Tension Test On Hot Rolled Plain Steel Bar (astm-a615/615-m)
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5. To perform tension test on hot rolled plain steel bar (ASTM-A615/615-M) (12-11-08) PURPOSE
To study stress strain behavior of the specimen To determine different mechanical properties of steel sample (e.g. yield strength, tensile strength, Modulus of Elasticity, Ductility etc.) To check the adequately of the specimen according to ASTM-A615/615-M standards.
APPARATUS
500 KN Shimadzu Universal Testing Machine Batty’s Extensometer (LC = 1/20000”) Spring Divider
Steel Ruler Vernier Caliper Weighing Balance and Weights Meter Rod
RELATED THEORY Manufacturing of Steel
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Flow Diagram showing the manufacturing of steel
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Hot Rolling
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Material Test and Stress-Strain Diagram The material strength depends on its ability to sustain a load without undue deformation or failure. The property is inherent in the material itself and must be determined by the experiment. One of the most important tests to be performed in the regard is the tension or compression test/ to do so a standard specimen is made. The test is performed in a universal testing machine. Shown in figure below is the specimen and test result of Stress-Strain Diagram.
The stress-strain diagram consists of four stages during the whole process i.e. Elastic Yielding Hardening and Necking stages respectively. From yielding stage some permanent plastic deformation occurs. About 90% of the engineering problems only concern with the elastic deformation in structural members and mechanical components. Only 10% of engineering work concerns plastic and other nonlinear stage (e.g. metal forming).
Components of Stress-Strain Diagram PROPORTIONAL LIMIT (P.L.) Maximum stress that may be developed during a simple tension test such that the stress is linear function of strain. (No proportional limit for brittle materials.)
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ELASTIC LIMIT (E.L.) Maximum stress that may be developed during a simple tension test such that there is no permanent set or residual deformation when the load is entirely removed. Hook’s Law is not valid after E.L. and the numerical values of P.L. and E.L. are usually identical. But the curve tends to flatten out causing a greater increment of strain for corresponding increment of stress.
Figure 1 Stress Strain Curve for Brittle materials
ELASTIC AND PLASTIC RANGES Region of stress-strain diagram extending from origin to the proportional limit or elastic limit is called as elastic range. When the material is unloaded within elastic range, it will come back to its original shape without any permanents plastic deformation. The region extending from P.L. to point of fracture is called as plastic range.
MODULUS OF ELASTICITY (E) It is the ratio of the unit stress to the unit strain and it is determined as the slope of straight line from zero to proportional limit from the stress-strain diagram. The stress strain linear relationship was discovered by Robert Hook in 1676 and is known as Hook’s Law. It is mathematically represented by the equation 𝜍 = 𝐸𝜖, Where E is termied as Modulus of Elasticity or Young’s Modulus with units of stress, for mild steel, E ~ 200 GPa (29 X 10^6 Psi)
Figure 2 Stress & Strain Curves for different Materials
YIELD POINT (Y.P.)
Steel Grade UTS
A point on the stress strain curve after which there is an increase in strain with no significant increase in stress is called as yield point. The phenomenon is called as yielding. The stress
G 40 G 60 G 75
5
Tension Test on Hot Rolled Plain Steel Bar
In KSI 70 KSI 90 KSI 100 KSI
Yield Strength In Mpa 300 Mpa 420 Mpa 500 Mpa
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in Psi 40000 Psi 60000 Psi 75000 Psi
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corresponding to Y.P is known as the yield strength of the material which is represented in Ksi. Which gives the grade of the steel is also known as Proof Stress.
METHODS OF DETERMINING YIELD STRENGTH
Halting of machine/drop of beam method Offset method Lunder line method Specific strain method
1. HALTING OF MACHINE METHOD The stress may actually decrease momentarily resulting in upper and lower yield points. The yield point during a simple tension test can be observed by Halting of machine.
2. OFFSET METHOD For the materials that do not gave well defined yield point, yield strength is determined by offset method. This consists of drawing a line parallel to the initial tangent of the stress strain diagram at 0.2% (0.002 m/m or in/in) strain.
