Mechanical Engineering: Stress Types and Fasteners
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Questions and Answers

What type of stress elongates fibers?

Tensile Stress

What type of stress shortens fibers?

Compressive Stress

What type of stress occurs when a force makes adjacent planes slide past each other?

Shear Stress

What is the definition of strain?

<p>Deformation per unit length</p> Signup and view all the answers

A thin cylinder has a ratio greater than 0.7.

<p>False (B)</p> Signup and view all the answers

Where are stress concentrations found?

<p>Holes, scratches, cracks</p> Signup and view all the answers

What is the purpose of threads?

<p>To hold machine parts together using threaded bolts and screws</p> Signup and view all the answers

Which of the following are common types of threads for screws?

<p>Sellers (B), V-thread (C), Whitworth (D)</p> Signup and view all the answers

What does 'P' stand for in terms of threads, and what does it represent?

<p>Pitch, axial distance between corresponding adjacent planes</p> Signup and view all the answers

What is the main design objective for bolts?

<p>To ensure safe external tensile load application</p> Signup and view all the answers

What is the purpose of initial tension and tightening torque?

<p>To induce a load on the bolt during tightening</p> Signup and view all the answers

What is the main function of a power screw?

<p>To convert angular motion into linear motion with friction considerations</p> Signup and view all the answers

What are the three main classifications of power screws?

<p>Square thread (B), Buttress thread (C), Acme thread (D)</p> Signup and view all the answers

What is the main advantage of Acme threads?

<p>Overcoming thread friction</p> Signup and view all the answers

What are the main types of threads used in the Unified National Thread System?

<p>8UN (A), UNC (B), UNF (C), UNEF (D)</p> Signup and view all the answers

What does UNC stand for, and what is it used for?

<p>Unified National Coarse Series, for general-purpose applications</p> Signup and view all the answers

Flashcards

Tensile Stress

The force applied to an object that causes it to stretch or elongate along its axis.

Compressive Stress

The force applied to an object that causes it to shorten or compress along its axis.

Shear Stress

The force applied to an object that causes it to deform along parallel planes.

Strain

The amount of deformation that occurs in an object when subjected to stress, expressed as the change in length per unit length.

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Thin Cylinder

A type of cylinder where the diameter is significantly smaller than the length, resulting in a ratio of diameter to length less than 0.7.

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Stress Concentrations

Areas in a material where stress is concentrated, often found at the edges of holes, scratches, or cracks.

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Threads

Threaded fasteners like bolts and screws that are used to join machine parts together by creating a strong connection.

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Common type of threads for screw

V-shaped threads commonly found in bolts and screws, including Sellers, Whitworth, and others.

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P, Pitch

The axial distance between two adjacent threads on a screw or bolt. It's measured along the axis of the screw.

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L, Lead

The axial distance a screw or bolt travels in one complete revolution. It's the distance the screw moves forward or backward in one turn.

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Design of Bolts

The design of bolts must ensure that they can safely withstand the external tensile force applied to them.

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Initial Tension and Tightening Torque

The load induced in a bolt during tightening, created by tensioning the bolt.

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Power Screws

A device that converts rotational motion into linear motion, using threads to create a mechanical advantage.

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Classification of Power Screws

Common types of power screw threads include Square thread, Acme thread, and Buttress thread, each with different strengths and applications.

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Acme Thread

A type of power screw thread with a trapezoidal shape, often used in applications requiring high load-carrying capacity.

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Types of Threads

Different standards for screw threads based on size and pitch, including UNC, UNF, UNEF, and 8UN.

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Unified National Coarse Series, UNC

A standard thread series used for general applications, often found in everyday bolts and screws.

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Unified National Fine Series, UNF

A standard thread series used for applications where a finer thread is needed, such as in automobiles and aircrafts.

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Unified National Extra Fine, UNEF

A high-precision thread series used in aeronautical applications where extreme accuracy and strength are required.

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Unified 8-Thread Series, 8UN

A standard thread series featuring 8 threads per inch, commonly used for bolts in high-pressure flange connections.

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Study Notes

Stress Types

  • Tensile Stress: Force elongates fibers
  • Compressive Stress: Force shortens fibers
  • Shear Stress: Force makes adjacent planes move

Deformation

  • Strain: Deformation per unit length

Cylinders

  • Thin Cylinder: A type of cylinder, with a thickness-to-radius ratio less than 0.7

Stress Concentrations

  • Stress concentrations occur at areas like holes, scratches, and cracks.

Mechanical Fasteners

  • Threads: Used in threaded bolts and screws to hold machine parts together.
  • Common Thread Types: V-thread, Sellers, Whitworth
  • Pitch (P): Axial distance between corresponding, adjacent planes.
  • Lead (L): Axial distance in one revolution.

Bolt Design

  • Bolt Design: Aim for safe external tensile stress.
  • Initial Tension and Tightening Torque: Force used to induce tight fastening.

Power Screws

  • Power Screws: A device that uses friction to convert rotational motion into linear motion or vice versa.

Power Screw Classifications

  • Screw classifications: Square thread, Acme thread, Buttress thread

Acme Thread

  • Acme Thread: Type of thread that overcomes thread friction.

Thread Series

  • Types of Threads: UNC, UNF, UNEF, 8UN
  • UNC (Unified National Coarse Series): General-purpose screw thread.
  • UNF (Unified National Fine Series): For use in automobiles and aircraft.
  • UNEF (Unified National Extra Fine): For aeronautical applications.
  • 8UN (Unified 8-Thread Series): For bolts and high-pressure flanges.

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Description

This quiz explores various types of stresses, including tensile, compressive, and shear stress, along with strain and mechanical fastener concepts. It also covers the characteristics of thin cylinders and the principles of bolt design and power screws. Test your knowledge on these fundamental mechanical engineering principles!

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