Lap Beres Smoga Dapat B

7/31/2019 Lap Beres Smoga Dapat B

1/17

I. Objectives

1. To understand what hardness is, and how it can be used to indicate some

properties of materials.

2. Student can decide how far the estimate value for materials (value of tensile

strength, hardness brinell, Rockwell, yield point, and ultimate point) and what is

the suitable test method for materials.

3. To be able to understand the correlation between hardness numbers and the

properties of materials.

4. To learn the advantages and limitations of the common hardness test methods.

II. Basic Theory

1. Brinell Test

- Brinell test use to determine hardness metal which has hardness

between for 50 HB 750 HB. There two kind type of brinell there are :

brinell S which is hardness < 450 HBS with the indenter is made from

steel ball (S) and brinell W which is hardness < 650 HBW with the

indenter is made from carbide (wolfram).

- Brinell test method does to specimen with indenter for gaining ex-

pressure plastic and the diameter which is left in specimen measured

with loop ruler.

- Brinell test method :

1. The indenter is pressed into the sample by an accurately

controlled test force.

2. The force is maintained for a specific dwell time, normally 10 -

15 seconds.

3. After the dwell time is complete, the indenter is removed

leaving a round indent in the sample.

4. The size of the indent is determined optically by measuring

two diagonals of the round indent using either a portable loop or one

that is integrated with the load application device.

5. The Brinell hardness number is a function of the test force

divided by the curved surface area of the indent. The indentation is

considered to be spherical with a radius equal to half the diameter

of the ball.1


2/17

6. Determining indenter which is will use (D)

7. Determining C (weight of constant)

8. Value of force that will use in testing F = C X D2

9. Measure diameter after test (d)

10. Accounting dept after test (h), h =

11. The formula follow as :

- Determining of diameter indenter has aim to determine result of

diameter (d) can enter range of testing condition (0,24D < d < 0,6D).

- The thickness of sample is minimal must be 8 times thicker than h (dept

after test). This rule is to aim that value of hardness isnt influence with

base of testing, because its could be deformation plastic on the bottom

surface.

- Because of the wide test force range the Brinell test can be used on

almost any metallic material.

- advantages

1. One scale covers the entire hardness range, although comparable

results can only be obtained if the ball size and test force

relationship is the same.

2. A wide range of test forces and ball sizes to suit every application.

3. Nondestructive, sample can normally be reused.

Weaknesses

2


3/17

1. The main drawback of the Brinell test is the need to optically

measure the indent size. This requires that the test point be

finished well enough to make an accurate measurement.

2. Slow. Testing can take 30 seconds not counting the sample

preparation time.

- Center pressure distance allowed

2. Rockwell 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 HRand the scale designation.

- Principal 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 .

- There are two types of Rockwell tests:

3

4d

2.5


4/17

1. Rockwell: the minor load is 10 kgf, the major load is 60, 100, or 150

kgf.

2. Superficial Rockwell: the minor load is 3 kgf and major loads are

15, 30, or 45 kgf. In both tests, the indenter may be either a diamond

cone or steel ball, depending upon the characteristics of the material

being tested.

- Using Rockwell Machine :

1. Cleaning indenter and test-piece to be clear of dirt, grease, rust or

paint.

2. Turn on rockwell machine and set the machine with rockwell type

C.

3. Ensuring that the thickness of the test-piece is at least 10 times the

depth of the indentation

4. Move around the panel till the machine show at start position.

5. After machine at start position automatically machine read the

hardness of material.

6. Move around back to realease sample from machine.

- There are 4 kind of type Rockwell with application :

1. Rockwell C : 20 till 70 HRC

Application : hardened steel, hardened alloy, annealed alloy

2. Rockwell A : 60 till 88 HRA

Application : hardened metal such as carbide.

3. Rockwell B : 35 till 100 HRB

4


5/17

Application : material with medium hardness. Such as low

carbon steel, annealed Cu-Zn, Cu.

4. Rockwell F : 60 till 115 HRF

Application : sheet metal cold work, annealed Cu-Zn,Cu

- Indenter of rockwell has two type there are conus and steel ball.

3. Tensile Strength

- Definition of Tensile Strength

There are three definitions of tensile strength:

Yield strength

The stress at which material strain changes from elastic deformation

to plastic deformation, causing it to deform permanently.

Ultimate strength

The maximum stress a material can withstand when subjected to

tension, compression or shearing. It is the maximum stress on the

stress-strain curve.

Breaking strength

The stress coordinate on the stress-strain curve at the point of

rupture.

