did u check Dis!?

http://link.springer.com/article/10.1007%2FBF01543202

Representing the impact of irradiation damage in macroscale simulations can be a difficulty thing to do. A significant effect of irradiation on mechanical behavior is irradiation induced hardening. However, it is very material specific. Most models of irradiation induced hardening are empirical, so unless you can find a significant amount of data on mechanical testing of neutron irradiated graphite to allow for an empirical fit, then you can't just use macroscale FEA models. You can use multiscale modeling to supplement experimental data when necessary, but it is a significant amount of work. People have used MD-informed Monte Carlo models to estimate defect distributions. Then, dislocation dynamics with some representation of the defects to determine the impact on dislocation motion. Then, they use that information in a crystal plasticity model to quantify the overall impact on the mechanical behavior.

Wediditforone and two  element targets so far. For example SiC and Ni. You can refer to our paper in 'Nuclear Science and Engineering, 172,151-163 (2012)'. If more pertinent question then please write.

We did it for one and two  element targets so far. For example SiC and Ni. You can refer to our paper in 'Nuclear Science and Engineering, 172,151-163 (2012)'. If more pertinent question then please write.

You are actually asking a number of questions.

All all the answers are dependent on the grade of graphite you are using. Most nuclear graphite are transversely isotropic. Subsequently you have to program your constitutive relation in the FEA yourself.

Any ideas about mechanical testing in presence of neutron irradiation?

Get a large amount of funding since this is very expensive. Another alternative is to use the IAEA database on historic tested grades of graphite if your country is a member. You can find some papers with test data but due to the high cost of these tests the information is usually kept secret by the owners. But you need test data on your grade of graphite!

The effect of irradiation on graphite is difficult to understand,

The properties that need to be modelled in the FEA are influenced but two parameters. The neutron irradiation and temperature at which the component is irritated. Due to the graphite being a moderator the irradiation is not constant throughout the components you will try to model.

When graphite is subject to damage by fast neutron irradiation, the following occurs:

1. The material experiences dimensional change, initially shrinking and later swelling. This dimensional change is not isotropic, but is transversely anisotropic as per the virgin material.

2. The elastic modulus of the material changes. The change in elastic modulus is coupled with a corresponding change in the material's strength.

3. The Coefficient of Thermal Expansion (CTE) changes.

4. The thermal conductivity changes.

5. The material is subject to creep under stress at significantly lower temperatures than graphite would creep at without irradiation.

There is significant uncertainty in determination of these irradiation effects for several reasons. Some of which are:

• Paucity of experimental data;

• Variability in the basic material;

• Variability in the irradiation conditions during the irradiation of specimens, and

• The need to use small specimens to reduce the cost of irradiating the material.

If you have information on this you need to model these changes using your constitutive equations inside the FEA code. Most models and test data is Isothermal. We used this for a while and it worked well. FEA however allows for changes in temperature and irradiation via viscoelastic material models which use the material properties as rate dependant functions. We only had this implemented for irradiation induced creep 

Significance of primary irradiation creep in graphite

Journal of Nuclear Materials  05/2013; 436(s 1–3):167–174.

I do believe this the best way to model changes for other properties since it can handle changes in temperature and dose easily.