3. LUDER LINE METHOD When the specimen yields, a pattern of fine lines appears on the polished surface, they roughly interact at right angle to each other and 45 degrees approximately to the longitudinal axis of the bar.
Figure 3 Offset method for determining yield
Figure 4 Lunder Lines
4. SPECIFIC STRAIN METHOD In this method simply 0.5% of the total strain is marked to determine the corresponding stress, which is yielding stress.
Figure 5 Specific Strain Method
0.5%
TENSILE/ULTIMATE STRENGTH
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Maximum or highest ordinate (Stress) on the stress-strain diagram is called as the tensile or ultimate strength of the sample. It is commonly considered as the maximum strength of the material.
RAPTURE/FRACTURE/BREAKING STRENGTH Rapture strength or Breaking strength is the stress at the failure. Rapture strength is always less than the ultimate strength. For brittle material, the ultimate and rupture strength are almost the same.
STRAIN HARDENING ZONE If a ductile material can be stressed considerably beyond the yield point without failure, the material is said to be “Strain hardened”. It is a zone after yielding when the particles of material rearrange themselves and start taking load again, so stress starts increasing. This is true for many structural metals.
NECKING Localized decrease in cross sectional area of the sample after the ultimate strength is called Necking. This continues up to rupture/failure.
Figure 6 Necking of steel specimen at failure (cup/cone)
Due to necking (cup and cone formation) the cross sectional area is reduces and hence actual rupture strength can be obtained by dividing the rupture load with actual rupture area. So, the point of actual rupture strength will obviously be higher that the rupture strength on the stress strain diagram because the rupture area is less than the original cross sectional area of sample.
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MODULUS OF RESILIENCE (M.O.R.) Resilience: the ability of a material to absorb energy in the elastic range (i.e. without permanent deformation) is called as resilience. 𝑈𝑟 =
2 1 1 𝜍𝑃𝑙 𝜍𝑃𝑙 𝜖𝑃𝑙 = 2 2 𝐸
Modulus of Resilience is the amount of work done on a unit volume of material as a simple tensile force is increased from zero to proportional limit (P.L.). It is calculated as the area under the stress strain diagram from zero to P.L. (Units: Psi or MPa)
MODULUS OF TOUGHNESS (M.O.T.) Toughness: the ability of a material to absorb energy in the plastic range (i.e. permanent deformation) is called as toughness. Modulus of Toughness is the amount of work done on a unit volume of material as s simple tensile force is increased from zero to failure of the specimen. It is calculated as the total area under the stress-strain diagram. (Units: Psi or MPa)
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RESIDUAL STRAIN When Material is loaded beyond the elstic limit then after unloading the material does not come back to its origional position and there is a permanent set in the specimen, which is called Residual Strain.
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SPECIFIC STRENGTH Ratio of ultimate/tensile strength to the specific weight (weight per unit volume) is called specific strength. (Units: Length)
SPECIFIC MODULUS Ration of Modulus of Elasticity/Young’s Modulus to the specific weight is called as specific modulus. (Units: Length)
ELASTICITY The ability of material to regain its original shape and size after the removal of load is known as elasticity. The elastic strain is reversible change in the dimensions of body.
PLASTICITY The property of material by virtue of which it retains the shape given to it, is known as plasticity. Plastic strain is deformation or change in dimensions which is irreversible and remains in after the load has been removed.
Ductile Materials Any material that can be subjected to large strains before it rupture is called a ductile materials, e.g. mild steel.
