Fraunhofer ISC, Center for High Temperature Materials and Design HTL, Bayreuth
Fraunhofer-Center HTL characterizes materials and determines material properties (e.g. composition, microstructure, application properties). If required, application-specific characterization methods are developed, and customers are advised on suitable processes for process monitoring and quality control. The focus of the material testing at Fraunhofer-Center HTL is on non-destructive as well as mechanical and thermal measurements on ceramics and composite materials. Various process accompanying test methods are also available for material analysis. The evaluation of measurement data focuses on operation behaviour, service life and reliability.
In the case, where no suitable test methods for the customer-specific issue exist, the HTL develops new methods. The area of application, the requirements for the measuring range, resolution and measurement uncertainty as well as further restrictions are agreed with the customer. Subsequently, the HTL develops a test concept. For the design, finite element simulations are used if required. Commercially available components are used in the best possible way. Existing standards are taken into consideration. The test concept is agreed with the customer. Subsequently, construction and procurement of the single components, assembly, software development as well as verification and documentation are performed.
For evaluation of the measurement data, the HTL develops special software. For example, measurement data of imaging systems (computer tomography, scanning electron microscope, laser scan microscope) are analyzed concerning characteristic features defined by the user, and segments of this data are extracted. These can then be simulated, e.g. in FE models. One application is the quantitative evaluation of microstructural characteristics such as surface roughness, internal pores or homogeneity for the strength and reliability of the respective components. With the knowledge of the effects of defects, materials can be optimized and components suitably designed.
A further focus is the development of high-temperature measurement methods for large components and test volumes. For example, the flexural strength of 2 m long transport rollers for roller furnaces at temperatures up to 1200 °C can be measured at the HTL. Special sample holders allow an efficient high-temperature strength testing of up to 7 standard samples in a single heating process. Computer tomograms can be recorded at temperatures up to 2000 °C using special furnaces. Many of the high-temperature measurement methods were implemented in so-called ThermoOptical measurement devices (TOM). Special measuring methods are also being developed for testing external furnace systems (see Furnace analysis).
As a combination of mechanical and non-destructive testing, it is possible to perform in-situ-CT-measurements. Samples are subjected to bending, tension or pressure and several CT measurements are taken during this process. It is thus possible to record the material damage within the sample for the respective load and to track it down to complete failure.