iMechanica - PHD position - Comments

Dear Prof. Hong, My name

Tung Nguyen — Wed, 26 Nov 2008 10:26:16 -0500

Dear Prof. Hong,

My name Nguyen Thanh Tung. I am looking for a PhD position in metamaterial which exhitbits the negative refractive behavior. I am getting Msc degree in Department of Physics, Hanyang University, Korea (expected Winter 2009). Is it possible for me to apply to these topics you mentioned above (still working in metamaterial field is my dream)? If you need my CV, pls take a look in this link http://www.imechanica.org/user/10026

Best regards,

Tung Nguyen

Smoothness of crack tip fields in X-FEM and error estimation

Stephane Bordas — Wed, 29 Oct 2008 06:44:15 -0400

Dear Pooyan,

What you are describing is not a problem with your code (at least not necessarily).

There are many papers on this topic, for instance, I recommend the following:

http://doi.wiley.com/10.1002/nme.1601 by Karihaloo Improving the accuracy of XFEM crack tip fields using higher order quadrature and statically …

Direct evaluation of accurate coefficients of the linear elastic crack tip asymptotic field by Karihaloo again

XFEM for direct evaluation of mixed mode SIFs in homogeneous and bi-materials still by Karihaloo

Derivative recovery and a posteriori error estimate for extended finite elements by Marc Duflot and Stephane Bordas

http://www3.interscience.wiley.com/journal/119054430/abstract by Marc Duflot and Stephane Bordas

A recovery-type error estimator for the extended finite element method based on singular+smooth … by Rodenas, etc.

A Global Explicit Residual Based Error Estimator for the eXtended Finite Element Method in … by Geniaut and Delmas

A simple error estimator for extended finite elements (Marc Duflot and Stephane Bordas and Phong Le)

Numerical Aspects of the extended Finite Element Method by Peters and Hackl

Do let me know if you would like preprints of those articles, which I could provide.Our XFEM matlab code could be of interest to check your code as well. I wonder if you could describe what you mean by extrapolation technique specifically?

Many thanks,

Dr Stephane Bordas

http://people.civil.gla.ac.uk/~bordas

X-FEM tip enrichments

pooyan broumand — Tue, 28 Oct 2008 10:33:26 -0400

Hi ;

I am modeling quasi-static crack propagation with x-fem .

for calculation of SIFs I used the extrapolation method , but I found that the displacements at the tips are not very smooth and are turbulated. and as the result the SIF calculated are not correct .

Why the displacements are not smooth, and there exist a high gradient in the tip element. is it in X-Fem nature or it is my code problem?!

another thing is that where should the points to be used in SIF calculation be located ?

In FEM they are located at the edges of the crack but in X-FEM there are turbulances near the crack edge and this will affect the results.

thanks