The fracture toughness for the parent material favours PVC by a factor of more than 3 - that is interesting. However the foam performance depends significantly on the foam structure.
Your proposed bucket test will not give the same sort of shear loading as the core experiences in a composite because you need to control the strain. Without controlled strain the sample will fail as soon as the maximum shear stress is reached. You really need to determine the breaking strain and that requires controlled strain.
I believe a simple bending test with the actual composite gives a more complete picture. That way you are testing more elements at once - core shear strength, skin tensile strength, skin stability under buckling, bond strength etc. For bending test I just use gym weights for loading.
The specific tests for shear might give insight into why one core is better than the other under specific conditions. However having higher shear breaking strain may not be significant in the performance of the composite (it is a possibility not a certainty). Any testing I have done with equal thin skins on PVC core typically fail on the compressive side due to skin buckling and separating/tearing from the core. I have note done a bending test on XPS cored composite but should. I have a bonding test piece already prepared for the Knauf XPS but have not loaded it.
Rick
On 21 Nov 2018, at 7:14 am, Björn bjornmail@gmail.com [harryproa] <harryproa@yahoogroups.com.au> wrote:Thanks for the datasheet on the Divinycell. It had much more info than the one I've been using.And I wish there was better data on these PS insulation foam boards. The data from Finnfoam is even less detailed than the datasheet I linked to.Regarding impact strength, I found some properties from a Dielectric corporation. It shows slightly higher fracture toughness for PVC.But since the data is for electrical purposes, it might not be the same grade as for insulation or structural foam.
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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