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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

In Vitro Simulation of Modular Neck Fracture, Wear, Corrosion, and Distraction in Total Hip Replacements

Aljenaei, Fahad January 2015 (has links)
Total hip replacements are being used to relieve pain and restore the hip function of unhealthy hip joints. The various sizes and geometries of the modular femoral neck implants allow the surgeon to optimize the range of motion and patient’s leg length. However, some in vivo modular femoral neck retrievals have shown early fatigue and advanced wear-corrosion at the neck-stem taper interface, which can lead to adverse tissue reactions and failure of the implant. The overall objective of this study was to simulate in vivo fatigue fracture, wear, and corrosion of modular necks at the neck-stem taper interface in a laboratory setting (in vitro) to better predict the failure mechanisms and implant limitations. More specifically, after optimizing the laboratory setup and the testing conditions, this study aimed to compare the effects of the modular neck material (Ti6Al4V and CoCrMo) and the implant assembly technique (hand and impact assembly) on fatigue life, wear-corrosion resistance, and distraction force. The PROFEMUR® Modular Neck System with CoCrMo femoral heads and Ti6Al4V stems was used in this study. The in vitro simulation was divided into two types of tests: fatigue tests (high compression load for a short cyclic loading duration) and corrosion tests (low compression load for a long cyclic loading duration). The neck-stem interface was submersed in a phosphate buffered saline solution, which was maintained at a temperature of 80 ºC to accelerate the corrosion reaction. The simulation results showed that the Ti6Al4V necks were more vulnerable to fatigue fracture than CoCrMo necks. In addition, impact assembly of the components resulted in an increased implant fatigue life compared to hand assembly, but also increased the distraction force. The observed wear-corrosion damage was higher in fatigue tests than corrosion tests, suggesting that the level of mechanical load was a major factor influencing implant surface damage and fatigue fracture. On the other hand, corrosion tests showed that longer exposure resulted in more fluid accumulation in the stem pocket. This may lead to the formation of a corrosion cell with strongly acidic conditions in the stem pocket, as well as the potential for larger metal ion release. Overall, the in vitro simulation was successful in reproducing femoral modular neck fracture and wear-corrosion damage similar to retrieved in vivo specimens. Results may play a major role in the future development of total hip replacements and international standards for implant testing.
2

Tribological and corrosion properties of Al–12Si produced by selective laser melting

Prashanth, K.G., Debalina, B., Wang, Z., Gostin, P. F., Gebert, A., Calin, M., Kühn, U., Kamara, M., Scudino, S., Eckert, J. 03 June 2020 (has links)
The effect of annealing on the tribological and corrosion properties of Al–12Si samples produced by selective laser melting (SLM) is evaluated via sliding and fretting wear tests and weight loss experiments and compared to the corresponding material processed by conventional casting. Sliding wear shows that the as-prepared SLM material has the least wear rate compared to the cast and heat-treated SLM samples with abrasive wear as the major wear mechanism along with oxidation. Similar trend has also been observed for the fretting wear experiments, where the as-prepared SLM sample displays the minimum wear loss. On the other hand, the acidic corrosion behavior of the as-prepared SLM material as well as of the cast samples is similar and the corrosion rate is accelerated by increasing the heat treatment temperature. This behavior is due to the microstructural changes induced by the heat treatment, where the continuous network of Si characterizing the as-prepared SLM sample transforms to isolated Si particles in the heat-treated SLM specimens. This shows that both the wear and corrosion behaviors are strongly associated with the change in microstructure of the SLM samples due to the heat-treatment process, where the size of the hard Si particles increases, and their density decreases with increasing annealing temperature.
3

Tribological investigations on additively manufactured surfaces using extreme high-speed laser material deposition (ehla) and laser powder bed fusion (LPBF)

Holzer, Achill, Koß, Stephan, Matthiesen, Gunnar, Merget, Daniel, Ziegler, Stephan, Schleifenbaum, Johannes Henrich, Schmitz, Katharina 25 June 2020 (has links)
Today's economic and ecological directives demand for highly sustainable machine parts by low production cost and energy consumption. Consequently, it is crucial to guarantee a long service life by protecting all components against wear and corrosion. However, hydraulic components always include stressed surfaces, which suffer from heavy loads at high relative speeds. To prevent fretting, coating processes like thermal spraying or hard chrome have a long history in the field of hydraulics. New additive laser-based processes like EHLA and LPBF offer the potential to apply new coatings without environmentally hazardous substances such as chromium or to manufacture complex parts with new functionalities. So far, additively manufactured surfaces with relative movements are post-processed to obtain surface qualities similar to subtractive methods, as the tribological properties of additive surfaces have not been investigated to date. Therefore, this paper investigates the frictional behavior of 316L surfaces produced by laser-based EHLA and LPBF processes using a disc-disc tribometer.

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