- Example of curve of low carbon steel

5
http://en.wikipedia.org/wiki/Yield_(engineering)http://en.wikipedia.org/wiki/Ultimate_strengthhttp://en.wikipedia.org/wiki/Stress-strain_curvehttp://en.wikipedia.org/wiki/Rupture_(engineering)http://en.wikipedia.org/wiki/Yield_(engineering)http://en.wikipedia.org/wiki/Ultimate_strengthhttp://en.wikipedia.org/wiki/Stress-strain_curvehttp://en.wikipedia.org/wiki/Rupture_(engineering)


6/17

- Stress vs. Strain curve typical of structural steel

1. Ultimate Strength2.Yield Strength

3. Tensile strength

4. Strain hardening region

5. Necking region.

- Metals including steel have a linear stress-strain relationship up to the yield point, as shown

in the figure. In some steels the stress falls after the yield point. This is due to the interaction

of carbon atoms and dislocations in the stressed steel. Cold worked and alloy steels do not

show this effect. For most metals yield point is not sharply defined. Below the yield

strength all deformation is recoverable, and the material will return to its initial shape when

the load is removed. For stresses above the yield point the deformation is not recoverable,

and the material will not return to its initial shape. This unrecoverable deformation is known

asplastic deformation. For many applications plastic deformation is unacceptable, and the

yield strength is used as the design limitation.

- After the yield point, steel and many other ductilemetals will undergo a period of strainhardening, in which the stress increases again with increasing strain up to the ultimate

strength. If the material is unloaded at this point, the stress-strain curve will be parallel to

that portion of the curve between the origin and the yield point. If it is re-loaded it will

follow the unloading curve up again to the ultimate strength, which has become the new

yield strength.

- After a metal has been loaded to its yield strength it begins to "neck" as the cross-sectional

area of the specimen decreases due to plastic flow. When necking becomes substantial, itmay cause a reversal of the engineering stress-strain curve, where decreasing stress

6
http://en.wikipedia.org/wiki/Yield_(engineering)http://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Necking_(engineering)http://en.wikipedia.org/wiki/Dislocationhttp://en.wikipedia.org/wiki/Cold_workhttp://en.wikipedia.org/wiki/Plastic_deformationhttp://en.wikipedia.org/wiki/Ductilehttp://en.wikipedia.org/wiki/Metalshttp://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Necking_(engineering)http://en.wikipedia.org/wiki/Yield_(engineering)http://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Necking_(engineering)http://en.wikipedia.org/wiki/Dislocationhttp://en.wikipedia.org/wiki/Cold_workhttp://en.wikipedia.org/wiki/Plastic_deformationhttp://en.wikipedia.org/wiki/Ductilehttp://en.wikipedia.org/wiki/Metalshttp://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Strain_hardeninghttp://en.wikipedia.org/wiki/Necking_(engineering)


7/17

correlates to increasing strain because of geometric effects. This is because the engineering

stress and engineering strain are calculated assuming the original cross-sectional area before

necking. If the graph is plotted in terms oftrue stress and true strain the curve will always

slope upwards and never reverse, as true stress is corrected for the decrease in cross-

sectional area. Necking is not observed for materials loaded in compression. The peak stress

on the engineering stress-strain curve is known as the ultimate strength. After a period of

necking, the material will rupture and the stored elastic energy is released as noise and heat.

The stress on the material at the time of rupture is known as the tensile strength.

- Ductile metals do not have a well defined yield point. The yield strength

is typically defined by the "0.2% offset strain". The yield strength at 0.2%

offset is determined by finding the intersection of the stress-strain curve

with a line parallel to the initial slope of the curve and which intercepts

the abscissa at 0.2%. A stress-strain curve typical of aluminum along

with the 0.2% offset line is

shown in the figure below.

- Stress vs. Strain curve typical of aluminum

1. Ultimate Strength

2.Yield strength

3. Proportional Limit Stress

4. Tensile strength

5. Offset Strain (typically 0.2%).

7
http://en.wikipedia.org/wiki/Yield_strengthhttp://en.wikipedia.org/wiki/Yield_strength


8/17

- Stress vs. Strain curve of a very untypical brittle material

1. Ultimate Strength

2. Tensile strength.

- Tensile strength is measured in units of force per unit area. In the SI

system, the units are newtons per square metre (N/m) or pascals (Pa),

with prefixes as appropriate. The non-metric units are pounds-force per

square inch (lbf/in or PSI). Engineers in North America usually use units

of ksi which is a thousand psi. One MegaPascal is 145.037738 pounds-force per square inch.

- The breaking strength of a rope is specified in units of force, such as

newtons, without specifying the cross-sectional area of the rope. This is

often loosely called tensile strength, but this is not a strictly correct use

of the term.

