TY - JOUR A1 - Dendorfer, Sebastian A1 - Hammer, Joachim A1 - Lenich, Andreas T1 - Characterisation and testing of biomaterials JF - Technology and Health Care KW - Testing biomaterials KW - Characterisation testing KW - Biomaterial KW - Test Y1 - 2011 U6 - https://doi.org/10.3233/THC-2011-0644 VL - 19 IS - 5 SP - 357 EP - 371 ER - TY - JOUR A1 - Dendorfer, Sebastian A1 - Maier, Hans Jürgen A1 - Taylor, David A1 - Hammer, Joachim T1 - Anisotropy of the fatigue behaviour of cancellous bone JF - Journal of Biomechanics N2 - The fatigue behaviour of materials is of particular interest for the failure prediction of materials and structures exposed to cyclic loading. For trabecular bone structures only a few sets of lifetime data have been reported in the literature and structural measures are commonly not considered. The influence of load contributions which are not aligned with the main physiological axis remains unclear. Furthermore site and species dependent relationships are not well described. In this study five different groups of trabecular bone, defined in terms of orientation, species and site were exposed to cyclic compression. In total, 108 fatigue tests were analysed. The lifetimes were found to decrease drastically when off-axis loads were applied. Additionally, species and site strongly affect fatigue lifetimes. Strains at failure were also found to be a function of orientation. KW - Ermüdung KW - Knochen KW - Spongiosa KW - Anisotropie Y1 - 2008 U6 - https://doi.org/10.1016/j.jbiomech.2007.09.037 VL - 41 IS - 3 SP - 636 EP - 641 ER - TY - CHAP A1 - Dendorfer, Sebastian A1 - Hammer, Joachim A1 - Lenich, Andreas ED - Lee, T. Clive ED - Niederer, Peter F. T1 - Characterisation and testing of biomaterials T2 - Basic Engineering for Medics and Biologists: An ESEM Primer KW - Biomaterial KW - Werkstoff KW - Test Y1 - 2010 SN - 978-1607505266 IS - Chapter IV.4. PB - Non Basic Stock Line ER - TY - CHAP A1 - Hammer, Joachim A1 - Dendorfer, Sebastian T1 - Cyclic loading and microstructure of cancellous bone T2 - Journal of Biomechanics Y1 - 2008 U6 - https://doi.org/10.1016/S0021-9290(08)70409-3 VL - 41 IS - Suppl. 1, July 2008 SP - S410 ER - TY - JOUR A1 - Wilhelm, Franz A1 - Affeldt, Ernst Eugen A1 - Fleischmann, Ernst W. A1 - Glatzel, U. A1 - Hammer, Joachim T1 - Modeling of the deformation behavior of single crystalline Nickel-based superalloys under thermal mechanical loading JF - International Journal of Fatigue N2 - The focus of this paper is the simulation of the thermal-mechanical fatigue behavior (TMF) of two single crystalline Nickel-based superalloys in a temperature range between 400 degrees C and 980 degrees C. The newly developed rhenium-free alloy Astra-3OptW and the rhenium-free alloy CMSX-6 are analyzed concerning the basic deformation mechanisms, i.e. elasticity, time-independent and time-dependent plasticity contributing to hardening. In detail, the relevant parameters for high temperature deformation are identified from isothermal creep experiments and used in a numerical model to simulate the deformation behavior under instationary thermal and mechanical loading. Special attention is focused on the determination of the hardening by the second phase (gamma'-precipitates) and their influence on time-dependent deformation and relaxation mechanisms. Therefore, the parameters describing the stress and temperature dependence of the creep rate (i.e. stress exponent n and activation energy Q) are interpreted in terms of a threshold stress taking into account the hardening contribution of the gamma'-phase. Thus, only a reduced effective stress is active for plastic deformation. Particular attention is focused on the accurate determination of the threshold stress as a function of temperature and applied stress from the Langeborg-Bergmann-plot. The comparison of the simulated TMF-deformation to the experimental TMF-data clearly indicates the accuracy of the model in predicting the resulting stresses induced by instationary thermal and mechanical loading. (C) 2016 Elsevier Ltd. All rights reserved. KW - Creep KW - MICROSTRUCTURAL MODEL KW - Modeling KW - PARTICLES KW - Plasticity KW - Single crystalline Nickel-based superalloys KW - Thermal-mechanical fatigue KW - THERMOMECHANICAL FATIGUE KW - Threshold stress concept Y1 - 2017 U6 - https://doi.org/10.1016/j.ijfatigue.2016.12.003 VL - 97 SP - 1 EP - 8 PB - Elsevier ER - TY - JOUR A1 - Spachtholz, Josef A1 - Affeldt, Ernst Eugen A1 - Maier, Hans Jürgen A1 - Hammer, Joachim T1 - Modelling of the fatigue crack growth of a coated single crystalline nickel based superalloy under thermal mechanical loading JF - International Journal of Fatigue N2 - The focus of this paper is the simulation of fatigue crack growth of the coated single crystalline nickel-based superalloy PWA 1484 under thermal mechanical loading. Thus, two physical models are superimposed in terms to firstly calculate the deformation behavior under instationary thermal and mechanical loading (TMF) and secondly to model crack propagation after initial brittle cracking of the coating layer on the basis of cyclic crack tip opening displacement (CTOD). All material parameters implemented in the models were evaluated