Miniature CoCr laser welds under cyclic shear: Fatigue evolution and crack growth

M. Kanerva, Z. Besharat, T. Pärnänen, J. Jokinen, M. Honkanen, E. Sarlin, M. Göthelid, D. Schlenzka

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)
27 Downloads (Pure)


Miniature laser welds with the root depth in the range of 50–300 μm 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.

Original languageEnglish
Pages (from-to)93-103
Number of pages11
JournalJournal of the Mechanical Behavior of Biomedical Materials
Publication statusPublished - 1 Nov 2019
Publication typeA1 Journal article-refereed


  • CoCr
  • Crack growth
  • Fatigue
  • Implant
  • Laser weld

Publication forum classification

  • Publication forum level 1

ASJC Scopus subject areas

  • Biomaterials
  • Biomedical Engineering
  • Mechanics of Materials


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