august 27, 2015 1 dr. alagiriswamy a a, (m.sc, phd, pdf) asst. professor (sr. grade), dept. of...
TRANSCRIPT
April 19, 2023 1
Dr. Alagiriswamy A A, (M.Sc, PhD, PDF)Asst. Professor (Sr. Grade),
Dept. of Physics, SRM-University,Kattankulathur campus,
Chennai
UNIT VLecture 1
MECHANICS OF MATERIALS
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Introduction
Fundamental mechanical properties
Stress-strain relation for different engineering materials
Introduction to Ductile materials /Brittle material
Outline of the presentation
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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.
MaterialsMechanical 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.
Properties of Materials
Manufacturing Processes for
MetalsCasting: 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
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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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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
What Does our Experience Tell Us?
When do materials deform/break?
Why do they deform/break ?
How do they??
Central Questions
Why Do Materials Differ in Their Mechanical Response ???
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Internal/External stress
relaxation is the key
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ENGINEERS NEED A WAY TO QUANTIFY THESE
DIFFERENCES
Why don’t you think in terms of the chemical bonds and
chemical structures that are present
A deeper approach
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Isotropy ; physical properties – direction independent. Ex: Aluminum, steels/cast irons Anisotropy; direction dependent, Ex: Various composite materials, wood and laminated plasticsElasticity; • able to regain its original shape/size after the deformation
within the elastic limit (Hooke’s law)• Stress is linearly proportional to strainPlasticity; • able to permanently deform, after the stress is removed• Stress and strain no longer linearly relatedYield strength (an important ENGINEERING parameter); • defines the stress at which plastic DEFORMATION begins (Al -
370 Mpa, Steel-1500 Mpa, Cu 490 Mpa)
Some Important Definitions
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Different means of load applied
When a metal stretches, but does not break under a certain load, this point is called the _________ Point.
A: yield B: tensileC: stretch D: ultimate strength
Quiz time
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A close correlation/analogy
Necking begins
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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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Resilience property- stores energy and resists shocks or impacts
ToughnessAmount of energy absorbed by a material up to the fracture
Endurance property - withstand varying stresses or repeated application of stress.
Some More terms
Amount of energy absorbed by a material in the ELASTIC
regionToughness
CREEPING; deformation increases even under constant load
E.g..- Rubber stretching, concrete bridge
To be Precise ; A compelling competition
between elastic and plastic deformation
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Stress-Strain Relation for Different Engineering Materials
ferrous metals
non - ferrous metals
Brittle; don’t exhibit yielding before failure
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All dim. in mm
An another example
Structural steel
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Polyamide
Yet another piece of information
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A deeper look on stress-
strain curves
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A close comparison
areationalcrosseousIns
loadeousInsStressTrue T sectantan
tan)(
Original/actual area
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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. 0
n0
n L
L1or1
L
L
iT A
P)(
L
dL.
L
L
0t
0L
LIn
)1(0
nL
L
)1(In nt
Engineering stress/strain diagrams - elastic range, while true stress – strain diagrams
plastic range.
0L
Lnt