As an electromechanical coupling
between strain gradients and polarization,
flexoelectricity is largely enhanced at the nanoscale. However, directly
observing the evolution of flexoelectric fields at the nanoscale usually
suffers from the difficulty of producing strain gradients and probing
electrical responses simultaneously. Here, we introduce nanocracks
in SrTiO
3, Ba
0.67
Sr
0.33
TiO
3, and TiO
2 samples and apply continuously
varying mechanical loading to them, and as a result, huge strain gradients
appear at the crack tip and result in a significant flexoelectric
effect. Then, using atomic force microscopy, we successfully measure
the evolution of flexoelectricity around the crack tips. For the case
of SrTiO
3, the maximum induced electric
field reaches 11 kV/m due to the tensile load increasing. The proposed
method provides a reliable way to identify the significance of the
flexoelectric effect. It may also open a new avenue for the study
of flexoelectricity involving multiple physics phenomena including
flexoelectronics, the flexo-photovoltaic effect, and others.
Due to the stress concentration near crack tips, strong flexoelectric effect would be observed there, which might lead to new applications of flexoelectricity in material science and devices. However, different from the flexoelectric effect in cantilever beams or truncated pyramids, at the crack tip, multiple components of strain gradients with nonuniform distribution contribute to the flexoelectric effect, which makes the problem extremely complex. In this paper, with the consideration of both direct and converse flexoelectricity, the electromechanical coupling effect around the tip of a Mode III crack is studied analytically. Based on the Williams' expansion method, the displacement field, polarization field, strain gradient field along with the actual physical stresses field are solved. A path independent J-integral for Mode III cracks in flexoelectric solids is presented. Our results indicate that the existence of flexoelectricity leads to a decrease of both the J-integral and the out-of-plane displacement in Mode III cracks, which means that the flexoelectric effect around the tip of Mode III cracks enhances the local strength of materials.
Natural defects such as nano inclusions and nanocracks are inevitable in dielectric materials. When materials are subjected to mechanical loading, the strain gradient around crack tips and inclusions would become large and induce significant flexoelectric fields. In contrast to classical crack-inclusion problems, the interactions between these flexoelectric fields may locally change the electromechanical behaviors of materials, and result in some interesting phenomena. To better understand the crack-inclusion interactions in flexoelectric solids, in this work, we use a collocation mixed finite element method to model and analyze the flexoelectric fields around the crack tip and inclusion. Based on the J-integral, we analyze how the flexoelectric effect affect the interactions energy between nanocracks and nearby nano inclusions. This work proposes a new coupling mechanism in crack-inclusion problems and may inspire future experiments in flexoelectric solids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.