Displacement - Stress analysis - ElasticIsotropic

[Jhno]

Hi,
I am modelling a soil deposit using quadElement. I use a ElasticIsotropic material for the moment. I define a grid 10x10 (meters) with meshing at 1 m in both directions. I assign mass to the element in their vertical direction to simulate gravity effect and I plots the results using R (you can see attached).

Then I add a single nodal load at the middle of the model. (you can see the model is something like this, where every dots reprsent a node. They are all linked togheter, see scketch of the model here :

)

When I run the analysis, I get very odd result. The nodes on the left side of the load do go upward whilst the nodes on the right side goes downward.
Also, I notice that every node do moves in the x direction, even if there is no loads!

I specified the Young's modulus as being 90 000 Pa and the Poisson's ratio as 0.49 (I tried 0.1 to 0.4999, no differences).
All noce at bottom (y = 0) are constrainted in their 2DOF whilst all node on the side of the model (X=0 and X = 10) are constrainted in the first (Xdirection) DOF.
You can see the ploted displacement here (circle are original position and triangle are position after displacement)

Any1 got a idea what might causes this messes? Thanks !

 

[Mustaine3]

Maybe Hourglassing.

 

[Jhno]

Thanks for the answer.
I did look unto that following your reply. I wasn't aware of this problems. Turns out it was not the problems here.
The real problems was that I defined the node of the quad element clock-wise instead of counter-clock wise... took a while to realize !