### 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:

**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: = 420 MPa and = 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.**

= *88.95 MPa**Öm*

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