Welded, Riveted and Bolted Joints MCQ Quiz - Objective Question with Answer for Welded, Riveted and Bolted Joints - Download Free PDF

Explanation:

The Motion of a Nut on a Threaded Bolt

• The motion of a nut on a threaded bolt is classified as helical motion. This type of motion occurs when an object moves in a helical path, which is a combination of rotational and translational motion. In this case, the nut exhibits rotational motion about the axis of the bolt while simultaneously moving linearly along the axis due to the interaction of the threads.
• The helical motion of the nut on a threaded bolt is governed by the geometry of the threads. Threads are helical grooves cut into the surface of the bolt and the corresponding internal surface of the nut. When the nut is rotated about the bolt's axis, the inclined surface of the threads causes the nut to move linearly along the axis of the bolt. The pitch of the thread determines the amount of linear displacement for each revolution of the nut.

Key Characteristics:

• The motion is a combination of rotation (about the bolt's axis) and translation (along the bolt's axis).
• The pitch of the thread, defined as the distance the nut advances along the axis in one complete revolution, plays a crucial role in determining the nature of the motion.

Applications: The helical motion of a nut on a threaded bolt is widely used in various engineering and industrial applications, including:

• Fastening: Threaded joints are commonly used to fasten components together in mechanical assemblies.
• Linear actuation: Lead screws and ball screws, which rely on helical motion, are used in applications requiring precise linear motion, such as CNC machines and jacks.
• Adjustment mechanisms: Threaded components are used in adjustable mechanisms, such as micrometers and telescopic devices.

Explanation:

Tearing Efficiency of a Riveted Joint

• Tearing efficiency of a riveted joint refers to the ratio of the strength of the joint in tearing to the strength of the uncut plate. It is a measure of how effectively the riveted joint resists tearing under a load compared to the original plate without rivet holes. This efficiency is an important factor in the design and analysis of riveted joints in engineering structures.

The tearing efficiency (η_t) is given by the formula:

η_t = (p - d) / p

Where:

• p = Pitch of the rivet, which is the distance between the centers of two consecutive rivet holes.
• d = Diameter of the rivet hole.

The formula indicates that the tearing efficiency depends on the ratio of the rivet hole diameter to the pitch of the rivet.

Calculation:

Given:

• Ratio of rivet hole diameter to pitch, d/p = 0.25

From the formula for tearing efficiency:

η_t = (p - d) / p

Substitute d = 0.25p into the equation:

η_t = (p - 0.25p) / p

Simplify:

η_t = (1 - 0.25)

η_t = 0.75

Concept:

In a riveted joint, the tensile resistance of the plate is determined based on the net cross-sectional area left between rivet holes.

Net area between two rivets =

Given:

= pitch of rivets (mm)

= diameter of rivet hole (mm)

= thickness of plate (mm)

= permissible tensile stress of plate material (N/mm²)

Calculation:

Concept:

The efficiency of a riveted joint is the ratio of the strength of the joint (minimum of tearing, shearing, or crushing strength) to the strength of the solid plate without holes.

Given:

Plate thickness, t = 10 mm

Rivet diameter, d = 20 mm

Pitch of rivets, p = 50 mm

Permissible tensile stress in plate = 150 MPa

Permissible shear stress in rivet = 100 MPa

Permissible crushing stress in rivet = 200 MPa

π = 3.14

Calculation:

Tearing strength of plate,

Shearing strength of rivet,

Crushing strength of rivet,

Strength of joint is minimum of tearing, shearing and crushing:

Strength of solid plate (without rivet hole),

Efficiency of the joint,

Concept:

For fillet welds subjected to torsion, the torque capacity is given by:

Where, is the permissible shear stress, is the weld leg size, and is the length of the weld.

Calculation:

Given:

Permissible shear stress, τ = 90 MPa

Weld size, a = 10 mm

Length of weld, b = 1 m = 1000 mm

Substitute in the formula:

Convert to kN-m:

Now express the answer in the form given in options:

The closest value to 636.4 kN-m is 150√2 kN-m

Explanation:

Explanation:

Function of a washer:

• A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a screw or nut. 
• Washers are used to distribute the clamping pressure over a larger area and prevent surface damage. They also provide an increased bearing surface for bolt heads and nuts.

Types of Washers:

Figure: Lock Washer

A rivet is a permanent mechanical joint which are broadly used to joint structure, ships, barrels etc. These joints are widely used in ship and boiler industries to join the structure member.

The general nomenclature of rivet is given as follows

Types of Rivet heads:

Concept:

Eccentric Loading of Riveted Joints:

• An eccentrically loaded joint is one in which line of application of load does not pass through centre of gravity (c.g) of rivets.
• It passes away from c.g axis.
• This has two effects, primary/direct load and secondary load.

Direct Load:

• This load acts parallel to the load acting and vertically downwards.
• The magnitude for the direct load is \(\rm P'=\frac{Load\;acting}{No.\;of\;rivets}\)
• It is represented by P'.

Secondary load:

• It acts perpendicular to the line joining the centre of gravity of rivets assembly to individual rivets.
• The direction of the secondary load is the same as given by external load i.e. the moment produced due to external load is clockwise so the secondary load will also be clockwise.
• The magnitude for the secondary load is for rivet 1 and similarly for other rivets by changing r₂, r₃ and r₄ in the numerator.

Now, both the load are added vectorially.

