experts help please
experts help please
(OP)
hi
i am working on modeling tig arc welding of thin aluminum plate (simple but weld). i have done this :
1.writing fortran code -dflux- for moving double ellipsoid heat source
2.create part (a .5 m *.5 m square with thickness .005 m)
3. define material (temperature dependent k,density,Cp,...)
4.difine load,body heat flux
5.predifined condition for temperature (ambient=25)
6.inteaction : convection( -h- dependent on temperature) and radiation - constant
7.step1 : 75 sec(welding time) - heat transfer and step2: 325 sec(cooling time)-heat transfer
8.mesh : standard-heat transfer - linear
9.job : load dflux
10. submmit
heat transfer problem is solved but now what is the problem ?!!
conduction is not sensed by the elements as well as it should!
a node .12 m appart from the weld line should have a maximum temp (200 c) as an experimental work reported.but temperature variation is just 25 c ! also nodes dont sense the temperature of the heat source till it reaches them
a node has constant temp till the time the heat source pass it. if it is on the weld line temp varies good but from .05 m to the end of plate side we have no sensible temp change.is this a basical problem of code ABAQUS or ????
thanks alot
i am working on modeling tig arc welding of thin aluminum plate (simple but weld). i have done this :
1.writing fortran code -dflux- for moving double ellipsoid heat source
2.create part (a .5 m *.5 m square with thickness .005 m)
3. define material (temperature dependent k,density,Cp,...)
4.difine load,body heat flux
5.predifined condition for temperature (ambient=25)
6.inteaction : convection( -h- dependent on temperature) and radiation - constant
7.step1 : 75 sec(welding time) - heat transfer and step2: 325 sec(cooling time)-heat transfer
8.mesh : standard-heat transfer - linear
9.job : load dflux
10. submmit
heat transfer problem is solved but now what is the problem ?!!
conduction is not sensed by the elements as well as it should!
a node .12 m appart from the weld line should have a maximum temp (200 c) as an experimental work reported.but temperature variation is just 25 c ! also nodes dont sense the temperature of the heat source till it reaches them
a node has constant temp till the time the heat source pass it. if it is on the weld line temp varies good but from .05 m to the end of plate side we have no sensible temp change.is this a basical problem of code ABAQUS or ????
thanks alot





RE: experts help please
RE: experts help please
aluminium 1100 :
density = 2710 kg/m3
k= 220 w/m.c (varies with temp)
h = 25 w/m2.c
Cp= order 900 j/kg.c
dimensions : .5 m * .5 m * .005 m
Q= n VI w
it is about 10 days that i am checking units and values !!!
please help
what is happening that i cant find it !! :(
RE: experts help please
Input files or .cae files can be uploaded here, providing they're not too big.
RE: experts help please
RE: experts help please
i will check what you said ....
i will become thankful of you so much if you check these files
best regards sir
RE: experts help please
RE: experts help please
RE: experts help please
no difference
load is user defined - dflux -
i am realy confused - when i change k from 222 to 2220 , or changing density from 2710 to 2.7 , heat transfers to the further elements and they sense the moving heat source
but with real data of aluminium 1100 , no conduction to further elements . it is not what happens in reality
RE: experts help please
RE: experts help please
RE: experts help please
excatly this is the problem !
on the weld line and distanses about .05 m from it (transverse direction), temperature is sensed and it is ok . but as you see nodes further from this distance dont sense any temp change.
as an example :
from an experimental work , temp. of point (x=.12,y=0,z=.05) has a maximum temp of 200 c . but this modeling reports max temp about 55c!
heat is not conducted as it is conducted in reality.why?
aluminum has high conductivity.if we have a temp raise in one point, the other points of plate sense it and temp change is sensible.
Abaqus cant model high conductivities?!! there many works done with abaqus for aluminum.so what is the problem with my work.why temperature change is just around weld line?
i am realy confused :(
RE: experts help please
Abaqus solves for any material thermal conductivity obviously, however it may be less accurate where there is a 'thermal shock' at a surface. Normally you can see this in the results as they show some instability. In these cases you need a much finer mesh, and a smaller time step. As I said before, use symmetry along the weld line and partition the mesh to be much finer towards the weld. I doubt this would alter your results much, though it may increase the calculated maximum temperature where the thermal shock is most severe from your applied heat flux.
