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Production techniques_material properties Mohsen Badrossamay 1 Dep. of Mech. Eng. DEPARTMENT OF MECHANICAL ENGINEERING ISFAHAN UNIVERSITY OF TECHNOLOGY روﺷﻬﺎي ﺗﻮﻟﯿﺪ و ﻛﺎرﮔﺎهPRODUCTION TECHNIQUES FUNDAMENTALS OF MATERIALS: BEHAVIOR AND MANUFACTURING PROPERTIES PART ONE Dep. of Mech. Eng. Diversity of used materials in automobiles 2

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Page 1: Diversity of used materials in automobiles · Ferrous Amorphous Nonferrous Plastics Thermop lastics Thermosets Elastomers ceramics and others Composites 3 ... Solidified metal, showing

Production techniques_material properties

Mohsen Badrossamay 1

Dep. of Mech. Eng.

DEPARTMENT OF MECHANICAL ENGINEERINGISFAHAN UNIVERSITY OF TECHNOLOGY

روشهاي تولید و كارگاه PRODUCTION TECHNIQUES

FUNDAMENTALS OF MATERIALS: BEHAVIOR AND MANUFACTURING PROPERTIES

PART ONE

Dep. of Mech. Eng.

Diversity of used materials in automobiles

2

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Production techniques_material properties

Mohsen Badrossamay 2

Dep. of Mech. Eng.

Engineering Materials

Engineering materials

Metals

Ferrous

Amorphous

NonferrousPlastics

Thermoplastics

Thermosets Elastomers

ceramics and others

Composites

3

Dep. of Mech. Eng.

Selecting Materials

Considerations:

Properties of materials

Mechanical properties

Physical properties

Chemical properties

Manufacturing properties

Cost and availability

Appearance, service life, and recycling

4

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Production techniques_material properties

Mohsen Badrossamay 3

Dep. of Mech. Eng.

Behavior & Manufacturing Properties

5

Dep. of Mech. Eng.

The Structure of Metals

6

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Production techniques_material properties

Mohsen Badrossamay 4

Dep. of Mech. Eng.

Crystal Structure of Metals

Body-centered cubic (BCC) - alpha iron, chromium, molybdenum, tantalum, tungsten, and vanadium.

Face-centered cubic (FCC) - gamma iron, aluminum, copper, nickel, lead, silver, gold and platinum.

Hexagonal close-packed - beryllium, cadmium, cobalt, magnesium, alpha titanium, zinc and zirconium

Common crystal structures for metals:

Why different crystal structure?To minimize the energy required to fit together in a regular pattern

7

Dep. of Mech. Eng.

Body-centered Cubic Crystal Structure

The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells

8

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Production techniques_material properties

Mohsen Badrossamay 5

Dep. of Mech. Eng.

Face-centered Cubic Crystal Structure

The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells

9

Dep. of Mech. Eng.

Hexagonal Close-packed Crystal Structure

The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells.

10

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Production techniques_material properties

Mohsen Badrossamay 6

Dep. of Mech. Eng.

Deformation and strength of single crystal

Elastic deformation Plastic deformation Mechanisms of plastic deformation:

Slipping of one plane of atoms over an adjacent plane (called slip plane) under a shear stress The shear stress required to cause slip in a single crystal is directly

proportional to the b/a ratio, where a is the spacing of the atomic planes and b is inversely proportional to the atomic density in the atomic plane.

As b/a decreases, the shear stress required to cause slip decreases Slip in a single crystal takes place along planes of maximum atomic density,

i.e. slip takes place in closely packed planes and in closely packed directions Because b/a ratio properties varies for different directions within crystal, a

single crystal has different properties that is called anisotropic Twinning: a portion of the crystal forms a mirror image of itself across

the plane of twinning Twins form abruptly and are the cause of the creaking sound (tin cry) that occurs when

a tin or zinc rod is bent at room temperature 11

Dep. of Mech. Eng.

Permanent Deformation

Permanent deformation (also called plastic deformation) of a single crystal subjected to a shear stress: (a) structure before deformation; (b) permanent deformation by slip.

The shear stress required to cause slip in a single crystal is directly proportional to the b/a ratio, where a is the spacing of the atomic planes and b is inversely proportional to the atomic density in the atomic plane.

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Production techniques_material properties

Mohsen Badrossamay 7

Dep. of Mech. Eng.

