compression, tension and shear of a test material

I made a simple definition to corroborate the behavior of a test material under compression, tension and shear. The motivation behind this definition is to corroborate the properties of Poly Lactic Acid, a kind of plastic commonly using in 3d printing. In my experiments I have seen that it works well under compression but terrible under tension.

If someone is interested I can share the sources from which I calculated the material properties for Karamba. It would be helpful to me since I had to do a number of conversions to obtain values compatible with Karamba and there could be errors.

I am also planning in the near future to graphically compare different kind of materials. For example, the deformation of steel, concrete and plastic beams under the same loads.

Your review of the consistency of the definition, inputs and suggestions would be greatly appreciated.

Regards

Diego

Attachments:

force test.gh, 23 KB
test force.png, 1.2 MB

Replies to This Discussion

Permalink Reply by Karamba3D on November 14, 2012 at 12:29am

Hi Diego,

it would be very interesting to include the material properties of printed materials in the default material library of Karamba. Could you please send me a link to the paper where you found the material properties?

Currently Karamba is limited to linear elastic calculations. So when you plan to compare the behavior of e.g. steel, concrete and plastic beams their calculated deflection will be different by a constant factor which is determined by their respective values of Young's Modulus. In reality this is only valid for low to medium material utilization: at higher levels non-linear effects enter the picture (e.g. yielding of steel, cracking of concrete). The yield stress in Karamba does not affect the computation of deflections but only cross section optimization.

You simulate three kinds of tests in your definition. In material testing laboratories the shape of test specimens depends on the type of material to be tested: for brittle materials like e.g. concrete they use a simply supported prism with two uniform point loads at one third of the span for determining the tension strength under pure bending. This gives constant bending moment between the loads.

Best,

Clemens

Permalink Reply by Diego Gil on November 14, 2012 at 9:02am

Hello Clemens:

The main plastics used nowadays in 3D printing are ABS and PLA. I sent you via PM the information I have related to the mechanical properties of Poly lactic acid.

My main interest is in PLA due to the possible future environmental benefit it might bring.

The values I am using to simulate PLA in Karamba are:

Young´s modulus: 300 Kn/cm2

Shear modulus: 90 Kn/cm2

Specific weight: 1.24 Kn/m3

Yield strength 0.48 Kn/cm2

(Remember that these values could be completely wrong)

Regards

Diego

PD: I will modify the definition based on your observation.

Permalink Reply by Karamba3D on November 15, 2012 at 5:28am

Hello Diego,

thank's for the two tables and the literature links.

From what I can see from the first table Young's Modulus and Shear modulus you gave above are correct. When converting the units from the first table I arrive at a specific weigth of 12.4kN/m3 and a tensile strength of 4.5kN/cm2 though.

Best,

Clemens

Permalink Reply by Diego Gil on November 21, 2012 at 12:15pm

Thank you Clemens I appreciate your help.

Regards

Diego

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