Metal Properties and Tests

8/11/2019 Metal Properties and Tests

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Physical properties of metalsDr. Dmitri Kopeliovich

Optical properties

Physical state

Electrical properties

Thermal properties

Thermal Conductivity

Coefficient of Thermal Expansion

Specific Heat Capacity

Magnetic properties

Optical properties

Optical propertiesMetals reflect equally nearly all visible electro-magnetic waves. Therefore the color of the

most of the metals is white or silvery-white (except copper and gold).

Metals are lustrous due to themetallic bonding,contributingfree electronsto the

metalcrystal structureand providing an ability of metals to reflect light when polished.

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Physical stateMetals are solid at normal temperatures (except mercury).

Metals transform to liquid from solid and to gas from liquid at definite temperatures(melting

and boiling points), which are high for most of metals (except mercury, sodium and

potassium).

Most of metals have relatively high densities (except sodium and potassium with densities

lower, than density of water).

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Electrical propertiesMetals have high electrical conductivity, provided by free electrons available in the metal

crystal structure.

Peltier effect:When there is an electric current, passing through a junction of two different metals, one of

them evolves heat and another absorbs heat.

Thomson effect:

A current is produced in a metal conductor when there is a temperature gradient along its

length.
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The Peltier and Thomson effects are widely used in thermocouples.

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Thermal propertiesThermal Conductivity

Thermal Conductivity ()is amount of heat passing in unit time through unit surface in adirection normal to this surface when this transfer is driven by unite temperature gradient

under steady state conditions.

Thermal conductivity may be expressed and calculated from the Fouriers law:

Q/ t =*S *T/ x

Where

Q-heat, passing through the surface S;

t- change in time;

- thermal conductivity;

S- surface area, normal to the heat transfer direction;

T/x-temperature gradient along xdirection of the heat transfer.

Fouriers law is analogue of the First Ficks law, describing diffusion in steady state.

Metals have high thermal conductivity. Heat is transferred through the metalcrystalbyfree

electrons.Compare:

of alumina = 47 BTU/(lb*F) (6.3 W/(m*K)).

of Al = 1600 BTU/(lb*F) (231 W/(m*K)).

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Coefficient of Thermal Expansion

Thermal Expansion (Coefficient of Thermal Expansion) is relative increase in length

per unite temperature rise:

= L/ (LoT)

Where

-coefficient of thermal expansion (CTE);

Llength increase;

Loinitial length;

Ttemperature rise.

Thermal expansion of metals is generally higher, than that ofceramics.

Compare:

CTEof SiC = 2.3 F (4.0 C).

CTEof Al = 13 F (23 C).

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Specific Heat Capacity

Heat Capacityis amount of heat required to raise material temperature by one unit.
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Specific Heat Capacity is amount of heat required to raise temperature of unit mass of

material by one unit:

c= Q/(mT)

Where

c-specific heat capacity;Qamount of heat;

mmaterial mass;

Ttemperature rise.

Specific Heat Capacity of metals is lower, than that of ceramics.

Compare:

cof alumina = 0.203 BTU/(lb*F) (850 J/(kg*K)).

cof steel = 0.115 BTU/(lb*F) (481 J/(kg*K)).

to topMagnetic propertiesMost of metals are slightly magnetic, but only few of them (iron, nickel, cobalt and their

alloys) display pronounced magnetic properties, called ferromagnetism.

Magnetically soft metals metals, which are demagnetized after the magnetic field is

removed. Magnetically soft metals are used in electric motors and transformers.

Magnetically hard metals metals, retaining their magnetization after the magnetic

field is removed.Magnetically hard metals are used for permanent magnets.

Magnetostriction effect of changing dimensions of a ferromagnetic metal when its

magnetization is changed.to top

Tensile test and Stress-Strain DiagramDr. Dmitri Kopeliovich

Stress-Strain Diagramexpresses a relationship between a load applied to a material and

the deformation of the material, caused by the load .

Stress-Strain Diagram is determined by tensile test.

Tensile tests are conducted in tensile test machines, providing controlled uniformly

increasing tension force, applied to the specimen.

The specimens ends are gripped and fixed in the machine and its gauge length L0(a

calibrated distance between two marks on the specimen surface) is continuously measured

until the rupture.

Test specimen may be round or flat in the cross-section.

In the round specimens it is accepted, that L0= 5 * diameter.

The specimen deformation (strain) is the ratio of the increase of the specimen gauge length

to its original gauge length:
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= (L L0) / L0

Tensile stressis the ratio of the tensile load Fapplied to the specimen to its original cross-

sectional area S0:

= F / S0

The initial straight line (0P)of the curve characterizes proportional relationship between the

stress and the deformation (strain).

