riveted joints
TRANSCRIPT
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Riveted Joints
ME2140 Machine Elements and Innovative DesignDr Hans GrayDr Udaya KahangamageDepartment of Mechanical Engineering
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Riveted Joint
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Rivets …
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Applications …
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Applications …
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Heavy Machinery …
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Heavy Machinery – Car Dumper
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Steel Bridges …
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Fourth Bridge - Scotland
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Sydney Harbour Bridge
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Sydney Harbour Bridge
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Sydney Harbour Bridge
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Airplanes
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Airplanes
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Ships
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Buses
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Outline…
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Introduction Advantages of riveted joints Disadvantages of riveted joints Types of rivets & Types of riveted
joints Failure mechanism Strength calculations under static
loads
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Learning Outcomes
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At the end of this section, you should be able to:
Select appropriate joint type for a given application
Design the size of the rivets considering strength requirements
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Introduction
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Riveted joints have been widely employed in various engineering structures, such as ships, boilers, bridges, etc.
The use of riveted joints has considerably been reduced due to the rapid development of welding techniques
Rivets are the main kind of fasteners in light frames and thin sheet shells made of light metals and alloys such as aluminium
Light alloys are difficult to weld
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Rivets
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The material of the rivets must be tough and ductile
Usually made of steel, brass, aluminium or copper
When strength and a fluid tight joint is the main consideration, steel rivets are used
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Types of Rivets
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Riveted Joints
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Riveted Joint – Cross Section
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Advantages of Riveted Joints
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Riveted joints have high resistance against vibrational loads.
Can join difficult to weld parts: Dissimilar metals Thin plates Joints that cannot be subjected to heating
Riveted joints can be dismantled by cutting off the rivet heads.
Quality control is easier
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Disadvantages of Riveted Joints
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Rivet holes weaken the working cross section of the joint.
More metal is required for the joint owing to the necessity of overlapping the joined plates
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Types of Riveted Joints (1)
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Riveted joints may be classified according to:
The purpose for which it is used Strong joints – strength is the prime
requirement Tight strong joints – strength & leak proof
Method of placing joining member (eg. Lap and Butt)
The type of rivets employed (eg. Solid and tubular)
The number of rows of rivets used (eg. Single, double, triple)
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Types of Riveted Joints (2)
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Design Tips
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At least two rivets should be used for each joint to avoid relative turning motion
Avoid placing rivets in constricted areas
Arrange rivets in Zig-zag pattern when using 2 or more rows of rivets
Use equal diameter rivets in a particular joint
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Failure of Riveted Joints (1)
A rivet joint may fail in the following ways:
Shear of the rivets
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Failure of Riveted Joints (2)
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Failure of Riveted Joints (3)
Crushing of the rivets and plates
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Failure of Riveted Joints (4)
Rupture of the plate in the section weakened by the holes
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Tearing of plate at edge Tearing of plate across the rows of rivets
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Strength Calculation under Static Loads
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The method of strength calculation is based on the following assumptions:
The force is uniformly distributed between all elements
There is no friction force between the elements to be joined
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Tearing of plate at edge
This can be avoided by maintaining a margin, m = 1.5d
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Tearing of plate across the rows of rivets
p= ptich of rivets d= diameter of rivet t= thickness of plate σt= permissible tensile
stress for the plate material
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Tearing area per pitch length At= (p-d)t Pull required to tear off plate Pt = At * σt
= (p-d)t*σt
If the applied load P is smaller than Pt no tearing will occur.
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Strength Calculation under Static Loads (2)
Shear strength of rivets
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4
4dn
P
dn
P
areastressShear
rivettheonForce ss
If the joint is lapped by two straps ??
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Strength Calculation under Static Loads (3)
Crushing strength
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ccc ndt
P
areastressCrushing
rivettheonForce
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Strength of a riveted joint
The strength of a joint is the maximum force, which it can transmit, without causing it to fail
Joint can fail by (i) tearing off the plate (Pt)(ii) shearing off the rivet (Ps) & (iii) crushing off the rivet (Pc)
The strength of a riveted joint is the smallest of
Pt, Ps, and Pc
For continuous joints as in the case of a boiler, the calculations are done for a pitch.
For small joints the calculations are done for the entire joint
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Efficiency of Riveted Joints (1)
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The ratio of the strength of the riveted joint to the strength of the plate section
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Efficiency of Riveted Joints (2)
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tpt cst P and P ,P ofleast
where, p = pitch length, t = thickness of plates, σt = tensile stress of plates
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Example
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A single riveted lap joint is made of 15mm thick plates with 20mm diameter rivets. Determine the strength of the joint, if the pitch of rivets is 60mm. Take [σt]= 120MPa, τ = 90MPa, and [σc]= 160MPa.
What is the efficiency of this riveted joint
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Eccentrically loaded riveted joints
A = Cross-section area of each rivet x1, x2, x3 etc. = Distance of rivets from OY
y1, y2, y3 etc. = Distance of rivets from OX
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An
AxAxx
...21
_
An
AyAyy
...21
_
cos222 FPFPR ss
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Average Ratios and Dimensions of Riveted Joints
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