I was looking for data on fracture toughness but could only find data for shear on both materials.
This is the link I used for the 30kg/Cu.m Styrofoam properties:
It gives shear strength 250kPa and shear modulus 8MPa. From that data I calculated the breaking strain of 3.1%; assuming a brittle failure.
This link has the data I used for H80:
The table on page 4 gives the shear strain as 12%. The 8% I stated was for the H60 rather than H80 (meaning I transposed columns when I looked down them).
If I calculate the breaking strain from the shear values for H80 using stated values 0.9/23 then that gives 3.9% if it was brittle failure, which it isn't. On this basis the H80 is only 25% better than 30kg/Cu.m Styrofoam. However it is the actual breaking strain that matters because the skins are taking the load. As long as the core stays intact the structure retains its strength.
The link you provided for the Styrofoam HD 300F-X has a density of 45kg/Cu.m. It gives a shear strength of 0.5MPa and shear modulus of 14MPa so 3.6% breaking strain for brittle failure. Its shear breaking strain may or may not be comparable with Divinycell H80 depending on its failure mode. If you can find actual breaking strain in shear then that would be insightful.
My comparison in handling and working 30kg/Cu.m Styrofoam compared with Divinycell H80 (actually these days Gurit PVC80) is that the PVC foam is considerable tougher. I regard the blue Styrofoam as brittle but I have not actually measured the fracture toughness.
Rick
On 19 Nov 2018, at 4:01 pm, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:Rick, where did you get the number for shear braking strain of only 3% for the XPS?The max compressive strength of these insulation boards is measured at 10% deformation, and I don't expect a large difference regarding the shear strength.My hands on experience with Divinycell and Finnfoam is that the Divinycell feels more brittle. For example, while bending a small sample of Divinycell, it just breaks at a certain point. The Finnfoam deforms and forms a curve instead. It also seems to rebound better from the same compressive or bending force while playing with both.Mx7-7XPS 700The breaking strains are about the same, but with a larger modulus of elasticity for the XPS.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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