Question

7. Draw one stress strain diagram for ductile material and indicate the elastic, plastic region, toughness and resilience?

-Explain the mechanism of necking in details?

9. What is the unite for stress and strain?

10. What are the mechanical requirements to design a material for high temperature applications?

Answer 1

7 Q.

MECHANISM OF NECKING ::

Necking is a mode of tensile deformation where large amounts of strain occurs in a small region of the material.

As the resultant strains in the necking are large Necking results decrease in cross-sectional area. Necking occurs with ductile materials.

Necking results from the instability during tensile deformation when a materials cross-sectional area decreases by a greater proportion.

As deformation proceeds the instability causes strain to continue concentrating in the neck until the material either ruptures (or) fracture (or) break the material.

9 Q.

STRESS : Force / Area.

​​​​​Units for STRESS are = Newton / metre ^2.

Stress = N/m^2. (or) N/mm^2. (or) MPA (or) GPA.

STRAIN : Change in length/ Original length.

Units of STRAIN :: Strain has no units.

10 Q.

MECHANICAL REQUIREMENTS TO DESIGN A MATERIAL FOR HIGHER TEMPERATURE APPLICATION::

At high temperatures the strength of metal decreases.

1.One of the most important material property that is used in design at high temperatures application is CREEP STRENGTH.

Creep strength of a material is to move slowly or deform permanently under the influence of continuous mechanical Stresses.

Creep is more severe in materials which are subjected to heat for long periods of time and generally increases as they reach their melting point.

2. Fatigue Strength.

Fatigue is the weakening of a material caused by cyclic loading that results in increase of structural damage and the growth of cracks.

Fatigue life decreases as temperature increases.

3. Abrasive and wear conditions to be checked.

4. Type and magnitude of applied forces.

5. Frequency of temperature cycles.