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Starting from an introduction into important Basic questions of failure analysis and fracture mechanics, the author specifies what kind of questions in failure analysis can be effectively solved by fracture mechanics (and which can't). He illustrates his discussion with a number of case studies. Much more pronounced than in the design stage the benefit of fracture mechanics in failure analysis depends on ist accuracy. This is limited by both, intrinsic factors of the method and the availability and quality of the input information. The author discusses the various aspects and provides the participants with background information helpful for better understanding the prospects and limitations of fracture mechanics in failure analysis and the conditions of its application.
Modular hip prostheses are attractive for fitting the prosthesis to the individual anatomical conditions with a positive impact on the patient's quality of life. Especially for revision when the stem may remain, modular prosthesis are established in surgery. The additional taper interface between the stem and the neck bears the risk of micromotion, resulting in continuous damage of the passivation layer and subsequent fretting corrosion. In the present failure case bone particles in the taper connection between the stem and neck were detected using Raman spectroscopy. These particles caused high local stress on the taper surface, followed by fretting and fatigue cracking of the stem.
The advent of the Industrial Revolution was accompanied by several accidents of dramatic dimensions. The analysis of these events was the fundament for the continuous improvement in the reliability of technical systems. In the year 1871 the Prussian state created a technical institution dedicated for this task – the origin of BAM. Failure analysis and prevention is until today a central objective of our institute; due to its complex nature an interdisciplinary task. In our talk we will present an overview of the activities of BAM in the area of failure analysis; especial attention will be given to the corrosion aspects in the analysis of these cases.
Embrittlement of spent fuel claddings during long-term dry interim storage - Current approach at BAM
(2019)
The integrity of fuel rods and cladding tubes must be demonstrated throughout the dry interim storage of spent nuclear fuel in Germany. For at least a relevant number of casks, an extension of interim storage between 40 and 100 years is foreseeable. The drying procedure for the fuel rods in conjunction with the thermomechanical storage conditions may change the microstructure of the cladding tubes and lead to their possible embrittlement. The failure probability might increase under mechanical load by handling procedures (transport after storage) on potentially embrittled cladding tubes of fuel rods especially at low temperatures after long-term storage. Results of ring compression tests on unirradiated pre-hydrided as well as irradiated samples with radial hydrides are investigated by finite element analyses to be able to describe the failure process and to identify failure criteria.
In order to demonstrate the safety of both spent fuel and the storage system, a good understanding of the processes that might cause deterioration is required. The International Atomic Energy Agency (IAEA) continued the coordinated research on Spent Fuel Performance Assessment and Research (SPAR) into a fourth phase starting in 2015 to evaluate fuel and materials performance under wet and dry storage and to assess the impact of interim storage on associated spent fuel management activities (such as handling and transport). BAM’s understanding and experiences in the field of long-term storage of spent fuel and especially spent fuel characterization are presented to assist the preparation of the final project report.