TY - CONF A1 - Eisenacher, Germar A1 - Scheidemann, Robert A1 - Neumann, Martin A1 - Wille, Frank A1 - Droste, Bernhard T1 - Approach for a finite element material model for wood for application in mechanical safety cases of transport packages T2 - 52nd INMM Annual meeting (Proceedings) N2 - BAM Federal Institute for Materials Research and Testing is the competent authority for mechanical safety assessment of transport packages for radioactive material in Germany. The further development of state-of-the-art technology concerning assessment methods is essential for a qualified work of involved designers and authority experts. The paper gives an example of current development done to improve understanding and modeling capabilities of wood filled impact limiter. In order to reduce the loads applied to the package containment, which result from regulatory drop tests, most packages are protected by energy dissipating impact limiter. Wood, encapsulated by steel sheets, is one of the materials typically used for energy dissipation in these impact limiter. Very often, mechanical safety cases regarding the 9 m drop test are performed computationally, where it is essential to use reliable and verified computational methods and models. In this context, the paper presents an approach for a finite element material model for wood. Thereby, the mechanical behavior of wood under compression loading is the focus of the development work. Additionally, material orientation as well as strain rate, temperature and lateral constraint may vary. A large number of experiments, particularly compression tests, was designed and performed to establish an adequate experimental database for modeling verification. The experimental results enabled the derivation of necessary requirements: The material model has to take into account strain rate and temperature dependencies as well as the anisotropic characteristics of the material, a proper yield criterion, flow rule and hardening law. Such a material model is currently not available in established commercial dynamic finite element codes. Thus it is necessary to create a user-defined material model considering the mentioned requirements. A first step was done by determining a yield surface as well as detecting flow and hardening mechanisms from experimental force-deflection curves. In a next step the LS-DYNA material model MAT_75 was altered according to conclusions of former BAM development work, regarding the modeling of post-peak softening as a function of lateral constraint. Future research will contain the further development, implementation and verification of a material model for wood. T2 - 52nd INMM Annual meeting CY - Palm Desert, CA, USA DA - 17.07.2011 KW - Impact limiter KW - Material model wood KW - Transport package PY - 2011 SP - 1 EP - 8 AN - OPUS4-24236 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Eisenacher, Germar A1 - Scheidemann, Robert A1 - Neumann, Martin A1 - Droste, Bernhard A1 - Völzke, Holger T1 - Dynamic crushing characteristics of spruce wood under large deformations JF - Wood science and technology N2 - An extensive series of large deformation crushing tests with spruce wood specimens was conducted. Material orientation, lateral constraint and loading rate were varied. Regarding material orientation, a reduction in the softening effect and the general force level was observed with a higher fiber-load angle. A comparison with characteristics gained by application of Hankinson's formula showed discrepancies in compression strength and the beginning of the hardening effect. Lateral constraint of the specimens caused a multiaxial stress state in the specimens, which was quantified with the applied measuring method. Further, a higher force level compared to specimens without lateral constraint and significant hardening effect at large deformations resulted. Thus, the influence of a multiaxial stress state on the force level could be determined. An increase in the loading rate led to higher force levels at any displacement value and material orientation. KW - Crushing test KW - Dynamic crushing characteristics KW - Spruce wood KW - Lateral constraint KW - Multiaxial stress state KW - Hankinson's formula PY - 2013 DO - https://doi.org/10.1007/s00226-012-0508-5 SN - 0043-7719 SN - 1432-5225 VL - 47 IS - 2 SP - 369 EP - 380 PB - Springer CY - Berlin AN - OPUS4-27743 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Eisenacher, Germar A1 - Kuschke, Christian A1 - Schubert, Sven A1 - Neumann, Martin A1 - Sterthaus, Jens A1 - Nitz, Thilo A1 - Wille, Frank T1 - Moisture content of wood - influence on mechanical behavior of wood filled impact limiter and importance for quality surveillance during manufacturing T2 - RAMTRANSPORT 2012 - 9th International Conference on the Radioactive Materials Transport and Storage (Proceedings) N2 - The moisture content of wood is known to have a significant influence on the wood’s mechanical properties. Using wood as an energy absorber in impact limiter of packages for the transport of radioactive material, it is of particu-lar importance to ensure the moisture content and thus relevant mechanical properties to be in specified limits. The paper surveys the influence of wood moisture content on the mechanical properties of wood. Different measuring methods are discussed with respect to in-situ applicability, accuracy