Amir Abdollahi's blog

I would like to share our recent work published in Nature Communications.

I would like to share our recent work published in Physical Review Letters.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.205502

Bones generate electricity under pressure, and this electromechanical behavior is thought to be essential for bone's self-repair and remodeling properties. The origin of this response is attributed to the piezoelectricity of collagen, which is the main structural protein of bones. In theory, however, any material can also generate voltages in response to strain gradients, thanks to the property known as flexoelectricity.

The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences.

This work has been recently published in Nature Nanotechnology. 

Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity in fracture: the resistance to fracture increases as structural size decreases, and it becomes asymmetric with respect to the sign of polarization. The latter phenomenon manifests itself in a range of intermediate sizes where piezo- and flexoelectricity compete.

Flexoelectricity is an electromechanical effect coupling polarization to strain gradients. It fundamentally differs from piezoelectricity because of its size-dependence and symmetry. Flexoelectricity is generally perceived as a small effect noticeable only at the nanoscale. Since ferroelectric ceramics have a particularly high flexoelectric coefficient, however, it may play a significant role as piezoelectric transducers shrink to the sub-micrometer scale.

Flexoelectricity is a size-dependent electromechanical mechanism coupling polarization and strain gradient. It exists in a wide variety of materials, and is most noticeable for nanoscale objects, where strain gradients are higher. Simulations are important to understand flexoelectricity because experiments at very small scales are difficult, and analytical solutions are scarce.

We simulate the fracture processes of ferroelectric polycrystals in
three dimensions using a phase-field model. In this model, the grain
boundaries, cracks and ferroelectric domain walls are represented in a
diffuse way by three phase-fields. We thereby avoid the difficulty of
tracking the interfaces in three dimensions. The resulting model can
capture complex interactions between the crack and the polycrystalline
and ferroelectric domain  microstructures. The simulation results show
the effect of the microstructures on the fracture response of the
material. Crack deflection, crack bridging, crack branching and
ferroelastic domain switching are observed to act as the main fracture
toughening mechanisms in ferroelectric polycrystals. Our fully 3-D

This is an accepted manuscript in Journal of the Mechanics and Physics of Solids

Title: Phase-field modeling of crack propagation in piezoelectric and ferroelectric materials with different electromechanical crack conditions

Authors: Amir Abdollahi and Irene Arias, Universitat Politecnica de Catalunya (UPC), Barcelona

Abstract:

This is the preprint of an article that will appear in Smart Materials and Structures (SMS)

Title: Crack initiation patterns at electrode edges in multilayer ferroelectric actuators

Authors: Amir Abdollahi and Irene Arias, Universitat Politecnica de Catalunya (UPC), Barcelona

Abstract:

This is the preprint of an article that will appear in International Journal of Fracture (IJF)

Title: Numerical simulation of intergranular and transgranular crack propagation in ferroelectric polycrystals

Authors: Amir Abdollahi and Irene Arias, Universitat Politecnica de Catalunya (UPC), Barcelona

Abstract:

Dear Colleague,

I have uploaded a video which shows the simulation of Slow-Fast crack propagation in ferroelectric single crystals:

http://www.youtube.com/watch?v=6E7WSVOVAWM

For technical details, please refer to our recently published paper in Acta Materialia:

http://www.sciencedirect.com/science/article/pii/S1359645411001777

Best regards,

Amir Abdollahi