Abstract
For processing of litter, wood and lop, stationary and mobile choppers are often used. Thereby, the integrated mechanical components are subjected to a high local loading condition, in particular the cutting tools, which are, besides the complex structural stresses, exposed to abrasive wear. To overcome this issue, a common practice is to strengthen the related surfaces with hard layers. This complex manufacturing step has a positive effect on the wear behaviour, whereby the service life is extended, maintenance time and repair costs are reduced and an efficient operation can be ensured. On the contrary, the brittle hard layer and the thermo-mechanical weld process influence the local material properties in the highly-stressed area, which may lead to a reduction of the fatigue strength. Hence, the aim of this thesis is to determine the effect of welded hard layers on the local fatigue life under typical structural stresses. For investigation of the fatigue strength, at first, an appropriate specimen geometry and testing method was evaluated, which is able to reproduce the operating conditions of the structural component on sample size. Based on an extensive experimental study, a multitude of welded specimens involving different filler metals and welding parameters were fabricated. In the sample series, the impact of weld orientation and end-of-seam areas was also analyzed. The results of the tests revealed that the hard layers have a significant influence on the fatigue behaviour with a reduction of the high-cycle fatigue limit by about thirty percent in comparison to the mild steel base metal. Metallographic and fracture surface analyses as well as hardness surface measurements provide additional data for the characterization of the local properties and the effects on the resulting hard-coated lifetime. Summing up, the results achieved in this thesis lead to an enhanced selection of the hard facing layer, taking the structural fatigue stress state under consideration, whereby a load-dependent manufacturing of the tools is enabled.
Translated title of the contribution | Influence of wear-reducing hard layers on the fatigue strength behaviour |
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Original language | German |
Qualification | Dipl.-Ing. |
Supervisors/Advisors |
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Award date | 1 Jul 2016 |
Publication status | Published - 2016 |
Bibliographical note
embargoed until 25-04-2021Keywords
- fatigue behaviour
- hard facing
- hard layer
- overlay welding
- wear protection