@article{SpachtholzAffeldtMaieretal., author = {Spachtholz, Josef and Affeldt, Ernst Eugen and Maier, H. J. and Hammer, Joachim}, title = {The effect of temperature gradients in thermo-mechanical fatigue testing}, series = {Materials at high temperatures}, volume = {36}, journal = {Materials at high temperatures}, number = {2}, publisher = {Taylor \& Francis}, doi = {10.1080/09603409.2018.1466500}, pages = {97 -- 103}, abstract = {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.}, language = {en} } @article{SpachtholzAffeldtMaieretal., author = {Spachtholz, Josef and Affeldt, Ernst Eugen and Maier, Hans J{\"u}rgen and Hammer, Joachim}, title = {Modelling of the fatigue crack growth of a coated single crystalline nickel based superalloy under thermal mechanical loading}, series = {International Journal of Fatigue}, volume = {116}, journal = {International Journal of Fatigue}, number = {November}, publisher = {Elsevier}, doi = {10.1016/j.ijfatigue.2018.06.015}, pages = {268 -- 274}, abstract = {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.}, language = {en} } @article{DendorferMaierHammer, author = {Dendorfer, Sebastian and Maier, Hans J{\"u}rgen and Hammer, Josef}, title = {Fatigue damage in cancellous bone: an experimental approach from continuum to micro scale}, series = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {2}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, number = {1}, doi = {10.1016/j.jmbbm.2008.03.003}, pages = {113 -- 119}, abstract = {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.}, subject = {Knochen}, language = {en} } @incollection{DendorferMaierHammer, author = {Dendorfer, Sebastian and Maier, Hans J{\"u}rgen and Hammer, Josef}, title = {How do age and anisotropy affect the fatigue behaviour of cancellous bone?}, series = {Medicine Meets Engineering}, booktitle = {Medicine Meets Engineering}, publisher = {IOS Press}, pages = {68 -- 74}, abstract = {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.}, subject = {Knochenbruch}, language = {en} }