## General Mechanical

#### Making a material that does not revert in properties after passing a threshold

• Zhi Wei Ang
Subscriber

Case 1

I'm currently conducting a transient thermal analysis which includes a material that changes in thermal conductivity and specific heat capacity that changes after a certain threshold of 120°C.
I will be referring to the thermal conductivity as "W/mK" as "Wm^-1K^-1".

Therefore in regards to the situation, is it possible to assign a material a thermal conductivity of the following scenario:
Initially, the temperature and the thermal conductivity would be the following as the temperature rises:
22°C, 2Wm^-1K^-1
120°C, 2Wm^-1K^-1
150°C, 0.05Wm^-1K^-1
1100°C, 0.05Wm^-1K^-1

However, I would like to assign that the material remains at 0.05Wm^-1K^-1 after the temperature of 150°C, even after it rises to 1100°C, and after it drops back to 22°C it will remain at 0.05Wm^-1K^-1 instead of returning to 2Wm^-1K^-1.

What was describes means, afterwards as the material decreases in temperature, it would be like this:
1100°C, 0.05Wm^-1K^-1
150°C, 0.05Wm^-1K^-1
120°C, 0.05Wm^-1K^-1
22°C, 0.05Wm^-1K^-1

In this case, I would like for a property of the material to continue to stay at a certain value after passing a threshold.

Is there any way to achieve this?

Case 2

The shape of the curve is as shown below, from Engineering Data when editing the heat capacity of a material. This is for purpose for simulating the change in property as it gets burnt.

As there is a huge change in the material property across a small amount of temperature change, would this cause problems in the simulation such as non-convergence when solving? If so, are there any ways to solve it? Is changing the 2 sharp points at 120°C and 150°C to smoother curves better?

Note, I am using Ansys Workbench 2021R2.

Thank you so much everyone!

Ang Zhi Wei

• Ashish Khemka
Ansys Employee

Hi Zhi,

For case one - the properties will remain the same as the nearest defined input properties.

For case 2 - try running the model, there may not be any issues. But please comment if you get any error.

Regards,

Ashish Khemka

• peteroznewman
Subscriber

Hello Zhi,

In this transient thermal model, you have a temperature-dependent thermal conductivity material and you want that material property to permanently change on an element-by-element basis after the element crosses the 150 C threshold.

I’m not an expert at APDL, but I believe code could be written that executes after each time step to change the material assignment of any element whose current temperature was above 150 C to a different material that has a constant value of thermal conductivity.  MPCHG is an APDL command to change material. You need code to select the elements to apply that change to. A simple loop through every element with a simple IF statement that checks if the temperature is > 150 then changes material would do it. Maybe there is a command to get all elements that meet that condition without needing a loop.