Afreshly annealed glass containing flaws of maximum length of 0.1 microns breaks under a tensile stress of 120 mpa. if a sample of this glass is now subjected to stress of 30 mpa, failure is found to occur after 10 days. assuming that the specific surface energy (or fracture toughness) does not change, the average rate at which the crack has grown during the period of the test is

0.16 micron per day

Explanation:

Given:

The initial crack length, a₁ = 0.1 micron = 0.1 × 10⁻⁶ m

Initial tensile stress, σ₁ = 120 MPa

Final stress = 30 MPa

now from Griffith's equation, we have

where,

Gc and E are the material constants

now,

for the initial stage

 ........{1}

and for the final case

  ............{2}

on dividing 1 by 2, we get

or

a₂ = 4² × 0.1 × 10⁻⁶ m

or

a₂ = 1.6 micron

Now,

the change from 0.1 micron to 1.6 micron took place in 10 days

therefore, the rate at which the crack is growing =

or

average rate of change of crack = 0.16 micron per day

energy can cross the boundaries of a closed system in the form of heat and mass

explanation:

the equation above shows how temperature f, measured in degrees fahrenheit, relates to a temperature c, measured in degrees celsius. based on the equation, which of the following must be true?

a temperature increase of 1 degree fahrenheit is equivalent to a temperature increase of

5

9

degree celsius.

a temperature increase of 1 degree celsius is equivalent to a temperature increase of 1.8 degrees fahrenheit.

a temperature increase of

5

9

degree fahrenheit is equivalent to a temperature increase of 1 degree celsius.

a) i only

b) ii only

c) iii only

d) i and ii only