IE 337: Introduction to Manufacturing Systems

IE 337: Material & Proses PembuatanTopik 2: Sifat Alam dan Mekanik Sebuah LogamChapters 2 and 3

IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre12Tempo DuluHubungan Proses Material - GeometriPembutan materialProses PembuatanBagaimana kita memproses karakterisasinya?

IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre23Masa KiniLogamSifat Original Logam (Chapter 2)Sifat Mekanik (Chapter 3)IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre3Ikatan IonikGambar 2.4 Tiga bentuk ikatan utama: (a) Ionic

Atom dari salah satu unsur melepaskan elektron terluar mereka (s), yang pada gilirannya tertarik pada atom dari beberapa unsur lain untuk meningkatkan jumlah elektron di kulit terluar menjadi delapan

4IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre4Ikatan KovalenGambar 2.4 Tiga bentuk ikatan utama: (b) kovalen

Elektron dipakai bersama (sebagai lawan ditransfer) antara atom dalam kulit terluarnya untuk mencapai sekumpulan yang stabil dari delapan

5IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre5Ikatan LogamGambar 2.4 Tiga bentuk ikatan utama: (c) logam

Membagi elektron kulit terluar oleh semua atom untuk membentuk awan elektron secara umum yang menembus seluruh blok

6IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre6Gambar 2.1 Tabel Periodik Unsur. Nomor atom dan simbol terdaftar dalam 103 unsur.

Tabel Periodik7Notice that the vast majority of metals have a dearth of electrons.IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre7 Struktur Makroskopik Sebuah MateriAtom dan molekul adalah blok bangunan dari struktur makroskopik suatu materialKetika bahan memperkuat dari keadaan cair, material cenderung menyatu dengan erat/kuat, mengatur diri menjadi salah satu dari dua struktur : KristalNonkristal

8IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre8Struktur KristalStruktur di mana atom berada pada posisi teratur dan berulang dalam tiga dimensiSel satuan - mengelompokkan dengan geometris dasar atom yang berulangPola ini dapat ditiru jutaan kali dalam kristal tertentuKarakteristik struktur hampir semua logam, maupun banyak keramik serta beberapa dari polimer9IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre9Tiga Struktur Kristal pada LogamBody-centered cubicFace centered cubicHexagonal close-packed

Gambar 2.8 Tiga jenis struktur kristal dalam logam10IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre10Struktur kristal untuk Logam UmumSuhu kamar/ruang struktur kristal untuk beberapa logam biasa:Bodycentered cubic (BCC) Kromium, Besi, Molibdenum, TungstenFacecentered cubic (FCC) Aluminium, Tembaga, Emas, Timbal, Perak, NikelHexagonal closepacked (HCP)Magnesium, Titanium, Seng11BCC has highest number of slip planes + are strongest materials which requires higher forces to cause slip.IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre11Ketidaksempurnaan (Cacat) dalam KristalKetidaksempurnaan sering muncul akibat ketidakmampuan memperkuat bahan untuk melanjutkan replikasi sel satuan, misalnya, batas butir dalam logamKetidaksempurnaan bisa juga diperkenalkan dengan sengaja, misalnya, penambahan bahan paduan dalam sebuah logamJenis jenis dari cacat: Cacat TitikCacat GarisCacat Permukaan12IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre12

Cacat TitikKetidaksempurnaan dalam struktur kristal yang melibatkan baik satu atom atau beberapa jumlah atomGambar 2.9 Cacat Titik: (a) kekosongan, (b) pasangan ion lowongan, (c) interstitialcy, (d) ion pengungsi (Frenkel Defect).13IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre13Cacat GarisTerhubung kelompok cacat titik yang membentuk garis dalam struktur kisiCacat garis yang paling penting adalah dislokasi, yang dapat mengambil dua bentuk:Dislokasi tepiDislokasi putaran14IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre14Dislokasi TepiGambar 2.10 Cacat garis: (a) Dislokasi tepi

Pinggiran suatu bidang tambahan atom yang ada di kisi

15IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre15Dislokasi Putaran Imperfections that extend in two directions to form a boundary Examples:External: the surface of a crystalline object is an interruption in the lattice structure Internal: grain boundaries are internal surface interruptions 16IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre16Elastic StrainWhen a crystal experiences a gradually increasing stress, it first deforms elasticallyIf force is removed lattice structure returns to its original shape

Figure 2.11 Deformation of a crystal structure: (a) original lattice: (b) elastic deformation, with no permanent change in positions of atoms.17IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre17Plastic StrainIf stress is higher than forces holding atoms in their lattice positions, a permanent shape change occurs

Figure 2.11 Deformation of a crystal structure: (c) plastic deformation (slip), in which atoms in the lattice are forced to move to new "homes.18IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre18Effect of Dislocations on StrainIn the series of diagrams, the movement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice

Figure 2.12 Effect of dislocations in the lattice structure under stress19Motion of the edge dislocations is what provides for slipIE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre19Mechanical Properties in Design and ManufacturingMechanical properties determine a materials behavior when subjected to mechanical stresses Properties include elastic modulus, ductility, hardness, and various measures of strength Dilemma: mechanical properties desirable to the designer, such as high strength, usually make manufacturing more difficult The manufacturing engineer should appreciate the design viewpoint And the designer should be aware of the manufacturing viewpoint20IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre20StressStrain RelationshipsThree types of static stresses to which materials can be subjected: Tensile - tend to stretch the materialCompressive - tend to squeeze itShear - tend to cause adjacent portions of material to slide against each other Stressstrain curve - basic relationship that describes mechanical properties for all three types21IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre21Tensile TestMost common test for studying stressstrain relationship, especially metals In the test, a force pulls the material, elongating it and reducing its diameter

Figure 3.1 Tensile test: (a) tensile force applied in (1) and (2) resulting elongation of material

22IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre22Tensile Test SpecimenASTM (American Society for Testing and Materials) specifies preparation of test specimen

Figure 3.1 Tensile test: (b) typical test specimen

23IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre23Tensile Test Setup

24IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre24Tensile 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.

25IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre25Engineering StressDefined as force divided by original area:

where e = engineering stress, F = applied force, and Ao = original area of test specimen

26IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre26Engineering StrainDefined at any point in the test as where e = engineering strain; L = length at any point during elongation; and Lo = original gage length

27IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre27Stress-Strain RelationshipsFigure 3.3 Typical engineering stressstrain plot in a tensile test of a metal.

28IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre28Two Regions of StressStrain CurveThe two regions indicate two distinct forms of behavior: Elastic region prior to yielding of the materialPlastic region after yielding of the material29IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre29Elastic Region in StressStrain CurveRelationship between stress and strain is linearMaterial returns to its original length when stress is removed

Hooke's Law: e = E e

where E = modulus of elasticity

E is a measure of the inherent stiffness of a materialIts value differs for different materials 30IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre30Yield Point in StressStrain CurveAs stress increases, a point in the linear relationship is finally reached when the material begins to yieldYield point Y can be identified by the change in slope at the upper end of the linear region Y = a strength propertyOther names for yield point = yield strength, yield stress, and elastic limit31IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre31Plastic Region in StressStrain CurveYield point marks the beginning of plastic deformationThe stress-strain relationship is no longer guided by Hooke's Law As load is increased beyond Y, elongation proceeds at a much faster rate than before, causing the slope of the curve to change dramatically 32IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre32Tensile Strength in StressStrain CurveElongation is accompanied by a uniform reduction in crosssectional area, consistent with maintaining constant volume Finally, the applied load F reaches a maximum value, and engineering stress at this point is called the tensile strength TS (a.k.a. ultimate tensile strength)

TS =

33IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre33Ductility in Tensile TestAbility of a material to plastically strain without fractureDuctility measure = elongation ELwhere EL = elongation; Lf = specimen length at fracture; and Lo = original specimen lengthLf is measured as the distance between gage marks after two pieces of specimen are put back together

34IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre34True StressStress value obtained by dividing the instantaneous area into applied loadwhere = true stress; F = force; and A = actual (instantaneous) area resisting the load

35IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre35True StrainProvides a more realistic assessment of "instantaneous" elongation per unit length

36IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre36True Stress-Strain CurveFigure 3.4 True stressstrain curve for the previous engineering stressstrain plot in Figure 3.3.

37IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre37Strain Hardening in Stress-Strain CurveNote that true stress increases continuously in the plastic region until neckingIn the engineering stressstrain curve, the significance of this was lost because stress was based on an incorrect area valueIt means that the metal is becoming stronger as strain increases This is the property called strain hardening 38IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre38True Stress-Strain in Log-Log PlotFigure 3.5 True stressstrain curve plotted on loglog scale.

39IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre39Flow Curve Because it is a straight line in a log-log plot, the relationship between true stress and true strain in the plastic region is where K = strength coefficient; and n = strain hardening exponent

40IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre40Compression TestApplies a load that squeezes the ends of a cylindrical specimen between two platens

Figure 3.7 Compression test: (a) compression force applied to test piece in (1) and (2) resulting change in height.

41IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre41Compression Test Setup

42IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre42Shear PropertiesApplication of stresses in opposite directions on either side of a thin element

Figure 3.11 Shear (a) stress and (b) strain.

43IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre43HardnessResistance to permanent indentation Good hardness generally means material is resistant to scratching and wearMost tooling used in manufacturing must be hard for scratch and wear resistance 44IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre44Hardness Tests Commonly used for assessing material properties because they are quick and convenientVariety of testing methods are appropriate due to differences in hardness among different materials Most wellknown hardness tests are Brinell and Rockwell Other test methods are also available, such as Vickers, Knoop, Scleroscope, and durometer45IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre45Widely used for testing metals and nonmetals of low to medium hardness A hard ball is pressed into specimen surface with a load of 500, 1500, or 3000 kgFigure 3.14 Hardness testing methods: (a) Brinell

Brinell Hardness Test46IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre46Brinell Hardness NumberLoad divided into indentation area = Brinell Hardness Number (BHN)

where HB = Brinell Hardness Number (BHN), F = indentation load, kg; Db = diameter of ball, mm, and Di = diameter of indentation, mm47IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre47Rockwell Hardness TestAnother widely used testA cone shaped indenter is pressed into specimen using a minor load of 10 kg, thus seating indenter in materialThen, a major load of 150 kg is applied, causing indenter to penetrate beyond its initial positionAdditional penetration distance d is converted into a Rockwell hardness reading by the testing machine48IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre48Rockwell Hardness TestFigure 3.14 Hardness testing methods: (b) Rockwell: (1) initial minor load and (2) major load.

49IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre49Effect of Temperature on Properties

Figure 3.15 General effect of temperature on strength and ductility.50IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre50Hot HardnessAbility of a material to retain hardness at elevated temperatures

Figure 3.16 Hot hardness typical hardness as a function of temperature for several materials.

51IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre5152You should have learned:The nature of metalsDifferent crystalline structuresDifferent crystalline defects that affect propertiesThe properties of metalsMechanical propertiesWhat they are and what they meanIE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre5253Next ClassManufacturing Materials (Chapter 6)How can we modify mechanical properties in metals? (Chapter 6 and 27)How are metal alloys classified and how are they used? (Chapter 6)

Assignment #1IE 337 Lecture 1: Introduction to Manufacturing SystemsS.V. Atre53