You input a material Stress-Strain curve into a model that has the geometry in a lattice structure and when you plot material Stress-Strain results, you get back the input, is that what you are saying?
Say your Lattice Structure is 80% void and 20% material, you might expect that the Effective Stress vs Strain curve would be reduced to about 20% of the material stress value.
To measure this, you can't plot the material Stress value, you have to request the Tension Force and divide by the Area of the cross section (counting both the void and the material) to get the Effective Stress.