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Proper predictions of the behaviour of shock absorber materials are of utmost importance in safety assessments for licensing casks for transport and storage of highly active waste. After having identified significant discrepancies between numerical results and the actual response of polyurethane foam limiters subjected to accidental scenarios, a new research project ENREA was established by BAM. A major objective is to enhance and to develop advanced material models intended to simulate limiters under impact loading. They should account for all major factors influencing the load–deformation relationship like temperature, strain rate and specific stress state. The corresponding test program, applicable plasticity models, the overall parameter identification strategy based on local and global optimization techniques as well as experimental and numerical results are presented here in particular for closed cell foams.
For validation of structural integrity under normal and hypothetical accident conditions during transport and storage of radioactive material the Federal Institute for Materials Research and Testing (BAM) focuses its safety related scientific research on advanced mechanical safety assessment methods including simulation of high rate impact of model components and structures. A drop and crash test facility with an unyielding target and a load capacity of 1.200 kg was designed for materials testing of component size specimen under impact conditions at elevated and higher loading rates. The maximum drop height is 12 meters which enables impact velocities up to 15 m/s. An exactly falling test object or drop weight allows impact, bending, compression as well as crash and crush tests with maximum input energy of 118 kJ. An arresting unit has been developed to avoid multiple impacts during instrumented drop tests. The paper presents experimental techniques and examples of various measurement methods and advancements in order to assess assumption of materials and components behavior by definite displacement and stresses within mechanical testing. Instrumented drop weight tests are performed to complete materials data base and energy absorption of shock-absorbing materials and structures as well as to implement materials and structural parameters into FEA of reference structures. Furthermore, fracture mechanics parameters of thick walled DCI containers by means of dynamic bending tests are characterized by crack initiation and crack resistance behavior at the lowest operational temperature depending on the strain rate.
The shock absorbing material damping concrete is for the foundation in dry interim storage facilities for radioactive waste in Germany. In case of a potential cask drop damping concrete minimizes the mechanical loads to the cask. In course of safety analyzes this accident scenario is considered by numerical simulations using the finite element method. To get reliable results of numerical simulations a suitable material model is needed to take the characteristics of damping concrete into account. Due to the lack of sufficient material knowledge a research project was started to characterize the material’s behavior under different load conditions. This paper presents the test program to analyze the material behavior of damping concrete which is characterized by large volume change and
strain rate hardening dependence. The determined Parameters were used to adapt an existing material model of the FE-code ABAQUS®. This model has to handle the mechanical damage behavior of damping concrete which occurs under compression and shear loads during a potential cask drop. To verify the material model numerical simulations are compared with dynamic penetration tests, which were conducted with specimens assembled similar to the real application of the damping concrete footings. The transferability of the material
model to a real accident scenario was verified by a drop test with a full-scale cask on a damping concrete footing.