The stress value at the point Pis called the limit of proportionality:

p= FP/ S0

This behavior conforms to the Hooks Law:

= E*

Where Eis a constant, known as Youngs ModulusorModulus of Elasticity.

The value of Youngs Modulus is determined mainly by the nature of the material and is

nearly insensitive to theheat treatmentand composition.

Modulus of elasticity determines stiffness- resistance of a body to elastic deformation

caused by an applied force.

The line 0Ein the Stress-Strain curve indicates the range of elastic deformation

removal of the load at any point of this part of the curve results in return of the specimen

length to its original value.

The elastic behavior is characterized by the elasticity limit(stress value at the point E):

el= FE/ S0

For the most materials the points Pand Ecoincide and therefore el=p.
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A point where the stress causes sudden deformation without any increase in the force is

called yield limit (yield stress, yield strength):

y= FY/ S0The highest stress (point YU) , occurring before the sudden deformation is called upper

yield limit.

The lower stress value, causing the sudden deformation (point YL) is called lower yield

limit.

The commonly used parameter of yield limit is actually lower yield limit.

If the load reaches the yield point the specimen undergoesplastic deformationit does not

return to its original length after removal of the load.
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Hard steels and non-ferrous metals do not have defined yield limit, therefore a stress,

corresponding to a definite deformation (0.1% or 0.2%) is commonly used instead of yield

limit. This stress is calledproof stress or offset yield limit (offset yield strength):

0.2%= F0.2%/ S0The method of obtaining the proof stress is shown in the picture.

As the load increase, the specimen continues to undergo plastic deformation and at a

certain stress value its cross-section decreases due to necking (pointSin the Stress-

Strain Diagram). At this point the stress reaches the maximum value, which is

called ultimate tensile strength(tensile strength):

t= FS/ S0

Continuation of the deformation results in breaking the specimen - the point B in the

diagram.

The actual Stress-Strain curve is obtained by taking into account the true specimen cross-section instead of the original value.

Other important characteristic of metals is ductility- ability of a material to deform under

tension without rupture.

Two ductility parameters may be obtain from the tensile test:
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Relative elongation - ratio between the increase of the specimen length before its rupture

and its original length:

= (LmL0) / L0

Where Lmmaximum specimen length.

Relative reduction of area - ratio between the decrease of the specimen cross-section

area before its rupture and its original cross-section area:= (S0Smin) / S0

Where Sminminimum specimen cross-section area.

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Hardness test methodsDr. Dmitri Kopeliovich

Hardness is resistance of material toplastic deformationcaused by indentation.

Sometimes hardness refers to resistance of material to scratching or abrasion.

In some cases relatively quick and simple hardness test may substitutetensile test.

Hardness may be measured from a small sample of material without destroying it.

There are hardness methods, allowing to measure hardness onsite.

Principle of any hardness test methodis forcing an indenter into the sample surface

followed by measuring dimensions of the indentation (depth or actual surface area of the

indentation).

Hardness is not fundamental property and its value depends on the combination ofyield

strength, tensile strengthandmodulus of elasticity.

Benefits of hardness test:

Easy

Inexpensive

Quick

Non-destructive

May be applied to the samples of various dimensions and shapes

May be performed in-situ

Depending on the loading force value and the indentation dimensions, hardness is defined

as a macro- , micro- or nano-hardness.

Macro-hardness tests (Rockwell, Brinell, Vickers) are the most widely used methods

for rapid routine hardness measurements. The indenting forces in macro-hardness tests are

in the range of 50N to 30000N.

Micro-hardness tests (micro-Vickers, Knoop)is applicable when hardness ofcoatings,

surface hardness, or hardness of differentphasesin the multi-phase material is measured.

Small diamond pyramid is used as indenter loaded with a small force of 10 to 1000gf.
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Nano-hardness test uses minor loads of about 1 nano-Newton followed by precise

measuring depth of indentation.

Brinell Hardness Test

Rockwell Hardness Test

Rockwell Superficial Hardness Test Vickers Hardness Test

Knoop Hardness Test

Shore Scleroscope Hardness Test

Brinell Hardness Test

In this test a hardened steel ball of 2.5, 5 or 10 mm in diameter is used as indenter.

