# Problem regardfing Addforce

Dear All,

I am using “addforce” command for tensile deformation of a beam of 70 nm.
I have fixed the ends and rest of the body is mobile.
But when I use addforce, it streches the specimen in only one direction.
How to apply bi-directional tensile force using addforce command?

I have assigned the regions and grouped them.

region fixd block INF INF -352.1789856 -322.1789856 INF INF
region mobile block INF INF -322.1789856 322.1789856 INF INF
region fixd1 block INF INF 322.1789856 352.1789856 INF INF
.

.

group fixd region fixd
group fixd1 region fixd1
group mobile region mobile
.

.
.

timestep 0.002
pair_style eam/fs
pair_coeff * * Ni1_Mendelev_2012.eam.fs Ni

thermo 1000

velocity mobile create 500.0 873847 rot yes mom yes dist gaussian

.
.
.

Finally, I have added addforce to the fixed regions.

fix 7 fixd addforce 0 0.005 0
fix 8 fixd1 addforce 0 0.005 0

I want the specimen to be in tension (stretched out)…But the specimen moves in a single direction.

Hi,

I guess you mean tension along -y and y direction simultaneously.

Firstly, I suggest you use this:

region fixd block INF INF INF -322.1789856 INF INF
region mobile block INF INF -322.1789856 322.1789856 INF INF
region fixd1 block INF INF 322.1789856 INF INF INF

For tensile, you can use fix move linear command.

Hope this helps.

Thank you, sir. But I want to move the atoms at constant load (creep). Will it be possible with fix move command?

Dear All,

I am using "addforce" command for tensile deformation of a beam of 70 nm.
I have fixed the ends and rest of the body is mobile.
But when I use addforce, it streches the specimen in only one direction.
How to apply bi-directional tensile force using addforce command?

I have assigned the regions and grouped them.

region fixd block INF INF -352.1789856 -322.1789856 INF INF
region mobile block INF INF -322.1789856 322.1789856 INF INF
region fixd1 block INF INF 322.1789856 352.1789856 INF INF
.
.
group fixd region fixd
group fixd1 region fixd1
group mobile region mobile
.
.
.
timestep 0.002
pair_style eam/fs
pair_coeff * * Ni1_Mendelev_2012.eam.fs Ni

thermo 1000

velocity mobile create 500.0 873847 rot yes mom yes dist gaussian
.
.
.

Finally, I have added addforce to the fixed regions.

fix 7 fixd addforce 0 0.005 0
fix 8 fixd1 addforce 0 0.005 0

I want the specimen to be in tension (stretched out)...But the specimen
moves in a single direction.

you are adding force in the same direction to both regions​, so you get
what you are asking for.

axel.

Thank you for your response sir.

I have also tried adding force in different direction (with a negative sign)

fix 7 fixd addforce 0 -0.005 0

fix 8 fixd1 addforce 0 0.005 0

But I guess it just means compression in one direction and tension in other.

Please help me out.

Thank you once again.

Thank you for your response sir.

I have also tried adding force in different direction (with a negative
sign)

fix 7 fixd addforce 0 -0.005 0

fix 8 fixd1 addforce 0 0.005 0

But I guess it just means compression in one direction and tension in
other.

​no, it doesn't. please read the documentation more carefully.