Permanent Deformation and Twinning in Crystal

(a) Permanent deformation of asingle crystal under a tensileload. Note that the slip planestend to align themselves in thedirection of the pulling force.This behavior can be simulatedusing a deck of cards with arubber band around them.

(b) Twinning in a single crystal intension.

13

Dep. of Mech. Eng.

Slip systems Slip system: the combination of a slip plane and its

direction of slip Generally metals with 5 or more slip systems are ductile In bcc crystals

There are 48 possible slip systems i.e. high probability to slip Because of relatively high b/a ratio, the required shear stress is high Generally have good strength and moderate ductility

In fcc crystals There are 12 possible slip systems i.e. moderate probability to slip The required shear is low because of the relatively low b/a ratio Generally have moderate strength and good ductility

In hcp crystals There are 3 possible slip systems i.e. low probability to slip More slip systems become active at elevated temperatures Brittle at room temperature 14

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Production techniques_material properties

Mohsen Badrossamay 8

Dep. of Mech. Eng.

Slip Lines and Slip Bands in Crystal

Schematic illustration of slip lines and slip bands in a single crystal (grain) subjected to a shear stress. A slip band consists of a number of slip planes. The crystal at the center of the upper illustration is an individual grain surrounded by several other grains

15

Dep. of Mech. Eng.

Imperfections in the crystal structure

The actual strength of metals is approximately one to two orders of magnitude lower than the strength levels obtained from theoretical calculations

the reason is addressed by imperfections and defects Structure-sensitive and structure-insensitive properties

Types of defects in crystals:1. Point defects, such as a vacancy (missing atom), an interstitial

atom (extra atom in the lattice), or an impurity (foreign atom that has replaced the atom of the pure metal)

2. Linear, or one-dimensional defects called dislocations3. Planar, or two-dimensional imperfections such as grain boundaries

and phase boundaries4. Volume, or bulk imperfections such as voids, inclusions, other

phases, or cracks16

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Production techniques_material properties

Mohsen Badrossamay 9

Dep. of Mech. Eng.

Defects in a Single-Crystal Lattice

Schematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional

17

Dep. of Mech. Eng.

Dislocations in Crystals

Dislocations are defects in the orderly arrangement of a metal’s atomic structure and help explain the discrepancy between the actual and theoretical strengths of metals

Presence of dislocation lowers the shear stress required to cause slip

Types of dislocations in a single crystal: (a) edge dislocation; and (b) screw dislocation18

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Production techniques_material properties

Mohsen Badrossamay 10

Dep. of Mech. Eng.

Edge Dislocation Movement

Movement of an edge dislocation across the crystal lattice under a shear stress. Dislocations help explain why the actual strength of metals is much lower than that predicted by theory.

19

Dep. of Mech. Eng.

Work hardening Dislocations can:

1. Become entangled and interfere with each other; and2. Be impeded by barriers, such as grain boundaries and impurities

and inclusions in the material

Entanglements and impediments increase the shear stress required for slip

The effect of an increase in shear stress, thus causing an increase in overall strength and hardness of the metal, is known as work hardening or strain hardening

Work hardening is used for strengthening metals in metalworking processes at ambient temperature

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Production techniques_material properties

Mohsen Badrossamay 11

Dep. of Mech. Eng.

Solidification of Molten Metal

Schematic illustration of the stages during solidification of molten metal; each small square represents a unit cell.

(a) Nucleation of crystals at random sites in the molten metal; note that the crystallographic orientation of each site is different.

(b) and (c) Growth of crystals as solidification continues.

(d) Solidified metal, showing individual grains and grain boundaries; note the different angles at which neighboring grains meet each other.

21

Dep. of Mech. Eng.

Grain Size

where

N = Grains per square inch at 100x magnification

n = ASTM grain size number

N = 2n-1

ASTM Grain Size:

22

Mechanical properties of metals are affected from grain size

Large grain size generally is associated with low strength, low hardness, and low ductility

Grain size is measured by counting the number of grains in a given area, or by counting the number of grains that intersect a length of a line randomly drawn on an enlarged photograph of the grains

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Mohsen Badrossamay 12

Dep. of Mech. Eng.

Plastic Deformation of Idealized Grains

Plastic deformation of idealized (equiaxed) grains in a specimen subjected to compression (such as occurs in the forging or rolling of metals): (a) before deformation; and (b) after deformation. Note the alignment of grain boundaries along a horizontal direction; this effect is known as preferred orientation.