The loading force is in the range of 300N to 30000N (300N for testing lead alloys, 5000N for

testing aluminum alloys, 10000N for copper alloys, 30000N for testing steels). The Brinell

Hardness Number (HB) is calculated by the formula:

HB = 2F/ (3.14D*(D-(D - Di)))

Where

F- applied load, kg

Dindenter diameter, mm

Diindentation diameter, mm.In order to eliminate an influence of the specimen supporting base, the specimen should be

seven times (as minimum) thicker than indentation depth for hard alloys and fifteen times

thicker than indentation depth for soft alloys.

Rockwell Hardness Test
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In the Rockwell test the depth of

the indenter penetration into the specimen surface is measured. The indenter may be either

a hardened steel ball with diameter 1/16, 1/8 or a spherical diamond cone of 120 angle

(Brale).

Loading procedure starts from applying a minor load of 10 kgf (3kgf in Rockwell Superficial

Test) and then the indicator, measuring the penetration depth, is set to zero. After that the

major load (60, 100 or 150 kgf)is applied. The penetration depth is measured after removal

of the major load.

Hardness is measured in different scales (A, B, C, D, E, F, G, H, K) and in numbers, having

no units (in contrast to Brinell and Vickers methods).
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Aluminum alloys,copper alloysand softsteelsare tested with 1/16 diameter steel ball at

100 kgf load (Rockwell hardness scale B).

Harder alloys and hard cast iron are tested with the diamond cone at 150 kgf (Rockwell

hardness scale C).

An example of Rockwell test result: 53 HRC. It means 53 units, measured in the scale C by

the method HR (Hardness Rockwell).

Rockwell Superficial Hardness TestRockwell Superficial Test is applied for thin strips, coatings, carburized surfaces.

Reduced loads (15 kgf, 30 kgf, and 30 kgf) as a major load and deduced preload (3kgf) are

used in the superficial test.

Depending on the indenter, two scales of Rockwell Superficial method may be used: T

(1/16 steel ball) or N (diamond cone).

62 R30T means 62 units, measured in the scale 30T (30 kgf, 1/16 steel ball indenter) by

the Rockwell Superficial method (R).

Vickers Hardness TestThe principle of the Vickers Hardness method is similar to the Brinell method.

The Vickers indenter is a 136 degrees square-based diamond pyramid.

The impression, produced by the Vickers indenter is clearer, than the impression of Brinell

indenter, therefore this method is more accurate.

The load, varying from 1kgf to 120 kgf, is usually applied for 30 seconds.

The Vickers number (HV) is calculated by the formula:
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11/27

HV = 1.854*F/ D

Where

F-applied load, kg

Dlength of the impression diagonal, mm

The length of the impression diagonal is measured by means of a microscope, which isusually an integral part of the Vickers Tester.

Knoop Hardness Test
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12/27

A diamond pyramid indenter with angles 130 and 17030 is used in this method.

The Knoop Hardness Test is applied for testing soft material and thin coating, since the

penetration depth is very small (about 1/30 of the impression length).

The loading force in the Knoop method are usually in the range of 10 gf to 1000gf (micro-

hardness range).

The Knoop number (HK) is calculated by the formula:

HK = 14.229*F/L

Where

F-applied load, kg

Llong diagonal of the impression, mm

Shore Scleroscope Hardness TestThe Shore Scleroscope hardness is associated with theelasticityof the material.

The appliance consists of a diamond-tipped hammer, falling in a graduated glass tube from

a definite height. The tube is divided into 140 equal parts.

The height of the first rebound is the hardness index of the material.

The harder the material, the higher the rebound.
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The Shore method is widely used for measuring hardness of large machine components like

rolls, gears, dies, etc.

The Shore scleroscope is not only small and mobile, it also leaves no impressions on the

tested surface.

to top

Hardness Conversion Table(submitted by the website administration)

