Lap Beres Smoga Dapat B
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Transcript of Lap Beres Smoga Dapat B
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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
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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
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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:
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4d
2.5
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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
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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
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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) -
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- 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
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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) -
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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%).
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- 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
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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 -
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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
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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
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Brinell Test for :
1. FC 25
HB =
=
=
= 210.65 HB
2. FCD
HB =
=
=
= 259.69 HB
3. St
HB =
=
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=
=
= 113.75 HB
Rockwell Test
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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
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`
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
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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
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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.
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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
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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.
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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.
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http://www.instron.us/http://www.wikipedia.com/http://www.instron.us/http://www.wikipedia.com/