the toughening mechanism of epoxy matrix with nylon particle

[peak]

I want to use abaqus to simulation the toughening mechanism of Nylon-12 toughening epoxy. Many reference think that the toughening mechanisms are
1 the large plastic strain of Nylon particle before failure ;
2 the traciton force of particle to close crack face;
3 the cold draw of nylon particle;
so, my problem is that if i want use usdfld to simulate crack propagation in epoxy matrix with nylon particle, which model in abaqus is suitable for nylon-12 behavior (elastic and plastic)? and which model is suitable for epoxy? My plan is that the stiffness of matrix or nylon particle should be degrade when their strain is reached critical value.
thanks :)

[hhspiny]

this is a rather complex problem. depening how large you nylon particle is. but normally, you probably want to model the entire composite as a homogeneous material and get the toughness from testing. there is no method that I am aware of that allows you to calculate or even approximate the toughness of the composites from that of constituents.

on the physics side, the toughing is due to multiple reason
1. the nylon is generally tougher than epoxy
2. the interferface is weak, and get generally release energy and reduces stress intensity. but one step ahead, if micro-crack finds its way through these interface, it is easier to crack.
3. the nylon particular can deflect or blunt the crack tip, thus reduces intensity.

these are just a few mechanism, the the micromechanics of composites cracking is far from mature. realistic method would be treat the composite as single material.

[Jorgen]

I agree with hhspiny that your problem is challenging, and more of a research problem than an industrial approach to predicting the behavior of Nylon toughened epoxy. But I also think that if you create an appropriate micromechanical model of the filled polymer then you can learn a lot about how the composite material behave. In fact, it sounds quite interesting.

My first advice is that you check out the literature on particle filled polymers. A number of micromechanical models have been studied, although on top of my head I don't recall any study on toughened epoxy.

Nylon-12 is capable of undergoing large deformations, so you need an appropriate material model. I would use the Hybrid Model (http://www.polymerfem.com/modules.php?name=News&new_topic=5) (HM), although there are other possible choices.

How brittle is the epoxy that you are focusing on? You may be able to use a linear viscoelastic model.

- Jorgen

[hhspiny]

also keep in mind the fact nylon is embedded in epoxy limits the large deformation, i.e. the epoxy would crack first. therefore, it might not be that critical that you model the exact behavior of nylon. the fracture certainly will be dominated by the epoxy , rather than failure in Nylon. The fracture mechanics will not be valid in this situation either.