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Why are metals tested ?Why are metals tested ?

Ensure quality Test propertiesPrevent failure in useMake informed choices in using materials

Factor of Safety is the ratio comparing the actual stress on a material and the safe useable stress.

Two forms of testingTwo forms of testing

Mechanical tests – the material may be physically tested to destruction. Will normally specify a value for properties such as strength, hardness, toughness,etc

Non-destructive tests (NDT) – samples or finished articles are tested before being used.

IntroductionIntroductionHardness is determined by the resistance to plastic deformations and fracture of interatomic and crystalline bonds in the material, which also determines the mechanical strength of a material.

There are three standard methods for measuring the hardness which depends upon the manner in which the test is conducted.

These are:

1- Scratch hardness measurement.

2- Rebound hardness measurement.

3- Indentation hardness measurement

Why Use a Hardness Test?Why Use a Hardness Test?

Easy to perform Quick - 30 seconds Relatively inexpensive Non-destructive Finished parts can be testedany size and shape can be tested

Indentation hardness measurement

A load is applied by pressing the indenter at right angles to the surface being tested.

The three commonly used indentation hardness tests is:

BRINELL HARDNESS TESTsphere indenter of 10 mm in dia,, varying load, measure the size of indentation

Dr. J. A. Brinell invented the Brinell test in Sweden in 1900

ROCKWELL HARDNESS TESTusing different scale (various sized indenter, different loads)

Stanley P. Rockwell invented the Rockwell hardness test

VICKERS PYRAMID HARDNESS TESTdiamond used as indenter

The Vickers (HV) test was developed in England is 1925

CH-07 LEC 27 Slide 7

Hardness

The resistance of a material metal to penetration by a pointed tool

is called Hardness. It is the property of a metal, which gives it the

ability to resist being permanently, deformed (bent, broken, or

have its shape changed), when a load is applied. The greater the

hardness of the metal, the greater resistance it has to deformation.

3-4 Hardness3-4 Hardness


Hardness Measurement Methods Rockwell hardness test Brinell hardness VickersKnoop hardness Shore


HARDNESS TESTINGHARDNESS TESTING

Hardness is the ability to withstand dents or scratches

Fundamentals of HardnessFundamentals of Hardness

Hardness is thought of as the resistance to penetration by an object or the solidity or firmness of an object

– Resistance to permanent indentation under static or dynamic loads– Energy absorption under impact loads (rebound hardness)– Resistance toe scratching (scratch hardness)– Resistance to abrasion (abrasion hardness)– Resistance to cutting or drilling (machinability)

Principles of hardness (resistance to indentation)– indenter: ball or plain or truncated cone or pyramid made of hard steel or diamond– Load measured that yields a given depth– Indentation measured that comes from a specified load– Rebound height measured in rebound test after a dynamic load is dropped onto a surface

GAMBAR MACAM-MACAM MEDIA PENGUJIANGAMBAR MACAM-MACAM MEDIA PENGUJIAN

BRINELL ROCKWELL VICKERS

Hardness testing machineHardness testing machine

The indenter is pressed into the metal

Softer materials leave a deeper indentation

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Brinell hardness testBrinell hardness test

Uses ball indentor. Cannot be used for thin

materials. Ball may deform on very

hard materials Surface area of indentation

is measured.

Brinell HardnessBrinell Hardness


A spherical indenter (1 cm diameter) is shot with 29 kN force at the target

Frequently the indenter is steel, but for harder materials it is replaced with a tungsten carbide sphere

The diameter of the indentation is recorded The indentation diameter can be correlated

with the volume of the indentation.


Brinell Hardness Test Brinell hardness is determined by forcing a hard steel or carbide sphere of a specified diameter under a specified load into the surface of a material and measuring the diameter of the indentation left after the test. The Brinell hardness number, or simply the Brinell number, is obtained by dividing the load used, in kilograms, by the actual surface area of the indentation, in square millimeters. The result is a pressure measurement, but the units are rarely stated.


For steelsThe relationship between the minimum ultimate strength and

the Brinell harness number for is

0.495

3.41B

uB

H kpsiS

H MPa

200 450BH

Cast IronThe minimum strength, as defined by the ASTM, is found to be

0.238 12.5

1.58 86B

uB

H kpsiS

H MPa


22

2

dDDD

PBHN


ASTM and ISO use the HB value. It can be HBS (Hardness, Brinell, Steel) or the HBW (Hardness, Brinell, Tungsten)

HBW = 0.102 BHNSometimes written as HBW 10/3000

(Tungsten, 10 mm diameter, 3,000 kg force)

Typical HB valuesTypical HB valuesMaterial Hardness

Softwood (e.g., pine) 1.6 HBS 10/100

Hardwood 2.6–7.0 HBS 1.6 10/100Aluminum 15 HBCopper 35 HBMild steel 120 HB

18-8 (304) stainless steel annealed 200 HBGlass 1550 HB

Hardened tool steel 1500–1900 HB

Rhenium diboride 4600 HB

Hardness Mechanical TestsHardness Mechanical Tests Brinell Test Method

– One of the oldest tests– Static test that involves pressing a hardened steel ball (10mm) into a test

specimen while under a load of 3000 kg load for hard metals, 1500 kg load for intermediate hardness metals 500 kg load for soft materials