and effort. The results of an experimental ana-lysis of the accuracy of hand-held moisture meters using the electrical resistance method are discussed. Conclu-sions are drawn regarding the measurement of moisture content of wood upon delivery as well as of complete im-pact limiter assemblies. Requirements for quality surveillance during manufacturing of wood filled impact limiter are derived and it is exemplified how to meet them. Construction, manufacturing and inspection of impact limiter encapsulation with regard to leak-tightness are addressed. T2 - RAMTRANSPORT 2012 - 9th International Conference on the Radioactive Materials Transport and Storage CY - London, UK DA - 2012-05-22 KW - Mechanical behavior of wood KW - Moisture content KW - Impact limiter PY - 2012 IS - 4.4 RAM 30 SP - 1 EP - 11 AN - OPUS4-26241 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Neumann, Martin A1 - Ballheimer, Viktor A1 - Sterthaus, Jens A1 - Schubert, Sven A1 - Eisenacher, Germar A1 - Wille, Frank T1 - Material characterization and modeling within safety analysis of packages for transport of radioactive material T2 - PVP2012 - Proceedings of the ASME 2012 Pressure vessels & piping division conference T2 - ASME 2012 Pressure vessels & piping division conference CY - Toronto, Ontario, Canada DA - 2012-07-15 PY - 2012 SP - PVP2012-78297, 1-6 PB - American Society of Mechanical Engineers CY - New York AN - OPUS4-26271 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Eisenacher, Germar A1 - Kuschke, Christian A1 - Schubert, Sven A1 - Neumann, Martin A1 - Sterthaus, Jens A1 - Nitz, Thilo A1 - Wille, Frank T1 - Moisture content of wood: influence on mechanical behaviour of wood filled impact limiters and importance for quality surveillance during manufacturing JF - Packaging, transport, storage & security of radioactive materials (RAMTRANS) N2 - The moisture content of wood is known to have a significant influence on the wood's mechanical properties. Using wood as an energy absorber in impact limiters of packages for the transport of radioactive material, it is of particular importance to ensure the moisture content and thus relevant mechanical properties to be in specified limits. The paper surveys the influence of wood moisture content on the mechanical properties of wood. Different measuring methods are discussed with respect to in situ applicability, accuracy and effort. The results of an experimental analysis of the accuracy of hand held moisture metres using the electrical resistance method are discussed. Conclusions are drawn regarding the measurement of moisture content of wood upon delivery as well as of complete impact limiter assemblies. Requirements for quality surveillance during manufacturing of wood filled impact limiters are derived and it is exemplified how to meet them. Construction, manufacturing and inspection of impact limiter encapsulation with regard to leak tightness are addressed. KW - Electrical resistance method KW - Impact limiter KW - Moisture content KW - Moisture metre KW - Wood PY - 2012 DO - https://doi.org/10.1179/1746510913Y.0000000023 SN - 1746-5095 SN - 1746-5109 SN - 0957-476X VL - 23 IS - 3-4 SP - 179 EP - 185 PB - Ramtrans Publ. CY - Ashford AN - OPUS4-29243 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Eisenacher, Germar A1 - Scheidemann, Robert A1 - Neumann, Martin A1 - Wille, Frank A1 - Droste, Bernhard T1 - Crushing characteristics of spruce wood used in impact limiters of type B packages T2 - PATRAM 2013 - 17th International symposium on the packaging and transportation of radioactive materials (Proceedings) T2 - PATRAM 2013 - 17th International symposium on the packaging and transportation of radioactive materials CY - San Francisco, CA, USA DA - 2013-08-18 KW - Spruce wood KW - Crush test KW - Impact limiter PY - 2013 SP - 1 EP - 10(?) PB - Omnipress AN - OPUS4-30219 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Eisenacher, Germar A1 - Wille, Frank A1 - Droste, Bernhard A1 - Neumann, Martin T1 - Modeling of wood filled impact limiters for transport packages - 14111 T2 - WM2014 Conference (Proceedings) N2 - Packages for the transport of SNF and HLW are usually equipped with impact limiters to reduce the loads that result from the regulatory 9 m drop test. A common impact limiter design in Germany is a welded steel sheet structure filled with wood. The material wood is the main energy absorber, while the steel sheet provides the integrity of the impact limiter. The IAEA allows mechanical safety cases of transport packages to be carried out computationally, as long as the models used are reliable. In this context, a Finite Element (FE) modeling approach for wood and its application to impact limiters in the calculation of a 9 m drop test is presented. A user material model for wood was developed for the dynamic FE-Code LS-DYNA. Its features are based on a series of crush tests with spruce wood specimens. The model considers wood as a material with transversely isotropic properties, i.e. in the directions parallel and perpendicular to the fiber. The plastic material behavior depends on the state of stress. This has shown to be important to account for the lateral constraint of wood in impact limiters resulting from steel sheet encapsulation. Lateral constraint or respectively, a multiaxial stress state, increases the compression strength level of