23

Dep. of Mech. Eng.

Recovery, recrystallization, and grain growth

Plastic deformation at room temperature causes: 1. The deformation of grains and grain boundaries2. A general increase in strength3. A decrease in ductility4. Anisotropic behavior

Heating the metal to a specific temperature range for a period of time (annealing) can reverse those effects

The events take place during heating1. Recovery (stress relief)

Occurs at a certain temperature range below the recrystalization temperature

2. Recrystallizationnew equiaxed and strain-free grains are formedTemperature range approximately between 0.3 and 0.5 melting point of the metalRecrystallization decreases the density of dislocations, lowers the strength, and

rises the ductility

3. Grain growth 24

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Production techniques_material properties

Mohsen Badrossamay 13

Dep. of Mech. Eng.

Recovery, Recrystallization, and Grain Growth Effects

Schematic illustration of the effects of recovery, recrystallization, and grain growth on mechanical properties and on the shape and size of grains. Note the formation of small new grains during recrystallization.

25

Dep. of Mech. Eng.

Temperature Ranges for Cold, Warm and Hot Working

26

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Mohsen Badrossamay 14

Dep. of Mech. Eng.

DEPARTMENT OF MECHANICAL ENGINEERINGISFAHAN UNIVERSITY OF TECHNOLOGY

PRODUCTION TECHNIQUES

ACADEMIC YEAR 90-91, SEMESTER TWO

FUNDAMENTALS OF MATERIALS BEHAVIOR AND MANUFACTURING

PART TWO

Dep. of Mech. Eng.

Mechanical Behavior, Testing, and Manufacturing Properties of Materials

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Mohsen Badrossamay 15

Dep. of Mech. Eng.

Mechanical Properties

Strength, toughness, hardness, elasticity, fatigue and creep

Mechanical test methods:

Tension, compression, torsion, bending, hardness, fatigue, creep, impact

The properties that a material reveals under loading

29

Dep. of Mech. Eng.

Relative mechanical Properties of Materials

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Mohsen Badrossamay 16

Dep. of Mech. Eng.

Tension Test The most common test for determining such mechanical

properties of materials as strength, toughness, elastic modulus, and strain-hardening capability

Three types of strain: (a) tensile, (b) compressive and (c) shear

31

Dep. of Mech. Eng.

Tensile-test Specimen and Machine

(a) A standard tensile-test specimen before and after pulling, showing original and final gage lengths.

(b) A tensile-test sequence showing different stages in the elongation of the specimen. 32

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Mohsen Badrossamay 17

Dep. of Mech. Eng.

Tension Test Stress-strain Curve

A typical stress-strain curve obtained from a tension test, showing various features 33

Dep. of Mech. Eng.

Tension test stresses and strains

Engineering Stess,

Engineering Strain,

Modulus of Elasticity,

True stress, =

True strain, =ln

o

o

o

o

PA

l le l

E ePAll

Engineering stress: the ratio of applied load, P, to the original cross-sectional area A0, specimen

Young’s modulus: the ratio of stress to strain in the elastic region

True stress: the ratio of the load, P, to the instantaneous cross-sectional area, A, of the specimen

Ultimate tensile strength (UTS): the maximum engineering stress

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Mohsen Badrossamay 18

Dep. of Mech. Eng.

Tension test stresses and strains Hooke’s law: the linear relationship between stress and

strain E: a measure of the slope of the elastic portion and,

hence, the stiffness of the material The higher the E value, the higher the load required to

stretch the specimen to the same extent and, thus the stiffer the material

Poisson’s ratio: the absolute value of the ratio of the lateral strain to the longitudinal strain

35

Dep. of Mech. Eng.

Mechanical Properties of Materials

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Mohsen Badrossamay 19

Dep. of Mech. Eng.

Loading and Unloading of Tensile-test Specimen

Schematic illustration of the loading and the unloading of a tensile-test specimen. Note that, during unloading, the curve follows a path parallel to the original elastic slope.

37

Dep. of Mech. Eng.

Ductility

There are two common measures of ductility Elongation:

Reduction of area:

The extent of plastic deformation that the materialundergoes before fracture

100 Elongation0

0

l

ll f

100 area ofReduction 0

0

A

AA f

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Mohsen Badrossamay 20

Dep. of Mech. Eng.