– Various types of Brinell Method of load application:oil pressure, gear-driven screw, or weights with a lever Method of operation: hand or electric power Method of measuring load: piston with weights, bourdon gage, dynamoeter, or

weights with a lever Size of machine: stationary (large) or portable (hand-held)

Brinell Test ConditionsBrinell Test ConditionsBrinell Test Method (continued)

– Method Specimen is placed on the anvil and raised to contact the ball Load is applied by forcing the main piston down and presses the ball

into the specimen A Bourbon gage is used to indicate the applied load When the desired load is applied, the balance weight on top of the

machine is lifted to prevent an overload on the ball The diameter of the ball indentation is measured with a micrometer

microscope, which has a transparent engraved scale in the field of view

Brinell Test ExampleBrinell Test ExampleBrinell Test Method (continued)

– Units: pressure per unit area– Brinell Hardness Number (BHN) = applied load divided by area

of the surface indenter

22

2

dDDD

LBHN

Where: BHN = Brinell Hardness Number

L = applied load (kg) D = diameter of the ball (10 mm) d = diameter of indentation (in mm)

• Example: What is the Brinell hardness for a specimen with an indentation of 5 mm is produced with a 3000 kg applied load.

•Ans: 2

22/6.142

)5()10(10)10(

)3000(2mmkg

mmmmmmmm

kgBHN

Brinell Test Method Brinell Test Method (continued)(continued)

Range of Brinell Numbers– 90 to 360 values with higher number indicating higher hardness– The deeper the penetration the higher the number– Brinell numbers greater than 650 should not be trusted because the

diameter of the indentation is too small to be measured accurately and the ball penetrator may flatten out.

– Rules of thumb 3000 kg load should be used for a BHN of 150 and above 1500 kg load should be used for a BHN between 75 and 300 500 kg load should be used for a BHN less than 100 The material’s thickness should not be less than 10 times the depth of the

indentation

Advantages & Disadvantages Advantages & Disadvantages of the of the

Brinell Hardness TestBrinell Hardness Test Advantages

– Well known throughout industry with well accepted results– Tests are run quickly (within 2 minutes)– Test inexpensive to run once the machine is purchased– Insensitive to imperfections (hard spot or crater) in the material

Limitations– Not well adapted for very hard materials, wherein the ball deforms excessively– Not well adapted for thin pieces– Not well adapted for case-hardened materials– Heavy and more expensive than other tests ($5,000)

Rockwell TestRockwell Test

Hardness is a function of the degree of indentation of the test piece by action of an indenter under a given static load (similar to the Brinell test)

Rockwell test has a choice of 3 different loads and three different indenters

The loads are smaller and the indentation is shallower than the Brinell test

Rockwell test is applicable to testing materials beyond the scope of the Brinell test

Rockwell test is faster because it gives readings that do not require calculations and whose values can be compared to tables of results (ASTM E 18)

Rockwell Test DescriptionRockwell Test Description

Specially designed machine that applies load through a system of weights and levers– Indenter can be 1/16 in hardened steel ball, 1/8 in steel ball, or 120°

diamond cone with a somewhat rounded point (brale)– Hardness number is an arbitrary value that is inversely related to the

depth of indentation– Scale used is a function of load applied and the indenter

Rockwell B- 1/16in ball with a 100 kg load Rockwell C- Brale is used with the 150 kg load

– Operation Minor load is applied (10 kg) to set the indenter in material Dial is set and the major load applied (60 to 100 kg) Hardness reading is measured Rockwell hardness includes the value and the scale letter



Rockwell Hardness Test

The Rockwell Hardness test is a hardness measurement based on

the net increase in depth of impression as a load is applied.

Hardness numbers have no units and are commonly given in the

R, L, M, E and K scales. The higher the number in each of the

scales means the harder the material.

Rockwell hardness testsRockwell hardness tests

Gives direct reading. Rockwell B (ball) used

for soft materials. Rockwell C (cone) uses

diamond cone for hard materials.

Flexible, quick and easy to use.

Rockwell HardnessRockwell Hardness

Rockwell Hardness Measurements In the Rockwell hardness test either a 120° conical diamond (C scale) or a steel ball (B scale) indentor is pushed into the surface of the test piece with a load of .

