If S is the applied stress, c 1s the width of the crack and r the radius of curvature at the tip of the crack, Griffith's crack theory gives the concentrated stress $$S_{c}$$ as

A

2 S $$(\frac{c}{r})^{\frac{1}{2}}$$

B

2 S $$(\frac{c}{r})^{\frac{1}{3 }}$$

C

S $$(\frac{c}{r})^{\frac{1}{2}}$$

D

2 S $$(2 \frac{c}{r})^{\frac{1}{2}}$$