Figure 8 Ductile failure of a specimen strained axially
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MEASUREMENT OF DUCTILITY Ductility is a quantity, subjective property of a material. In general, measurements of ductility are of interest in three ways: 1. To indicate the extent to which a metal can be deformed without fracture in metalworking operation such as rolling and extrusion. 2. To indicate to the designer, in a general way, the ability of the metal to flow plastically before fracture. A high ductility indicates that the material is “forgiving” and likely to deform locally without fracture should the designer err in the stress calculation or the prediction of severe loads. 3. To serve as an indicator of changes in impurity level or processing conditions. Ductility measurements may be specified to assess material quality even though no direct relationship exists between the ductility measurement and performance in service. The conventional measures of ductility that are obtained from the tension test are the strain at fracture (usually called elongation) and the reduction of area at fracture. Both of these properties are obtained after fracture by putting the specimen back together and taking measurement of length and cross sectional area. Because a appreciable fracture of the plastic deformation will be concentrate in the necked region of the tension specimen, the value of rupture strain (elongation) will depend on the gauge length over which the measurement was taken. The smaller the gauge length the greater will be the contribution to the overall elongation from the necked region and the higher will be the value of rupture strain. Therefore, when reporting values of percentage elongation, the gauge length L0 always should be given.
PERCENTAGE ELONGATION “The change in length per unit original length expressed in percentage” % 𝐸𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 =
𝐿𝑂 − 𝐿𝑓 𝑋 100, 𝑤𝑒𝑟𝑒 𝐿𝑂 = 𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡, 𝐿𝑓 = 𝐹𝑖𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡 𝐿𝑂
PERCENTAGE REDUCTION IN AREA “Reduction in cross-sectional area per unit original area expressed in percentage” % 𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑖𝑛 𝑋. 𝐴𝑟𝑒𝑎 =
11
𝐴𝑂 − 𝐴𝑓 𝑋 100, 𝑤𝑒𝑟𝑒 𝐴𝑂 = 𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎, 𝐴𝑓 = 𝐹𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎 𝐴𝑂
Tension Test on Hot Rolled Plain Steel Bar
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Ductile and Brittle Materials Materials having a relatively larger tensile strain up to the point of rupture or failure are called as ductile materials, e.g. Structural Steel, Aluminum, etc. Whereas, the materials having a relatively small tensile strain up to the point of rupture are called as brittle materials, e.g Cast Iron, Concrete, etc.
Procedure for Experiment 1. Note the shape and size of specimen, measure the length of specimen and weight it to find the cross sectional area of specimen, firm this area effective diameter of the bar is found in mm. compare this diameter with nominal size of bar. 2. Mark the gauge length on the specimen throughout the length of the specimen for determination of % elongation after fracture, i.e. Ductility. 3. Fix the Battey extensometer to measure the elongation up to its region and grip the specimen in machine jaws. Note the gauge length of extensometer and its least count. 4. Calculate the expected Yield and Ultimate load and decide suitable load increment and draw a table for recording readings of loads and extensions. 5. Apply the load in desire increment and take readings of extensometer. 6. Remove the Battey extensometer at its limit and record the elongation with a spring divider and steel ruler up to breaking point. 7. Join the two broken pieces together and measure the approximate diameter at failure zones for determination of final cross sectional area. 8. Measure the change in lengths for gauge lengths marked throughout the lengths of specimen for estimation of effect of gauge length on % age elongation (ductility).
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Calculations and Observations L= 613 mm M= .578 Kg = 578 grams Density: 7.850 g/cm3
Marking Length = GL/4 = 50.8 mm = 2” Gauge Length of Extensometer = 50.8 mm
In order to calculate diameter, we will use the relation𝜌 = 𝑚/𝑉, where rho is 7.850 g/m3. 𝑑=