from monotonic isothermal tensile and creep tests as well as from isothermal low cycle fatigue (LCF) experiments. The calculated fatigue crack growth was validated by in situ crack growth measurements using the beachmark technique. Hence, crack propagation initiated by the brittle coating system closely to the experimental results using rectangular flat specimen geometry instead of corner-crack (CC) specimens. The comparison of the simulated lifetimes to the experimental results provides remarkable accuracy of the physically-based lifetime model. KW - Deformation KW - Diffusion coating KW - DISLOCATION CLIMB KW - Fatigue crack growth measurement KW - HARD PARTICLES KW - KINETICS KW - Lifetime modelling KW - Nickel-based superalloy KW - Thermo-mechanical fatigue (TMF) KW - TIP Y1 - 2018 U6 - https://doi.org/10.1016/j.ijfatigue.2018.06.015 VL - 116 IS - November SP - 268 EP - 274 PB - Elsevier ER - TY - JOUR A1 - Dendorfer, Sebastian A1 - Maier, Hans Jürgen A1 - Hammer, Joachim T1 - Fatigue damage in cancellous bone: an experimental approach from continuum to micro scale JF - Journal of the Mechanical Behavior of Biomedical Materials N2 - Repeated loadings may cause fatigue fractures in bony structures. Even if these failure types are known, data for trabecular bone exposed to cyclic loading are still insufficient as the majority of fatigue analyses on bone concentrate on cortical structures. Despite its highly anisotropic and inhomogeneous structure, trabecular bone is treated with continuum approaches in fatigue analyses. The underlying deformation and damage mechanism within trabecular specimens are not yet sufficiently investigated. In the present study different types of trabecular bone were loaded in monotonic and cyclic compression. In addition to the measurement of integral specimen deformations, optical deformation analysis was employed in order to obtain strain distributions at different scale levels, from the specimens' surface to the trabeculae level. These measurements allowed for the possibility of linking the macroscopic and microscopic mechanical behaviour of cancellous bone. Deformations were found to be highly inhomogeneous across the specimen. Furthermore strains were found to already localise at very low load levels and after few load cycles. Microcracks in individual trabeculae were induced in the very early stage of cyclic testing. The results provide evidence of the capability of the method to supply essential data on the failure behaviour of individual trabeculae in future studies. KW - Knochen KW - Spongiosa KW - Ermüdungsbruch KW - Fatigue KW - Cancellous bone KW - Deformation behaviour KW - Damage KW - Measurement and testing KW - Mechanical behaviour Y1 - 2009 U6 - https://doi.org/10.1016/j.jmbbm.2008.03.003 VL - 2 IS - 1 SP - 113 EP - 119 ER - TY - CHAP A1 - Dendorfer, Sebastian A1 - Maier, Hans Jürgen A1 - Hammer, Joachim T1 - How do age and anisotropy affect the fatigue behaviour of cancellous bone? T2 - Medicine Meets Engineering N2 - The fatigue behaviour of materials is of particular interest for the failure prediction of materials and structures exposed to cyclic loading. For trabecular bone structures only a few sets of lifetime data have been reported in the literature and structural measures are commonly not considered. The influence of load contributions not aligned with the main physiological axis remains unclear. Furthermore age effects on the fatigue behaviour are not well described. In the present study, different groups of human vertebral cancellous bone were exposed to cyclic compression. The inital modulus and therefore lifetimes were found to be highly dependent on age. The decrease in both with increasing age was much more pronounced in specimens which were not aligned with the main physiological axis. This implies that old bone is much more sensitive to (cyclic) failure loads in general but particularly to loads which are not coincident with the physiological main axis. KW - Knochenbruch KW - Spongiosa KW - Alter KW - Anisotropie Y1 - 2008 SP - 68 EP - 74 PB - IOS Press ER - TY - JOUR A1 - Spachtholz, Josef A1 - Affeldt, Ernst Eugen A1 - Maier, Hans Jürgen A1 - Hammer, Joachim T1 - The effect of temperature gradients in thermo-mechanical fatigue testing JF - Materials at high temperatures N2 - The focus of this paper is the characterization of the influence of the temperature rates on the TMF lives. Therefore static and the dynamic calibrations of the temperature measurement devices were compared by a custom-built calibration specimen, which included five internal mantle thermocouples. Additionally the temperatures were measured on the specimens' surface. The experimental setups used were compared by executing TMF pre-test with the identical single-crystalline specimen. Subsequently TMF tests on coated single-crystalline Nickel-based superalloy PWA 1484 were carried out with temperature rates of 10K/s and 20 K/s. Finally the deviations of the determined TMF lives were evaluated. KW - experimental setup KW - temperature field effect KW - Thermo-mechanical fatigue (TMF) Y1 - 2019 U6 - https://doi.org/10.1080/09603409.2018.1466500 VL - 36 IS - 2 SP - 97 EP - 103 PB - Taylor & Francis ER -