Rockwell C Diamond Indenter Test Rockwell B Indenter test

HR = E - e

Rockwell HardnessRockwell Hardness

Rockwell Hardness ScalesRockwell Hardness ScalesScale Code Load Indenter Use

A HRA 60 kgf 120° diamond coneTungsten carbide

B HRB 100 kgf 1/16 in diameter steel sphere Al, brass, and soft steels

C HRC 150 kgf 120° diamond cone Harder steelsD HRD 100 kgf 120° diamond cone

E HRE 100 kgf 1/8 in diameter steel sphere

F HRF 60 kgf 1/16 in diameter steel sphere

G HRG 150 kgf 1/16 in diameter steel sphere

Conversion/ComparisonConversion/Comparison

HBW 10/3000 HRA 60KG HRB 100KG HRC 150KG

Tensile Strength (Approx)

638 80.8 - 59.2 329,000

578 79.1 - 56 297,000

461 74.9 - 48.5 235,000

375 70.6 - 40.4 188,000

311 66.9 - 33.1 155,000

241 61.8 100 22.8 118,000

207 - 94.6 16 100,000

179 - 89 - 87,000

149 - 80.8 - 73,000

111 - 65.7 - 56,000

Rockwell ValuesRockwell ValuesScale Indenter Applied Load(kg)

A Brale 60B 1/16 in 100C Brale 150D Brale 100E 1/8 in 100F 1/16 in 60G 1/16 in 150

•B Scale: Materials of medium hardness (0 to 100HRB) Most Common

•C Scale: Materials of harder materials (> 100HRB) Most Common•Rockwell scales divided into 100 divisions with each division (point of hardness) equal to 0.002mm in indentation. Thus difference between a HRB51 and HRB54 is 3 x 0.002 mm - 0.006 mm indentation•The higher the number the harder the number

Rockwell and Brinell ConversionRockwell and Brinell ConversionFor a Rockwell C values between -20 and 40, the

Brinell hardness is calculated by

For HRC values greater than 40, use

For HRB values between 35 and 100 use

CHR

xBHN

100

1042.1 6

CHR

xBHN

100

105.2 4

BHR

xBHN

130

103.7 3

Rockwell and Brinell ConversionRockwell and Brinell ConversionFor a Rockwell C values, HRC, values

greater than 40,

Example,– Convert the Rockwell hardness number HRc 60

to BHN

CHR

xBHN

100

105.2 4

60100

105.2 4

xBHN 625BHN

T a r a r a n g k y uT a r a r a n g k y u


Vickers hardness testVickers hardness test

Uses square pyramid indentor.

Accurate results. Measures length of

diagonal on indentation.

Hardness Test• The hardness test offers the engineer a

quick, inexpensive and nondestructive way to estimate the tensile strength of a specimen.

• Hardness tests all make a small (sometimes microscopic) indentation into the surface of a specimen, and then use the force applied and the size of the indentation to calculate a "hardness number."

• The correlation between this value and the tensile strength allows this to be used as a quality control parameter

Brinell Hardness Test

• The Brinell Hardness Test utilizes a steel sphere which is usually 10mm in diameter.

• The sphere is forced into the surface of a material. Then, the diameter of the resulting impression is measured. The corresponding Brinell Hardness number is then calculated.

– D; diameter of indenter– Di; diameter of impression in mm– F; applied load in Kg

• Hardness correlates well with wear resistance

• For steel, nondestructive testTensile strength (psi)=500*HB

22

2 iDDDD

FHB

• The Rockwell Hardness Test utilizes two kinds of indentors.

• A small steel ball is used for soft materials and a diamond-shaped cone called a Brale is used for hard materials. To perform the test, the indentor is pushed into the surface of the material being tested. The test machine measures the depth of penetration and automatically converts this data into a Rockwell Hardness number

Relationship between hardness & StrengthRelationship between hardness & Strength

For steel, HB between 200 to 400

Su=0.495 HB Kpsi

Su=3.42 HB Mpa

Cast iron (ASTM data)

Su=0.23 HB–12.5 Kpsi

Su=1.58 HB-86 Mpa

SAE minimum strength

Su=0.2375 HB-16 Kpsi

Example 3.2Example 3.2

It is necessary to ensure that a certain part supplied by a foundry always meets or exceeds ASTM No. 20 specifications for cast iron. What hardness should be specified?

Solution of Example 3.2Solution of Example 3.2

Su=0.23 HB–12.5 Kpsi

If the foundry can control within 20 points

145< HB <165

14123.0

5.12

u

B

SH

Example 3.3Example 3.3

Brinell hardness tests were made on a random sample of five steel parts during processing

The results were HB values of 248, 247, 244, and 246

Estimate the mean and the standard deviation of the ultimate strength in SI units

The ASTM minimum is established at a level that 99 % of the population can meet or exceed. On the basis of this definition, what minimum ultimate strength corresponds to this sample testing?

Solution of Example 3.2Solution of Example 3.2

7600432.0*326.213.844)1(

5.360432.0*3.844ˆ

0432.00136.0041.0)(

3.8446.247*41.3

)0136.0 ,1(6.247)041.0 ,1(41.3

)041.0 ,1(41.3

450200

0136.0

36.3ˆ

6.247ˆ

99.0

2222

Suuu

SuuSu

yssu

meanu

u

Bu

B

HB

HB

B

CzSS

MPaCS

CCC

MPAS

S

MPaHS

Hfor

C

MPa

MPaH

Five data, normal distribution

Eq 3.21

(z)=0.01, then z=-2.326

Conversion of Data to DPHConversion of Data to DPH

Vickers hardness (HV) - DPH (Diamond Pyramid Hardness) DPH covers entire range from HRF up to HRC

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