Material Science: Short answer type questions from AMIE exams

What is the magnitude of maximum stress that exists at the tip of a surface crack having a radius of curvature of 0.264 nm and crack length of 1 µm when a tensile stress of 57 MPa is applied?

779.84 GPa

Hint: {\sigma _m} = 2{\sigma _0}{\left( {\frac{a}{{{\rho _t}}}} \right)^{1/2}}

Define a fatigue life.

Fatigue life: The total number of stress cycles that will cause a fatigue failure at some specified stress amplitude.

Define the endurance ratio.

The ratio of endurance limit for completely reversed flexural stress to the tensile strength is termed as endurance ratio.

What is thermal transformation?

Thermal transformation is heat that during a change of phase is absorbed. This occurs at constant pressure and temperature.

The distance between (111) planes in the FCC crystal structure is 2 A. Find the lattice parameter and atomic diameter.

3464A, 2.45A

A 45 kN force was applied on a Cu-Ni alloy tensile specimen having 12.5 mm diameter and 50 mm gauge length. Determine whether the specimen will undergo necking. Given: {\sigma _{UTS}} = 420 MPa and {\sigma _y} = 250 MPa.

Engineering stress = 366.89 MPa (do yourself), mean stress = (250 + 420)/2 = 335 MPa

As engineering stress is (i) > yield stress and (ii) < UTS and (iii) more than mean stress, there will be plastic deformation and necking.

Steel has a tensile strength of 1.6 GPa. A large tensile piece of such steel has a crack of length 7 mm in the interior and fracture at 0.6 GPa. Calculate its fracture toughness.

K = \sigma \sqrt {\pi a} = 88.95 MPaÖm


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