THEORY EXAMINATION (SEM–VIII) 2016-17 EXPERIMENTAL STRESS ANALYSIS

SECTION – A

Explain the following (Short Answer Type)

Principal planes are the planes on which shear stress is zero, and only normal stress acts. The stresses acting on these planes are called principal stresses.

A null balancing Wheatstone bridge circuit is used to measure unknown resistance by balancing the bridge so that no current flows through the galvanometer.

The stress optic law states that the difference between principal stresses in a photoelastic material is proportional to the fringe order observed.

Strain gauge calibration is done by applying known loads and measuring the corresponding strain output to ensure accuracy.

Photoelastic materials should be transparent, isotropic, sensitive to stress, and stable under temperature changes.

Dark and light fields in a circular polariscope are obtained by adjusting polarizer and analyzer positions.

Non-destructive testing (NDT) methods include ultrasonic testing, radiography, magnetic particle testing, and dye penetration testing.

A stress gauge is a device used to measure stress in materials by detecting strain.

Three-dimensional photoelasticity studies stress distribution in thick models, while two-dimensional photoelasticity is used for thin models.

Isochromatic fringe patterns represent lines of constant principal stress difference in photoelastic analysis.

Questions (Section A)

What are principal stresses?

What is a Wheatstone bridge circuit?

Define stress optic law.

What are NDT methods?

What is an isochromatic fringe?

SECTION – B

Attempt any five (Long Answer Type)

The Wheatstone bridge circuit measures resistance changes caused by strain gauges. The output voltage changes based on resistance variation.

An acoustical strain gauge measures strain by detecting changes in sound wave frequency in a stretched wire.

Elastic strain energy is the energy stored in a material due to deformation, while complementary strain energy represents energy released during unloading.

Strain compatibility equations ensure continuity of deformation in a structure under load.

Strain rosettes consist of multiple strain gauges arranged to measure strain in different directions. They help determine principal stresses.

Expressions for maximum and minimum stresses can be derived using Mohr’s circle concepts.

Sensitivity of strain gauge circuits depends on gauge factor, current, and resistance.

Questions (Section B)

Explain Wheatstone bridge operation.

What is an acoustical strain gauge?

Define strain compatibility equations.

What are strain rosettes?

Derive principal stress equations.

SECTION – C

Attempt any two (Detailed Explanation)

Separation techniques in photoelasticity are used to separate principal stresses. Methods include shear difference and shear stress integration techniques.

Stress freezing technique in three-dimensional photoelasticity involves heating the model, applying load, and cooling to freeze stress patterns.

Ultrasonic testing uses high-frequency sound waves to detect internal defects in materials. Radiography uses X-rays or gamma rays for internal inspection.

Isoclinics represent principal stress directions, while isochromatics represent stress magnitude differences. Compensation techniques help improve measurement accuracy.

Questions (Section C)

What is stress freezing technique?

Explain ultrasonic testing.

What are isoclinics and isochromatics?