Thank you for your answer.
For my part, I continue my research because, in the case of foams, stiffness is not a constant and is subject to the following variables:
- Sinking speed: the apparent modulus of elasticity increase according to the rate of deformation
-Temperature: stiffness increases as the temperature drops
-the depth of sinking: There is first an increase in stiffness during crushing then a plateau and an exponential increase when the cells/cells of the foam are crushed and it is pure compression.
In my case, I am not trying to do a dynamic study but a static study, constant temperature, and without taking into account impact kinetics. So I would need a compression curve of a seat foam.
However, because I don't have this value (if you have any, I'm a taker) I looked at the fact that foams have a characteristic called lift. The latter corresponds to the force in kPa needed to drive a foam 40% thick
Lift corresponds to the hardness of the foam. Lift is related to density, because for a given density there is a possible lift ceiling.
A 35kg/m3 foam, for example, can have several different load-bearing capacities ranging from 2.5 kpa to 4 kpa for a seat.
For your information I found a seat cushion with a lift of 80 kg/m² with a thickness of 6.5-1 cm
What makes with your formula, if we take the average thickness of this cushion (3.75 mm) a stiffness of:
Bearing capacity 80 kg/m² or 784.5 N/m²
Average depth 3.75 cm or 0.0375 m
Stiffness: lift/sinking: 20928 N/m/m²
For lack of anything better, I'll try a first calculation with this value;)