Elongation vs. reduction of area

Approximate relationship between elongation and tensile reduction of area for various groups of metals 39

Dep. of Mech. Eng.

Tension and Stress Curves(a) Load elongation curve in tension

testing of a stainless steel specimen.

(b) Engineering stress-engineering strain curve, drawn from the data in Fig. a.

(c) True stress-true strain curve, drawn from the data in Fig. b. Note that this curve has a positive slope, indicating that the material is becoming stronger as it is strained.

(d) True stress-true strain curve plotted on the log-log paper and based on the corrected curve in Fig. c. The correction is due to the tri-axial state of stress that exists in the necked region of the specimen.

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Mohsen Badrossamay 21

Dep. of Mech. Eng.

Power Law Constitutive Model

Kn

where

K = strength coefficient

n = strain hardening exponent

41

Dep. of Mech. Eng.

True Stress-strain CurvesTrue stress-strain curves in tension at room temperature for various metals. The curves start at a finite level of stress: The elastic regions have too steep a slope to be shown in this figure, and thus each curve starts at the yield stress, Y, of the material

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Mohsen Badrossamay 22

Dep. of Mech. Eng.

Resilience and Toughness• Area under stress–strain curve up to the yield point, Y, of the

material is known as the modulus of resilience,

• Area has the units of energy per unit volume.E

YYe22

resilience of Modulus2

0

• The area under the true stress–true strain curve is known as toughness,

where εf is the true strain at fracture.

• Toughness is the energy per unit volume (specific energy) dissipated up to the point of fracture.

df

0

Toughness

43

Dep. of Mech. Eng.

Temperature effects on stress-strain curves

44

Typical effects of temperature on stress-strain curves. Note that increasing the temperature generally 1) raises the ductility and toughness (area under the curve) ; 2) lowers the yield stress, the ultimate tensile strength, and the modulus of elasticity of materials.

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Mohsen Badrossamay 23

Dep. of Mech. Eng.

Strain and deformation rate in manufacturing

45

Deformation rate: the speed at which a tension test is being carried out strain rate is a function of the specimen lengthIncreasing strain rate increases the strength of material (strain-rate hardening)

Dep. of Mech. Eng.

Effect of Strain Rate on Tensile Strength of Al

The effect of strain rate on the ultimate tensile strength for aluminum. Note that, as the temperature increases, the slopes of the curves increase; thus, strength becomes more and more sensitive to strain rate as temperature increases.

46

mC where

C = strength coefficient

= true strain rate

m = strain-rate sensitivity exponent

Cold working: up to 0.05

Hot working: 0.05 to 0.4

Superplastic materials: 0.3 to 0.85

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Mohsen Badrossamay 24

Dep. of Mech. Eng.

Compression - Disk Test

Disk test on a brittle material, showing the direction of loading and the fracture path.

Tensile stress, 2Pdt

where

P = load at fracture

d = diameter of disk

t = thickness of disk

47

Dep. of Mech. Eng.

Torsion-Test Specimen

A typical torsion-test specimen; it is mounted between the two heads of a testing machine and twisted. Note the shear deformation of an element in the reduced section of the specimen.

2Shear stress, =2

Shear strain, =

Tr t

rl

where

T = torque

r = average tube radius

t = thickness of tube at narrow section

l = length of tube subjected to torsion

= angle of twist

48

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Mohsen Badrossamay 25

Dep. of Mech. Eng.

Bend-test Methods

Two bend-test methods for brittle materials: (a) three-point bending; (b) four-point bending. The areas on the beams represent the bending-movement diagrams, described in texts on mechanics of solids. Note the region of constant maximum bending movement in (b); by contrast, the maximum bending moment occurs only at the center of the specimen in (a).

49

Dep. of Mech. Eng.

Hardness-testing methods and formulas

General characteristics of hardness-testing methods and formulas for calculating hardness.

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Mohsen Badrossamay 26

Dep. of Mech. Eng.

Indentation Geometry for Brinell Testing

Indentation geometry in Brinellhardness testing:

(a) annealed metal;

(b) work-hardened metal;

(c) deformation of mild steel under a spherical indenter. Note that the depth of the permanently deformed zone is about one order of magnitude larger than the depth of indentation. For a hardness test to be valid, this zone should be developed fully in the material

51

Dep. of Mech. Eng.

Hardness Scale

Conversions

Chart for converting various hardness scales. Note the limited range of most scales. Because of the many factors involved, these conversions are approximate.

