Hi Robert,

I thought it over, and I noticed what I wanted to do just could not help that much in scientific point of view but complicate solving procedure. So, I will use periodic displacement boundary condition. Anyway, thanks always for your help.

Regards
Ronghai

在 2016年3月18日星期五 UTC+1上午11:16:37，Robert Cimrman写道：

Hi Ronghai,

So you mean something like enforcing a symmetric deformation of the neck? That
should be automatic, provided the mesh is good enough and the loads/BCs are
symmetric.

As for constraining the strain, maybe you would need some kind of a mixed
formulation, where strain is an independent variable, but I am not sure I
understand what you want to achieve.

r.

On 03/16/2016 12:00 PM, Ronghai Wu wrote:
> Hi Robert,
>
> Thanks for your reply. Here I do not mean periodic displacement boundary
> condition, but periodic strain boundary condition. The reason is, still
> taking 2D uniaxial tension along y direction as example. If I fix the "u.x"
> both at top and bottom boundary. There will be necking at left and right
> boundary as tension goes on (but I do not want to have free surface
> boundary condition). However, if using periodic displacement boundary
> condition, there would be no displacement at left and right boundary, and
> the elastic stress-strain would be larger than free surface case. I am
> thinking if there is periodic strain boundary condition, then the necking
> is retained and stress-strain would be between free surface and periodic
> displacement cases. So, I am wondering is it possible to have periodic
> strain boundary condition in sfepy, sounds kind of odd though.
>
> Regards
> Ronghai
>
>
> 在 2016年3月15日星期二 UTC+1下午10:28:54，Robert Cimrman写道：
>>
>> Hi Ronghai,
>>
>> you can constrain the displacements using the periodic boundary conditions
>> -
>> then the strain on the boundaries would be the same as well. Or you need
>> something else?
>>
>> r.
>>
>> On 03/15/2016 03:26 PM, Ronghai Wu wrote:
>>> Hi sfepy developers and users,
>>>
>>> I am wondering is it possible to have periodic strain boundary condition
>> in
>>> sfepy? For example, in a 2D uniaxial tension along y direction, how to
>>> constrain the strain at left and right boundary to be same when solving
>>> mechanical equilibrium equation?
>>>
>>> Regards
>>> Ronghai
>>>
>>
>>
>