Filtern
Dokumenttyp
- Zeitschriftenartikel (2)
- Beitrag zu einem Tagungsband (2)
- Vortrag (1)
Sprache
- Englisch (5)
Schlagworte
- Loading rate (5) (entfernen)
Eingeladener Vortrag
- nein (1)
The challenge of how to adequately characterize the toughness behavior of ductile cast iron (DCI) materials had been solved through the development and application of fracture mechanics concepts. Outstanding examples are found in the design and safety assessment procedures of sophisticated DCI components for wind turbines or transport and storage casks for radioactive materials. An essential requirement for these procedures is to have adequate fracture mechanics toughness data available.
Because DCI materials may substantially change their deformation, damage and fracture behavior from ductile to brittle by increasing loading rate, decreasing temperature, increasing pearlite share and increasing stress triaxiality, the corresponding experimental measuring techniques and analysis concepts have to be chosen and adapted with deliberation. Long-time experience in this field is imperative to provide valuable data.
BAM has been dealing with mechanical and fracture mechanical characterization of DCI materials for more than 30 years. This paper demonstrates state-of-the-art fracture mechanics test methods for the determination of quasi-static and dynamic fracture toughness. Among others, it is exemplarily shown for a variety of DCI materials conforming to grade EN-GJS-400 how mechanical and fracture mechanical properties are influenced by temperature, loading rate and microstructure. A major lesson to be learned is that fracture toughness data of DCI should always be discussed, reported and used in correlation with microstructural parameters.
Modern structural integrity assessment procedures in the field of nuclear related technology incorporate fracture
mechanical concepts. Therefore, they inevitably require the availability of both, loading parameters as well as material
characteristics in terms of fracture mechanical quantities. Especially in case of dynamic loading conditions, the methods
for the determination of the loading parameters need further improvement and there is a lack of material characteristics
as well. In Germany, ductile cast iron (DCI) is used for heavy-sectioned casks for radioactive materials. New developments
in cask design and efforts to extend the application limits require further investigations. The present study is part
of an ongoing fracture mechanics research programme of BAM which is focused on the systematic mechanical and
fracture mechanical material characterisation of DCI materials under dynamic loading conditions. In this study, results
of fracture mechanics investigations on ductile cast iron from an original DCI container with a wide variety of microstructure
under dynamic loading conditions in the temperature range from -50 °C to +22 °C are presented. Large scale
as well as small scale single edge crack bend specimens SE(B) with thicknesses of 140 mm and 15 mm, respectively
were tested. Furthermore, it is reported on the results of a finite element simulation of the dynamic large scale fracture
mechanics tests. Strength and deformation characteristics were determined in dynamic tensile tests. They are discussed
with respect to the influence of pearlite content and test temperature. The material specific experimental difficulties in
the determination of reliable dynamic crack initiation toughness values of DCI are outlined.
Epoxy resins are frequently used for advanced fiber reinforced composites applications. Even though the fibers are dominating strength and stiffness of the composites, specifically when loaded in fiber direction, the failure usually initiates in the matrix near or directly at the interface. Especially in plies loaded transverse to the fiber direction, the mechanical behaviour is highly influenced by the mechanical properties of the epoxy matrix. Accordingly the mechanical properties of the matrix are of great importance.
Design and safety assessment of advanced ductile cast iron (DCI) components like wind turbines or transport and storage casks for radioactive materials require appropriate material data in terms of strength and fracture toughness. Therefore, it is of vital importance to characterize and understand the deformation, damage and fracture behaviour of DCI which may substantially change from ductile to brittle by increasing loading rate, decreasing temperature and/or increasing stress triaxiality. This paper reports on recent BAM inverstigations on different qualities of the widely used DCI grade EN-GJS-400 with varying pearlite shares (none and 18% respectively). The focus was on the influences of microstructure, temperature (ambient and -40 °C) and loading rate (quasi-static to crash) on strength (YS, UTS, flow curve) and fracture mechanical properties (R-curve, crack initiation toughness, fracture toughness). Systematic metallographical and fractographical analyses were performed accompanying the whole test program and a systematics of specific damage behaviour and fracture mechanisms was derived from the results.