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Mohsen Badrossamay 27

Dep. of Mech. Eng.

FatigueS-N Curves

(a) Typical S-N curves for two metals. Note that, unlike steel, aluminum does not have an endurance limit. (b) S-N curves for common polymers

S: stress amplitudes, N: the number of cycles

53

Dep. of Mech. Eng.

Endurance Limit vs. Tensile Strength

Ratio of endurance limit to tensile strength for various metals, as a function of tensile strength. Because aluminum does not have an endurance limit, the correlations for aluminum are based on a specific number of cycles, as is seen in previous figure.

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Mohsen Badrossamay 28

Dep. of Mech. Eng.

Creep Curve

Schematic illustration of a typical creep curve. The linear segment of the curve (secondary) is used in designing components for a specific creep life.

Creep: the permanent elongation of a component under a static load maintained for a period of time 55

Dep. of Mech. Eng.

Impact Test Specimens

Impact test specimens: (a) Charpy; (b) Izod.

Impact tests are useful particularly in determining the ductile-brittle transition temperature of materials

Materials that have high impact resistance generally are those that also have high strength and high ductility, and hence high toughness 56

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Mohsen Badrossamay 29

Dep. of Mech. Eng.

Material Failures

Schematic illustrations of types of failures in materials:

(a) necking and fracture of ductile materials;

(b) buckling of ductile materials under a compressive load;

(c) fracture of brittle materials in compression;

(d) cracking on the barreled surface of ductile materials in compression57

Dep. of Mech. Eng.

Fracture Types in Tension

Schematic illustration of the types of fracture in tension:

(a) brittle fracture in polycrystalline metals;

(b) shear fracture in ductile single crystals;

(c) ductile cup-and-cone fracture in polycrystalline metals;

(d) complete ductile fracture in polycrystalline metals, with 100% reduction of area. 58

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Mohsen Badrossamay 30

Dep. of Mech. Eng.

Ductile Fracture in Low-carbon Steel

Surface of ductile fracture in low-carbon steel, showing dimples. Fracture usually is initiated at impurities, inclusions, or preexisting voids (microporosity) in the metal. Source: Courtesy of K. H. Habig and D. Klaffke

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Dep. of Mech. Eng.

Progression of a Fracture

Sequence of events in the necking and fracture of a tensile-test specimen:

(a) early stage of necking;

(b) small voids begin to form within the necked region;

(c) voids coalesce, producing an internal crack;

(d) the rest of the cross-section begins to fail at the periphery, by shearing;

(e) the final fracture surfaces, known as cup- (top fracture surface) and cone-(bottom surface) fracture.

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Mohsen Badrossamay 31

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Temperature Transition in Metals

Schematic illustration of transition temperature in metals.61

Dep. of Mech. Eng.

Fracture Surface of Steel

Fracture surface of steel that has failed in a brittle manner. The fracture path is transgranular (through the grains). Magnification: 200x. Source: Courtesy of B. J. Schulze and S.L. Meinley and Packer Engineering Associates, Inc.

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Mohsen Badrossamay 32

Dep. of Mech. Eng.

Intergranular Fracture

Intergranular fracture, at two different magnifications. Grains and grain boundaries are clearly visible in this micrograph. The fracture path is along the grain boundaries. Magnification: left, 100x; right, 500x. Source: Courtesy of B.J. Schulze and S.L. Meiley and Packer Engineering Associates, Inc. 63

Dep. of Mech. Eng.

Fatigue-Fracture Surface

Typical fatigue-fracture surface on metals, showing beach marks. Magnification: left, 500x; right, 1000x. Source: Courtesy of B.J. Schulze and S.L. Meiley and Packer Engineering Associates, Inc.

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Mohsen Badrossamay 33

Dep. of Mech. Eng.

Reduction in Fatigue Strength vs. Ultimate Tensile Strength

Reductions in fatigue strength of cast steels subjected to various surface-finishing operations. Note that the reduction becomes greater as the surface roughness and the strength of steel increase. Source: Courtesy of M. R. Mitchell

65

Dep. of Mech. Eng.

Residual Stresses in Bending a Beam

Residual stresses developed in bending a beam having a rectangular cross-section. Note that the horizontal forces and moments caused by residual stresses in the beam must be balanced internally. Because of nonuniform deformation and especially during cold-metalworking operations, most parts develop residual stresses.

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