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How to model debonding/cracking of nanotubes and nanoclay in polymers?

Leon Mishnaevsky's picture

Hi,

During last days, I went over the literature on strength and fracture in nanoreinforced polymers. I observed a strange tendency: when the elastic properties are discussed, the interphase region (around nanoparticles) is usually taken into account and cited as a most important feature of nanocomposites, determining their mechanical properties. But when the crack growth in nanocomposites is modelled, most authors simulate nanotubes and other nanoreinforcement using the common fiber composite models (without taking the interphases into account). Does anyone know references about the debonding strength or damage conditions of interphases in nanocomposites? Or how do they debond?

 

Leon

Comments

 

Leon Mishnaevsky's picture

Dear Alireza,

 Thank you very much!

Yuli Chen's picture

Dear Leon,

A recently published paper discussed exactly your problem: the interface effects, including interface debonding and CNT break, on the toughness of the CNT composites.

In this paper, the fracture zone bridged by CNTs at the polymer crack tip is studied, the critical condition for interfacial debonding is set up, and the whole debonding process is described by both analytical equations and force-displacement curve. The properties of both the interface and the CNT are obtained from the atomistic simulation.

In order to study the interface effect on the composites, the hierarchical failure analysis is carried out, involving three different levels:
1) macroscopic-level model with equivalent bridging nonlinear springs (CNTs) at the crack tip;
2) mesoscopic-level model for studying CNT failure and obtaining the force-displacement relation of equivalent nonlinear spring;
3) atomistic-level failure model for characterizing CNT/matrix interfacial bond breaking.

The main conclusion of this paper is that neither weak nor strong CNT/matrix interfaces can definitely lead to the better fracture toughness of these composites. The optimal interface strength is that making the failure mode just in the transition from CNT pull-out to CNT break.

The effect of interface length is also studied in this paper.

The full paper can be found at: http://dx.doi.org/10.1016/j.compscitech.2010.04.015

And a different debonding process, partial steady and partial unsteady debonding, which occurs when the matrix is very hard, such as metal- and ceramic-matrix, can be found in another paper http://dx.doi.org/10.1155/2011/746029.

Hopefully those papers would be helpful to you.

Yuli

michele.zappalorto@unipd.it's picture

Michele Zappalorto PhD

Hi...

Different from traditional microsized composites, in
nanoscale materials and structures, the surface effects become significant
, due to the high surface/volume ratio and for this
reason the amount of interphase volume may represent a large part of the
matrix.
Recently we have developed a closed form
expression for the critical debonding stress accounting for the existence of an
interphase zone of properties different from those of the matrix. Since different
functionalizers lead to different elastic properties of the interphase, this
solution shows that the debonding stress is affected by the surface treatment
depending also on the interphase radius to the nanoparticle radius  ratio, a/r0. (see http://www.sciencedirect.com/science/article/pii/S0266353811003563)

The effect of the interphase has also been accounted for fracture toughness predictions (see http://www.sciencedirect.com/science/article/pii/S1877705811006813 and http://www.sciencedirect.com/science/article/pii/S1877705811007351) while an overview of the modelling strategy useful for prediction of nanocomposite mechanical properties can be found in (http://www.sciencedirect.com/science/article/pii/S1359836812000030)

 

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