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Experimental notch fracture testing to calculate KII


I am doing a v-notch fracture testing (experimental) with opening angles from 0,30,60,90,120 to 150 deg and need to calculate KII. I need a equation that could be used to calculate KII for both 0 deg and also for non-zero opening notch angles. I am using TestResources machine to do this shear testing and I will get results in terms of load vs. d. The material is PMMA. What could be the appropriate displacement/min or load to break the specimen.

I am also using Ansys to predict the same. My KI value is 0 and KII value seems to be between 1-2 MPa.sqm. The specimen is fixed with 6 holes, 3 holes on each side. and I have applied displacement on that area (3 holes-fixed and 3 holes-applied with Y-displacement, x,z-fixed). Now I want to know what is the force in that area.

Pls let me know the answers.

Thanks in advance.

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You can use a loading rate of about 1 mm/min or lesser (if your machine will allow it) for quasi-static loading for PMMA.

Your first picture shows a specimen with a notch and a sharpened crack tip. So this will allow you to calculate KI and KII in Ansys. However, in your second picture you show a specimen with a V-notch. In Williams original paper (1952), the asymptotic derivation is for a notch where a crack is a special case with notch angle of 0. In case of a V-notch, it would be more appropriate to use Generalized SIF, since you cannot split the SIF's into individual components. You also need a crack initiation criterion to predict when fracture is going to happen. One such criterion is the Leguillon's criterion which would be useful in your case. 


Thanks Arun for your comments.

As you said, can I use KII=P*F(a/w)/BW^1/2 to calculate experimentally the KII value.This eqn is not valid for crack. 

 But in ansys, I have used Generalized SIF eqn. as KII=τ*sqrt(2PI*a). Is this correct. 


You can use an equation or even Ansys to calculate the value of KII for a crack. However, in case of a notch, you don't have a simple formula to calculate the 'stress intensity factors' as in this case SIF is expressed as K=K1+iK2. Again, it depends on what you want to calculate. If you want the crack initiation load, you should use a criterion to predict the onset. I recommend you read this very famous paper (Hutchinson and Suo, 1992 ) to get a good understanding of the problem. Maybe others can also chip in with their thoughts.


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