Determine compressive modulus from compressive strength data in spec sheet?

Is it possible to determine the compressive modulus of a polyethylene foam using the following spec sheet?

Minicel Type M Foam

It doesn’t contain any information regarding the compressive modulus, but does have compression strength in terms of a compressive stress at 25% and 50% compression. Could I just determine the strain at 25% compression (delta L/L) and then simply divide the stress at 25% by that?

Thanks

1 Answer

I'm hardly an expert on the mechanical behavior of polyethylene foam, but a quick Google lead me to this paper by Patel et al. (2008):

Young's modulus values were 0.08–0.93 MPa for the 0.09 gcm-3 foam and from 15.1–151.4 MPa for the 0.16 and 0.32 g.cm-3 foam. Yield strength values were 0.01–0.07 MPa for the 0.09 gcm-3 foam and from 0.9–4.5 MPa for the 0.16 and 0.32 g.cm-3 foam. The energy absorbed to yield was found to be negligible for all foam cylinders.

Stress-strain and Young's modulus-strain curves. (a) Stress-strain curve from a 7.7 mm length sample of open cell PU foam (0.09 g.cm-3) used to model very low density human cancellous bone and (b) the Young's modulus determined from it as the gradient of the curve. The yield point is defined by the point at which the Young's modulus decreases by 3% from its maximum value. The area under the stress-strain curve up to the yield point is defined as the energy absorbed to yield.

The numbers themselves likely aren't relevant for your material. What should be observed is how non-uniform the elastic modulus is (obtained as the derivative of the stress/strain curve), varying by an order of magnitude depending on the deformation.

This makes it hard to give a good estimate of the elastic modulus based on two points, but the best possible guess would be to plot a straight-lines chart with three points (the origin and the two known stress/strain points) and then calculate the slope for each of the segments, which will be equal to the elastic modulus for each segment.