Interfacial strength reduction by chemical-physical ageing?

Thread by John Clarck on 12 May 2010 at 11:07:37 
Thanks for the nice website, and CheFEM. I like the inclusion of rigorous FEM chemical thermodynamics in the study and simulation of composite materials!

My question is on physical and chemical ageing. As we all know ageing relaxes internal stresses, no matter generated by mechanical loading, residual thermal stresses or a diffusing permeant. But, will this ageing influence the interfacial toughness of for example, an epoxy composite reinforced with Graphene? Let us suppose that the interface is not weakened by chemical reaction and/or plastification.

I suppose this is included in CheFEM Module 103 (Gibbs Free - Mechanical Fracture) analysis, so what do you think / simulate?

Thanks, and keep up this really good work!!!

John

    Comment by Composite Agency on 17 May 2010 at 16:07:54  | |responses: 0|
    John,

    Thanks for your kind feedback.

    According to the most reputable models on ageing, physical ageing (including creep and free volume contraction of polymers, think of an epoxy below the glass transition) does not influence the interfacial toughness (expressed in Joule per square meter) if determined in the correct manner. This has been extracted from very rigorous experiments and modelling on fibre pull-out.

    However, chemical ageing resulting in matrix plasticizing, chemical degradation of an interfacial adhesive/sizings and matrix material expansion by mass uptake and thermal, certainly influence interfacial strength. No matter whether a microscopic particles (fibres / graphite filler) or nanoscopic particles (carbon nanotubes, a.k.a. CNT's / functionalized partially oxygenated graphene sheets, a.k.a. FGS) based composite are involved. Of course the magnitude of these effects are different, also between microscopic and nanoscopic materials. Indeed check CheFEM for a logical approach / simulation of these effects.

    Best Regards,
    Composite Agency