𝑚 7.850 𝑋 𝐿 𝑋 𝜋 4
=
.578 7850 𝑋 .613 𝑋 .7853
Extension = %age strain = Stress = Length of steel bar = Area of steel bar = Mean Fracture Diameter = Reduced Area = % Reduction in Area = True Rupture strength =
13
= 0.01236 𝑚 = 12.36 𝑚𝑚
(R – I.R ) X L.C. X 25.4 (∆L/L) X 100, where L= Gauge Length Load/Area 613 mm m/lρ = 578/(613 X .007850) = 120.11 mm2 8 mm 58.08 mm2 ((120.11-58.08)/120.11)X100 = 51.64% (fracture load/reduced area) = 1076.101 MPa
Tension Test on Hot Rolled Plain Steel Bar
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S.N o
Load (kN)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
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Extensometer/ Extension Spring Divider (mm) reading
%age Strain
1400 1402 1404 1408 1412 1416 1424 1432 1438 1510 1515 1600 1615 1700 1800 1850 1890 2110 2500 54 56 57 62 67 70
0 0.005 0.01 0.02 0.03 0.04 0.06 0.08 0.095 0.275 0.2875 0.5 0.5375 0.75 1 1.125 1.225 1.775 2.75 7.874016 11.81102 13.77953 23.62205 33.46457 39.37008
0 5 10 15 20 25 30 35 40 43.5 43.7 43.7 43.7 43.7 43.7 43.7 45 48 50 52.5 61 65 67.2 63.3 62.5
0 0.00254 0.00508 0.01016 0.01524 0.02032 0.03048 0.04064 0.04826 0.1397 0.14605 0.254 0.27305 0.381 0.508 0.5715 0.6223 0.9017 1.397 4 6 7 12 17 20
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Stress Remarks (MPa) 0 41.62851 83.25701 124.8855 166.514 208.1425 249.771 291.3996 333.0281 362.168 363.8332 363.8332 363.8332 363.8332 363.8332 363.8332 374.6566 399.6337 416.2851 437.0993 507.8678 541.1706 559.4871 527.0169 520.3563
P.L./E.L. Y.P.
U.T.S. N.R.S
Stress Strain Curve
600 500
stress
400 300
200 100 0 0
14
10
20 30 percentage strain
Tension Test on Hot Rolled Plain Steel Bar
40
50
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Sr. no
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Deformed Length
G.L
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Elongation
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% elongation
L-R 1 2 3 4
50 100 150 200
70 126 181 233
20 26 31 33
40 26 20.67 16.5
50 100 150 200
68 126 186 244
18 26 36 44
36 26 24 22
R-L 1 2 3 4
G.L. ~ %Elog. L to R 50 %age Elong.
40 30 20 10
Gauge Length
0 0
50
100
150
200
250
G.L. ~ %Elog. R to L 40
%age Elong.
30
20 10 0 0
16
Gauge Length 50
100
150
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Results True Rupture strength =
(fracture load/reduced area) = 1076.101 MPa
Modulus of Elasticity = Modulus of Resilience = 𝑈𝑟 =
1 𝜍 𝜖 2 𝑃𝑙 𝑃𝑙
2 1 𝜍𝑃𝑙 = 𝐸
=2
½(333.02*0.04825/50) = 0.1607 MPa
Modulus of Toughness = area of one box = (5/400)*20 = .25, total boxes= 807, total area = 807*.25 = 20.175 Mpa
S.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
17
Property Proportional Limit Elastic Limit Yield Strength/Proof Stress Ultimate Strength Nominal Rupture Strength True Rupture Strength %age elongation %age reduction in area Modulus of Elasticity Modulus of Resilience Modulus of Toughness Weight/unit length
Specimen Results 333.02 MPa 333.02 MPa 362.168 MPa 559.4871 MPa 520.35 MPa 1076.101 MPa 40 % 51.64%
Standard Values
12% min. 200 GPa
0.1607 MPa 201 MPa 0.9429 kg/m
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0.994 kg/m
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Conclusion and Comments
1. Grade of Steel Specimen The yield strength of our steel specimen in 363.8332 MPa which is 52769.53 psi. Thus we can conclude our steel specimen falls in the category of Grade 40 [300]. Steel specimens having yield strength From 40000 psi to 60000 psi are said to be grade 40 steel. Grade 40 is less brittle than grade 60 because it has less about of carbon contents which make it comparatively brittle.
2. Discussion over Failure and Fracture The specimen did not break in a proper cup cone manner. This may be due to impurities present or due to non-uniformity of the specimen. A cup cone manner of the specimen helps us to predict the homogeneity if a material. If the material is made of standard proportions then it will break in perfect manner. More over mild steel is weaker in shear and strong in tension. So it should be noted here that the cup cone manner is only for mild steel i.e. a material strong in tension and weaker in shear. So if we see the breaking or fracture pattern of a cast iron then it would be cleared that cast iron is weak in tension because it does not fracture in a cup cone manner.