RA

60

Brale

RB

100

1/16

RC

150

Brale

RD

100

Brale

R15N

Brale

R30N

Brale

R45N

Brale

R15T

1/16

R30T

1/16

R45T

1/16

HB

50010mm

HB

300010mm

HV

Diamond

Pyramid

Shore

92 - 80 87 97 92 87 - - - - - 1865 -

92 - 79 86 96 92 87 - - - - - 1787 -

91 - 78 85 96 91 86 - - - - - 1710 -

91 - 77 84 96 91 85 - - - - - 1633 -

90 - 76 83 96 90 84 - - - - - 1556 -

90 - 75 83 95 89 83 - - - - - 1478 -

89 - 74 82 95 89 82 - - - - - 1400 -

89 - 73 81 95 88 81 - - - - - 1323 -

88 - 72 80 95 87 80 - - - - - 1245 -

87 - 71 80 94 87 79 - - - - - 1160 -

87 - 70 79 94 86 78 - - - - - 1076 101

86 - 69 78 94 85 77 - - - - - 1004 99

85.6 - 68 76.9 93.2 84.4 75.4 - - - - - 940 97

85 - 67 76.1 92.9 83.6 74.2 - - - - - 900 95

84.5 - 66 75.4 92.5 82.8 73.3 - - - - - 865 92

83.9 - 65 74.5 92.2 81.9 72 - - - - 739 832 91

83.4 - 64 73.8 91.8 81.1 71 - - - - 722 800 88

82.8 - 63 73 91.4 80.1 69.9 - - - - 705 772 87

82.3 - 62 72.2 91.1 79.3 68.8 - - - - 688 746 85

81.8 - 61 71.5 90.7 78.4 67.7 - - - - 670 720 83

81.2 - 60 70.7 90.2 77.5 66.6 - - - - 613 697 81

80.7 - 59 69.9 89.8 76.6 65.5 - - - - 599 674 80

80.1 - 58 69.2 89.3 75.7 64.3 - - - - 587 653 78

79.6 - 57 68.5 88.9 74.8 63.2 - - - - 575 633 76

79 - 56 67.7 88.3 73.9 62 - - - - 561 613 75

RA

60

Brale

RB

100

1/16

RC

150

Brale

RD

100

Brale

R15N

Brale

R30N

Brale

R45N

Brale

R15T

1/16

R30T

1/16

R45T

1/16

HB

50010mm

HB

300010mm

HV

Diamond

Pyramid

Shore
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78.5 120 55 66.9 87.9 73 60.9 - - - - 546 585 74

