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Difficulty: Very hardTypes of Stress and Strain

A marine vessel is cruising forward at a constant speed. Its propulsion system uses an internal engine to drive a solid steel shaft, which extends out the rear of the hull to turn the propeller. A heavy-duty thrust bearing inside the ship absorbs the forward driving force generated by the propeller. During this forward motion, what primary combination of internal stresses is the section of the shaft located between the propeller and the thrust bearing experiencing?

  1. Torsion and compressionAnswer
  2. B
    Torsion and tension
  3. C
    Shear and tension
  4. D
    Shear and compression

Answer

Torsion and compression
The correct answer is torsion and compression because the engine twists the shaft to rotate the propeller (creating torsion), and the forward thrust generated by the propeller pushes the shaft into the internal thrust bearing (creating compression).

Step-by-Step Solution

1
Identify the stress caused by power transmission.
The engine applies a rotational force to turn the propeller against water resistance, resulting in twisting, which is torsional stress.
Rotational power transmission through a solid shaft always induces torsion.
2
Determine the direction of the thrust force.
To move the ship forward, the propeller pushes water backward. According to Newton's Third Law, the water exerts an equal forward reaction force on the propeller.
Thrust requires an opposing reaction force to generate motion.
3
Analyze how the thrust force affects the shaft.
The forward reaction force on the propeller pushes the shaft forward into the thrust bearing inside the hull. This squeezes the section of the shaft between them, creating compressive stress.
A structural member being squeezed inward from opposite ends is under compression.

Key Concept

Internal stresses induced by combined rotational and axial loads.
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Topics

Types of Stress and Strain

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