Evaluation of the lower shelf toughness properties of high strength steels using fracture and damage mechanics approaches
| Autor: | Golisch, Georg |
|---|---|
| Přispěvatelé: | Bleck, Wolfgang Peter, Münstermann, Sebastian, Langenberg, Peter |
| Jazyk: | angličtina |
| Rok vydání: | 2018 |
| Předmět: | |
| Zdroj: | Aachen 1 Online-Ressource (xi, 166 Seiten) : Illustrationen (2018). doi:10.18154/RWTH-2018-229713 = Dissertation, RWTH Aachen University, 2018 |
| DOI: | 10.18154/rwth-2018-229713 |
| Popis: | Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (xi, 166 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018 This work concentrates on the toughness properties of ferritic and bainitic structural steels in the lower toughness transition region as well as their assessment by means of fracture mechanics and damage mechanics approaches. In the first step, the standardized concept of the Eurocode 3 1-10 is used to test it for the application of slim weld seams, such as electron beam weld seams. Furthermore, the analytical approach of Eurocode 3 1-10 is investigated with regard to its applicability to such weld seams. Here, numerical mismatch analyzes are used in order to account for the influence of the strength difference on the toughness requirements.As an application example, the structural component of an offshore wind energy tower is used, which orbital weld seam is electron beam welded. The toughness requirements are determined by considering a defect in the weld. The EB weld seams of two steel grades S355ML and S460N are investigated as test materials. These material data are included in the toughness measurement and compared to the required toughness value for the lower toughness transition region, T27J,req. In a second step, a damage mechanics model for determining the lower toughness transition region is developed. Due to the use of local magnitudes for the toughness assessment, a better exploitation of the material toughness can be obtained. The developed damage mechanics model uses a phenomenological approach which is based on the combination of a strain based and a stress based criterion. The cleavage fracture damage mechanics model is developed in which the underlying mechanisms for the provocation of cleavage fracture are taken into consideration. The model is calibrated using steel grade S460N and incorporates the influences of temperature, strain rate, stress state and the scatter of brittle material behavior. While the temperature and strain rate parameters can be calibrated by performing tensile tests on round bar specimens, the stress state calibration demands a variation of specimens. Here, three plane strain geometries and three notched round bar geometries are used possessing different notch radii. In order to provoke fracture, the model calibration concerning the stress state dependency is carried out in liquid nitrogen. In addition, 15 specimens per geometry are used to take account of the scatter of the brittle material behavior. The model is subsequently validated using the instrumented Charpy impact toughness test. For this purpose, simulations are carried out in the temperature range of the lower toughness transition region. As fracture mechanics concepts already found their way into the standards, they are a well accepted method to derive requirements for steel constructions. Consequently, an assessment following fracture mechanics contains the majority of steel grades and geometries of structures. Demands for investigations only arise in cases of validating new steel grades or methods to join materials, as for instance the electron beam welding process. While this work tries to extend the Eurocode 3 1-10 to the toughness assessment of electron beam weld seams, it additionally utilizes a continuum damage mechanics approach to develop this lower shelf toughness model. The development of such a model aims to eventually assess toughness requirements on the basis of continuum damage mechanics, which can assess less conservative requirements in contrast to fracture mechanics approaches. Published by Aachen |
| Databáze: | OpenAIRE |
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