Hello guys!
I am a beginner in Karamba and I am trying to create a custom material with data out of a birch plywood table from a supplier.
I have checked my conversion many times but I always get this message:
“1. Material #0 : For isotropic materials G must be larger than E/3 and smaller than E/2. If this condition is not fulfilled the material behaves very strange. It may lead to an unstable structure. May cause errors in exported models.”
I am not sure if I am using the wrong data or if there is something wrong with the conversion that I am missing.
Data source:
My conversion in yellow:
I highly appreciate any help 
Hello @fernandagraciano.s,
the condition that G must be larger than E/3 and smaller than E/2 applies to isotropic materials. For orthotropic materials other constraints apply (Abs(nue)>= Sqrt(E1/E2)). If for orthotropic materials ‘nue12’ is left unspecified, the corresponding value gets calculated according to Huber’s formula (see ‘Huber M.T.:The theory of crosswise reinforced ferroconcrete slabs and its application to variousconstructional problems involving rectangular slabs. Der Bauingenieur, 1923.’). In order to arrive at one value for nue12 in Karamba3D 1.3.3 the simplified formula nue12 = E1/(2*G12) - sqrt(E1/E2) is used. Interesting material covering the subject of orthotropic material constants can be found here.
You could try to specify an orthotropic material with E1=1273kN/cm², E2=476kN/cm² and G12=200kN/cm².
– Clemens