3. Discussion over Weight/Unit Length The specimen results gives us the value of mass/unit length as 0.8429 kg/m, while the standard value of it as ASTM-A615/615M 2005, it is 0.994 kg/m. the result gives us value lesser than standard value. This means that for one meter of length the mass is lesser that that of standard. So, it shows that the strength of bar will ultimately be lower than the required one as standard one. Hence it would not be safe to use.
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4. Discussion over Percentage Elongation The percentage elongation in over case is 40 %, while according to ASTM-A615/615M 2005, it must be 12%. It means our specimen has elongated more than it should. This shows that it does not satisfy the standards and more percentage elongation tells us that it is not made up accurate proportions. Moreover it also tells us that or particular value of load our specimen will elongate more that the standard value so it is not suited for the valuable structures.
5. Discussion over Percentage Reduction of Area Percentage reduction of area in specimen is 51% where as in standards it should be less than that It shows that it has elongate more than it should. This can be due to impurities present in the material or the non-homogeneity of the material. It has showed larger reduction in area when the load is applied. From this we can conclude that it can show abnormal behavior in the structure during any unfavorable circumstances.
6. Discussion over True Rupture and Nominal Rupture Strength True rapture is always greater than the nominal rupture strength of the specimen. In our case nominal rupture strength is 520.3536MPa, which is obtained by diving the applied load by the original area of the steel bar, where as we have in our case true rupture strength is 1076 MPa, which is obtained by diving applied load by the reduced area i.e. average area of cup and cone.
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5. To perform tension test on hot rolled plain steel bar (ASTM-A615/615-M) (12-11-08) PURPOSE
To study stress strain behavior of the specimen To determine different mechanical properties of steel sample (e.g. yield strength, tensile strength, Modulus of Elasticity, Ductility etc.) To check the adequately of the specimen according to ASTM-A615/615-M standards.
APPARATUS
500 KN Shimadzu Universal Testing Machine Batty’s Extensometer (LC = 1/20000”) Spring Divider
Steel Ruler Vernier Caliper Weighing Balance and Weights Meter Rod
RELATED THEORY Manufacturing of Steel
1
Tension Test on Hot Rolled Plain Steel Bar
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Flow Diagram showing the manufacturing of steel
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Hot Rolling
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Material Test and Stress-Strain Diagram The material strength depends on its ability to sustain a load without undue deformation or failure. The property is inherent in the material itself and must be determined by the experiment. One of the most important tests to be performed in the regard is the tension or compression test/ to do so a standard specimen is made. The test is performed in a universal testing machine. Shown in figure below is the specimen and test result of Stress-Strain Diagram.
The stress-strain diagram consists of four stages during the whole process i.e. Elastic Yielding Hardening and Necking stages respectively. From yielding stage some permanent plastic deformation occurs. About 90% of the engineering problems only concern with the elastic deformation in structural members and mechanical components. Only 10% of engineering work concerns plastic and other nonlinear stage (e.g. metal forming).
Components of Stress-Strain Diagram PROPORTIONAL LIMIT (P.L.) Maximum stress that may be developed during a simple tension test such that the stress is linear function of strain. (No proportional limit for brittle materials.)
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ELASTIC LIMIT (E.L.) Maximum stress that may be developed during a simple tension test such that there is no permanent set or residual deformation when the load is entirely removed. Hook’s Law is not valid after E.L. and the numerical values of P.L. and E.L. are usually identical. But the curve tends to flatten out causing a greater increment of strain for corresponding increment of stress.
Figure 1 Stress Strain Curve for Brittle materials
ELASTIC AND PLASTIC RANGES Region of stress-strain diagram extending from origin to the proportional limit or elastic limit is called as elastic range. When the material is unloaded within elastic range, it will come back to its original shape without any permanents plastic deformation. The region extending from P.L. to point of fracture is called as plastic range.