Calculation:

Given:

Direct load and secondary load diagram is given above.

The resultant of two forces acting at an angle is given by \(R=\sqrt{(P')^2\;+\;(P")^2\;+\;2P'P"cos\;\theta}\)

The angle made by primary shear force causing direct shear and secondary force causing bending stress is minimum for Q and R, ∴ these two rivets are heavily stressed.

Explanation:

Pitch (p): It is the distance from the center of one rivet to the center of the next rivet measured parallel to the seam.

Back pitch (p_b): It is the perpendicular distance between the center lines of the successive rows.

Diagonal pitch (p_d): It is the distance between the centers of the rivets in adjacent rows of zig-zag riveted joint.

Explanation:

A fillet weld joins two surfaces at an approximate right angle to each other. There are several types of fillet weld:

• Full fillet weld is a weld where the size of the weld is the same as the thickness of the thinner object joined together.
• Staggered intermittent fillet weld refers to two lines of intermittent welding on a joint. An example is a tee joint (see below) where the fillet increments that are in one line are staggered in comparison to the other line.
• Chain Intermittent fillet weld refers to two lines of intermittent fillet welds in a lap joint or T where the welds in one line are approximately opposite those in the other line.

Additional Information Other terms associated with fillet welds include:

• Boxing refers to the continuation of a fillet weld around a corner of a member. It is an extension of the principal weld.
• Convexity: Refers to the maximum perpendicular distance from the face of a convex fillet weld to a line joining the weld toes.

Groove Welds:

• The second most popular type of weld is the groove weld. There are seven basic types of groove welds, which are shown in figure.
• The groove weld refers to beads that are deposited in a groove between two members to be joined.

Surfacing Weld:

• These are welds composed of one or more strings or weave beads deposited on an unbroken surface to obtain desired properties or dimensions.
• This type of weld is used to build up surfaces or replace metal on worn surfaces. It is also used with square butt joints.

Plug Weld:

• Plug welds are circular welds made through one member of a lap or tee joint joining that member to the other.
• The weld may or may not be made through a hole in the first member; if a hole is used, the walls may or may not be parallel and the hole may be partially or completely filled with weld metal.

Slot Weld:

• This is a weld made in an elongated hole in one member of a lap or tee joint joining that member to the surface of the other member that is exposed through the hole.
• This hole may be open at one end and may be partially or completely filled with weld metal

Flash Weld:

• Flash welding is referred to as a resistance welding process where fusion is produced over the entire abutting surface.
• Heat is created by the resistance to the current flow between two surfaces and by the application of pressure after heating is mostly complete.
• Flashing is accompanied by the expulsion of metal from the joint.

Seam Weld:

• A weld made by arc seam or resistance seam welding where the welding process is not specified.
• This term infers resistance seam welding.

Spot Weld:

• A spot weld is a weld made by arc spot or resistance spot welding where the welding process is not specified.
• This term infers a resistance spot weld.

Upset Weld:

• An upset weld is a resistance welding process where fusion occurs progressively along a joint of over the entire abutting surface.
• The application of pressure before heating is required and occurs during the heating period.

Explanation:

The strength of a rivet joint

• The strength of a rivet joint is measured by its efficiency.
• The efficiency of a joint is defined as the ratio between the strength of a riveted joint to the strength of an un-rivetted joint or a solid plate.
• The efficiency of the riveted joint not only depends upon the size and the strength of the individual rivets but also on the overall arrangement and the type of joints.

Tension: 

Tearing resistance or pull required to tear off the plate per pitch length.

Pt = σt × (p - d) × t

Shear: 

Shearing resistance or pull required to shear off the rivet per pitch length.

 (single shear)

 (double shear)

Crushing: 

Crushing resistance or pull required to crush the rivet per pitch length.

P_c = n × σ_c × d × t

Strength of the riveted joint: Least of Pt, Ps and Pc

Strength of the un-riveted or solid plate per pitch length: P = σt × p × t

The joint efficiency is:

Concept:

Efficiency of rivet:

The efficiency of the rivet joint is defined as the ratio of the strength of rivet joint to the strength of the un-riveted or solid plate.

The efficiency of the riveted joint,

Where Ps = Shearing resistance, Pt = Tearing resistance, Pc = Crushing resistance, P = Strength of plate.

Calculation:

Given:

P_s = 100 N, P_t = 120 N, P_c = 150 N and P = 200 N.

The lowest among P_s, P_t and P_c is 100 N.

Explanation:

Diamond rivetted:

• In diamond rivetting, rivets are arranged in a diamond pattern and decrease gradually from the inner row to the outer row.
• All the rivets are arranged symmetrically about the centre line of the plate
• In diamond riveting, there is a saving of material, and efficiency is more. Diamond riveting is used in bridge trusses generally

Additional Information

Chain Rivet: 

• When the rivets in the various rows are opposite to each other, then the joint is said to be chain riveted. 

Zig - Zag rivetted:

• If the rivets in the adjacent rows are staggered in such a way that every rivet is in the middle of the two rivets of the opposite row as shown in fig then the joint is said to be zig-zag riveted.

Explanation:

Transverse fillet weld:

The transverse fillet weld is designed for tensile strength  

In design, a simple procedure is used assuming that entire load P acts as a shear force on the throat area, which is the smallest area of the cross-section in a fillet weld.

Important Points

• In order to simplify the design of fillet welds many times, shear failure is used as a failure criterion.