I want to test toughened PMMA with CT specimen but I don't have any experience about it.
The ASTM say B (thickness) should was be smaller than 2.5*(Kic/sigmay)**2 but h don't know how much B is better for this.
I calculate for pure PMMA B=2mm and I think for toughened one Bmin was smaller than it. Isn't this?
if Read correctly it should be greater than this formula, not smaller than this formula, and with the increase in toughness, the thickness of specimen increases not to decrease, Best Wishes
yes it is true i mistake
i see another article about toughened PMMA that thickness is 1.7mm
how much thickness you offer for my test for toughened PMMA
I dont know the properties (Tensile) of PMMA material that you are using, so I cant say. Also the application for which u r going to use it, understanding of that is also equally important.
yeild stress=30.7 e7
Kic=10e6
it is my Thesis
can you say me a good and reliable B?
Also specified ultimate strength and % elongation % area reduction if any
stress is pascall
and K is pascall*squeare (m)
i dont know elongation
The specimens used to measure KIc must be designed to ensure that the size of the plastic zone accompanying the crack tip very small relative to the specimen thickness, and plane strain conditions dominate around the crack tip. According to the ASTM standard, the minimum characteristic specimen dimensions, including the specimen thickness B, the crack length α and the specimen width W, must be fifty times greater than the radius of the plane strain plastic zone at fracture. When the plastic zone size is determined according to the Irwin model this condition implies that
B>2.5(KIC /σy )2
.
Because the PMMA is a perfect brittle material, almost all the thicknesses B, are valid. The problem is the phenomenon of the buckling out of plane. Thus, to avoid this situation, you must to choose the suitable thickness B, which depend from dimensions of the specimen.
I calculate B_min from Irwin model for PMMA is 2mm but my material isn't pure pmma and my material is rubber toughed pmma and for this B_min is smaller than 2mm because we use from another equation:
B=25*(J/sigma_y)
in your mind if I use 2 cm my test is good
I fear my specimen sweeping in during tensile test
If the experiment is tensile test, I think the use 2 cm is good.
no it is fracture test
my cast is 5mm and i forced use B=5mm
i fear my CT specimen torsion at during test
what can i do for remain straight my specimen at during test?
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