Optimization of clamped beam geometry for fracture toughness testing of micron-scale samples

Abstract

Fracture toughness measurements at the small scale have gained prominence over the years due to the continuing miniaturization of structural systems. Measurements carried out on bulk materials cannot be extrapolated to smaller length scales either due to the complexity of the microstructure or due to the size and geometric effect. Many new geometries have been proposed for fracture property measurements at small-length scales depending on the material behaviour and the type of device used in service. In situ testing provides the necessary environment to observe fracture at these length scales so as to determine the actual failure mechanism in these systems. In this paper, several improvements are incorporated to a previously proposed geometry of bending a doubly clamped beam for fracture toughness measurements. Both monotonic and cyclic loading conditions have been imposed on the beam to study R-curve and fatigue effects. In addition to the advantages that in situ SEM-based testing offers in such tests, FEM has been used as a simulation tool to replace cumbersome and expensive experiments to optimize the geometry. A description of all the improvements made to this specific geometry of clamped beam bending to make a variety of fracture property measurements is given in this paper.

Keywords:

• microbeam bending
• focused ion beam
• fracture toughness
• finite element modelling
• in situ electron microscopy

Acknowledgement

The authors would like to thank Dr Md.Z. Alam and Dr D.K. Das, Defence Metallurgical Research Laboratory, Hyderabad for providing PtNiAl bond coat samples for the present study and Dr C. Eberl, Fraunhofer Institute for Materials Mechanics, Freiburg, for help with the DIC calculations.

Additional information

Funding

This work was supported by the Defense Research Development Organisation.