Riveted Joint MCQ Quiz in मराठी - Objective Question with Answer for Riveted Joint - मोफत PDF डाउनलोड करा

Concept:

The efficiency of riveted joints id defined as the ratio of strength of riveted joint to the strength of unriveted solid plate. The strength of the rivested joint is the lowest value of P_s, P_t and P_c.

Strength of solid plate is given by 

P = ptσ_t

Therefore the efficiency is given by 

η = \(\frac{least \ of \ P_t, P_s \ and \ P_c}{P}\)

(i) Tensile strength of Plate between rivets

Due to the tensile stresses in the main plates, themain plate or cover plates may tear off across a row of rivets as shown in Fig:

Pt is the tensile strength of plate between rivets and is given by

The resistance offered by the plate against tearing is known as tearing resistance

\({P_t} = {A_t}{σ _t} = \left( {p - d} \right)t.{σ _t}\)

(ii) Shear Strength of Rivet

Shearing of the rivets: The plates which are connected by the rivets exert tensile stress on

the rivets, and if the rivets are unable to resist the stress, they are sheared off.

The resistance offered by a rivet to be sheared off is known as shearing resistance or shearing strength or shearing value of the rivet

d = Diameter of the rivet hole, τ = Safe permissible shear stress for the rivet material, and n = Number of rivets per pitch length

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

\({P_s} = n \times \frac{\pi }{4}{d^2} \times \tau \;\;\;\;\;\;\left\{ {{\rm{Single\;Shear}}} \right\}\)

\({P_s} = 2n \times \frac{\pi }{4}{d^2} \times \tau \;\;\;\;\;\;\left\{ {{\rm{Double\;Shear}}} \right\}\)

So, the strength equation for the rivet in the double-riveted joints is given by:

\({P_s} = 2 \times \frac{\pi }{4}{d^2} \times \tau \Rightarrow {P_s} = \frac{\pi }{2}{d^2}\tau \)

(iii) Crushing Strength Pc of the plate is given by 

P_c = d x t x σ_c x n

d = Diameter of the rivet, t= thickness of the plate, σ_c = compressive strength of the plate.

Explanation:

Pitch:

• The pitch of the rivet is defined as the distance between the centre of one rivet to the centre of the adjacent rivet in the same row.

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

Back Pitch:

•  It is the perpendicular distance between the centre lines of the successive rows as shown in Figure.

Transverse pitch (pb):

• Transverse pitch also called back pitch or row pitch.
• It is the distance between two consecutive rows of the rivet on the same plate.

Margin/Edge distance:

• The margin is the distance between the edge of the plate to the centre line of the rivets in the nearest row. 

Mistake Points Back pitch is the perpendicular distance between the centre lines of the successive rows. As the keyword perpendicular is not mentioned in the question. Hence the most appropriate answer of this question is diagonal pitch. This is the official question of UPRVUNL AE ME 2021 Official Paper (Held on 5 July 2021), and UPRVUNL has considered the diagonal pitch as the correct answer.

Explanation:

Riveted joint: 

A rivet consists of a cylindrical shank with a head at one end.

• This head is formed on the shank by an upsetting process. In rivet terminology, the closing head is called point
• The cylindrical portion of the rivet is called the shank or body and the lower portion of the shank as a tail.
• The rivets are used for a permanent fastening.
• The rivets joints are widely used for joining light metals.

The terminology of Riveted joints:

Pitch:

• The pitch of the rivet is defined as the distance between the centre of one rivet to the centre of adjacent rivet in the same row.

Margin / Edge distance:

• The margin is the distance between the edge of the plate to the centre line of the rivets in the nearest row. 

Transverse pitch (p_b):

• Transverse pitch also called back pitch or row pitch.
• It is the distance between two consecutive rows of the rivet on the same plate.

Diagonal pitch (p_d):

Diagonal pitch is the distance between the centre of one rivet to the centre of adjacent rivet located in the adjacent row. 

Explanation:

The fillet welds are subjected to tensile stress. The minimum cross-section of the fillet is at the throat. Therefore the failure due to tensile stress occurs at the throat section. Thus the weakest area of the weld is the throat.