RE: experts help please
i used finer mesh and submmit
i deactivated radiation and submit
i used less 'h' = about 2.5-9 and submmit
but just temperature along weld line changes
max temperature of nodes in transverse direction dont increase as much as it should
i will have an experimental work too
if abaqus show me max temperature of 55c for point (.12,0,.05),and experiment shows 200c(as the experiment already done by a friend), how can i trust answers?!!!
RE: experts help please
RE: experts help please
RE: experts help please
i did what you said (as you have done) and as you said there is no difference. i called one of my friends who worked weld modeling by Ansys.
he said he had some problems like this in points near the sides (far from weld line). but not such an error !
it is really unacceptable for aluminium that the points dont sense heat (such a heat that raise the centerline temp. from 25 to 600!)
i am really really confused!
my thesis has stoped for about 3 weeks just for this problem.i dont know what to do ?!! :(
i dont know anyone who is expert in this field.you and maybe your friends are my last hope.
thanks a lot ...
here is experiment data for point (.12,0,.05)
RE: experts help please
make the parameters a,b,cf,cr so small (concentrating the heat source)- the temperature of weld line raise to 2500c.but no change to the temperature of the points near the side or in the middle of semi-plate.
why?
question 2 :
make the input power 10times greater (for example volt*10=240 volt). the temperature on weld line rise to 4000c but the temperature of the points near the side or in the middle of semi-plate just rise to 70-75 (from 55 when we had real source with volt=24 !!)
the problem is in conduction or maybe heat storage terms (density*Cp)?!?!?
RE: experts help please
RE: experts help please
Just a thought.
RE: experts help please
thanks for your suggestion. I have 3D model and all dimensions in m . 0.5*0.5*.005 m plate
to corus :
i have read many papers (steel and aluminium).you are right.some of them report conciderable temperature drop from weld line.but we are engineers.we cant tell lie to ourselves!! :)
we have a plate with k=220 w/m.c in contact with a heat source which melt the aluminium at the middle. now the temp. of a point at the side of plate should change from 25 to 50 ! unacceptable.
my friend who used abaqus told me that he had such a problem and he used t/tmax and it was solved.but here it doesnt work.i dont have time to learn Ansys and Abaqus doesnt answer.i dont know what to do?
i want to solve mechanical problem (for residual stress) with data achieved from thermal one(temp. distribution).wrong temp. dist. will result in wrong stresses.
RE: experts help please
RE: experts help please
the dimension .12 m is correct ...
did you checked the dflux code? was any problems there?
if we make a,b,cr,cf so small,temp. on weldline goes up (700 or more). it is more than melting point.but just centerline senses this variation.temp. on weldline goes up but at sides no .
consider the results of experiment are wrong.
what should we expect?temp. rise at sides is expected.
forget my code and modeling.think about what should happen in such a case in reality and what does happen in abaqus modeling?!!!
believe me it is a basic question !
thanks again and waiting for any idea from anybody!
RE: experts help please
i validated the method in this points by changing a,b,cr,cf of heat source (which are near weld line)
but when i check temp at points more than 40 mm from weldline, we dont see any sensible temp. change
maybe this method of simulating welding with abaqus is just effective in HAZ area?!!
any other methods available?does it mean that ansys is better?! :(
RE: experts help please
RE: experts help please
i checked that
steady-state has no problem (effect of density and Cp is ignored and everything will be ok-heat is conducted through plate with no resistanse)
thanks a lot again
i will check this topic
if you found something, i will be glad (so glad! :)) to know ...
RE: experts help please
RE: experts help please
if i solve the problem in steady-state manner( in "step" , mark "steady state" instead of "transient"), density and Cp are ignored and it soves it as a complete steady problem([k]{T}=0)
how is it possible to solve this form : [alpha=k/pCp]{delT}+[u]{Tx}=0 ??