Disclaimer: I’m an industrial designer and not an engineer. That means I’m a right brained artsy fartsy person who does not do well with numbers, but I think it would be useful to learn some basic things here…
However, the first thing I encounter is that there are not a lot of materials bundled in Prepomax. So the second thing is how to add one that I need. But what Prepomax wants and what the data sheet says seems to be very different things.
Could someone please ELI5 (if that’s possible) which of these numbers correspond to which in a Prepomax material? For example, naively I hope that “flexural strength” corresponds to “young’s modulus” but there’s nothing which looks like “poisson’s ratio” in that list.
It’s a polyurethane foam usually milled for tooling, but I’m currently tasked to use it in a rather different sort of application so that’s why I want to test the strength in Prepomax and see if we’re within the ballpark or way out of line…
It depends on what kind of simulations you want to perform but assuming basic static structural analysis, you need at the very least:
- Young’s modulus also known as tensile modulus
- Poisson’s ratio
Then you also need density for dynamic simulations or when using gravity or centrifugal loading.
If you want to use a nonlinear material model - linear elasticity with plasticity, you will also need at least the yield strength but it’s good to also specify (ultimate) tensile strength - UTS and strain (elongation) at failure/break.
There are also some thermal properties needed for heat transfer analyses but I assume you don’t need them now. You may need the coefficient of thermal expansion though.
Even if something is not in your material’s datasheet, you can usually find it online for this or similar material. Just be careful about the units.
Flexural properties are determined in a different kind of test - three-point bending in this case. You need properties from a tensile test but those are usually easy to find. For example:
Poisson’s ratio varies quite a lot depending on the source but it’s less important and I would probably just assume 0.4 in this case.
To add a material to the library, you have to create it in the model tree first and then move it to the library using its editor. Check the manual for detail description.
Pay atention that foam materials are very compressible and should be modeled using the *HYPERFOAM Calculix card/definition. As far as I remember is not implemented yet in PrePoMax GUI, but you can use it by means of custom editions on the input file. You will have to digg in some papers of foam simulations using Abaqus maybe to find out the material constants, I don´t have experience with your particular material, only with rubber sponges from door sealing.
Maybe you could do some elastic approximation playing with the Poisson coefficient, for rubber that are almost incompresibles (the oposite behavieur) I have used high values near to 0.49, maybe for foams is the oposite, something like 0.1… for reference steels/aluminiums/casts are about to 0.27-0.30
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Yeah, materials such as plastics and (especially) rubbers and foams usually should be modeled with *HYPERELASTIC or *HYPERFOAM nonlinear elasticity models (not supported in PrePoMax yet but there’s a keyword editor for that). But those require proper constants or test data (stress-strain curve). You can look for that for generic polyurethane but I would start simple with linear elasticity. It’s good enough for small strains.
Sorry, I should have used a different word. This is a very hard and rigid material (made for tooling as I mentioned). It’s not really flexible at all but will break and shatter.
Is that why it doesn’t have a modulus/poisson value?
