The critical stress σc for crack propagation in a brittle material, using the principles of fracture mechanics is1) \({\left( {\frac{{3E{\gamma _s}}}{{3\pi a}}} \right)^{\frac{1}{2}}}\)2) \({\left( {\frac{{3E{\gamma _s}}}{{2\pi a}}} \right)^{\frac{1}{2}}}\)3) \({\left( {\frac{{2E{\gamma _s}}}{{\pi a}}} \right)^{\frac{1}{2}}}\)4) \({\left( {\frac{{3E{\gamma _s}}}{{\pi a}}} \right)^{\frac{1}{2}}}\)Where: E = Modulus of elasticityγs = Specific surface energya = One half the length of an internal crack.

The critical stress σc for crack propagation in a brittle material, u

1.	The critical stress σc for crack propagation in a brittle material, using the principles of fracture mechanics is1) \({\left( {\frac{{3E{\gamma _s}}}{{3\pi a}}} \right)^{\frac{1}{2}}}\)2) \({\left( {\frac{{3E{\gamma _s}}}{{2\pi a}}} \right)^{\frac{1}{2}}}\)3) \({\left( {\frac{{2E{\gamma _s}}}{{\pi a}}} \right)^{\frac{1}{2}}}\)4) \({\left( {\frac{{3E{\gamma _s}}}{{\pi a}}} \right)^{\frac{1}{2}}}\)Where: E = Modulus of elasticityγs = Specific surface energya = One half the length of an internal crack.
A.	1
B.	2
C.	3
D.	4
Answer» D. 4