78 120 54 66.1 87.4 72 59.8 - - - - 534 577 72

77.4 119 53 65.4 86.9 71.2 58.6 - - - - 519 560 71

76.8 119 52 64.6 86.4 70.2 57.4 - - - - 500 544 69

76.3 118 51 63.8 85.9 69.4 56.1 - - - - 487 528 68

75.9 117 50 63.1 85.5 68.5 55 - - - - 475 513 67

75.2 117 49 62.1 85 67.6 53.8 - - - - 464 498 66

74.7 116 48 61.4 84.5 66.7 52.5 - - - - 451 484 64

74.1 116 47 60.8 83.9 65.8 51.4 - - - - 442 471 63

73.6 115 46 60 83.5 64.8 50.3 - - - - 432 458 62

73.1 115 45 59.2 83 64 49 - - - - 421 446 60

72.5 114 44 58.5 82.5 63.1 47.8 - - - - 409 434 58

72 113 43 57.7 82 62.2 46.7 - - - - 400 423 57

71.5 113 42 56.9 81.5 61.3 45.5 - - - - 390 412 56

70.9 112 41 56.2 80.9 60.4 44.3 - - - - 381 402 55

70.4 112 40 55.4 80.4 59.5 43.1 - - - - 371 392 54

69.9 111 39 54.6 79.9 58.6 41.9 - - - - 362 382 52

69.4 110 38 53.8 79.4 57.7 40.8 - - - - 353 372 51

68.9 110 37 53.1 78.8 56.8 39.6 - - - - 344 363 50

68.4 109 36 52.3 78.3 55.9 38.4 - - - - 336 354 49

67.9 109 35 51.5 77.7 55 37.2 - - - - 327 345 48

67.4 108 34 50.8 77.2 54.2 36.1 - - - - 319 336 47

66.8 108 33 50 76.6 53.3 34.9 - - - - 311 327 46

RA

60

Brale

RB

100

1/16

RC

150

Brale

RD

100

Brale

R15N

Brale

R30N

Brale

R45N

Brale

R15T

1/16

R30T

1/16

R45T

1/16

HB

50010mm

HB

300010mm

HV

Diamond

Pyramid

Shore

66.3 107 32 49.2 76.1 52.1 33.7 - - - - 301 318 44

65.8 106 31 48.4 75.6 51.3 32.5 - - - - 294 310 43

65.3 105 30 47.7 75 50.4 31.3 - - - - 286 302 42

64.7 104 29 47 74.5 49.5 30.1 - - - - 279 294 41

64.3 104 28 46.1 73.9 48.6 28.9 - - - - 271 286 40.5

63.8 103 27 45.2 73.3 47.7 27.8 - - - - 264 279 40

63.3 103 26 44.6 72.8 46.8 26.7 - - - - 258 272 38

62.8 102 25 43.8 72.2 45.9 25.5 - - - - 253 266 37.5

62.4 101 24 43.1 71.6 45 24.3 - - - - 247 260 37

62 100.5 23 42.1 71 44 23.1 - - - - 243 254 36

61.5 100 22 41.6 70.5 43.2 22 93 82 72 201 237 248 251

61 99 21 40.9 69.9 42.3 20.7 92.5 81.5 71 195 231 243 246

60.5 98.5 20 40.1 69.4 41.5 19.6 92.4 81.2 70.5 192 228 238 243


15/27

60 98 20 - - - - 92.3 81 70 189 226 237 241

59.5 97 19 - - - - 92 80.5 69 184 222 234 236

59 96 18 - - - - 91.8 80 68 179 216 230 231

58 95 16 - - - - 91.5 79 67 175 210 222 226

57.5 94 14 - - - - 91.3 78.5 66 171 205 213 221

57 93 13 - - - - 91 78 65.5 167 200 208 216

56.5 92 11 - - - - 90.5 77.5 64.5 163 195 200 211

56 91 10 - - - - 90.8 77 63.5 160 190 196 206

RA

60

Brale

RB

100

1/16

RC

150

Brale

RD

100

Brale

R15N

Brale

R30N

Brale

R45N

Brale

R15T

1/16

R30T

1/16

R45T

1/16

HB

50010mm

HB

300010mm

HV

Diamond

Pyramid

Shore

toNext page of Hardness Conversion Table

Hardness Conversion Table (second page)RA 60Brale

RB 1001/16

RC 150Brale

RE 1001/8

R15T1/16

R30T1/16

R45T1/16

HB 50010mm

HB 300010mm

HV DiamondPyramid

Knoop

55.5 90 9 - 90 76 62.5 157 185 192 201

55 89 8 - 89.5 75.5 61.5 154 180 188 196

54 88 7 - 89.3 75 60.5 151 176 184 192

53.5 87 6 - 89 74.5 59.5 148 172 180 188

53 86 5 - 88.5 74 58.5 145 169 176 184

52.5 85 4 - 88.3 73.5 58 142 165 172 180

52 84 3 - 88 73 57 140 162 168 176

51 83 2 - 87.5 72 56 137 159 164 173

50.5 82 1 - 87.3 71.5 55 135 156 160 170

50 81 - - 87 71 54 133 153 156 167

49.5 80 - - 86.5 70 53 130 150 152 164

49 79 - - 86.3 69.5 52 128 147 148 161

48.5 78 - - 86 68 51 126 144 144 158

48 77 - - 85.5 68 50 124 141 141 155

47 76 - - 85.3 67.5 49 122 139 139 152

46.5 75 - - 85 67 48.5 120 137 137 150

46 74 - - 84.8 66 47.5 118 135 135 147

45.5 73 - - 84.5 65.5 46.5 116 132 132 145

45 72 - - 84 65 45.5 114 130 130 143

44.5 71 - 100 83.8 64 44.5 112 127 127 141

RA 60

Brale

RB 100

1/16

RC 150

Brale

RE 100

1/8

R15T

1/16

R30T

1/16

R45T

1/16

HB 500

10mm

HB 3000

10mm

HV Diamond

PyramidKnoop

44 70 - 99.5 83.5 63.5 43.5 110 125 125 139
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43.5 69 - 99 83 62.5 42.5 109 123 123 137

