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Chapter: Mechanical - Design of Machine Elements - Design of Temporary and Permanent Joints

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Important Answers: Design of Temporary and Permanent Joints

Mechanical - Design of Machine Elements - Design of Temporary and Permanent Joints


1.   Define self locking screws.

 

If the friction angle is greater that the helix angle of the power screw, the torque required lowering the load will be positive, indicating that an effort is applied to lower the load. This type of screw is known as self locking screw. This efficiency of the self locking screw is less than 50%.

 

2.   What is meant by single start and double start thread?

 

Single-start means that there is only one ”ridge” wrapped around the cylinder of the screw’s body. Each time that the screw’s body rotates one turn (3600)’ it has advanced axially by the one pitch distance. “double-start”that there is are two ”ridge” wrapped around the cylinder of the screw’s body. Each time that the screw’s body rotates one turn (3600)’ it has advanced axially by the two pitch distance.

Classify the rivet heads.

 

Rivet heads for general purposes (below 12 mm diameter) according to IS: 2155 - 1982 (Reaffifmed 1996)

 

Rivet heads for general purposes (below 12 mm to 48 mm diameter) according to IS: 1929 - 1982 (Reaffifmed 1996)

 

Rivet heads for boiler work (below 12 mm to48 mm diameter) according to IS: 1928 - 1961 (Reaffifmed 1996)

 

What are the assumptions made in the design of welded joints?

 

It is assumed that the tensile stress is distributed uniformly across the section of the butt weld.

 

It is assumed that the shear stress in a parallel fillet weld is uniformly distributed along the entire lengthof the weld.

 

Stress situation in a fillet weld is complicated because of bending action of the force.

 

 

 

List the advantages and disadvantages of threaded fasteners.

Advantage:

 

Screwed joints are highly reliable in operation

 

Screwed joints are convenient to assemble and dis assemble Disadvantage:

 

The stress concentration in the threaded portions which are vulnerable points under variable load conditions.

 

What are the initial stresses induced due to screwing up forces?

Tensile stress due to stretching of the bolt

Compression or bearing stresses on the thread

Shearing stresses across threads

Bending stress

 

 

 

What is bolt of uniform strength?

A bolt of uniform strength has equal strength at the thread and shank position.

 

How are the welding process classified?

 

Forge welding

Fusion welding

Electric resistance welding

 

Define the theory of bonded joints.

 

A rivet is a short cylindrical bar with a head integral to it. The cylindrical portion of the rivet is called shank or body and lower portion of the shank is known as tail.The riveted joints are widely used for jointing light metals.

 

 

Write the advantages of welded joints over the riveted joints.

 

It is assumed that the tensile stress is distributed uniformly across the section of the butt weld.

 

It is assumed that the shear stress in a parallel fillet weld is uniformly distributed along the entire length of the weld.

 

Stress situation in a fillet weld is complicated because of bending action of the force.

 

What is a stud?

 

A stud is a bolt in which the head is replaced by a threaded end. It passes through one of the parts to be connected and is crewed into the other part.

 

12. How is bolt designated?

A bolt is designated by a letter M followed by nominal diameter and pitch in mm.

 

13.State the advantages of threaded joints?

 

High clamping

Small tightening force requirement

 

Easy manufacturing

 

Simple design

 

14.How is welding classified?

Forge welding

Electric resistance welding

Fusion welding

 

15.Name the possible modes of failure of riveting joint.

Crushing of rivets

Shear of rivets

Tearing of the plate at the edge

Tearing of the plate between rivets.

 

 

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