Question

(a) An Al2O3 specimen is being pulled in tension. The specimen contains flaws having a size of 100 um. If the specific surface energy of Al2O3 is 0.8 J/m², what is the fracture stress? Use the Griffith criterion, E = 380 GPa. Use internal crack. (3 points) (b) Estimate the fracture stress if the fracture toughness is 4 MPa m12 Assume two positions for flaw: in the center of an infinite body (2 points) and at the edge (2 points). (c) Comment on the differences obtained in part (b) (1 point).

Answer 1

0 stress fracture patino AH Grififth criterion 2E Ua ac Ta 3 E = modulus of Elasticity Va = specific surface energy -0.050 mm loo = so um a / 1/2 2 X 380 X 0,8 ac 1 3.14 x 0.050 11 62.2 MPa ac (6) 4 MPasm ginen, fracture toughness ( at center of infinite body la= 0.050 k = 4 M Palm arta a = fracture stress K = OK 2010 X 4 osta 53.148 0.050 do 10.2 MPa Ans. fracture stoess can - 10.2MPa = 10.2 MPa

2 at the edge aco 3.14 X 9 - 2 3.14 xo Nowl, we can see in in the above Stress fracture the at the end of the edge of infinite Body the fracture stress in @ (infinite) and center of the fracture stress is = 000 mas Body - 10.2 Mpa