Speaker
Description
Barium Titanate (BTO) is a widely accepted lead-free piezoelectric ceramic used at micron length scales and in thin film forms in MEMS applications. Deviation in material properties from its bulk counterpart due to size effects makes it essential to estimate the properties in the real length scale of applications. Here we study the mechanical behaviour BTO single crystals and thin film systems using different micromechanical experiments and finite element modelling (FEM). Our micropillar compression studies on single crystal BTO show that the elastic limit is extended by 400% at sub-micron length scales. The strain accommodation mechanism at smaller length scales is by plastic flow, with a size exponent close to 1. Deformation response of BTO single crystal uniaxial micropillar experiments is used as a benchmark to compare the stress strain response of thin films from nanoindentation experiments. FEM models are used to eliminate substrate effects to obtain actual response from the film.
Microcantilever fracture measurements show that, while the single crystal showed a 45% higher KIC than the bulk, the film showed a 60% lower KIC due to the weak inter-columnar boundaries. Different geometrical aspects and loading parameters on the stress intensity factor of single cantilevers are investigated using finite element modelling (FEM) to propose testing standards that can be used by future users. The variation of stress intensity factor and mode mixity (KII/KI) with respect to the relative position of the notch, beam cross-section, notch tip radius, notch geometry and arm length of the cantilever and loading direction are studied. Effect of bilayers and elastic modulus mismatch between the layers on the crack driving force are also discussed.
| Speaker Country | India |
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