43 68 - 98 82.8 62 41.5 107 121 120 135

42.5 67 - 97.5 82.5 61.5 40.5 106 119 118 133

42 66 - 97 82 60.5 39.5 104 117 116 131

41.8 65 - 96 81.8 60 38.5 102 116 115 129

41.5 64 - 95.5 81.5 59.5 37.5 101 114 114 127

41 63 - 95 81 58.5 36.5 99 112 113 126

40.5 62 - 94.5 80.8 58 35.5 98 110 112 124

40 61 - 93.5 80.5 57 34.5 96 108 111 122

39.5 60 - 93 80.3 56.5 33.5 95 107 110 120

39 59 - 92.5 80 56 32 94 106 108 118

38.5 58 - 92 79.5 55 31 92 104 107 117

38 57 - 91 79.3 54.5 30 91 102 106 115

37.8 56 - 90.5 79 54 29 90 101 105 114

37.5 55 - 90 78.5 53 28 89 99 104 112

37 54 - 89.5 78.3 52.5 27 87 - 103 111

36.5 53 - 89 78 51.5 26 86 - 102 110

36 52 - 88 77.5 51 25 85 - 101 109

35.5 51 - 87.5 77.3 50.5 24 84 - 100 108

35 50 - 87 77 49.5 23 83 - 100 107

RA 60

Brale

RB 100

1/16

RC 150

Brale

RE 100

1/8

R15T

1/16

R30T

1/16

R45T

1/16

HB 500

10mm

HB 3000

10mm

HV Diamond

PyramidKnoop

34.8 49 - 86.5 76.5 49 22 82 - 99 106

34.5 48 - 85.5 76.3 48.5 20.5 81 - 98 105

34 47 - 85 76 47.5 19.5 80 - 97 104

33.5 46 - 84.5 75.5 47 18.5 79.5 - 96 103

33 45 - 84 75.3 46 17.5 79 - 95 102

32.5 44 - 83.5 75 45.5 16.5 78 - 95 101

32 43 - 82.5 74.5 45 15.5 77 - 94 100

31.5 42 - 82 74.3 44 14.5 76 - 93 99

31 41 - 81.5 74 43.5 13.5 75 - 92 98

30.8 40 - 81 73.5 43 12.5 74.5 - 91 97

30.5 39 - 80 73.3 42 11 74 - 90 96

30 38 - 79.5 73 41.5 10 73 - 90 95

29.5 37 - 79 72.5 40.5 9 72 - 89 94

29 36 - 78.5 72.3 40 8 71.5 - 88 93

28.5 35 - 78 72 39.5 7 71 - 88 -

28 34 - 77 71.5 38.5 6 70 - 87 -


17/27

27.8 33 - 76.5 71.3 38 5 69 - 87 -

27.5 32 - 76 71 37.5 4 68.5 - 86 -

27 31 - 75.5 70.8 36.5 3 68 - 86 -

26.5 30 - 75 70.5 36 2 67 - 85 -

26 29 - 74 70 35.5 1 66.5 - 85 -

RA 60

Brale

RB 100

1/16

RC 150

Brale

RE 100

1/8

R15T

1/16

R30T

1/16

R45T

1/16

HB 500

10mm

HB 3000

10mm

HV Diamond

PyramidKnoop

25.5 28 - 73.5 69.8 34.5 - 66 - 84 -

25 27 - 73 69.5 34 - 65.5 - 84 -

24.5 26 - 72.5 69 33 - 65 - 83 -

24.3 25 - 72 68.8 32.5 - 64 - 83 -

24 24 - 71 68.5 32 - 63.5 - 82 -

23.5 23 - 70.5 68 31 - 63 - 82 -

23 22 - 70 67.8 30.5 - 62.5 - 81 -

22.5 21 - 69.5 67.5 29.5 - 62 - 81 -

22 20 - 68.5 67.3 29 - 61.5 - 80 -

21.5 19 - 68 67 28.5 - 61 - 80 -

21.3 18 - 67.5 66.5 27.5 - 60.5 - 79 -

21 17 - 67 66.3 27 - 60 - 79 -

20.5 16 - 66.5 66 26 - 59.5 - 78 -

20 15 - 65.5 65.5 25.5 - 59 - 78 -

- 14 - 65 65.3 25 - 58.5 - 77 -

- 13 - 64.5 65 24 - 58 - 77 -

- 12 - 64 64.5 23.5 - 57.7 - 76 -

- 11 - 63.5 64.3 23 - 57.3 - 76 -

- 10 - 62.5 64 22 - 57 - 75 -

- 9 - 62 63.8 21.5 - 56.7 - 75 -

- 8 - 61.5 63.5 20.5 - 56.3 - 74 -

- 7 - 61 63 20 - 56 - 74 -

- 6 - 60.5 62.8 19.5 - 55.5 - 73 -

- 5 - 60 62.5 18.5 - 55 - 73 -

- 4 - 59 62 18 - 54.7 - 72 -

- 3 - 58.5 61.8 17 - 54.3 - 72 -

- 2 - 58 61.5 16.5 - 54 - 71 -

- 1 - 57.5 61 16 - 53.5 - 71 -

- - - 57 60.8 15 - 53 - 70 -

RA 60

Brale

RB 100

1/16

RC 150

Brale

RE 100

1/8

R15T

1/16

R30T

1/16

R45T

1/16

HB 500

10mm

HB 3000

10mm

HV Diamond

PyramidKnoop


18/27

Fracture ToughnessDr. Dmitri Kopeliovich

Fracture is a process of breaking a solid into pieces as a result ofstress.

