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Tensile test

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  • Propiedades mecnicas de materiales determinadas mediante el ensayo de traccinEn el ensayo de traccin las columnas giran a velocidad constante haciendo descender la plataforma inferior a velocidad constante v.La probeta est sujeta a la plataforma superior mediante una celda de carga que registra la fuerza aplicada a ella.

  • Mordazas

  • Celdas de Carga Extensmetro

  • Tensin (S) y deformacin (e) de IngenieraEngineering stress:Engineering strain:Original areaS = F/A0

  • Curva tensin (S) deformacin (e) de IngenieraTensile stress strain curveUTSMPa

  • Curva tensin deformacin verdaderas

  • DefinicionesYield strength (Y)Stress at which plastic deformation starts to occurYoungs modulus (E) S = Ee

    The slope of the linear elastic part of the curve

    Ultimate tensile strength (UTS)Maximum engineering stressStress at which necking or strain localization occurs

    2% Offset yield strength Y(0.002)

  • Tension test sequenceFigure 3.2 Typical progress of a tensile test: (1) beginning of test, no load; (2) uniform elongation and reduction of crosssectional area; (3) continued elongation, maximum load reached; (4) necking begins, load begins to decrease; and (5) fracture. If pieces are put back together as in (6), final length can be measured.

  • Figure 2.2 (a) Original and final shape of a standard tensile-test specimen. (b) Outline of a tensile-test sequence showing stages in the elongation of the specimen.Note: In this figure, length is denoted bylower case l.

  • DuctilidadDuctility: Measure of the amount of plastic deformation a material can take before it fractures.% Elongation to Fracture:

    % El is affected by specimen gage length. Short specimens show larger % El

    % Reduction in Area

    No specimen size effect when area in necked region is used

  • Typical mechanical properties a temperatura ambiente

    METALS (WROUGHT)

    E (GPa)

    Y (MPa)

    UTS (MPa)

    ELONGATION (%) in 50 mm

    POISSONS RATIO (

    Aluminum and its alloys

    Copper and its alloys

    Lead and its alloys

    Magnesium and its alloys

    Molybdenum and its alloys

    Nickel and its alloys

    Steels

    Stainless steels

    Titanium and its alloys

    Tungsten and its alloys

    69-79

    105-150

    14

    41-45

    330-360

    180-214

    190-200

    190-200

    80-130

    350-400

    35-550

    76-1100

    14

    130-305

    80-2070

    105-1200

    205-1725

    240-480

    344-1380

    550-690

    90-600

    140-1310

    20-55

    240-380

    90-2340

    345-1450

    415-1750

    480-760

    415-1450

    620-760

    45-5

    65-3

    50-9

    21-5

    40-30

    60-5

    65-2

    60-20

    25-7

    0

    0.31-0.34

    0.33-0.35

    0.43

    0.29-0.35

    0.32

    0.31

    0.28-0.33

    0.28-0.30

    0.31-0.34

    0.27

    NONMETALLIC MATERIALS

    Ceramics

    Diamond

    Glass and porcelain

    Rubbers

    Thermoplastics

    Thermoplastics, reinforced

    Thermosets

    Boron fiber

    Carbon fibers

    Glass fibers (S, E)

    Kevlar fibers (29, 49, 129)

    Spectra fibers (900, 1000)

    70-1000

    820-1050

    70-80

    0.01-0.1

    1.4-3.4

    2-50

    3.5-17

    380

    275-415

    73-85

    70-113

    73-100

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    -

    140-2600

    -

    140

    -

    7-80

    20-120

    35-170

    3500

    2000-5300

    3500-4600

    3000-3400

    2400-2800

    0

    -

    0

    -

    1000-5

    10-1

    0

    0

    1-2

    5

    3-4

    3

    0.2

    -

    0.24

    0.5

    0.32-0.40

    -

    0.34

    -

    -

    -

    -

    -

    Note: In the upper table the lowest values for E, Y, and UTS and the highest values for elongation are for the pure metals. Multiply GPa by 145,000 to obtain psi, and MPa by 145 to obtain psi. For example, 100 GPa = 14,500 ksi, and 100 MPa = 14,500 psi.

  • Tensin() y deformacin verdadera () Fig. 3.1 M. P. Groover, Fundamentals of Modern Manufacturing 3/e John Wiley, 2007True stress:True strain:

  • True Stress () & Strain ()More Accurate MeasurementTrue Stress

    True Strain

  • Comparacin deformacin de ingeniera y verdadera

  • Engineering Stress (S) /Strain (e) vs. True Stress () /Strain ()True Stress & Engineering Stress (Up to necking)

    True Strain & Engineering Strain (Up to necking)

    Conservacin de volumen:Al = A0l0

  • Relacin entre deformacin de Ingeniera y Deformacin Verdadera

  • Relacin tensin verdadera y tensin de ingenieraSSSSSeng = trueexp (- ) ; true = Sexp ()

  • Comparacin curvas tensin deformacin de ingeniera y verdaderae a la tensin mxima (UTS) a la tensin mxima (UTS)Trazo negro, la deformacin se mide con el rea del cuello

  • True Stress-Strain CurveConstitutive Eq. (plastic range)K :strength coefficient(true stress at unit true strain)n :strain hardening exponent ( coeficiente de endurecimientopor deformacin)

  • Papel grficoLog-Log

    Mdulos cuadrados.La escala progresa en mltiplos de 10.El origen puede ser elegido.