- In brittle materials such as rock, concrete, cast iron, or soil, tensile

strength is negligible compared to the compressive strength and it isassumed zero for many engineering applications. Glass fibers have a

tensile strength stronger than steel[1], but bulk glass usually does not.

This is due to the Stress Intensity Factor associated with defects in the

material. As the size of the sample gets larger, the size of defects also

grows. In general, the tensile strength of a rope is always less than the

tensile strength of its individual fibers.

- Tensile strength can be defined for liquids as well as solids. For example,

when a tree draws water from its roots to its upper leaves by

8
http://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Newtonhttp://en.wikipedia.org/wiki/Square_metrehttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/SI_prefixhttp://en.wikipedia.org/wiki/Pounds-force_per_square_inchhttp://en.wikipedia.org/wiki/Pounds-force_per_square_inchhttp://en.wikipedia.org/wiki/MPahttp://en.wikipedia.org/wiki/Ropehttp://www.fols.org/resources/faqDetail.cfm?ID=8http://en.wikipedia.org/wiki/Stress_Intensity_Factorhttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Treehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Areahttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/SIhttp://en.wikipedia.org/wiki/Newtonhttp://en.wikipedia.org/wiki/Square_metrehttp://en.wikipedia.org/wiki/Pascal_(unit)http://en.wikipedia.org/wiki/SI_prefixhttp://en.wikipedia.org/wiki/Pounds-force_per_square_inchhttp://en.wikipedia.org/wiki/Pounds-force_per_square_inchhttp://en.wikipedia.org/wiki/MPahttp://en.wikipedia.org/wiki/Ropehttp://www.fols.org/resources/faqDetail.cfm?ID=8http://en.wikipedia.org/wiki/Stress_Intensity_Factorhttp://en.wikipedia.org/wiki/Fiberhttp://en.wikipedia.org/wiki/Liquidhttp://en.wikipedia.org/wiki/Tree


9/17

transpiration, the column of water is pulled upwards from the top by

capillary action, and this force is transmitted down the column by its

tensile strength. Air pressure from below also plays a small part in a

tree's ability to draw up water, but this alone would only be sufficient to

push the column of water to a height of about ten metres, and trees can

grow much higher than that.

4. Leeb Test

- Principal of Leeb Testing

- The Leeb (also known as an Equotip) test is a modern electronic versionof the Scleroscope. It uses a carbide ball hammer that is spring rather

than gravity powered. An electronic sensor measures the velocity of the

hammer as it travels toward and away from the surface of the sample.

The Leeb value is the hammer's rebound velocity divided by the impact

velocity times 1000. The result is Leeb hardness from 0 to 1000 that can

be related to other hardness scales such as Rockwell and Vickers.

- Since the devise is electronic in nature, most instruments are designedto automatically convert from the Leeb number to a more conventional

hardness scale. By using a variety of different conversions to suit the

modulus of different materials, a wide range of metallic parts can be

tested. The main limitations are that the parts must have a good finish

and a minimum weight of 5kg. Leeb testers are portable and can be used

at different angles as long as they are perpendicular to the test surface.

III. Tool and Material

III.1 Tool

a. Brinell hardness tester with equipment

b. Rockwell hardness tester with equipment

c. Digital scale

d. Breaker glass

9
http://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Capillary_actionhttp://en.wikipedia.org/wiki/Transpirationhttp://en.wikipedia.org/wiki/Capillary_action


10/17

e. Tensile test machine

f. Leeb (equotip)

g. Vernier scale

III.2 Material

a. FC 25

b. Ni hard

c. Ni resist

d. Sample of tensile strength

e. Mild Steel

f. FeCr25

g. GXMn12

h. FeCr27

i. St 37

IV. Lab Data

10

No

Material F = 3000 Kgf Average

1 FC4.2 mm

4.2 mm4.2 mm4.2 mm

2 FCD3.8 mm

3.8 mm4 mm3.8 mm

3 St5.6 mm

5.6 mm5.6 mm


11/17

Brinell Test for :

1. FC 25

HB =

=

=

= 210.65 HB

2. FCD

HB =

=

=

= 259.69 HB

3. St

HB =

=

11


12/17

=

=

= 113.75 HB

Rockwell Test

12

No

Material Data at Xi (HRC) Average

1 FeCr25

37

3736.937.53638

2 GXMn12

41.7

39.439.639.241.838.8

3 FeCr27

44.7

43.543.543.543.343.4

4 Ni hard

38.7

59.258.459.259.260.3

5 Ni Resist

7.7

7.44.87.13.64.4

6 Mild Steel

4.8

8.15.28.56.37.7


13/17

`

Tensile Strength

Tensile strength sheet metal

Identification material

With magnetic test

When use magnetic the material does influence by magnetic so

structure of material is austenite

- With the hit by other things

When use kikir and the material abrasion with kikir, because structure

of kikir is martensit so the material structure is lower than kikir maybe

ferrit or perlit but the material has plastic behavior so the material hasferrit structure.

