1. Dr. Alagiriswamy A A, (M.Sc, PhD, PDF) Asst. Professor (Sr. Grade),
Dept. of Physics, SRM-University,
Kattankulathur campus,
Chennai
MECHANICS OF MATERIALS
UNIT V
Lecture 1
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2. Outline of the presentation
Introduction
Fundamental mechanical properties
Stress-strain relation for
different engineering materials
Introduction to Ductile materials /Brittle material
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3. Types of Materials Ferrous Metals: iron and steel.
Nonferrous Metals and Alloys: aluminum, magnesium, copper, nickel, titanium, super-alloys, beryllium, zirconium, low-melting alloys, precious metals.
Plastics: thermoplastics, thermosets, elastomers.
Ceramics: glass, graphite, diamond.
Composite materials: reinforced plastics, metal-matrix and ceramic-matrix composites, honeycomb structures.
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4. Properties of Materials
Mechanical Properties: strength, toughness, ductility, hardness, elasticity, fatigue, creep, Brittleness, toughness, stifness, resilience, endurance etc.
Behavior Under Loading: tension, compression, bending, torsion, shear.
Physical Properties: density, specific heat, thermal expansion, thermal conductivity, melting point, electrical and magnetic properties.
Chemical Properties: oxidation, corrosion, degradation, toxicity, flammability.

5. Manufacturing Processes for Metals
Casting: expendable mold and permanent mold.
Forming and Shaping: rolling, forging, extrusion, drawing, sheet forming, powder metallurgy, molding
Machining: turning, boring, drilling, milling, planning, shaping, broaching, grinding, ultrasonic machining, chemical machining, electrical discharge machining (EDM), electrochemical machining, high-energy beam machining
Joining: welding, brazing, soldering, diffusion bonding, adhesive bonding, mechanical joining
Finishing: honing, lapping, polishing, burnishing, deburring, surface treating, coating, plating

6. “The Process of Converting Raw Materials Into Products”
Manufacturing a Product: General Considerations
Material Selection
Processing Methods
Final Shape and Appearance
Dimensional and Surface Finish
Economics of Tooling
Design Requirements
Safety and Environmental Concerns
Manufacturing;
“The Process of Converting Raw Materials Into Products”
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7. Why Do Materials Differ in Their Mechanical Response ???
What Does our Experience Tell Us?
Bricks and glass do not deform and break easily.
Rubber bands deform a lot but return to their original shape
A paper clip easily deforms but does not easily return to its original shape
The thicker something is, the more force we have to exert to get it to break
Central Questions
When do materials deform/break?
Why do they deform/break ?
How do they??
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8. Internal/External stress relaxation is the key
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9. ENGINEERS NEED A WAY TO QUANTIFY THESE DIFFERENCES
A deeper approach
Why don’t you think in terms of the chemical bonds and chemical structures that are present
ENGINEERS NEED A WAY TO QUANTIFY THESE DIFFERENCES
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10. Some Important Definitions
Isotropy ; physical properties – direction independent.
Ex: Aluminum, steels/cast irons
Anisotropy; direction dependent,
Ex: Various composite materials, wood and laminated plastics
Elasticity;
able to regain its original shape/size after the deformation within the
elastic limit (Hooke’s law)
Stress is linearly proportional to strain
Plasticity;
able to permanently deform, after the stress is removed
Stress and strain no longer linearly related
Yield strength (an important ENGINEERING parameter);
defines the stress at which plastic DEFORMATION begins (Al -370 Mpa, Steel-1500 Mpa, Cu 490 Mpa)
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11. Different means of load applied
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12. Quiz time
When a metal stretches, but does not break under a certain load, this point is called the _________ Point.
A: yield
B: tensile
C: stretch
D: ultimate strength

13. A close correlation/analogy
Necking begins
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14. Some terminology of the term “Strength”
Elastic Strength;
The strength value of a material , it s’ behavior changes from elastic to plastic regime
Plastic Strength;
plastic to rupture regime
Tensile Strength;
Ultimate strength corresponds to maximum load
Compressive Strength;
The value of load applied to break-off by crushing.
Shear Strength;
The value of load applied (specifically tangential load)
Torsional Strength;
The value of load applied (specifically twisting load)
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15. Amount of energy absorbed by a material in the ELASTIC region
Some More terms
Resilience
property- stores energy and resists shocks or impacts
Toughness
Amount of energy absorbed by a material up to the fracture
Endurance
property - withstand varying stresses or repeated application of stress.
CREEPING; deformation increases even under constant load
E.g..- Rubber stretching, concrete bridge
Amount of energy absorbed by a material in the ELASTIC region
Toughness
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16. To be Precise ;
A compelling competition between elastic and plastic deformation
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17. Stress-Strain Relation for Different Engineering Materials
ferrous metals
Brittle; don’t exhibit yielding before failure
non - ferrous metals
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18. An another example Structural steel November 17, 2018November 17, 2018
All dim. in mm
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19. Yet another piece of information
Polyamide
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20. A deeper look on stress-strain curves
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21. A close comparison November 17, 2018November 17, 2018
Original/actual area
for copper
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22. The nominal stress σn = P/A0
where P is the force and A0 the original area of cross section
The nominal strain, εn = (L-L0)/L0
where L is the length of the original gauge length under force P, and L0 is the original gauge length.
Engineering stress/strain diagrams - elastic range,
while true stress – strain diagrams
plastic range.
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