Backing ring

• A metal ring used inside a butt-welded joint to reinforce the joint
• It is used to prevent weld metal from entering the pipe at the joint

Fillet welding 

• It is the process of joining two pieces of metal together irrespective of the fact that they are perpendicular or at an angle.
• These welds are commonly referred to as T joints which indicates that there are two pieces of metal perpendicular to each other

Butt welds

• These are the welds in which two pieces of metal to be joined are in the same plane.
• These types of welds require simple preparation and are used with thin sheet metals that can be welded with a single pass

Sleeve welding:

• This type of welding is commonly used for repairing of defective pipelines.
• In this type of welding, two half-sleeves are assembled around the damaged pipe section with a longitudinal butt weld and then a circumferential fillet weld is used to attach the sleeve to the pipe 

Socket Weld

• It is a pipe attachment detail in which a pipe is inserted into a recessed area of a valve or flange.
• This technique is mainly used for small pipe diameters (Small Bore Piping); generally for piping whose nominal diameter is smaller.

The efficiency of the riveted joint is defined as the ratio of the strength of the plate in an unpunched condition.

\(\eta = \frac{{Strength\;of\;riveted\;joint}}{{Strength\;of\;unriveted\;solid\;plate}}\)

As the strength of the riveted joint depends on the tearing strength, shearing strength or crushing strength of the joint, the efficiency can be tearing efficiency, shearing efficiency and crushing efficiency.

• Tearing efficiency: Tearing strength of the riveted joint/Strength of the unriveted solid plate

\(\begin{array}{l} {\eta _t} = \frac{{Tearing\;strength}}{{Strength\;of\;solid\;plate}}\\ {\eta _t} = \frac{{\left( {p - d} \right)t\;{\sigma _t}}}{{{p_t}\;{\sigma _t}}} = \frac{{p - d}}{p} \end{array}\)

• Shearing efficiency: Shearing strength of the riveted joint/Strength of the unriveted solid plate

\({\eta _s} = \frac{\pi }{4}\left( {\frac{{{\sigma _s}}}{{{\sigma _t}}}} \right)\left( {\frac{{{d^2}}}{{pt}}} \right)kn\)

k is effective surface area (For double shear, k = 2), n is number of rivets in a pitch length

• Crushing efficiency: Crushing strength of the riveted joint/Strength of the unriveted solid plate

\(\begin{array}{l} {\eta _c} = \frac{{Crushing\;strength}}{{Strength\;of\;solid\;plate}} = \frac{{ndt\;{\sigma _c}}}{{pt\;{\sigma _t}}} = n\left( {\frac{d}{p}} \right)\left( {\frac{{{\sigma _c}}}{{{\sigma _t}}}} \right)\\ \end{array}\)

Explanation:

Shearing of the rivets: 

• The plates which are connected by the rivets exert tensile stress on the rivets, and if the rivets are unable to resist the stress, they are sheared off.
• The resistance offered by a rivet to be sheared off is known as shearing resistance or shearing strength or shearing value of the rivet.

Single shear is given in the diagram below.

Additional Information

Pitch is the distance between two adjacent rows of rivet parallel to the direction of application of force. The minimum pitch will be 2.5 times the gross diameter.

Minimum pitch should not be less than 2.5 times the nominal diameter of the rivet.

As a thumb rule pitch equal to 3 times the nominal diameter of the rivet is adopted.

Explanation:

Rivet

Rivets are used as fasteners for making permanent joints of two or more pieces of metals.

Rivets are made of mild steel or wrought iron and comprise head, tail, and shank.

The rivet is specified by the diameter of its shank.

Concept:

\({\rm{Primary\;load\;}} = \frac{{load}}{{No.\;of\;rivets}}\)

For secondary load

Pr_com = x (r²₁ + r²₂)

r_com = distance of P from centre of mass of rivets

r₁, r₂ = distance of centre of rivets from their centre of mass

Secondary load = xr₁, xr₂

Calculation:

Primary \( = \frac{6}{2} = 3\;kN\)

Secondary \( = \frac{{6\; \times\; 2.2}}{{\left( {{{0.2}^2}\; +\; {{0.2}^2}} \right)}} \times 0.2 = 33\;kN\)