Strength of materials important interview questions

 

Definition. 

the strength of a material is its ability to withstand an applied load without failure or plastic deformation. The field of strength of materials deals with forces and deformations that result from their acting on a material.

1) What is stress

Stress is defined as the intensity of force that acts per unit area.

  stress [σ] = F/A

2) What is strain?

Strain is defined as the ratio of change in dimension to the original dimension.

 strain [ε] = Δl/l

3) What are the different kinds of stresses.

There are three kinds of stresses - Normal stress, Shear stress, and Volumetric stress.

Normal stress [σ] - Normal stress occurs when a force acts perpendicular to the surface area.

              Normal stress [σ] = F/A

 

Shear stress [τ] - Shear stress occurs when a force acts parallel to the surface area.

                 Shear stress [τ] = F/A

 

Volumetric stress [σv] - Volumetric stress occurs when a force acts such that it create in increase volume.

4) What are the different kinds of strains?

There are three kinds of strains. Linear strain, Shear strain, and Volumetric strain.

Linear strain [ε] - Linear strain is defined as the ratio of change in dimension to original dimension.

                 Linear strain [ε] = Δl/l

 

Shear strain [Φ] - Shear strain is defined as the ratio of change in shear dimension to the original dimension.

                  Shear strain [φ] = Δx/l

 

Volumetric strain [εv] - Volumetric strain is defined as the ratio of change in volume to the original volume.

              Volumetric strain [εv] = Δv/v

 

5) What is Stress-Strain curve?

Stress-Strain curve is a graph that shows the relation between stress and strain for a material. Stress-Strain curve is drawn on the stress-Strain graph which has Stress on X axis and Strain on Y axis.

6) What is Hooke's law?

Hooke's law states that for relatively small deformations of objects, the force required to create the deformation is directly proportional to the size of deformation.

7) What is Poisson's ratio?

Poisson's ratio [ν] is defined as the ratio of lateral strain to longitudinal strain.

Formula

Poisson's ratio [ν] = εlat/εlong

8) What is Young's modulas?

Young's modulus [E] is a measure of stiffness of an object, and is defined as the ratio of longitudinal stress to strain.

Young's modulus [E] = Stress [σ] / Strain [ε]

9) What is Rigidity modulus?

Rigidity modulus [G] is defined as the ratio of shear stress to shear strain.

Rigidity modulus [G] = Shear stress [τ] / Shear strain [γ]

 

10) What is the Bulk modulas?

Bulk modulus [G] is a measure of resistance of a body to external pressure. It is defined as the ratio of applied pressure to the decrease in volume (volumetric strain).

Bulk modulus [G] = Pressure [p] /Volumetric strain [εv]

 

11) What are shafts?

Shafts are mechanical components used for transmitting power through their rotational motion. Shafts are usually circular is in cross-section, and are subjected to torsional shear stresses within this cross-section.

11) How do you measure the strength of shafts?

Strength of shafts are measured by the maximum torque or power transmitted by the shaft.

12) How do you define the power of shafts?

Power of shaft is defined as the rotational work done per second. Rotational power is the product of torque and angular velocity.

13) What is torsional rigidity?

The minimum force required to deform a shaft by twisting through a nunit dimension is called torsional rigidity.

14) What is temperature stress?

An object undergoes a change in length when it is heated. If this length is restrained, then stress is induced in the object. This is known as temperature induced stress.

15) What is temperature coefficient of expansion?

Coefficient of Expansion [α] - is defined as the change in length in an object of unit length when heated by a temperature difference of 1 unit

16) What are different types of beams?

There are six different kinds of beams.

Cantilever beams, Simply supported beams, Overhanging beams, Continous beams, Fixed ended beams, and Cantilever - simply supported beams.

17) What are different kinds of loads that can act on a beam?

The different kinds of loads that can act on beams are - Point load, Uniformly distributed load [UDL], and Uniformly varying load [UVL]

18) What are different kinds of supports that can act on a beam?

The different kinds of supports that can act on beams are - Hinged support, Roller supports, and Fixed supports.

19) What is Shear Force Diagram (SFD)?

Shear force is an internal force that is induced in a beam when loads are applied to that beam. Shear force is defined as the algebraic sum of loads to the left or right of a point such that addition of these forces restores vertical equilibrium.

A Shear Fore Diagram (SFD) is a diagram that shows the variation in shear force along the length of a beam.

20) What is Bending Moment Diagram (BMD)?

Bending moment is an internal force that is induced in a beam when loads are applied to that beam. Bending moment is defined as the sum of all moments due to external forces at one side of a section of beam. Bending moment at a point, say A, is determined by multipling the external force with the distance between point A and the point at which the force is acting.

A Bending Moment Diagram (BMD) is a diagram that shows the variation in bending moment along the length of a beam.

21) What is the Point of Contraflexure?

Point of Contraflexure is the point in a bending beam where the bending moment is zero, i.e. it the point where the bending moment changes its sign from positive to negative or vice versa.

In a bending moment diagram, the point of Contraflexure is the point at which the bending moment curve intersects with the zero line.

22) What is the Point of Maximum Bending Moment?

Point of maximum bending moment is the point in a shear force diagram where the shear force curve crosses over the zero line. The value of the bending moment is maximum at this point.

23) What is Macaulay's method?

Macaulay's method is a method to find the deflections in a beam that is subject to point loads and discontinuous loads.

24) How are cylinders classified?

For the purposes for analysing the strength of cylinders - cylinders are broadly classified and thin cylinders and thick cylinders.

25) What are the different kinds of stress that act on cylinders?

There are two kinds of stresses that act on cylinders - circumferential stresses and longitudional stresses.

26) How are spheres classified?

For the purposes for analysing the strength of spheres - spheres are broadly classified and thin cylinders and thick cylinders.

27) What are the different kinds of stress that act on spheres?

Spheres are subjected to circumferential stress.

28) How do you define the efficiency of joints in cylinders?

Efficiency of joints is defined as the ratio of theoritical stress to actual stress.

Efficiency [η] = theoritical stress /actual stress

29) What are different kinds of springs?

There are three different kinds of springs.

1. Closed coil helical springs - Helical springs, in which wire is wrapped in a coil, are the most common springs. Closed coil helical springs can be designed to push, pull, or carry loads.

Equivalent springs - Equvalent springs are springs that replace combinations of springs - which can be springs in parallel, or springs in series.

Laminated springs - Laminated springs are semi elliptical springs, also known as leaf springs.

2. What are different kinds of loads that act on helical springs?

A closed coil helical spring can be subjected to two kinds of loads - Axial loads and Axial twists.

30) What are equivalent springs?

Equivalent springs are springs that replace combination springs. There are two kinds of combination springs - springs in series, and springs in parallel.