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สมบัติเชิงกลของวัสดุ PowerPoint PPT Presentation


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บทที่ 5. สมบัติเชิงกลของวัสดุ. 1. ความเค้น. ความเค้น ( stress) คือ  แรงกระทำในเนื้อวัสดุต่อหนึ่งหน่วยพื้นที่ที่ตั้งฉากหรือขนานกับแรงนั้น . มีหน่วยเป็น N/m 2 หรือ  Pa หรือ lb/in 2 1 N/m 2 = 1 Pa 1 lb/in 2 = 6.89 10 3 Pa.

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สมบัติเชิงกลของวัสดุ

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5


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1.

(stress)

N/m2 Pa lb/in2

1 N/m2 = 1 Pa

1 lb/in2 = 6.89103 Pa


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Ex = 0.500 2500 lb

= 2500/ (/4)(0.5)2

= 12700 lb/m2


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2. (Strain)

() = (l - lo) (lo)

Ex : 0.5 0.04 8 2.00 2.65


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3. Poisson Ratio

http://training.ce.washington.edu/WSDOT/Modules/03_materials/Images/Main%20Page%20Pictures/poisson.jpg


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Typical Values of Poissons Ratio


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4. Shear

http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Shear_scherung.svg/602px-Shear_scherung.svg.png

http://www.eng.uc.edu/~gbeaucag/RyanBreese/Rheolog/rheology_files/image001.jpg


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Tensile Testing

http://www.ssi.shimadzu.com/products/images/testing/iso527-tensile-image1.jpg


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http://www.mtec.or.th/labs/mech/tips7.html

http://www.twi.co.uk/twiimages/jk69f4.gif


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http://upload.wikimedia.org/wikipedia/commons/6/6f/Al_tensile_test.jpg


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Stress vs. Strain curve typical of structural steel

1. Ultimate Strength2. Yield Strength3. Rupture4. Strain hardeningregion5. Necking region

A: Apparent stress (F/A0)B: Actual stress (F/A)


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1. Elastic modulus

  • Elastic modulus : Hooks law

    • = E

  • E = /

  • E = Elastic modulus = Youngs modulus

  • : psi / Pa


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    2. Yield strength

    • 0.2% offset (proof strength/ offset yield strength)

    • (plastic deformation)

    3. Ultimate strength

    • -

    4. % Elongation

    5. % Reduction Area


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    http://www.auf.asn.au/const_images/stress_strain4.jpg


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    The Bend Test for Brittle Materials

    Yield strength, Tensile strength, Breaking strength : are the same

    Flexural strength = modulus of rupture

    F = fracture load

    L = distance between the two outer point

    w = width of the specimen

    h = height of the specimen

    http://www.emeraldinsight.com/fig/0180570504001.png


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    www.aws.org/itrends/11-03/feature1.html

    www.thefabricator.com/WeldingInspection/Weldi...

    http://meetjoeblog.net/wp-content/uploads/2009/02/bending_test.jpg


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    (Hardness Test)


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    Brinell Rockwell

    Shore , Vickers, Rockwell superficial Herbert

    (microhardness tester) Knoop


    Brinell

    Brinell

    • 10 mm.

    • 3000 kg 1500 kg 500 kg


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    www.twi.co.uk/content/jk74.html


    Rockwell

    Rockwell

    • Rockwell

    • Brinell Rockwell

    • Brinell Rockwell ASTM E 18


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    • 10 kg

    • 60 100 kg 150 kg 1/16 1/8 1/4 1/2


    Rockwell1

    Rockwell

    (kg)

    A 60

    B 1/16 100

    C 150

    D 100

    E 1/8 100

    F 1/16 60

    G 1/16 150


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    Principal of the Rockwell Test

    1. The indenter moves down into position on the part surface

    2. A minor load is applied and a zero reference position is established

    3. The major load is applied for a specified time period (dwell time) beyond zero

    4. The major load is released leaving the minor load applied

    The resulting Rockwell number represents the difference in depth from the zero reference position as a result of the application of the major load.

    home.iitk.ac.in/~kamalkk/ME-371.htm


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    The Hardness Test : Rockwell Hardness Test

    • Rockwell hardness values are expressed as a combination of a hardness number and a scale symbol representing the indenter and the minor and major loads.

    • The hardness number is expressed by the symbol HR and the scale designation. There are 30 different scales. The majority of applications are covered by the Rockwell C and B scales for testing steel, brass, and other metals. However, the increasing use of materials other than steel and brass as well as thin materials necessitates a basic knowledge of the factors that must be considered in choosing the correct scale to ensure an accurate Rockwell test.

    • The choice is not only between the regular hardness test and superficial hardness test, with three different major loads for each, but also between the diamond indenter and the 1/16, 1/8, 1/4 and 1/2 in. diameter steel ball indenters.

    • If no specification exists or there is doubt about the suitability of the specified scale, an analysis should be made of the following factors that control scale selection:

    • Type of material

    • Specimen thickness

    • Test location

    • Scale limitations


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    HR = E e

    F0 = preliminary minor load in kgf

    F1= additional major load in kgf

    F= total load in kgf

    e = permanent increase in depth of penetration due to major load F1 measured in units of 0.002 mm

    E= a constant depending on form of indenter: 100 units for diamond indenter, 130 units for steel ball indenter

    HR = Rockwell hardness number

    D = diameter of steel ball.

    home.iitk.ac.in/~kamalkk/ME-371.htm


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    Advantages of the Rockwell hardness method include the direct Rockwell hardness number readout and rapid testing time. Disadvantages include many arbitrary non-related scales and possible effects from the specimen support anvil (try putting a cigarette paper under a test block and take note of the effect on the hardness reading! Vickers and Brinell methods don't suffer from this effect).

    www.ami.ac.uk/courses/topics/0123_mpm/index.html


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    Rockwell 100

    0.002 mm 4 53 HRB 56 HRB 3 x 0.002 mm 0.006 mm

    B 0 100 HRB 100 HRB

    C 100 HRB 70 HRC C 20 HRC 20 HRC


    Vickers

    Vickers

    136

    5-120 5 Brinell


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    F= Load in kgfd = Arithmetic mean of the two diagonals, d1 and d2 in mmHV = Vickers hardness

    www.twi.co.uk/content/jk74.html

    www.bestar-steel.com/cn/hardnessTesting.php


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    http://www.nhml.com/i/resources_NHML_hardness_testing_fig2.gif


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    Hardness of plastics and elastomers

    www.engineeringpolymers.com/epbb/ch09.html


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    http://www.iun.edu/~geos/Zoran%20IUN/G%20101/Photos/Mohs%20%20scale.jpg


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    Impact Test

    www.wmtr.com/Content/impact_testing.htm

    www.castingmanufacturers.com/facilities.asp


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    Charpy impact test

    http://www.twi.co.uk/twiimages/jk71f2.gif


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    :

    www.steinwall.com/ART-impact-testing.html

    http://www.matweb.com/reference/images/izod_apparatus.gif


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    Creep Test

    http://www.pktooling.co.uk/pk-images/gm-aerosol-creep-test-fixture.jpg

    www.twi.co.uk/content/jk81.html


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    www.twi.co.uk/content/jk81.html

    www.engr.usask.ca/.../geoe118/geoe118.037.html


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    Fatigue Test

    http://www.surfaceng.com/photos/large/testing_fatigue1.jpg

    www.risoe.dk/afm/products/mechanical/fatigue.htm

    www.dynaflow-inc.com/Services/matr&d.htm


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    http://www.engrasp.com/doc/etb/mod/fm1/stresslife/Figure5.gif


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