# GATE MT 2018 Q28. A glass fibre of 5 micron diameter is subjected to a tensile stress of 20 MPa. The surface energy and elastic modulus of this material are 0.3 Jm^-2 and 70 GPa, respectively. Pick the correct answer based on the information provided above: Note: The glass fibre contains a population of flaws of different lengths.

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Based on Griffith theory σ = (2EΥs/πc)1/2 From which crack length on surface is 33.4 × 10-6 m And crack length inside is 66.8 × 10-6 m But the given crack dia is 5 micron So considering all the options option C is correct.

Based on Griffith theory σ = (2EΥ

_{s}/πc)^{1/2}From which crack length on surface is 33.4 × 10

^{-6 }mAnd crack length inside is 66.8 × 10

^{-6}mBut the given crack dia is 5 micron

So considering all the options option C is correct.

See lessOption C is correct answer

Option C is correct answer

See lessCorrect answer is option C. @Shetty described it best. Thank you.

Correct answer is option C. Sanjay Madishetty described it best. Thank you.

See lessWhy the option B is wrong? Why can't it undergo plastic deformation.

Why the option B is wrong?

Why can’t it undergo plastic deformation.

See lessnote that 20 MPa is applied tensile stress, not yield strength, then how can we say that it will go under elastic deformation only and not plastic.

note that 20 MPa is applied tensile stress, not yield strength, then how can we say that it will go under elastic deformation only and not plastic.

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