In the past this has been due to Cp being incorrect as described below. The other message can be ignored.
Knowledge Base Solution 845568:
Why am I getting the error message below with PLANE223? The calculated specific heat at constant strain is negative. Please verify the input of thermal material quantities for consistency.
Product Family: Structural Mechanics
Product: ANSYS Mechanical APDL
Version: 11.0
Area: General
SubArea: N/A
Last Updated: April 17 2020
Answer:
PLANE223 is different because it has two way thermal-structural coupling. You may be getting the negative Cv message because your value of Cp is too small. From the numerical values in your input, it appears as though you are using the length unit off mm. The table below from the Coupled Field Guide gives units of length^2 for specific heat, so the MKS value of 460 for specific heat should be multiplied by 1e6 to produce a value of 460e6. This will make the value of Cv very positive.
Refs:
Theory Manual Equation 11-31
Coupled Field Guide Section 2.6.2 points a through d.
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