Section 6: MECHANICAL PROPERTIES.


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2. 1. Starting. 2. Little load. 3. Empty. Versatile means reversible!. Flexible DEFORMATION. 3. 1. Introductory. 2. Little load. 3. Empty. Plastic means lasting!. PLASTIC DEFORMATION (METALS). 4.
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Slide 1

Part 6: MECHANICAL PROPERTIES ISSUES TO ADDRESS... • Stress and strain : What are they and why are they utilized rather than burden and twisting? • Elastic conduct: When burdens are little, what amount of distortion happens? What materials misshape minimum? • Plastic conduct: when do separations bring about changeless disfigurement? What materials are most impervious to changeless twisting? • Toughness and malleability : What are they and how would we gauge them? 1

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ELASTIC DEFORMATION 1. Introductory 2. Little load 3. Empty Elastic means reversible ! 2

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PLASTIC DEFORMATION (METALS) 1. Introductory 2. Little load 3. Empty Plastic means changeless ! 3

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ENGINEERING STRESS • Tensile anxiety, s : • Shear stress, t : Stress has units: N/m 2 or lb/in 2 4

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COMMON STATES OF STRESS • Simple pressure: link Ski lift (photograph civility P.M. Anderson) • Simple shear: drive shaft Note: t = M/A c R here. 5

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OTHER COMMON STRESS STATES (1) • Simple pressure: (photograph cordiality P.M. Anderson) Note: compressive structure part ( s < 0 here). (photograph kindness P.M. Anderson) 6

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OTHER COMMON STRESS STATES (2) • Bi-pivotal strain: • Hydrostatic pressure: Pressurized tank (photograph obligingness P.M. Anderson) (photograph affability P.M. Anderson) s < 0 h 7

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ENGINEERING STRAIN • Tensile strain: • Lateral strain: • Shear strain: Strain is constantly dimensionless. 8

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STRESS-STRAIN TESTING • Typical elastic example • Typical malleable test machine Adapted from Fig. 6.2, Callister 6e. • Other sorts of tests: - pressure: weak materials (e.g., concrete) - torsion: round and hollow tubes, shafts. Adjusted from Fig. 6.3, Callister 6e. (Fig. 6.3 is taken from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials , Vol. III, Mechanical Behavior , p. 2, John Wiley and Sons, New York, 1965.) 9

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LINEAR ELASTIC PROPERTIES • Modulus of Elasticity, E : (otherwise called Young\'s modulus) • Hooke\'s Law : s = e • Poisson\'s proportion, n : metals: n ~ 0.33 earthenware production: ~0.25 polymers: ~0.40 Units: E: [GPa] or [psi] n : dimensionless 10

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OTHER ELASTIC PROPERTIES • Elastic Shear modulus, G: straightforward torsion test t = g • Elastic Bulk modulus, K: weight test: Init. vol =V o . Vol chg. = D V • Special relations for isotropic materials: 11

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YOUNG\'S MODULI: COMPARISON Graphite Ceramics Semicond Metals Alloys Composites/filaments Polymers E(GPa) Based on information in Table B2, Callister 6e . Composite information in view of fortified epoxy with 60 vol% of adjusted carbon (CFRE), aramid (AFRE), or glass (GFRE) strands. 12

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USEFUL LINEAR ELASTIC RELATIONS • Simple pressure: • Simple torsion: • Material, geometric, and stacking parameters all add to redirection. • Larger versatile moduli minimize flexible diversion. 13

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PLASTIC (PERMANENT) DEFORMATION (at lower temperatures, T < T melt/3) • Simple strain test: 14

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YIELD STRENGTH, s y • Stress at which observable plastic disfigurement has happened. at the point when e p = 0.002 15

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YIELD STRENGTH: COMPARISON Room T values Based on information in Table B4, Callister 6e . a = toughened hr = hot moved ag = matured album = icy drawn cw = icy worked qt = extinguished & tempered 16

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TENSILE STRENGTH, TS • Maximum conceivable building stress in pressure. Adjusted from Fig. 6.11, Callister 6e. • Metals: happens when perceptible necking begins. • Ceramics: happens when split engendering begins. • Polymers: happens when polymer spines are adjusted and going to break. 17

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TENSILE STRENGTH: COMPARISON Room T values Based on information in Table B4, Callister 6e . a = strengthened hr = hot moved ag = matured album = chilly drawn cw = icy worked qt = extinguished & tempered AFRE, GFRE, & CFRE = aramid, glass, & carbon fiber-fortified epoxy composites, with 60 vol% strands. 18

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DUCTILITY, %EL • Plastic pliable strain at disappointment: Adapted from Fig. 6.13, Callister 6e. • Another flexibility measure: • Note: %AR and %EL are regularly similar. - Reason: gem slip does not change material volume. - %AR > %EL conceivable if inward voids structure in neck. 19

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TOUGHNESS • Energy to break a unit volume of material • Approximate by the territory under the anxiety strain bend. 20

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HARDNESS • Resistance to for all time indenting the surface. • Large hardness implies: - imperviousness to plastic distortion or breaking in pressure. - better wear properties. Adjusted from Fig. 6.18, Callister 6e. (Fig. 6.18 is adjusted from G.F. Kinney, Engineering Properties and Applications of Plastics , p. 202, John Wiley and Sons, 1957.) 21

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HARDENING • An expansion in s y because of plastic twisting. • Curve fit to the anxiety strain reaction: 22

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DESIGN OR SAFETY FACTORS • Design instabilities mean we don\'t push the point of confinement. • Factor of wellbeing, N Often N is somewhere around 1.2 and 4 • Ex: Calculate a distance across, d, to guarantee that yield does not happen in the 1045 carbon steel pole underneath. Utilize an element of security of 5. 5 23

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SUMMARY • Stress and strain : These are size-free measures of burden and removal, separately. • Elastic conduct: This reversible conduct regularly demonstrates a straight connection amongst anxiety. To minimize misshapening, select a material with an extensive flexible modulus (E or G). • Plastic conduct: This lasting disfigurement conduct happens when the elastic (or compressive) uniaxial stress achieves s y . • Toughness : The vitality expected to break a unit volume of material. • Ductility : The plastic strain at disappointment. Note: For materials determination cases identified with mechanical conduct, see slides 22-4 to 22-10. 24

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ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: 0

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