USDFLD to represent powder melting in Additive Manufacturing

[D Higgins]

Hi,

I'm trying to use the USDFLD subroutine to change the material properites of a part depending on whether it is in powder or solid form.
The idea is as follows:
- Start in powder form (0)
- Apply heat using DFLUX subroutine to simulate laser
- Once Melting temp is reached use solid properties (1)
- Continue using solid properties for cooling and rest of simulation

I can't get the field variable to change, either only powder properties are used or solid properties. Could anyone help or have any examples of state change using USDFLD subroutines.

Some of the.inp is below and the .subroutine is attached:
*Material, name=Ti6Al4V
*Conductivity, dependencies=1
0.2, 298.15, 0.
19.4, 1873.15, 0.
28.3, 1923.15, 0.
7., 298.15, 1.
7.45, 373.15, 1.
8.75, 473.15, 1.
10.15, 573.15, 1.
11.35, 673.15, 1.
12.6, 773.15, 1.

 

[FEA way]

Actually I think that it would be easier to use properties dependent on the temperature instead of user defined field variable. You can easily define the properties to change when melting temperature is reached (even in CAE). Did you consider using AM plug-in for this simulation ? Its newest version works very well and can be used to easily set up additive manufacturing process simulation in Abaqus without having to write or modify subroutines manually.

Is actual phase change included in your simulation ?

 

[D Higgins]

Originally I had the properties as temperature dependent but depending on the state (powder/solid) there will be two values of conductivity (0.2/7 W/mk at 298K) for the one temperature.
I would prefer to use subroutines as in the future i plan to model the volume fraction of allotropic phases α+β in Titanium.
The actual phase change is included in the simulation.

 

[FEA way]

Right, this way when material cools down after melting it will have powder properties assigned again even though it’s still solid.
Could you also attach the subroutine used to model phase change (I guess you use HETVAL for that) ? I think that USDFLD needs proper connection with the subroutine used to model phase change.

 

[D Higgins]

I havn't used another subroutine to model the change from powder to solid. I thought that's what I was doing with my USDFLD subroutine, i.e. use field varable as 0 until the temperature reaches melting and then change the field variable to 1 representing the solid.
Ive attached a bit more of the input file to hopefully explain it better.

 

[D Higgins]

The following paper is an example of what I would like to use USDFLD for.

https://www.sciencedirect.com/science/article/pii/S1110016818302357

 

[FEA way]

I was rather thinking about full phase change definition including phase transformation kinetics models such as JMA (Johnson-Mehl-Avrami) or KM (Koistinen-Marburger). This approach is thoroughly described in the articles "A metallurgical phase transformation framework applied to SLM additive manufacturing processes" by Q. Zhang et al. and "Phase Transformations in Metals during Additive Manufacturing Processes" by J. Xie et al. Both discuss implementation in Abaqus. Second approach is described in the "Sequential thermomechanical analysis of a laser powder bed fusion build" chapter of the Example Problems Guide. It was added to Abaqus documentation few months ago and it features input files. Phase transformation is not included explicitly there but results show very good agreeement with referenced experiment.