    10x 10x+1 10x+2 10x+3 10x+4 10y+4

    10y+3

    10y+2

    10y+1

    10x

  • Typical Values for K and n at Room Temperature = Kn

    TABLE

    K (MPa)

    n

    Aluminum

    1100O

    2024T4

    6061O

    6061T6

    7075O

    Brass

    7030, annealed

    8515, cold-rolled

    Cobalt-base alloy, heat-treated

    Copper, annealed

    Steel

    Low-C annealed

    4135 annealed

    4135 cold-rolled

    4340 annealed

    304 stainless, annealed

    410 stainless, annealed

    180

    690

    205

    410

    400

    900

    580

    2070

    315

    530

    1015

    1100

    640

    1275

    960

    0.20

    0.16

    0.20

    0.05

    0.17

    0.49

    0.34

    0.50

    0.54

    0.26

    0.17

    0.14

    0.15

    0.45

    0.10

  • Coeficiente de endurecimiento por deformacin (n)Se puede demostrar fcilmente que la deformacin verdadera Fmax cuando se llega a la carga mxima es igual a n.F = AdF= ddA+Ad=0 Condicin carga mximad/ = - dA/A = dl/L= d (conservacin de volumen)d/d = Si = KnnKn-1 = Kn Se llega a n=

    Por tanto el valor de n sirve para estimar la magnitud de la deformacin a la carga mxima y consecuentemente la deformacin homognea que se puede aplicar a un material.

  • Typical values of K and n ( = Kn)

    MATERIAL

    K (MPa)

    n

    Aluminum, 1100-O

    2024-T4

    5052-O

    6061-O

    6061-T6

    7075-O

    Brass, 70-30, annealed

    85-15, cold-rolled

    Bronze (phosphor), annealed

    Cobalt-base alloy, heat treated

    Copper, annealed

    Molybdenum, annealed

    Steel, low-carbon, annealed

    1045 hot-rolled

    1112 annealed

    1112 cold-rolled

    4135 annealed

    4135 cold-rolled

    4340 annealed

    17-4 P-H annealed

    52100 annealed

    304 stainless, annealed

    410 stainless, annealed

    180

    690

    210

    205

    410

    400

    895

    580

    720

    2070

    315

    725

    530

    965

    760

    760

    1015

    1100

    640

    1200

    1450

    1275

    960

    0.20

    0.16

    0.13

    0.20

    0.05

    0.17

    0.49

    0.34

    0.46

    0.50

    0.54

    0.13

    0.26

    0.14

    0.19

    0.08

    0.17

    0.14

    0.15

    0.05

    0.07

    0.45

    0.10

    Note: 100 MPa = 14,500 psi.

  • Comportamiento elstico

  • Transicin elasto-plstica

    El comportamiento elstico termina cuando comienza a producirse deformacin plstica, la que ocurre por desplazamiento de dislocaciones (irreversible)La tensin de fluencia o lmite elstico seala el inicio perceptible de la deformacin plstica.En algunos metales (Cu, Al, etc) es difcil determinar la tesnin de fluencia, por tanto convencionalmente se define sta como el nivel de tensin desde el cual, descargando elsticamente, queda una deformacin plstica de 0,2% (0,002)

  • Comportamiento plsticoValores tpicos de n a temperatura ambiente:acero= 0,01 Cobre = 0,005 Aluminio 0

  • Tensin de fluencia o lmite elstico al subir la temperaturaLa tensin de fluencia se reduce al subir la temperatura, por esto un material en caliente ofrece menos resistencia a la deformacin plsticaLa tensin de fluencia de un acero de 0,15%C, a 25C es 500 Mpa, a 220C es 400MPa y a 600C es 200MPa

  • A alta temperatura el nivel de la curva sube si sube d/dt.Por tanto la resistencia a la deformacin plstica a alta temperatura depende de la velocidad de deformacin d/dt.

  • Coeficiente de sensibilidad a la velocidad de deformacin (m)

  • At high temperature strain rate is important, but strain hardening is not so important

    To calculate the flow stress at high (T/TM>0.5) temperature we will use:At low temperature strain hardening is important, but strain rate is not so important

    To calculate the flow stress at low (T/TM

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