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1 Teaching Innovation - Entrepreneurial - Global
The Centre for Technology enabled Teaching & Learning , N Y S S, India DTEL(Department for Technology Enhanced Learning)
Department of Mechanical Engineering
V-SEMESTERDesign Of Machine Element
CHAPTER NO.1Design philosophy and
Engineering materials and overview of design and manufacturing
DTEL 2
Syllabus
UNIT –IDefinition of design, it’s need, types, process, failure criteria and manufacturing considerations in design, basis of good design, machining tolerances, mechanical properties, selection of materials, temperature effects on properties of materials and their applications.
DTEL 3
LECTURE 1:- Design philosophy and Engineering materials
Learning ObjectiveBasic concept of design in general.
Concept of machine design and their types.
Factors to be considered in machine design
Important mechanical properties of materials
and its application.
Concept of limits and fits.
DTEL 4
LECTURE 1:- Design philosophy and Engineering materials
Introduction Design is essentially a decision-making process. If we
have a problem, we need to design a solution. In other
words, to design is to formulate a plan to satisfy a particular
need and to create something with a physical reality.A machine is a combination of several machine elements arranged to work together as a whole to accomplish specific purposes. Machine design involves designing the elements and arranging them optimally to obtain some useful work.
DTEL 5DTEL 5
LECTURE 1:- Design philosophy and Engineering materials
6YCCE,Nagpur Prof. D.Y.Shahare & Prof.
S.B.Deshpande
DTEL 6
LECTURE 2:- Design philosophy and Engineering materials
TYPES OF DESIGN1) ADAPTIVE DESIGN : This is based on existing design, for
example, standard products or systems adopted for a new application
2) DEVELOPMENT DESIGN : Here we start with an existing design but finally a modified design is obtained.
3) NEW DESIGN : This type of design is an entirely new one but based on existing scientific principles. No scientific invention is involved but requires creative thinking to solve a problem.
DTEL 7
LECTURE 2:- Design philosophy and Engineering materials
Based on Methods
1)Rational design : This is based on determining the stresses and strains of components and thereby deciding their dimensions.
2) Empirical design: It depends on empirical formulae based on practical & previous experiences & observations.
3) Industrial design: It is based on industrial considerations & norms viz. market survey, production facilities, use of existing standard products etc.
DTEL 8
LECTURE 2:- Design philosophy and Engineering materials
RECOGNIZATION/IDENTIFICATION OF NEED
DEFINATION OF PROBLEM
SYNTHESIS
ANALYSIS & OPTIMIZATION
EVALUATION
DOCUMENTATION
RECOGNIZATION / IDENTIFICATION OF NEED
DEFINATION OF PROBLEM
SYNTHESIS
ANALYSIS & OPTIMIZATION
EVALUATION
DOCUMENTATION
THE GENERAL DESIGN
PROCEDURE
ITERATION
DTEL 9
LECTURE 3:- Design philosophy and Engineering materials
Factors to be considered in Machine Design1)Strength
2)Rigidity
3)Reliability
4)Flexibility
5)Safety
6)Cost and weight
7)Manufacturing processes and workshop facilities
8)LifeDTEL 10
LECTURE 4:- Design philosophy and Engineering materials
Factors to be considered in Machine Design9) Noise and vibrations
10)Thermal considerations
11) Frictional resistance, wear and lubrication
12) Maintenance
13) Size and shape
14) Material selection
15) Assembly
16) Conformance to standards, ergonomics, aesthetics.YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof. D.Y.SHAHARE DTEL 11
LECTURE 4:- Design philosophy and Engineering materials
Factor of SafetyIn the design of a system or its components, there are certain areas of uncertainties. Sometimes it is difficult to determine the exact magnitude of various forces to which a machine component is subjected. In order to ensure the safety of a system against such uncertainties ‘factor of safety ‘ is used in machine design.In case of static loading F.S = Yield Strength/ working stress In case of fatigue loading F.S = Endurance limit/ working stress
DTEL 12
LECTURE 5:- Design philosophy and Engineering materials
Types of Loadsi) Static load- Does not change in magnitude and direction
and normally increases gradually to a steady value. ii) Dynamic load- a) changes in magnitude- for e.g. traffic of
varying weight passing a bridge. b) changes in direction- for e.g. load on piston rod of a
double acting cylinder. Vibration and shock loading are types of dynamic loading.
DTEL 13
LECTURE 5:- Design philosophy and Engineering materials
ENGG MATERIALS
METALS NONMETALS
FERROUS NON-FERROUS
e.g. -(i) cast iron (ii) wrought iron (iii) steel.
e.g.- wood, glass, plastics, Timber, leather
e.g.- aluminium and its alloys, magnesium and manganese alloys, nickel, silver, cupper based alloys like brass,Bronze, Duralumin,zinc, lead, ,tin
DTEL 14
LECTURE 6:- Design philosophy and Engineering materials
Material Properties1)Elasticity- This is the property of a material to regain its original shape after deformation when the external forces are removed. 2)Plasticity- This is associated with the permanent deformation of material when the stress level exceeds the yield point.3) Hardness- Property of the material that enables it to resist permanent deformation, penetration, indentation etc.4) Ductility- This is the property of the material that enables it to be drawn out or elongated to an appreciable extent before rupture occurs.
DTEL 15
LECTURE 6:- Design philosophy and Engineering materials
Material Properties5)Malleability- It is a special case of ductility where it can be rolled into thin sheets.6) Brittleness- Brittle materials show little deformation before fracture and failure occur suddenly without any warning. 7) Resilience- This is the property of the material that enables it to resist shock and impact by storing energy. 8) Toughness- This is the property which enables a material to be twisted ,bent or stretched under impact load or high stress before rupture. 9) Creep- When a member is subjected to a constant load over a long period of time it undergoes a slow permanent deformation and this is termed as “creep”.
DTEL 16
LECTURE 6:- Design philosophy and Engineering materials
Heat Treatment of Metals The heat treatment is defined as an operation or a combination of
operations, involving the heating & cooling of a metal or an alloy in the solid state for the purpose of obtaining certain desirable properties without change in chemical composition.
The is to achieve one or more of the followings 1)To increase the hardness of metals or alloys 2) To improve machinability 3) To soften the metal 4) To modify the structure of the material to improve its electrical & magnetic properties. 5) To refine the grain structure 6) To relieve residual stresses set up in the material.
DTEL 17
LECTURE 7:- Design philosophy and Engineering materials
Various heat treatment processes
1) Normalizing: This process consists of a) heating the metal from 300 to 500 C above its upper critical
temperatureb) holding it at this temperature for about 15 minutesc) cooling slowly in still air
2) Annealing: This process consists of a) heating the metal from 300 to 500 C above its upper critical
temperatureb) holding it at this temperature for some time to enable the
internal changes to take placec) cooling slowly in furnace. The rate of cooling varies from 300 to
2000 C/ hour.
DTEL 18
LECTURE 7:- Design philosophy and Engineering materials
Various heat treatment processes
3) Hardening: This process consists of a) heating the metal from 300 to 500 C above its upper critical
temperatureb) holding it at this temperature for considerable time depending
upon thicknessc) cooling suddenly in a suitable cooling medium like water, oil or
brine.
4) Tempering: The material hardened by quenching is very hard & brittle with residual stresses . It consists of reheating of metal below lower critical temperature, followed by any desired rate of cooling.
DTEL 19
LECTURE 7:- Design philosophy and Engineering materials
Limits, Fits and TolerancesA machine element, after design, requires to be manufactured to give it a shape of a product. a designer should have knowledge of basic manufacturing aspects.
First and foremost is assigning proper size to a machine element from manufacturing view point. In case the machine element is a mating part with another one, then dimensions of both the parts become important, because they dictate the nature of assembly.
DTEL 20
LECTURE 8:- Design philosophy and Engineering materials
Imp terms in Fits and TolerancesTolerance: It is the difference between maximum and minimum dimensions of a component, ie, between upper limit and lower limit. Tolerance is of two types, bilateral and unilateral. When tolerance is present on both sides of nominal size, it is termed as bilateral; unilateral has tolerance only on one side.
FITS: The nature of assembly of two mating parts is defined by three types of fit system, Clearance Fit, Transition Fit and Interference Fit.
DTEL 21
LECTURE 8:- Design philosophy and Engineering materials
Types of FitsClearance Fit :In this type of fit, the shaft of largest possible diameter can also be fitted easily even in the hole of smallest possible diameter.
Transition Fit : It is the clearance between the minimum dimension of the shaft and the minimum dimension of the hole. Interference Fit :In this case, no matter whatever may be the tolerance level in shaft and the hole, there is always a overlapping of the matting parts. This is known as interference fit. Interference fit is a form of a tight fit.
DTEL 22
LECTURE 8:- Design philosophy and Engineering materials
DTEL 23
LECTURE 8:- Design philosophy and Engineering materials
SummaryIn this topic the properties and uses of different types of
metals and nonmetals, generally used in machine design,
are discussed. Also we had discuss briefly about some of
the basic manufacturing requirements and processes.
DTEL 24
LECTURE 8:- Design philosophy and Engineering materials
REFERENCE BOOKS MECHANICAL ENGG. DESIGN – J.E. SHIGLEY MACHINE DESIGN – P.H.BLACK MACHINE DESIGN - B.D.SHIWALKAR MACHINE DESIGN - KHURMI & GUPTA DESIGN OF MACHINE ELEMENTS – V.B.BHANDARI
For more information use following link:-\\172.16.1.4\nptel\NPTEL VIDEOS PHASE1 - PART 2\Mechanical Engineering\Design of Machine Element I
DTEL 25
LECTURE 8:- Design philosophy and Engineering materials
Machine Design-II
Unit-II Design Cotter and Knuckle joint
Department of Mechanical Engineering
YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof. D.Y.SHAHARE
DTEL 26
LECTURE 9:- Design Cotter and Knuckle joint
Syllabus
UNIT -II : Design of cotter and knuckle joint.Riveted joint : Riveted joint for boilers, structural works (uniform strength joint), and eccentric loaded riveted joint.Welded joint : Design of single transverse, double transverse, parallel fillet, combination fillet butt joint, eccentrically loaded welded joints.Bolted joint : Design of bolted fasteners, bolts of uniform strength, bolted joints under eccentric loading.
DTEL 27
LECTURE 9:- Design Cotter and Knuckle joint
Learning Objective
A typical cotter joint, its components and
working principle.
Detailed design procedure of a cotter joint.
A typical knuckle joint, its components and
working principle.
Detailed design procedure of a knuckle joint.
DTEL 28
LECTURE 9:- Design Cotter and Knuckle joint
Introduction (Cotter joint)A cotter is a flat wedge-shaped piece of steel as shown in fig(a). This is used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints may be subjected to tensile or compressive forces along the axes of the tensile or compressive forces along the axes of the rods.
(c)
(b)
(a)
DTEL 29
LECTURE 9:- Design Cotter and Knuckle joint
Design of cotter jointIf the allowable stresses in tension, compression and shear for the socket, rod and cotter be σt , σc and τ respectively, assuming that they are all made of the same material, we may write the following failure criteria: Tension failure of rod at diameter d,
Tension failure of rod across slot,
YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof. D.Y.SHAHARE
DTEL 34
LECTURE 10:- Design Cotter and Knuckle joint
Tensile failure of socket across slot,
Shear failure of cotter,
Shear failure of rod end,
DTEL 35
LECTURE 11:- Design Cotter and Knuckle joint
Shear failure of socket end,
Crushing failure of rod or cotter,
Crushing failure of socket or rod,
DTEL 36
LECTURE 11:- Design Cotter and Knuckle joint
Crushing failure of collar,
Shear failure of collar,
DTEL 37
LECTURE 12:- Design Cotter and Knuckle joint
Continue…..Bending of cotter
Maximum bending moment =
The bending stress,
DTEL 38
LECTURE 12:- Design Cotter and Knuckle joint
Continue….Some typical proportions are given below:
DTEL 39
LECTURE 12:- Design Cotter and Knuckle joint
Knuckle joint A knuckle joint as shown in fig is used to connect two
rods under tensile load. This joint permits angular misalignment of the rods and may take compressive load if it is guided.
DTEL 40
LECTURE 13:- Design Cotter and Knuckle joint
Design of Knuckle jointSome typical proportions are given below:
Mean diameter of the split pin =
The analyses are shown below assuming the same materials for the rods and pins and the yield stresses in tension, compression and shear are given by σt, σc and τ.
DTEL 41
LECTURE 13:- Design Cotter and Knuckle joint
Failure of rod in tension,
Failure of knuckle pin in double shear,
Failure of knuckle pin in bending (if the pin is loose in the fork) Equating the maximum bending stress to tensile or compressive yield stress we have,
Bending of a knuckle pin
DTEL 42
LECTURE 13:- Design Cotter and Knuckle joint
Continue… Failure of rod eye in shear:
Failure of rod eye in crushing:
Failure of rod eye in tension:
Failure of forked end in shear:
Failure of forked end in tension:
Failure of forked end in crushing:
DTEL 43
LECTURE 14:- Design Cotter and Knuckle joint
Summary
In this topic cotter and knuckle joints constructional detail have been described. Then the detailed design procedures of both these joints are given with suitable illustrations.
44YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof.
D.Y.SHAHARE
DTEL 44
LECTURE 14:- Design Cotter and Knuckle joint
Machine Design-II
Unit-II Riveted joint
Department of Mechanical Engineering
DTEL 45
LECTURE 14:- Design Cotter and Knuckle joint
Syllabus
UNIT -II : Design of cotter and knuckle joint.Riveted joint : Riveted joint for boilers, structural works (uniform strength joint), and eccentric loaded riveted joint.Welded joint : Design of single transverse, double transverse, parallel fillet, combination fillet butt joint, eccentrically loaded welded joints.Bolted joint : Design of bolted fasteners, bolts of uniform strength, bolted joints under eccentric loading.
DTEL 46
LECTURE 14:- Design Cotter and Knuckle joint
Learning Objective
Basic types of riveted joint.
Different important design parameters of a riveted
joint.
Basic failure mechanisms of a riveted joints.
Concepts of design of a riveted joint.
Procedure for designing riveted joint under
eccentric loading.
DTEL 47
LECTURE 15:- Design Cotter and Knuckle joint
Introduction (Riveted joint)Riveting is an operation whereby two plates are joined withthe help of a rivet. Adequate mechanical force is applied to make the joint strong and leak proof. Smooth holes are drilled (or punched and reamed) in two plates to be joined and the rivet is inserted.
Riveting operationDTEL 48
LECTURE 15:- Design Cotter and Knuckle joint
Types of riveted jointRiveted joints are mainly of two types
Lap joints
Single riveted lap joint
49YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof.
D.Y.SHAHARE
DTEL 49
LECTURE 15:- Design Cotter and Knuckle joint
Types of riveted joint
Double riveted lap joint, chain arrangement
Double riveted lap joint, zig-zag arrangement
DTEL 50
LECTURE 15:- Design Cotter and Knuckle joint
Types of riveted joint Butt joints
Butt joint with single strap
Single riveted butt joint with single and double strapsDTEL 51
LECTURE 15:- Design Cotter and Knuckle joint
Types of riveted joint
Double riveted Butt joint with single and double straps (chain arrangement)
Double riveted Butt joint with single and double straps (zig-zag arrangement)
DTEL 52
LECTURE 15:- Design Cotter and Knuckle joint
Efficiencies of riveted joints in (%)
DTEL 53
LECTURE 16:- Design Cotter and Knuckle joint
Important design parameters of riveted joints
a) Pitch: This is the distance between two centers of the consecutive rivets in a single row. (usual symbol p)
b) Back Pitch: This is the shortest distance between two successive rows in a multiple riveted joint. (usual symbol Pt or Pb)
c) Diagonal pitch: This is the distance between the centers of rivets in adjacent rows of zigzag riveted joint. (usual symbol Pd)
DTEL 54
LECTURE 16:- Design Cotter and Knuckle joint
Important design parameters of riveted joints
d) Margin or marginal pitch: This is the distance between the centre of the rivet hole to the nearest edge of the plate. (usual symbol m) Strength of riveted jointThere are four possible ways a single rivet joint may fail.1) Tearing of the plate: The maximum force allowed in this
case iswhere st = allowable tensile stress of the plate materialp = pitch d = diameter of the rivet hole t= thickness of the plate
DTEL 55
LECTURE 16:- Design Cotter and Knuckle joint
Strength of riveted joints
Failure of plate in tension (tearing)2) Shearing of the rivet: The maximum force withstood by the joint to prevent this failure is
for lap joint, single strap butt joint
for double strap butt joint Where Ss=allowable shear stress of the rivet materialYCCE,NAGPUR Prof. S.B.DESHPANDE & Prof.
D.Y.SHAHARE
DTEL 56
LECTURE 16:- Design Cotter and Knuckle joint
Strength of riveted joints
Failure of a rivet by shearing
3) Crushing of rivet: If the bearing stress on the rivet is too large the contact surface between the rivet and the plate may get damaged.
With a simple assumption of uniform contact stress the maximum force allowed is
Where Sc=allowable bearing stress between the rivet and plate material
DTEL 57
LECTURE 16:- Design Cotter and Knuckle joint
Eccentrically loaded riveted joints
Consider, now, a bracket, which carries a vertical load F, the force, in addition to inducing direct shear of magnitude F/4 in each rivet, causes the whole assembly to rotate. Hence additional shear forces appear in the rivets.
DTEL 58
LECTURE 17:- Design Cotter and Knuckle joint
Eccentrically loaded riveted joints Taking moment about the centroid
Thus, the additional force is
DTEL 59
LECTURE 17:- Design Cotter and Knuckle joint
Eccentrically loaded riveted joints
The net force in the i-th rivet is obtained by parallelogram law of vector addition as
Where θi=angle between the lines of action of the forcesFor safe designing we must have
Where Ss=allowable shear stress of the rivet.
DTEL 60
LECTURE 17:- Design Cotter and Knuckle joint
Machine Design-II
Unit-IIWelded joint
Department of Mechanical Engineering
DTEL 61
LECTURE 18:- Design Cotter and Knuckle joint
Syllabus
UNIT -II : Design of cotter and knuckle joint.Riveted joint : Riveted joint for boilers, structural works (uniform strength joint), and eccentric loaded riveted joint.Welded joint : Design of single transverse, double transverse, parallel fillet, combination fillet butt joint, eccentrically loaded welded joints.Bolted joint : Design of bolted fasteners, bolts of uniform strength, bolted joints under eccentric loading.
DTEL 62
LECTURE 18:- Design Cotter and Knuckle joint
Learning Objective
Different types of welded joints.
Factors that affect strength of welded joint.
Symbols and specifications of welded joint.
Possible failure mechanisms of welded joint.
Procedure for designing welded joint under
eccentric loading.
DTEL 63
LECTURE 18:- Design Cotter and Knuckle joint
Welded jointWelding is a very commonly used permanent joining process. A welded joint has following advantages:(i) Compared to other type of joints, the welded joint has higher efficiency. An efficiency > 95 % is easily possible.(ii) Since the added material is minimum, the joint has lighter weight. (iii) Welded joints have smooth appearances.(iv) Due to flexibility in the welding procedure, alteration and addition are possible.(v) It is less expensive. (vi) Forming a joint in difficult locations is possible through welding.
DTEL 64
LECTURE 18:- Design Cotter and Knuckle joint
Types of welding processesWelding can be broadly classified in two groups 1) Liquid state (fusion) welding where heat is added to the
base metals until they melt. Depending upon the method of heat addition this process can be further subdivided, namely
Electrical heating: Arc welding Resistance weldingInduction welding
Chemical welding: Gas weldingThermit welding
Laser welding Electron beam welding.
DTEL 65
LECTURE 18:- Design Cotter and Knuckle joint
Types of welded jointsWelded joints are primarily of two kindsa) Lap or fillet joint: obtained by overlapping the plates and welding their edges. The fillet joints may be single transverse fillet, double transverse fillet or parallel fillet joints
DTEL 66
LECTURE 18:- Design Cotter and Knuckle joint
Types of welded joints
b) Butt joints: formed by placing the plates edge to edge and welding them. According to the shape of the grooves, the butt joints may be of different types, e.g., Square butt jointSingle V-butt joint, double V-butt joint Single U-butt joint, double U-butt jointSingle J-butt joint, double J-butt jointSingle bevel-butt joint, double bevel butt joint
DTEL 67
LECTURE 19:- Design Cotter and Knuckle joint
Types of welded joints
Different types of butt joints
Other types of welded joints
DTEL 68
LECTURE 19:- Design Cotter and Knuckle joint
Basic weld types & their symbols
DTEL 69
LECTURE 19:- Design Cotter and Knuckle joint
Design of butt jointThe main failure mechanism of welded butt joint is tensile failure. Therefore the strength of a butt joint iswhere =allowable tensile strength of the weld material. t= thickness of the weldl=length of the weld.For a square butt joint t is equal to the thickness of the plates.
DTEL 70
LECTURE 20:- Design Cotter and Knuckle joint
Design of parallel fillet joint
Each weld carries a load P/2.The allowable load carried by each of the joint is where the throat areaThe total allowable load isCombination of transverse and parallel fillet joint
The allowable load is
where At & At’ =throat area along the longitudinal & transverse direction DTEL 71
LECTURE 20:- Design Cotter and Knuckle joint
Design of circular fillet weld subjected to torsion
The shaft is subjected to a torque, shear stress develops in the weld in a similar way as in parallel fillet joint. Assuming that the weld thickness is very small compared to the diameter of the shaft, the maximum shear stress occurs in the throat area.
Thus, for a given torque the maximum shear stress in the weld is
DTEL 72
LECTURE 20:- Design Cotter and Knuckle joint
Design of circular fillet weld subjected to torsion
where T = torque applied.d = outer diameter of the shaft = throat thicknessIp=polar moment of area of the throat section.
When
The throat dimension and hence weld dimension can be selected from the equation
DTEL 73
LECTURE 21:- Design Cotter and Knuckle joint
Eccentrically loaded transverse fillet joint
74YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof.
D.Y.SHAHARE
Consider a cantilever beam fixed to a wall by two transverse fillet joints. The design is based upon the strength of the joint against failure due to shear force along the throat section.
(a)direct shear stress of magnitude F/2bt
where b = length of the weld, t= thickness of the throatand the factor 2 appears in the denominator for double weld.
DTEL 74
LECTURE 21:- Design Cotter and Knuckle joint
Eccentrically loaded parallel fillet joint The joint fails in shear along the throat section. For the given loading, the throat area is subjected to two shear stresses.(a) Direct shear of magnitude F/2ltwhere l = length of the weld t = thickness of the throat.
(b) Indirect shear stress owing to eccentricity of the loading. The shear stress at a point at a distance r from the centroid is given by
DTEL 75
LECTURE 21:- Design Cotter and Knuckle joint
Eccentrically loaded parallel fillet joint where L = distance of the line of action of F from centroid. Thus
Where is the polar moment of the throat section about its centroid.The weld size is designed such that the maximum shear stress does not exceed its allowable limiting value.
DTEL 76
LECTURE 21:- Design Cotter and Knuckle joint
Asymmetric welded sectionAn eccentricity in loading causes extra shear stress in a welded joint, thus it may be useful to reduce the eccentricity in loading. In some applications this is achieved by making the weld section asymmetric.
DTEL 77
LECTURE 22:- Design Cotter and Knuckle joint
Asymmetric welded sectionThe net length of the weld can be calculated from the strength consideration that is
where t = thickness of the throat. Thus the individual lengths of the weld are as following:
and
where b= width of the plate
DTEL 78
LECTURE 22:- Design Cotter and Knuckle joint
Machine Design-II
Unit-II Bolted joint
Department of Mechanical Engineering
DTEL 79
LECTURE 23:- Design Cotter and Knuckle joint
Bolted jointInitial tightening loadWhen a nut is tightened over a screw following stresses are induced:
(i) Tensile stresses due to stretching of the bolt.
(ii) Torsional shear stress due to frictional resistance at the threads.
(iii) Shear stress across threads.
(iv) Compressive or crushing stress on the threads.
(v) Bending stress if the surfaces under the bolt head or nut are not
perfectly normal to the bolt axis.
DTEL 80
LECTURE 23:- Design Cotter and Knuckle joint
Bolted jointb) Tensile stress:
c) Shear stress across the threads
where b is the base width of the thread and n is the number of threads sharing the load
DTEL 81
LECTURE 23:- Design Cotter and Knuckle joint
Bolted jointd) Crushing stress on threads:
e) Bending stress:
where x is the difference in height between the extreme corners of the nut or bolt head, L is length of the bolt head shank and E is the young’s modulus.
DTEL 82
LECTURE 24:- Design Cotter and Knuckle joint
Bolted jointStresses due to an external load
where for fine threads dc =0.88d and for coarse threads dc =0.84d, d being the nominal diameter.
DTEL 83
LECTURE 24:- Design Cotter and Knuckle joint
Summary
In this topic stresses developed in screw fastenings due
to initial tightening load and external load have been
discussed . Bolted joints with eccentric loading have been
described.
DTEL 84
LECTURE 24:- Design Cotter and Knuckle joint
Machine Design-II
Unit-III Design of power screw
Department of Mechanical Engineering
DTEL 85
LECTURE 25:- Design Cotter and Knuckle joint
Stresses in power screws
A power screw is subjected to an axial load and a turning moment. The following stresses would be developed due to the loading.
Compressive stresses is developed in a power screw due to axial load.
The compressive stress σc is given by
where dc is the core diameter
λ is defined as λ = L/kwhere I=Ak2
L is the length of the screw.
DTEL 86
LECTURE 25:- Design Cotter and Knuckle joint
Stresses in power screws
Buckling analysis yields a critical load PC
If both ends are assumed to be hinged critical load is given by
In general the equation may be written as
where n is a constant that depends on end conditions.
DTEL 87
LECTURE 25:- Design Cotter and Knuckle joint
Stresses in power screws
Torsional shear stresses in the screw due to turning moment.
It is given bywhere T is the torque applied Bending stresses are developed in the screw thread and is shown in fig(a).
The bending moment
and the bending stress on a single thread is given by
DTEL 88
LECTURE 25:- Design Cotter and Knuckle joint
Stresses in power screws
Here And F′ is the load on a single thread.Fig(b) shows a developed thread and fig(c) shows a nut and screw assembly. This gives the bending stress at the thread root to be
This is clearly the most probable place for failure. Assuming that the load is equally shared by the nut threads
DTEL 89
LECTURE 26:- Design Cotter and Knuckle joint
Stresses in power screws
Fig(a) Loading and bending stresses in screw threads
Fig(b) Dimensions of developed threads
DTEL 90
LECTURE 26:- Design Cotter and Knuckle joint
Stresses in power screws
Fig(c) Screw and nut assembly
DTEL 91
LECTURE 26:- Design Cotter and Knuckle joint
Stresses in power screws
• Bearing stress σbr at the threads is given by
• Again on similar assumption shear stress τ at the root diameter is given by.
Here n’ is the number of threads in the nut. Since the screw is subjected to torsional shear stress in addition to direct or transverse stress combined effect of bending, torsion and tension or compression should be considered in the design criterion.
DTEL 92
LECTURE 26:- Design Cotter and Knuckle joint
Design procedure of screw jackA typical screw jack is shown in fig(d) . It is probably more informative to consider the design of a jack for a given load and lift. We consider a reasonable value of the load to be 100KN and lifting height to be 500mm. The design will be considered in the following steps:
Fig (d) A typical screw jack
DTEL 93
LECTURE 27:- Design Cotter and Knuckle joint
Summary
In this topic firstly the stresses developed in a power
screw are discussed. Design procedure of a screw jack is
then considered and the components such as the screw,
and the nut are designed for strength.
DTEL 94
LECTURE 27:- Design Cotter and Knuckle joint
Machine Design-II
Unit-III Design of Helical springs
Department of Mechanical Engineering
DTEL 95
LECTURE 28:- Design of Helical springs
Syllabus
UNIT -II : Design of power screw.Derivation of expression for deflection and shear stress in helical spring, design of helical spring, design of leaf spring.
DTEL 96
LECTURE 28:- Design of Helical springs
Learning Objective
Stresses in a helical springs.
Deflection of a helical springs
DTEL 97
LECTURE 28:- Design of Helical springs
Helical SpringsSpring act as a flexible joint in between two parts or
bodies.• Objectives of spring.
Cushioning , absorbing , or controlling of energy
due to shock and vibration.
Control of motion.
Measuring forces .
Storing of energy .
DTEL 98
LECTURE 28:- Design of Helical springs
Commonly used spring materials Hard-drawn wire : This is cold drawn, cheapest spring steel. Normally used for low stress and static load. Oil-tempered wire : It is a cold drawn, quenched, tempered, and general purpose spring steel. Chrome Vanadium: This alloy spring steel is used for high stress conditions and at high temperature up to 220C. Chrome Silicon: This material can be used for highly stressed springs. Music wire: This spring material is most widely used for small springs. It is the toughest and has highest tensile strength and can withstand repeated loading at high stresses.
DTEL 99
LECTURE 28:- Design of Helical springs
Helical SpringsNomenclature
A Material constant
C Spring index=D/d
d Wire diameter
D Mean coil diameter
f Natural frequency of the spring
F Force/Load
G Shear Modulus (of Rigidity)
DTEL 100
LECTURE 28:- Design of Helical springs
NomenclatureJ Polar Moment of Inertia
k Spring rate or spring stiffness
K Stress correction factor
L Length
N Number of coils
T Torsional Moment
U Strain energy
Helix angle
y Deflection γ Density τ Shear stress in spring
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LECTURE 28:- Design of Helical springs
Design of coil springStresses in helical springThe flexing of a helical spring creates torsion in the wire and the force applied induces a direct stress.
Replacing the terms,
And re-arranging,
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LECTURE 28:- Design of Helical springs
Stresses in helical springWhere Ks is the shear-stress correction factor and is defined by the equation:
Curvature Effect
The curvature of the wire increases the stress on the inside of the spring, This effect can be neglected for static loading,
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LECTURE 28:- Design of Helical springs
Stresses in helical springThe combined effect of direct shear and curvature correction is accounted by Wahl’s correction factor and is given as:
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LECTURE 28:- Design of Helical springs
Deflection and stiffness of the spring
Where N is the number of active coils. The deflection in the spring, using Castigliano’s theorem,
Substituting C=D/d and rearranging
For normal range of C, the term within bracket (contribution of direct shear) is so negligible we can write
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LECTURE 29:- Design of Helical springs
Deflection and stiffness of the spring
The spring stiffness or springs rate,
End Construction
Coil compression springs generally use four different types of
ends. The ends of springs should always be of both squared
and ground, because a better or even transfer of the load is
obtained.
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LECTURE 29:- Design of Helical springs
End Construction
107YCCE,NAGPUR Prof. S.B.DESHPANDE & Prof.
D.Y.SHAHARE
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LECTURE 29:- Design of Helical springs
Spring at various positions
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LECTURE 29:- Design of Helical springs
Machine Design-II
Unit-III Design of Leaf spring
Department of Mechanical Engineering
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LECTURE 30:- Design of Helical springs
Learning Objective
Stresses in leaf spring.
Deflection of leaf spring.
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LECTURE 30:- Design of Helical springs
Multi-leaf springsMulti-leaf springs are widely used for automobile and rail road suspensions. It consists of a series of flat plates, usually of semi- elliptical shape as shown in fig. The longest leaf, called the master leaf. The extra full-length are provided to support the transverse shear force.
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LECTURE 30:- Design of Helical springs
Leaf spring
The leaves are divided into two groups namely master leaf along with graduated-length leaves forming one group and extra full-length leaves forming the other.Notations :nf = number of extra full-length leaves ng =number of graduated-length leaves including master leaf n= total number of leaves b= width of each leaf (mm) t= thickness of each leaf (mm) L=length of the cantilever or half the length of semi- elliptic spring (mm)
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LECTURE 31:- Design of Helical springs
Leaf Springs
The resultant shape is approximately a triangular plate of thickness t and a maximum width at the support as (ngb). The bending stress in the plate, which is uniform throughout, is given by
(a)
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LECTURE 31:- Design of Helical springs
Leaf SpringsIt can be proved that the deflection δg at the load point of the triangular plate is given by
(b)
Similarly, the extra full length leaves can be treated as a rectangular plate of thickness t and uniform width (nfb). The bending stress at the support is given by
(c)
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LECTURE 31:- Design of Helical springs
Leaf SpringsThe deflection at the load point is given by
(d)
or (e) Also (f)
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LECTURE 32:- Design of Helical springs
Leaf SpringFrom equation (e) and (f)
Substituting these valued in Eqs(a) and (c),
(h)
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LECTURE 32:- Design of Helical springs
Leaf Spring
It is seen from the above equations that bending stresses in full-length leaves are 50% more than those in graduated length leaves. The deflection at the end of the spring is determined from Eqs(b) and (h). It is given by
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LECTURE 32:- Design of Helical springs
Summary
In this topic firstly the stresses developed in a leaf
spring are discussed. Procedure to calculate deflection
and stiffness of spring as well nipping of leaf spring is
studied.
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LECTURE 32:- Design of Helical springs
Machine Design-II
Unit-IVDesign of Brakes &Clutches
Department of Mechanical EngineeringYCCE,Nagpur
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LECTURE 33:- Design of Brakes &Clutches
Syllabus
Unit –IVDesign of Friction Clutch, single plate, mutiplate, Cone,& Centrifugal Clutch.Design of Brake, shoe Brake, Band Brake, Internal Expanding Brake.
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LECTURE 33:- Design of Brakes &Clutches
Learning Objective
Recognize the basic geometries of Clutch and Brakes system.Calculate the frictional forces and torque capabilities in Brake system.Understand the principle of heat generation heat removal from the Brake system.Calculate frictional horsepower and recognize how it use.
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LECTURE 33:- Design of Brakes &Clutches
Introduction (Design of Clutch)A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driven shaft. A Clutch thus provides the interruptible connection between two rotating shaft. Clutches allow a high inertia load to be started with a small power.
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LECTURE 33:- Design of Brakes &Clutches
Single plate clutchBasically, the clutch needs three parts.These are the engine flywheel, a friction disc called the clutch plate and a pressure plate.Method of analysis:-uniform pressure condition uniform wear condition
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LECTURE 33:- Design of Brakes &Clutches
Design of Single plate clutch
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LECTURE 34:- Design of Brakes &Clutches
Design of Multiplate clutch
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LECTURE 34:- Design of Brakes &Clutches
Cone Clutch
A cone clutch consist of inner and outer conical working surfaces.The outer cone is keyed to the driving shaft, while the inner cone is free to slide axially on the driven shaft due to splines.Leather, cork or asbestos are used for the friction lining on the inner cone.DTEL 126
LECTURE 34:- Design of Brakes &Clutches
Design of Cone Clutch
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LECTURE 34:- Design of Brakes &Clutches
Centrifugal ClutchWhenever it is required to engage the load after the driving member has attained a particular speed, a centrifugal clutch is used.The centrifugal clutch permits the drive-motor or engine to start, warm up and accelerate to the operating speed without load.
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LECTURE 35:- Design of Brakes &Clutches
Design of Centrifugal Clutch
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LECTURE 35:- Design of Brakes &Clutches
Design of BrakeBrakes are devices that dissipate kinetic energy of the moving parts of a machine. In mechanical brakes the dissipation is achieved through sliding friction between a stationary object and a rotating part. Depending upon the direction of application of braking force.In a shoe brake the rotating drum is brought in contact with the shoe by suitable force. The contacting surface of the shoe is coated with friction material.
.
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LECTURE 36:- Design of Brakes &Clutches
Design of Shoe Brake Let, F=applied force to the shoe, Ffr=frictional force, Pressure distribution,
Coulomb’s law of friction,
Net normal force,
The total frictional torque,
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LECTURE 36:- Design of Brakes &Clutches
Continue…equivalent force,
Coulomb’s law of friction
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LECTURE 36:- Design of Brakes &Clutches
Design of Band Brake
A flexible band of leather or rope or steel with friction lining is wound round a drum. Frictional torque is generated when tension is applied to the band. It is known tensions in the two ends of the band are unequal because of friction and bear Let,T1=tension in the taut side, T2=tension in the slack side, μ =coefficient of kinetic friction and β =angle of wrap. Braking torque,
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LECTURE 37:- Design of Brakes &Clutches
Simple band brakeIn simple band brake one end of the band is attached to the fulcrum of the lever arm The required force to be applied to the lever is,
for clockwise rotation of the brake drum
for anticlockwise rotation of the brake drum,
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LECTURE 37:- Design of Brakes &Clutches
Differential band brake: In this type of band brake, two ends of the band are attached to two points on the lever arm other than fulcrum. for clockwise rotation of the brake drum and
for anticlockwise rotation of the brake drum,
for clockwise rotation of the brake drum,
for counterclockwise rotation of the brake drum.
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LECTURE 37:- Design of Brakes &Clutches
Design of Internal Expanding BrakeThe brake shoes are engaged with the internal surface of the drum.The forces required are ,
Let Mp & Mf are the moment equilibrium equation
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LECTURE 37:- Design of Brakes &Clutches
Machine Design-II
Unit-VThin and Thick Cylindrical Pressure Vessel.
Department of Mechanical EngineeringYCCE,Nagpur
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LECTURE 38:- Thin and Thick Cylindrical Pressure Vessel
Syllabus
Unit –VClassification of Thin and Thick cylindrical pressure vessel,Stresses in thin and cylindrical pressure vessels when it is subjected to internal pressure,Expression for circumferential and longitudinal stresses,Design of pressure Vessel, heads and cover plate
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LECTURE 38:- Thin and Thick Cylindrical Pressure Vessel
Learning Objective
Stresses developed in thin cylinders.
Formulations for circumferential and longitudinal stresses in thin cylinders.
Basic design principles.
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LECTURE 38:- Thin and Thick Cylindrical Pressure Vessel
Introduction(Thin Cylinder)
. If the wall thickness is less than about 7% of the inner diameter then the cylinder may be treated as a thin one. Thin walled cylinders are used as boiler shells, pressure tanks, pipes and in other low pressure processing equipments. Fig shows (a)circumferential or hoop stress,(b)longitudinal stress,(c)Radial stress
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LECTURE 38:- Thin and Thick Cylindrical Pressure Vessel
Stresses in thin cylinders In a thin walled cylinder the circumferential stresses may be assumed to be constant over the wall thickness and stress in the radial direction may be neglected for the analysis. Let, σθ =circumferential stress & σz =longitudinal stress ,r =thin cylinder of radius , t =wall thickness , L =length &P=internal pressure ,Consider now an element of included angle dθ at an angle of θ from vertical. For equilibrium we may write,
This gives,
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LECTURE 38:- Thin and Thick Cylindrical Pressure Vessel
Continue….
Considering a section along the longitudinal axis
Let,ri & ro are internal and external radii of the vessel,ri≈ ro = r ro – ri = tσz =
From the equilibrium condition in a cut section we have,
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LECTURE 39:- Thin and Thick Cylindrical Pressure Vessel
Design Principles Pressure vessels are generally manufactured from curved sheets joined by welding. Mostly V– butt welded joints are used. It is probably more instructive to follow the design procedure of a pressure vessel. We consider a mild steel vessel of 1m diameter comprising a 2.5 m long cylindrical section with hemispherical ends to sustain an internal pressure of 2MPa.The minimum plate thickness should conform to the “Boiler code” as given in table-Minimum plate thickness:-
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Summary Stresses developed in thin cylinders are first discussed in general and then the circumferential and longitudinal stresses are expressed in terms of internal pressure, radius and the shell thickness. Stresses in a spherical shell are also discussed. Basic design principle of thin cylinders are considered.
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Thick cylinders- Stresses due to internal For thick cylinders such as guns, pipes to hydraulic
presses, high pressure hydraulic pipes the wall thickness is relatively large and the stress variation across the thickness is also significant. In general the stress equations of equilibrium without body forces can be given as, For axisymmetry about z-axis
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Continue….
In a plane stress situation if the cylinder ends are free to expand σz = 0 and due to uniform radial deformation and symmetry τrz = τθz = τrθ = 0. The equation of equilibrium reduces to,
This can be written in the following form: If we consider a general case with body forces such as centrifugal forces in the case of a rotating cylinder or disc then the equations reduce to ,
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Continue….
It is important to remember that if σθ works out to be positive, it is tensile and if it is negative, it is compressive whereas σr is always compressive irrespective of its sign. if po = 0 i.e. there is no external pressure the radial and circumferential stress reduce to,
Fig shows the Radial & circumferential stress distribution within the cylinder wall when only internal pressure acts.
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Summary
Stresses and strains in thick cylinders are first discussed and Lame’s equations are derived. Radial and circumferential stress distribution across the wall thickness in thick cylinders have been illustrated.
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LECTURE 40:- Thin and Thick Cylindrical Pressure Vessel
Machine Design-II
Unit-VIDesign of Transmission Shaft and keys.
Department of Mechanical Engineering,
YCCE, Nagpur
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LECTURE 41:- Design of Transmission Shaft and keys
Syllabus
Unit –VIDesign of Transmission shafts on the Basis of strength, Rigidity and Critical speed,ASME Code for Shaft Design,Design of Stepped Shaft Axle Splined Shaft,Design of Keys.
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LECTURE 41:- Design of Transmission Shaft and keys
Learning Objective
At the end of this lesson, the students should be able to understand :-Definition of shaft Standard shaft sizes Standard shaft materials Design of shaft based on strength
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LECTURE 41:- Design of Transmission Shaft and keys
Standard sizes of Shafts Typical sizes of solid shaft that are available in the market are, Up to 25 mm 0.5 mm increments 25 to 50 mm 1.0 mm increments 50 to 100 mm 2.0 mm increments 100 to 200 mm 5.0 mm increments.
Material for Shafts The ferrous, non-ferrous materials and non metals are used as shaft material depending on the application. Some of the common ferrous materials used for shaft are discussed below. Hot-rolled plain carbon steel Cold-drawn plain carbon/alloy composition Alloy steels Hardening of surface Case hardening and carburizing Cyaniding and nitriding.
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LECTURE 41:- Design of Transmission Shaft and keys
Design considerations for shaft Design based on Strength In this method, design is carried out so that stress at any location of the shaft should not exceed the material yield stress. However, no consideration for shaft deflection and shaft twist is included. Design based on Stiffness Basic idea of design in such case depends on the allowable deflection and twist of the shaft.
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LECTURE 42:- Design of Transmission Shaft and keys
Design based on Strength The stress at any point on the shaft depends on the nature of load acting on it. The stresses which may be present are as follows. Basic stress equations : Bending stress,M : Bending moment at the point of interest do : Outer diameter of the shaft k : Ratio of inner to outer diameters of the shaft ( k = 0 for a solid shaft because inner diameter is zero )
Axial StressF: Axial force (tensile or compressive) α: Column-action factor(= 1.0 for tensile load)
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LECTURE 43:- Design of Transmission Shaft and keys
Here, α is defined as,n = 1.0 for hinged end n = 2.25 for fixed end n = 1.6 for ends partly restrained, as in bearing K = least radius of gyration, L = shaft length ycσ = yield stress in compression
Stress due to torsion ,T : Torque on the shaft τ : Shear stress due to torsion
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LECTURE 43:- Design of Transmission Shaft and keys
Continue….Combined Bending and Axial stress
Maximum shear stress theory
Substituting the values of σx and τxy in the above equation, the final form is,
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LECTURE 43:- Design of Transmission Shaft and keys
ASME Code for Shaft Design
The shafts are normally acted upon by gradual and sudden loads. Hence, the equation is modified in ASME code by suitable load factors,
Where, Cbm & Ct are the bending and torsion factors.
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LECTURE 44:- Design of Transmission Shaft and keys
Continue….
ASME code also suggests about the allowable design stress, τ allowable
to be considered for steel shafting, ASME Code for commercial steel shafting = 55 MPa for shaft without keyway = 40 MPa for shaft with keyway ASME Code for steel purchased under definite
specifications = 30% of the yield strength but not over 18% of the ultimate strength in tension for shafts without keyways. These values are to be reduced by 25% for the presence of keyways.
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LECTURE 44:- Design of Transmission Shaft and keys
Design based on Stiffness Design may be based on stiffness. In the context of shaft, design for stiffness means that the lateral deflection of the shaft and/or angle of twist of the shaft should be within some prescribed limit. Therefore, design for stiffness is based on lateral stiffness and torsional rigidity.
Torsional rigidity :-To design a shaft based on torsional rigidity, the limit of angle of twist should be known. The angle of twist is given as follows, Where, θ = angle of twist L = length of the shaft G = shear modulus of elasticity Ip= Polar moment of inertia
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LECTURE 45:- Design of Transmission Shaft and keys
Based on critical speedCritical speed of a rotating shaft is the speed where it becomes dynamically unstable. It can be shown that the frequency of free vibration of a non-rotating shaft is same as its critical speed.The equation of fundamental or lowest critical speed of a shaft on two supports is,
Where, W1, W2…. : weights of the rotating bodies δ1, δ2 …. : deflections of the respective bodies
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LECTURE 45:- Design of Transmission Shaft and keys
Design of KeysThe function of a key is to prevent the relative motion between the transmission shaft and the hub of a rotating element like gear, pulley or sprocket.The key transmits the torque from the shaft to the hub and vice-versa.Types of Keys:-(a) Square key(b)flat key(c)round key(d)kennedy key(e)Woodruff key(f)Gib-headed key(g)Feather Key
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LECTURE 46:- Design of Transmission Shaft and keys
Continue….
Details of Keys..
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LECTURE 46:- Design of Transmission Shaft and keys
Continue…
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LECTURE 46:- Design of Transmission Shaft and keys
Common type of splined shaft
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LECTURE 47:- Design of Transmission Shaft and keys
Summery:-In this unit student learn, the design of shaft and their application.Design of Key and their type as well as common type of Splined shaft.
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LECTURE 47:- Design of Transmission Shaft and keys
References :-J.E Shigley and C.R Mischke , Mechanical Engineering Design , McGraw Hill Publication, 5th Edition. 1989. M.F Spotts, Design of Machine Elements, Prentice Hall India Pvt. Limited, 6th Edition, 1991. Khurmi, R.S. and Gupta J.K., Text book on Machine Design, Eurasia Publishing House, New Delhi. Sharma, C.S. and Purohit Kamalesh, Design of Machine Elements, Prentice Hall of India, New Delhi, 2003
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LECTURE 47:- Design of Transmission Shaft and keys
For more information use below link:-
172.16.1.4\nptel\NPTEL VIDEOS PHASE1 - PART 2\Mechanical Engineering\Design of Machine Element I
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LECTURE 47:- Design of Transmission Shaft and keys
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