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Fatigue Life Control of Nitinol Flat Continuous Rolled Sheets with Staple Shaped Samples
Fatigue Life Control of Nitinol Flat Continuous Rolled Sheets with Staple Shaped Samples
Tuesday, May 7, 2024: 2:15 PM
Meeting Room I (Hotel Cascais Miragem)
Four-point bend testing of staple-shaped samples based on design used in the internal fixation of the musculoskeletal system was used for comparative investigation of the fatigue behavior of Nitinol sheets. The aim of the study is to optimize the microstructure and fatigue life of semi-finished continuous rolled sheets for the use in the biomedical implants under product-related conditions. Earlier work has shown significant impact of grain size on fatigue life of Nitinol sheet [LePage 2018, 91–107].
The test materials were produced using single ingot, hot rolled to initial grain size. Due to methods of grain growth control, different average grain sizes were realized over the length of the continuous flat rolling process at final sheet thickness of 0.72 mm. Therefore, the grain formation of different batches of pseudoelastic Nitinol sheets with a grain size between 5 and 40 µm were characterized by light microscopy and EBSD methods. Subsequently, EDM was used to generate a staple design with straight bridge, 90° staple legs and square cross section. The test specimens were post-processed due to mechanical and chemical processes. The staples were tested under single mean strain and four different constant strain amplitudes. The relation between microstructure in Nitinol sheets to fatigue life and understanding of these correlations is primary object of this study.
The test materials were produced using single ingot, hot rolled to initial grain size. Due to methods of grain growth control, different average grain sizes were realized over the length of the continuous flat rolling process at final sheet thickness of 0.72 mm. Therefore, the grain formation of different batches of pseudoelastic Nitinol sheets with a grain size between 5 and 40 µm were characterized by light microscopy and EBSD methods. Subsequently, EDM was used to generate a staple design with straight bridge, 90° staple legs and square cross section. The test specimens were post-processed due to mechanical and chemical processes. The staples were tested under single mean strain and four different constant strain amplitudes. The relation between microstructure in Nitinol sheets to fatigue life and understanding of these correlations is primary object of this study.