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Miniature CoCr laser welds under cyclic shear: Fatigue evolution and crack growth
Tampere Univ, Fac Engn & Nat Sci, POB 589, FI-33014 Tampere, Finland.;Orton Orthopaed Hosp, FI-00280 Helsinki, Finland.;Res Inst Orton, FI-00280 Helsinki, Finland..
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-9828-7753
Orton Orthopaed Hosp, FI-00280 Helsinki, Finland.;Res Inst Orton, FI-00280 Helsinki, Finland..
Tampere Univ, Fac Engn & Nat Sci, POB 589, FI-33014 Tampere, Finland..
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2019 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 99, p. 93-103Article in journal (Refereed) Published
Abstract [en]

Miniature laser welds with the root depth in the range of 50-300 pm represent air-tight joints between the components in medical devices, such as those in implants, growth rods, stents and various prostheses. The current work focuses on the development of a fatigue test specimen and procedure to determine fatigue lives of shear-loaded laser welds. A cobalt-chromium (CoCr) alloy is used as a benchmark case. S-N graphs, damage process, and fracture surfaces are studied by applying x-ray analysis, atomic force microscopy, and scanning electron microscopy both before and after the crack onset. A non-linear material model is fitted for the CoCr alloy to run finite element simulations of the damage and deformation. As a result, two tensile-loaded specimen designs are established and the performance is compared to that of a traditional torque-loaded specimen. The new generation specimens show less variation in the determined fatigue lives due to well-defined crack onset point and, therefore, precise weld seam load during the experiments. The fatigue damage concentrates to the welded material and the entire weld experiences fatigue prior to the final, fracture-governed failure phase. For the studied weld seams of hardened CoCr, a regression fatigue limit of 10.8-11.8 MPa, where the stress refers to the arithmetic average shear stress computed along the region dominated by shear loading, is determined.

Place, publisher, year, edition, pages
ELSEVIER , 2019. Vol. 99, p. 93-103
Keywords [en]
CoCr, Implant, Fatigue, Crack growth, Laser weld
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-260988DOI: 10.1016/j.jmbbm.2019.07.004ISI: 000484871500010PubMedID: 31349149Scopus ID: 2-s2.0-85069732362OAI: oai:DiVA.org:kth-260988DiVA, id: diva2:1359793
Note

QC 20191010

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-11-26Bibliographically approved

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Besharat, ZahraGöthelid, Mats

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