Question

If the specific surface energy for soda–lime glass is 0.30 J/m2 and its modulus of elasticity is (69 GPa), compute the critical stress required for the propagation of an internal crack of length 0.8 mm.

Answer 1

Answer: the critical stress for the sodalime glass = 5.7MPa

Explanation:

Ist Step

we Calculate  half length   of internal crack as

2a =0.8 mm

a = 0.8/2 = 0.4 mm

Changing  to meters becomes = 0.4 / 1000 =0.0004m

2nd Step

Now  the critical stress required for the propagation of the internal crack can be calculated using the formulae

Critical Stress (σc) =      (2 E γs/ πa) 1/2

where E= modulus of elasticity

γs= specific surface energy for soda–lime glass

a= Length

= (2 x 69 x 10 ^9 x 0.30/ π x 0.0004)1/2

=$\sqrt{ 32,940,802,036,919}$

= 5,739,407.8= 5.7 x 10^6 N/m^2

= 5.7MPa