meshing+kscon

[bram844]

Hi all,

For a Stress intensity factor calculation i need to mesh a 2d surface. I have the problem i get alot of triangle elements, but i want quad only. On the other hand i need singular elements at the crack tip, this location is variable.

How can i get singular elements at the tip, but not in the rest of the plane? i used KSCON to get the singular ones at the tip, and free mapping for the rest.

here a minimal working example:


finish
/clear
/title, cracktip
/PREP7

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!! define parameters !!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

b=0.5 !width plate
h=0.5 !hight plate
r_s=0.125 !radius spill
scon=b/100 !kscon element size
a=0.095 !half crack length
KXX=60 !thermal conductivity
C=300 !heat capacity
DENS=7850 !density

!!!create geometry, 1/4 of the plate is modelled

k,1,0,0
k,2,0,h/2
k,3,b/2,h/2
k,4,b/2,0
k,99,a,0

l,1,2
l,2,3
l,3,4
l,4,99
l,99,1

LSEL,ALL
KSCON,99,scon,1,8,0, !cracktip KP
AL,1,2,3,4,5
AESIZE,ALL,b/25,

!!!PLANE55 for thermal problem and surf152 for convection
ET,1,PLANE55
MP,KXX,1,KXX
MP,C,1,C
MP,DENS,1,DENS

AMESH,ALL


As you can see the mesh looks terrible, all help appreciated!

Cheers,

Bram

 

[lopessilva]

Hello,

I run your code in ANSYS, and unfortunately, I don´t think it is possible to mesh with quadrilaterals. In fact, only regular areas and volumes can be meshed with quarilaterals. I think triangles are the only way to go, but I cannot be sure, as I think there is a way you can circunvent this problem. Anyway, if you rebuild the area, defining new keypoints, then building smaller areas by keypoints, you should have the same object but It can allow you to choose quadrilaterals for the mesh on every one of those small areas, because they are regular (they should be squares or rectangles) and in the zone near the crack I think you must have some triangular elements around the semi circle formed by the segments around the crack. This is due to the fact that there must be a point where you can´t use squared elements everywhere because of the semi-circle caused by the elements.

Hope I have helped,

Regards,
Hugo Silva
Mechanical Eng. PhD student
Materials Eng. MSc.