusion between the ferrite and dielectric tapes was found by EDX measurements. Compared to pure ferrite laminates the permeability of co-sintered Ni-Cu-Zn ferrite layers is drastically reduced to 400, i.e. a decrease of more than 50 %.
To investigate the origin of this permeability reduction, Ni-Cu-Zn ferrite laminates were sintered separately, and in combination with alumina release tapes or dielectric tapes, respectively. SEM and EDX analysis of co-fired laminates reveal differences in the ferrite grain growth behavior. Ferrite laminates with homogeneous microstructure and grain size up to 50 pm exhibit large permeability. However, growth of ferrite grains does not take place near the interface between ferrite and release or dielectric tapes. There is a strong correlation between high permeability and volume fraction of large ferrite grains. Regions of fine and coarse grains inside the ferrite layers show different bismuth concentration; the Bi-content is larger in regions of fine ferrite grains.
Fatigue testing in the VHCF ränge requires testing machines with increased frequencies. However, application of energy-saving resonance testing leads to a linkage between test frequency and specimen Parameters. The frequency ränge and the available forces of the testing machine are limiting possible specimen dimensions.
Electrodynamic shakers combine test frequencies up to 4000 Hz with forces in the kN range. Thus, a relatively wide range of tests is possible which allows studying the influence of specimen size on VHCF behaviour.
Electrodynamic shakers as well as the respective Computer control Systems and Vibration measurement techniques are well established in scientific and technical applications. We present results of a first study of VHCF testing on electrodynamic shakers conducted at BAM. Test frequency, specimen size and stress levels have been varied. One goal is to balance the needs of materials testing with the Standard test Systems of environmental Simulation to provide a powerful and flexible tool for very high cycle fatigue testing. Further investigation to optimize the technique is required.
In the approval procedure of transport packages for radioactive materials, the mechanical and thermal safety assessment is carried out in Germany by competent authority BAM. In recent years BAM was involved in several licensing procedures of new spent fuel and HLW package designs, where the cask body was made of Ductile Cast Iron (DCI). According to IAEA regulations package designs have to fulfill requirements for specific conditions of transport. Type B(U) packages must withstand the defined accident conditions of transport. The temperature range from -40°C up to the operational temperature has to be considered. For the cask material DCI, it is necessary to determine the brittle fracture behavior. The German guideline BAM-GGR 007 defines requirements for the fracture mechanics of DCI. Due to complex structure of the cask body and the dynamic loading a fracture mechanical assessment in an analytical kind is not always possible. Experience of recent design approval procedures show that the application of numerical calculations are applicable to determine the fracture mechanical load in the cask body. At the first step a numerical analysis has to be done to identify the loading state at the whole cask body. Secondly an analysis of a detail of the cask body is made considering the displacement boundary conditions of the global model. An artificial flaw is considered in this detailed model to calculate the fracture mechanical loading state. The finite element mesh was strongly refined in the area of flaw. The size of the artificial flaw is characterized by the ultrasonic inspection used for the quality assurance of the package. The applicant developed additional analysis tools for calculation of stress intensity factor and/or J-Integral. The assessment approach by BAM led to the decision to develop own tools to the possibility for independent check of the results.
The paper describes the authority assessment approach for the DCI fracture mechanics analysis. The validation procedure incl. the development of own tools is explained. BAM developed a post-processor called JINFEM to determine the fracture mechanical loads. The regulatory 1 m puncture bar drop test is used to give an example of the assessment procedure.
Further miniaturization of electronic packaging calls for integration of magnetic functional components into LTCC modules. For integration of magnetic function into LTCC, low fired MnZn- and NiCuZn-ferrites which can be fully densified at the standard LTCC sintering temperature of 900°C were developed. To co-fire these ferrite tapes with dielectric tapes the sintering shrinkage and the coefficient of thermal expansion of ferrite and dielectric tapes must be matched. For each ferrite material a new LTCC dielectric material was designed. The embedded ferrite tapes into new LTCC dielectric tapes can be sufficiently densified during co-firing at 900°C without any cracking. Compared to separately sintered ferrites the permeability of embedded ferrite tapes is reduced. For embedded NiCuZn ferrites permeabilities between 230 and 570 (at 2 MHz) according to the thickness of the embedded ferrite layer were measured. For embedded MnZn ferrites a permeability of 300 was measured.
Manufacturing of CIGSe thin film solar modules involves typically one laser structuring step (P1) and two mechanical structuring steps (P2 and P3) for serial interconnection. In our approach, complete laser structuring is successfully demonstrated by application of short nanosecond laser pulses (<10 ns) with a single, visible wavelength of 532 nm. The P1 and the P3 trenches are scribed by induced and direct ablation, respectively. For the P2 scribe, the thermal input of the ns laser pulses is used to transform the CIGSe absorber layer locally into a highly conductive compound to provide proper electrical interconnection. These findings promise further simplification and flexibility to thin film solar cell production.
Structuring of thin-film photovoltaic modules requires basic knowledge of the laser – thin-film interaction in order to adapt the accessible laser parameters, like wavelength, power, repetition rate and scribing speed whilst taking into account the specific material properties of the layer. We have studied the nanosecond laserablation behavior of corresponding layers (i) of silicon based thin-film solar cells with a-Si/µc-Si tandem absorber type and (ii) of back contact and absorber layer of CIGSe solar cells. The respective ablation threshold fluences were determined as integrative parameters describing the specific laser – material interaction. For the threshold determination we used two different methods and developed a new analytical approach taking into account scribing through the glass substrate as it is preferred for most structuring processes. This was done by analyzing the thin film ablation results by means of optical microscopy, profilometry, scanning electron microscopy (SEM). Moreover, we determined the incubation coefficient of the regarded material layers which allows us to predict quantitatively the influence of the spot overlap on the scribing threshold.