There are two principal stages of the fracture process:

Crack formation

Crack propagation

Ductile fractureDuctilematerials undergo observableplastic deformationand absorb significant energy

before fracture.

A crack, formed as a result of the ductile fracture, propagates slowly and when the stress is

increased.

Plastic deformation of a multi-phasematerial causes formation and coalescence of voids on

the phase and inclusions boundaries. These voids are responsible for the specificappearance of the ductile fracture surface, consisting of numerous spherical micro-cavities

(dimples), initiating formation of the crack.

Tensile specimenfractured by the ductile mechanism is characterized by the cap and

coneappearance of the fracture.

Single-phasealloysand pure metals are more ductile, than metals, containing second

phases or inclusions.

Brittle fracture
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Brittle fracture is characterized by very low plastic deformation and low energy absorption

prior to breaking.

A crack, formed as a result of the brittle fracture, propagates fast and without increase of

the stress applied to the material.

The brittle crack is perpendicular to the stress direction.

There are two possible mechanisms of the brittle

fracture: transcrystalline(transgranular, cleavage) orintercrystalline

(intergranular).

Cleavagecracks pass alongcrystallographic planesthrough thegrains.

Intercrystallinefractureoccurs through thegrain boundaries,embrittled bysegregated

impurities,second phase inclusions and other defects.

The brittle fractures usually possess bright granular appearance.

ToughnessToughnessis ability of material to resist fracture.The general factors, affecting the toughness of a material are: temperature,strainrate,

relationship between thestrengthand ductility of the material and presence of stress

concentration (notch) on the specimen surface.

Fracture toughness is indicated by the area below the curve onstrain-stress diagram(see

the figure):
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As seen from the diagram toughness of the ductile materials is higher than toughness of

brittle materials.

Stress-intensity Factor (K) is a quantitative parameter of fracture toughness determininga maximum value of stress which may be applied to a specimen containing a crack (notch)

of a certain length.

Depending on the direction of the specimen loading and the specimen thickness, four types

of stress-intensity factors are used: KC, KICKIICKIIIC.

KCstress-intensity factor of a specimen, thickness of which is less than a critical value.

KCdepends on the specimen thickness. This condition is called plane stress.

KIC,KIIC, KIIICstress-intensity factors, relating to the specimens, thickness of which is

above the critical value therefore the values of KICKIICKIIIC do not depend on the specimen

thickness. This condition is called plane strain.

KIICand KIIICstress-intensity factors relating to the fracture modes in which the loading

direction is parallel to the crack plane. These factors are rarely used formetalsand are not

used forceramics;

KICplane strain stress-intensity factor relating to the fracture modes in which the loading

direction is normal to the crack plane. This factor is widely used for both metallic and

ceramic materials.

KICis used for estimation critical stress applied to a specimen with a given crack length:

CKIC/(Y( a))
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Where

KICstress-intensity factor, measured in MPa*m;

Cthe critical stress applied to the specimen;

athe crack length for edge crack or half crack length for internal crack;

Ygeometry factor.Impact test

Impact test is used for measuring toughness of materials and their capacity of resisting

shock.

In this test the pendulum is swing up to its starting position (height H) and then it is

allowed to strike the notched specimen, fixed in a vice. The pendulum fractures the

specimen, spending a part of its energy. After the fracture the pendulum swings up to a

height H.

The impact toughnessof the specimen is calculated by the formula:

a = A/ S

Where

a-impact toughness,

Athe work, required for breaking the specimen ( A = M*g*H0M*g*H),

M- the pendulum mass,

S- cross-section area of the specimen at the notch.

One of the most popular impact tests is the Charpy Test, schematically presented in the

figure below:
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The hammer striking energy in the Charpy test is 220 ft*lbf (300 J).

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FatigueDr. Dmitri Kopeliovich

Fatigue is a type of failure of a material, occurring under alternating loads.

Most of the failures of machine details are caused by fatigue.

Fatigue life is the number of cyclingstresses,causing failure of the material.

Frequency of these stresses is not important.

Fatigue limit is the maximum value of repeatedly applied stress that the material can

withstand after an infinite number of cycles (10-20 mln. Cycles in practice).
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Fatigue strength at N cycles is the load, producing the material fracture after N cycling

applications of the load.

Fatigue limit of a material is much lower, than its ultimate tensile strength.

Fatigue tests are carried out in the Whler-type machine, schematically shown in the

picture.

The rotating specimen in form of a cantilever is driven by an electric motor. The specimen is

loaded by the force F, applied to the ball bearing, mounted on the end of the specimen.

