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Slide Set by Lalithej Vvk, created more than 1 year ago

GATE Mechanical Engineering (Strength of Materials) Slide Set on Introduction, created by Lalithej Vvk on 24/06/2017.

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	Created by Lalithej Vvk almost 8 years ago

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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
1. Time
2. Cross Section
3. Load Distribution (Loading Type)

Load Classification wrt Time

Classification of Loads wrt Cross Section

Classification of loads wrt Type of Load

Loads wrt Time

Dead Load

Gradually Applied Load

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 Loading

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