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- Chantziara, Katerina, 1993-
(författare)
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Very HIgh Cycle Fatigue (VHCF) behavior of high strength alloys : A literature review
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Very High Cycle Fatigue (VHCF) response of metallic materials is considered of significance importance, particularly for high- demanding applications. Since it is proved that most of the engineering materials do not exhibit a conventional fatigue limit, but rather display a continuously decreasing stress-life response at longer lifetimes. Consequently, the investigation of the various mechanisms are taking place during VHCF is essential. The primary object of the present effort is to explore and summarize recent developments and current status of the VHCF phenomenon in high strength alloys.The development of the new ultrasonic machines made the fatigue testing beyond 107 life cycles possible in a very shorter time, leading to fatigue fractures at stress levels lower than the traditionally proposed “fatigue limit”. Nowadays, a classification between Low Cycle Fatigue (LCF), High Cycle Fatigue (HCF) and Very High Cycle Fatigue (VHCF) is commonly used. The main reasons for this specific grading are: i) the need for safe design of components and ii) the fact that the failure mechanisms are particular in each of the LCF, HCF and VHCF regimes.Ultrasound machines, also called piezoelectric, are resonance fatigue testing machines reducing the testing time at least 400 times compared to the conventional machines operating at frequencies up to 20 kHz.The crack initiation stage is one of the most investigated subjects when it comes to VHCF. Usually, the fatigue initiates from a defect (inclusion, pore, grain boundary triple points), while up to 99% of fatigue life is consumed in that stage. Different models have been proposed in the literature regarding the evolution of events that contribute to the fatigue crack initiation and growth. Proposed models are such as the ODA, the polygonization, continuous grain refinement with local plasticity, the matrix fragmentation and the NCP numerous cyclic pressing. Several studies have assessed the different models and further enriched the knowledge in the VHCF field.In the present literature review effort, the main VHCF mechanisms of crack initiation and growth as well as the proposed models are presented and analyzed. Moreover, the VHCF response and the recent experimental results referring to the most used engineering alloys, e.g. steels, Ti, Ni, Al and Mg alloys, are described, with a main attention to steels. The different testing parameters and the way they affect the VHCF response are also presented.Finally, the literature review is concluded by presenting the new challenges and directions for future work in the field, especially under the light of the new low-carbon society.
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- Bjurenstedt, Anton, 1979-
(författare)
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GRETA – Fallstudie återvunnen aluminium
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- GRETA – a case study on die-cast secondary aluminiumIn ongoing production at AGES in Kulltorp, die-cast components of a secondary aluminium alloy have been continuously taken out for mechanical testing and microstructure investigations. The aim has been to increase the understanding of whether properties vary and, if so, why. In an industrial and well-controlled process, the properties and performance of the obtained material has been analysed for comparison with the original secondary alloy and its specification to see how the material varies during production. The results showed a uniform quality of the produced castings. The hardness test also showed very even results for each component. No statistical difference between the samples could be demonstrated. This means that even if some data collected from the castings were on the edge of the desired range, the properties have not been significantly affected. In other words, there is a higher potential in recycled alloys than that reported in the standard SS-EN 1706:2021. Solidification rate, possible heat treatment and the amount of defects play a decisive role in the final properties of a cast part. By optimizing these, properties that exceed the standard can be obtained.
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| 8. |
- Bjurenstedtare, Anton
(författare)
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Examination of laser treated aluminium
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The laser treatments of the surfaces have influenced the surface appearance and the microstructure. The effect on the surface appearance is shown in Figure 6. Examination of cross sections revealed a 3-10 μm thick layer of, what appears to be aluminium (based on ocular examination), has formed. The examination in the SEM-EDS gave no answer on the composition of the surface layer formed.
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