Since the force direction does not change, the direction of the stress applied to the

specimen will be reversed each 180 of the shaft rotation.

This scheme provides cycling loading of the specimen, presented in the equivalent scheme.

To find the fatigue limit the fatigue test is repeated at different loads.
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The tests results are presented in form of S-N curve(stress vs. number of cycles):

Fatigue fracture is characterized by presence of two different types of the surface:

One part is smooth and discolored with ripple-like marks, indicating slow crack growth from

the center of the crack formation. Another part of the surface has coarse crystalline

appearance resulted from the final catastrophic crack propagation.

The following factors affect fatigue fracture:

Surface factor

Fatigue cracks form and initiate on the specimen surface therefore hardened and smooth

surface (without stress concentrations - notch, flaw) will increase the fatigue limit.

Compressive stress

Compressive stresses, produced in the specimen surface byShot peening,cold workorheat

treatmentresult in considerable increase of fatigue limit.

Micro-structure defects

Non-metallic inclusionsand other micro-defects may initiate formation of fatigue cracks.

Environmental factor

Fatigue in the presence of corrosive environment (Corrosion fatigue)occurs at lower cycling

stresses and after lower number of cycles.

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CreepDr. Dmitri Kopeliovich

Creepis a phenomenon of slowplastic deformation(elongation) of a metal at high

temperature under a constant load.

The creep mechanism:

At lowstressesthe creep is controlled by thediffusionof atoms through thegrain

boundaries.At higher stresses the creepstrainproceeds due to thedislocationsmovement.
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The rate of creepis a function of the material, the applied stress value, the temperature,

and the time exposure.

Considerable creep deformation, causing damage of machines and structures occur at high

temperatures (about a half of the melting point measured in the absolute temperature

scale). Therefore this phenomenon is taken into account in design and operation of heat

exchangers, steam boilers and pipes, jet engines and other loaded equipment, working athigh temperatures.

Soft metals (lead, tin) may experience creep at room temperature.

A typical creep behavior is presented in the diagram:

The initial strain is not time dependent and it is caused mainly byelastic deformation.

The first stage creep is characterized by relatively fastplastic deformationoccurring at

decreasing rate. During this stage resistance creep increases causing decrease the

deformation rate.

The second stage creep occurs at a constant and relatively low deformation rate. This

rate is used in the engineering design.

The rate of creep at the second stage depends on both the load (stress) and thetemperature.

The third stage creep is associated with accelerated strain rate caused by decrease of the

cross sectional area of the specimen (necking). This stage is finalized by the specimen

fracture.

At room temperature creep is negligible at any stress below the yield point.
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The quantity, which is used in precise design of machines and structures working at

elevated temperatures, is creep strength.

Creep strengthis a stress which causes a definite creep strain after a specified period of

time at a given temperature.

Creep strength of a material is much lower, than its tensile strength.

If a large amount of deformation is tolerated rupture strength is used in design.

Rupture strengthis a stress which causes a fracture of a metal after a specified period of

time at a given temperature.

Creep strength and rupture strength are determined in stress-rupture tests conducted in

[Tensile test and Stress-Strain Diagram|tensile test]] machines equipped with a furnace

providing uniform heating of the tested specimens.

This machine records amount of strain at every moment after the test has started and until

the specimen failure.

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Chemical Composition EvaluationDr. Dmitri Kopeliovich

Spectrometry is an analytical technique used in chemistry for quantitative and qualitative

analysis of substances by means studying the electromagnetic spectra either absorbing

(absorbtion spectroscopy) or radiating (emission spectroscopy) by the substance.

Spark or arc spectroscopy is a method of metals andalloysanalysis, using an electric

spark (or arc) passing through the metal sample, heating its surface and causing emission

of light by the excited atoms of the sample.

The waves of the emitted light are analyzed by spectroscopic methods.

X-Ray Fluorescence (XRF, X-Ray Emission) Spectroscopy is an analytical non-

destructive spectral method, using irradiation of the sample by intensive x-rays, causing

emission of fluorescent x-rays by the sample atoms.

The emitted x-rays are detected and analyzed by a spectrometer.

The qualitative analysis is based on either wavelength or energies of the emitted x-rays.

The quantities of the sample components are determined by intensities of the emitted x-

rays.

Atomic absorption is a destructive analytical method where a light of a definite

wavelength is passed through the atomized sample.

The waves transmitted by the sample are analyzed as compared to the waves passed

through the sample. Thus the energy, absorbed by the sample is determined.

The amount of the absorbed energy is related to the concentration of the certain

component.
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Metal Properties and Tests

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