Characterization of the fracture toughness of micro-sized tungsten single crystal notched specimens

Abstract

Fracture experiments using micrometer-sized notched cantilevers were conducted to investigate the possibility of determining fracture mechanical parameters for the semi-brittle material tungsten. The experiments were also used to improve the understanding of semi-brittle fracture processes for which single crystalline tungsten serves as a model material. Due to the large plastic zone in relation to the micrometer sample size, linear elastic fracture mechanics is inapplicable and elastic-plastic fracture mechanics has to be applied. Conditional fracture toughness values J _Q were calculated from corrected force vs. displacement diagrams. Crack growth was accessible by direct observation of in-situ experiments as well as with the help of unloading compliances. As a further tool, fracture toughness can be determined via crack tip opening displacement. The micro samples behave more ductile and exhibit higher fracture toughness values compared to macro-sized single crystals and fail by stable crack propagation.

Keywords:

• tungsten
• focused ion beam
• fracture mechanics
• micromechanics
• in-situ electron microscopy
• fracture toughness
• crack growth

Acknowledgements

The authors thank Prof. Monika Jenko at the Institute of Metals and Technology (Ljubljana, Slovenia) for performing the ion slicing sample preparation. S.W. appreciates fruitful discussions with A. Hohenwarter.