(SEM V) THEORY EXAMINATION 2020-21 STRENGTH OF MATERIAL

SECTION A (Any 2 Questions Explained Briefly)
 

What is the difference between bending moment and twisting moment?
Bending moment is the moment that causes a beam to bend about an axis due to transverse loads acting on it. Twisting moment, also known as torque, causes a shaft or member to twist about its longitudinal axis due to applied rotational forces. Bending moment produces normal stresses, whereas twisting moment produces shear stresses.
 

Why spherical containers are preferred over cylindrical containers for storing gases?
Spherical containers are preferred because the stress developed in a spherical shell is uniform and lower compared to a cylindrical shell for the same internal pressure. This makes spherical containers stronger and safer, requiring less material thickness to store gases at high pressure.
 

SECTION B (Any 2 Questions Explained)
 

Compare the resistance to torsion of a hollow shaft and a solid shaft of same material, weight, and length.
For shafts of the same material, length, and weight, a hollow shaft offers greater resistance to torsion than a solid shaft. This is because more material in a hollow shaft is distributed farther from the center, increasing the polar moment of inertia. Hence, hollow shafts are more efficient and commonly used in transmission systems.
 

Explain Euler’s buckling theory and derive the expression for crippling load for a column with both ends fixed.
Euler’s buckling theory applies to long columns subjected to axial compressive loads. It assumes the column is perfectly straight, homogeneous, and loaded centrally. For a column with both ends fixed, the effective length is half of the actual length. Using Euler’s formula, the critical or crippling load is obtained as proportional to the flexural rigidity and inversely proportional to the square of effective length. Fixed-end columns can withstand higher loads compared to other end conditions.
 

SECTION C (Any 2 Questions Explained)
 

Explain maximum principal stress theory of failure.
According to the maximum principal stress theory, failure occurs when the maximum principal stress in a material reaches the yield stress in simple tension. This theory is mainly applicable to brittle materials. Graphically, it is represented by a failure envelope where yielding occurs when the principal stress exceeds the allowable limit.

What is shear center? Explain its significance.
Shear center is the point in a cross-section through which the transverse load must pass to produce bending without twisting. If the load does not pass through the shear center, twisting occurs along with bending. Understanding shear center is important in designing unsymmetrical sections such as channels and angles.
 

Most Questions in This PDF Are Related To
 

Most questions in the Strength of Material (KME-502) paper are related to bending and torsion of members, stress and strain relationships, columns and buckling theories, thin and thick cylinders, failure theories, strain energy, springs, curved beams, shear center, and beam deflection analysis. The paper mainly focuses on numerical problem solving and fundamental mechanical behavior of materials.