Using Griffith fracture equation in design

Griffith fracture equation dictates a critical stress intensity factor for a given loading condition, stress, and flaw size. This can be used to design components that won't fracture.

[@Backburner1118]

Great studying for my materials exam!

[@nedisawegoyogya]

So if Kc = Yσy√πac : ac is the half crack size of the specified material that have yield strength = σy? Assuming Kc is constant given crystal structure, then also assuming similar yield strength, this mean tougher the material (Kc larger) means they have larger ac?

[@TaylorSparks]

Close. Kic is material specific(also a function of other parameters like temperature, grain size, stain rate etc). If you compare two different materials and one has a higher toughness, it will accommodate a larger critical flaw size before failure.

[@nedisawegoyogya]

@@TaylorSparks Thank you Professor Sparks for your answer. I'm still curious about the thing with Kic being larger in ductile materials and smaller in brittle ones. What is the equation of Kic for ductile material (like metal)? Is it σc/σy with σc = √2Epy/(πa)? And the brittle ones σc = √2Eps/(πa)? Then assuming similar tensile strength, it means the metal has a far smaller defect or the yield energy py is much larger than surface energy ps?

[@nedisawegoyogya]

@@TaylorSparks anyway thanks for the very informative video. But it seems that I have to accept in faith for now that Griffith Criterion on failure means no interaction between σxx and σyy if one of them is in tension and the other in compression. I'm just searching on why the Brazilian test for tensile strength gave smaller strength value than flexural test for tensile and got here.