Ao = p x l

Ao = 12.5 x 2.45

Ao = 30.625 mm2

Estimation of yield strength

13


14/17

y =

F = y.

F = 300 . 30,625

F = 9187,5 N = 918.75 Kgf

Estimation of ultimate strength

F = u . Ao

F = 400 . 30.625

F = 12,250 N = 1,225 Kgf

Real of yield strength

F = 970 Kgf

y =

=

= 310 N/mm2

Real of Ultimate strength

u =

u =

u= 376 N/mm 2 so possibility that the material is

St. 37

14


15/17

Elongation of material

E = x 100%

E = x 100%

E = 29.85 %

Tensile strength of material

V. Analyze

1. At sheet

metal on tensile

testing especially

at yield point area

there happens

cottrel effect which

is indicator arrow

move from up to bottom again and again after that indicator arrow up to the

next number of scale when I counting yield point estimation it will be happen

at 918.75 Kgf but in fact yield point happen at 950 Kgf.

15

No F l l1 lo Ao

1 200 0 47.5 47.5 20.42

2 250 0.15 47.65 47.5 20.423 300 0.25 47.75 47.5 20.42

4 350 0.5 48 47.5 20.42

5 400 0.6 48.1 47.5 20.42

6 450 0.7 48.2 47.5 20.42

7 500 0.8 48.3 47.5 20.42

8 550 0.9 48.4 47.5 20.42

9 600 1 48.5 47.5 20.42

10 650 1.1 48.6 47.5 20.42

11 700 1.15 48.65 47.5 20.42

12 750 1.3 48.8 47.5 20.42

13 800 1.35 48.85 47.5 20.42

14 825 47.5 20.42

15 850 1.9 49.4 47.5 20.42

16 875 2.05 49.55 47.5 20.42

17 900 2.1 49.6 47.5 20.42

18 925 2.15 49.65 47.5 20.42

19 950 2.2 49.7 47.5 20.42

20 975 2.25 49.75 47.5 20.42

21 1000 2.3 49.8 47.5 20.42

22 1025 2.45 49.95 47.5 20.42

23 1050 2.5 50 47.5 20.42

24 1075 47.5 20.42

25 1100 putus 47.5 20.42

26 1115 2.55 50.05 47.5 20.42


16/17

2. At sheet metal on tensile testing it did twice why?, in the first change

the machine not strong enough to pull it out (till break) and the yield point area

is 950 Kgf but in second change the yield point is increasing to 975 Kgf this

things is caused by plastic deformation in first change so the hardness material

is increasing in the second tensile testing.

3. At Rockwell testing for Ni hard has happened different hardness this

thing caused by treatment for Ni Hard before like heatreatment which is almost

structure of Ni Hard has transformed to martensit so the hardness was

increasing.

4. The sample must be drawn before do a tensile strength cause its

possibility that break not in the middle.

5. The person who wants to does kind testing have to take look error factor

so the result can valid.

VI. Conclusion

From the testing result, we can summarize that ;

1. Based on the curve shape, the materials that have cottrell effect is

concrete steel sample, so can be predicted that the material of

specimen is low carbon steel.

Before Practicum Understanding

1.Specimen standard is needed, so the united understanding about

interpretation of testing result is got.

Initial length is needed to known, so elasticity value could be known

later.

2.Plastic deformation occur over the course of linier zone, marked by

the increasing of elongation as increasing of stress given. If load is

negated, the length will be unchanged not return to initial length.

16


17/17

In atoms perspective, it related to atomic bond break and then

forming new atomic bond .Although stress is negated size wouldnt be

returned back.

For soft and ductile material, is not easy to determine exact position

on the stress-strain curve where yield limit occur. Because line slove(elastic) from the curve decrease slowly. So, for soft and ductile

material yield point is defined through offset method 0,2% or

elongation 0,002%.

After Practicum Understanding

1. The mistakes during testing process;

Non standard shape and size of specimen.

Loading velocity is too fast.

Loading velocity is too slow and unstable.

Testing load isnt in the same axis with the specimen.

VII. Literature

1. http://www.instron.us

2. http://www.wikipedia.com

3. Hardness testing book.

17
http://www.instron.us/http://www.wikipedia.com/http://www.instron.us/http://www.wikipedia.com/

Lap Beres Smoga Dapat B

Documents

Transcript of Lap Beres Smoga Dapat B