wood, limits the softening effect and increases the hardening effect. Lateral constraint also increases volumetric and reduces deviatoric deformation. The wood material model considers various hardening and softening characteristics via input flow curves. It considers effects of temperature and strain rate on strength as well. The development of a multi-surface yield criterion and a plastic potential that enables the user input of plastic Poisson's ratios were the challenges during the development of material model. A dynamic FE calculation of a horizontal drop test with an 18,000 kg test package was performed. The wood material model was used to model the wooden impact limiter inlays. The impact limiter deformation and the package deceleration were compared to the experimental drop test results to rate the performance of the wood material model. T2 - WM2014 Conference CY - Phoenix, Arizona, USA DA - 02.03.2014 KW - Transport package KW - Radioactive material KW - Spruce wood KW - Impact limiter KW - Material model KW - Finite element PY - 2014 SN - 978-0-9836186-3-8 SP - 1 EP - 10 AN - OPUS4-30653 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Neumann, Martin A1 - Eisenacher, Germar A1 - Schönfelder, Thorsten A1 - Wille, Frank T1 - Finite element simulation of the crush of package components made of encapsulated wood T2 - 11th International Conference on the Transport, Storage and Disposal of Radioactive Materials N2 - Typical transport packages used in Germany are equipped with encapsulated wooden impact limiting devices. We would like to present the current status regarding the development of a Finite Element (FE) material model for the crush of wood for the FE-code LS-DYNA. The crush of is a phenomenon governed by macroscopic fracture. Here, we would like to reproduce fracture and failure mechanisms over the continuous volume. In a first step we altered an existing LS-DYNA material model for foams, which considers an ellipse shaped yield surface. For the use for longitudinal compression of wood, we modified the existing material model to consider the deviatoric strain for the evolution of the yield surface as well. This is in accordance with the results of crush tests with spruce wood specimens, where the crushing deformation was rather deviatoric for uniaxial stress states and rather volumetric for multiaxial stress states We rate the basic idea of this approach to be reasonable, though other problems exist regarding the shape of the yield surface and the assumption of isotropic material properties. Therefore we developed a new transversal isotropic material model with two main directions, which considers different yield curves according to the multiaxiality of the stress state via a multi-surface yield criterion and a non-associated flow rule. The results show the ability to reproduce the basic strength characteristics of spruce wood. Nevertheless, problems with regularization etc. show that additional investigations are necessary. T2 - 11th International Conference on the Transport, Storage and Disposal of Radioactive Materials CY - London, UK DA - 15.05.2018 KW - Wood KW - FEM PY - 2018 SP - Paper 18517, 1 EP - 12 AN - OPUS4-45091 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Neumann, Martin A1 - Eisenacher, Germar A1 - Schönfelder, Thorsten A1 - Wille, Frank T1 - Development of a material model for the crush of spruce wood T2 - Proceedings of ASME PVP 2017 N2 - Typical transport packages used in Germany are equipped with wooden impact limiting devices. In this paper we give an overview of the latest status regarding the development of a finite element material model for the crush of spruce wood. Although the crush of wood – mainly in longitudinal direction – is a phenomenon governed by macroscopic fracture and failure of wood fibres we smear fracture and failure mechanisms over the continuous voume. In first step we altered an existing LS-DYNA material model for foams, which considers an ellipse shaped yield surface written in terms of the first two stress invariants. The evolution of the yield surface in the existing model depends on the volumetric strain only. For the use with spruce wood, we modified the existing material model to consider the deviatoric strain for the evolution of the yield surface as well. This is in accordance with the results of crush tests with spruce wood specimens, where the crushing deformation was rather deviatoric for uniaxial stress states and rather volumetric for multiaxial stress states We rate the basic idea of this approach to be reasonable, though other problems exist regarding the shape of the yield surface and the assumption of isotropic material properties. Therefore we developed a new transversal isotropic material model with two main directions, which considers different yield curves according to the multiaxiality of the stress state via a multi-surface yield criterion and a non-associated flow rule. The results show the ability to reproduce the basic strength characteristics of spruce wood. Nevertheless, problems with regularization etc. show that additional investigations are necessary. T2 - ASME PVP 2017 CY - Waikaloa, HY, USA DA - 16.07.2017 KW - Chrush KW - Spruce KW - Wood KW - FEM PY - 2017 SN - 978-0-7918-5802-8 VL - 7 SP - Article UNSP V007T07A037, 1 EP - 9 AN - OPUS4-41613 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -