Introduction

Mechanics

• Branch of Science which deals with the study of Internal and External Forces
• It deals with the effects of these forces on various structures, machines and fluids
• 

Strength Of Materials

• Study of Internal forces developed due to elastic deformation under the action of loads
• Stress
• Resisting force developed at a point
• Design Criterion
• Strength - Permissible strength
• Rigidity - Permissible deformation
• Design
• High Strength
• Rigidity
• Economic
• Low Weight
• High life

Differences

• Difference between Mechanics and MOS
• EM - Rigid Bodies
• MOS - Deformable bodies
• Difference between MOS and Machine Design(MD)
• MOS - Static Loading
• MD - Dynamic Loading

Criterion

• Strength Criterion
• Shear Stress = T/Zp
• Normal Stress = P/A
• Bending Stress = M/Z
• Rigidity Criterion
• Normal Strain = PL/AE
• Shear Strain = TL/GJ

Factor of Safety

• Factor of Safety (N) = Failure Stress / Permissible Stress
• Static Loading
• Ductile Material = Yield Strength
• Brittle Material = Ultimate Strength
• Yield Strength is considered in Ductile materials to avoid Permanent (Plastic) Deformation
• Margin of Safety (m) = N - 1
• In Pressure Vessels, N => 4.5
• Reserve Strength = Failure Strength - Permissible Strength
• Drawbacks: Cost increases

Deformation in Punching

• Deformation in Punching
• Punch - Elastic Deformation
• Plate - Plastic Deformation

Assumptions of MOS

• Material
• Isotropic
• Homogenous
• Prismatic
• Uniform Cross Section
• Static Load
• Follows Hooke's law
• Self Weight is neglected

Load

• Load is an external force applied on a body
• Load is classified on the basis of
• Time
• Cross Section
• Load Distribution (Loading Type)

Load Classification wrt Time

Classification of Loads wrt Cross Section

Classification of loads wrt Type of Load

Loads wrt Time

• 
• 
• Legenda: Dead Load
• Legenda: Gradually Applied Load

Impact Loading

• 
• Legenda: Impact Loading
• An Impact is a high force or shock applied over a short time period. (Δt tends to 0)
• Examples -
• IC Engine, Piston, Connecting Rod
• Springs in shock absorber
• Spur gears high pitch line velocity
• Punching, Forging etc.

Impact Factor

• 
• Used to determine the Impact Strength of a given material
• Ratio of Dynamic Deformation to Static Deformation is defined as Impact Factor
• when h--->0, I.F ---->2 which gives rise to Impact Loading
• Supports
• Rigid Support - Static Bending
• Flexible Support - Impact Bending

Fatigue Loads

• Failure of Machine Components is caused due to Fatigue Loads
• Type of Fatigue Loads
• Fluctuating
• Only Magnitude changes
• Completely Reversed
• Only Direction changes
• Alternating
• Both Magnitude and Direction change

Beams

• 
• Load is always perpendicular
• Span is defined as the distance between supports
• A beam is said to be statically determinate when
• No. of Reaction forces = No. of Equilibrium Equations
• A beam is said to be Statically indeterminate when
• No. of Reaction forces > No. of Equilibrium Equations
• Cantilever beam is always Statically Determinate
• Fixed and Continuous beams are always Statically Indeterminate
• In SSB
• Span = Length of the beam
• Is generally Statically Determinate but can be Statically Indeterminate under Variable Temperature condition

Bending

• 
• Bending is a process by which metal can be deformed by plastically deforming the material
• Sagging and Hogging
• Sagging
• Bending Moment is positive
• Sagging - u
• Sagging - Compressive Force
• Hogging
• Bending Moment is negative
• Hogging - n
• Hogging - Tensile Force

Pure Bending

• 
• Equal and Constant Couples
• Bending Moment is constant throughout the beam length
• Neutral Fibre - Axis where the length is the same before and after bending
• Point of Contraflexure
• Contra - Opposite. Flexure - Bending
• Point where Sagging and Hogging meet
• Bending Moment is zero

Shear Force

• 
• 
• Convention
• Clockwise - Positive
• AntiClockwise - Negative
• Bending Moment is maximum when Shear Force is Zero

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