Learning Forum

[passion971017]

Hi everyone,

I have been running some Thermal Strain simulations (on ANSYS Additive 2020 R2 version) to calculate the strain and stress during the AM process. The questions I had were:

1. For the values of maximum stress, does that correspond to the maximum stress during the entire process (start of the process until cooling down the preheat to room temperature) or the maximum stress during the laser process (start of the laser scan until the final laser scan)?

2. Again regarding the values of maximum stress, if a voxel is applied a certain amount of stress and the remelted afterward, would that transient amount of stress be counted as maximum stress if it is large enough?

3. When I run Thermal Strain simulations, I am asked to type in material properties such as Elastic Modulus and Yield Strength. Since material properties vary with temperature, I am wondering which value of these I should use. If I just type in room temperature values, would the simulation run on that value despite the temperature of the voxels?

Please let me know.

[John Doyle]

1.Since the build material has a metal plasticity model defined, the stress and strain are path dependent, so the max stress at a given point in the build history is a function of everything that came before it from beginning of the build until that point.
2.I am not sure I understand this question, but if build material is defined as elastic-perfectly plastic, the yield stress is the maximum stress that will be reached.
3.You need linear elastic modulus, PoissonÔÇÖs ratio and yield stress to fully define the material.It is best to enter temperature dependent properties that envelop the full range of temperatures that the material will experience during the build (i.e. room temperature up to melt temperature).

[passion971017]

thank you very much for your answer! I have follow-up questions for those which you so kindly answered!

1. In the ANSYS Additive Thermal Strain simulation, I can export a so-called "On plate stress/displacement" as an output (VTK file). Can I assume that this is the state when the entire build plate (and the prints) has cooled down to room temperature? Also, I am getting stress values over the yield strength (500 MPa where the YS is 380 MPa). Is this because I am running this in a "J2 Plasticity" (picture below) mode or is there something wrong with my simulations?

2. Let's assume that a voxel had a stress value of 500 MPa. However, this voxel reached melting temperature after some time. Then the voxel experienced a stress value of 400 MPa. In this case, will the maximum value of stress be 500 MPa or 400 MPa when we check the "On plate stress/displacement" result?

3. In order to input the temperature dependent properties of materials, do I need to use a JSON file (picture below)? Is there a template of this which I can use?

Please let me know and thank you again for all the help!

[John Doyle]

I apologize for my initial post. I think my comments have caused some confusion.

While it is true that the stress would not exceed yield for "elastic-perfectly plastic" behavior (hardening factor is set to zero), that is not the default in Additive Print.The hardening factor dictates the material stiffness beyond yielding. If you were to set it to zero, you would likely have convergence trouble, since material would have no stiffness response beyond the yield. Most real world materials are not elastic-perfectly plastic.

Also, you cannot define temperature dependent yield strength directly in Additive Print. My recommendation to do this only applies to Engineering Data GUI in a WB-Additive application, not Additive Print.

Sorry again for the confusion.