MODULUS OF ELASTICITY (E) It is the ratio of the unit stress to the unit strain and it is determined as the slope of straight line from zero to proportional limit from the stress-strain diagram. The stress strain linear relationship was discovered by Robert Hook in 1676 and is known as Hook’s Law. It is mathematically represented by the equation 𝜍 = 𝐸𝜖, Where E is termied as Modulus of Elasticity or Young’s Modulus with units of stress, for mild steel, E ~ 200 GPa (29 X 10^6 Psi)
Figure 2 Stress & Strain Curves for different Materials
YIELD POINT (Y.P.)
Steel Grade UTS
A point on the stress strain curve after which there is an increase in strain with no significant increase in stress is called as yield point. The phenomenon is called as yielding. The stress
G 40 G 60 G 75
5
Tension Test on Hot Rolled Plain Steel Bar
In KSI 70 KSI 90 KSI 100 KSI
Yield Strength In Mpa 300 Mpa 420 Mpa 500 Mpa
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in Psi 40000 Psi 60000 Psi 75000 Psi
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corresponding to Y.P is known as the yield strength of the material which is represented in Ksi. Which gives the grade of the steel is also known as Proof Stress.
METHODS OF DETERMINING YIELD STRENGTH
Halting of machine/drop of beam method Offset method Lunder line method Specific strain method
1. HALTING OF MACHINE METHOD The stress may actually decrease momentarily resulting in upper and lower yield points. The yield point during a simple tension test can be observed by Halting of machine.
2. OFFSET METHOD For the materials that do not gave well defined yield point, yield strength is determined by offset method. This consists of drawing a line parallel to the initial tangent of the stress strain diagram at 0.2% (0.002 m/m or in/in) strain.
3. LUDER LINE METHOD When the specimen yields, a pattern of fine lines appears on the polished surface, they roughly interact at right angle to each other and 45 degrees approximately to the longitudinal axis of the bar.
Figure 3 Offset method for determining yield
Figure 4 Lunder Lines
4. SPECIFIC STRAIN METHOD In this method simply 0.5% of the total strain is marked to determine the corresponding stress, which is yielding stress.
Figure 5 Specific Strain Method
0.5%
TENSILE/ULTIMATE STRENGTH
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Maximum or highest ordinate (Stress) on the stress-strain diagram is called as the tensile or ultimate strength of the sample. It is commonly considered as the maximum strength of the material.
RAPTURE/FRACTURE/BREAKING STRENGTH Rapture strength or Breaking strength is the stress at the failure. Rapture strength is always less than the ultimate strength. For brittle material, the ultimate and rupture strength are almost the same.
STRAIN HARDENING ZONE If a ductile material can be stressed considerably beyond the yield point without failure, the material is said to be “Strain hardened”. It is a zone after yielding when the particles of material rearrange themselves and start taking load again, so stress starts increasing. This is true for many structural metals.
NECKING Localized decrease in cross sectional area of the sample after the ultimate strength is called Necking. This continues up to rupture/failure.
Figure 6 Necking of steel specimen at failure (cup/cone)
Due to necking (cup and cone formation) the cross sectional area is reduces and hence actual rupture strength can be obtained by dividing the rupture load with actual rupture area. So, the point of actual rupture strength will obviously be higher that the rupture strength on the stress strain diagram because the rupture area is less than the original cross sectional area of sample.
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Tension Test on Hot Rolled Plain Steel Bar
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MODULUS OF RESILIENCE (M.O.R.) Resilience: the ability of a material to absorb energy in the elastic range (i.e. without permanent deformation) is called as resilience. 𝑈𝑟 =
2 1 1 𝜍𝑃𝑙 𝜍𝑃𝑙 𝜖𝑃𝑙 = 2 2 𝐸
Modulus of Resilience is the amount of work done on a unit volume of material as a simple tensile force is increased from zero to proportional limit (P.L.). It is calculated as the area under the stress strain diagram from zero to P.L. (Units: Psi or MPa)
MODULUS OF TOUGHNESS (M.O.T.) Toughness: the ability of a material to absorb energy in the plastic range (i.e. permanent deformation) is called as toughness. Modulus of Toughness is the amount of work done on a unit volume of material as s simple tensile force is increased from zero to failure of the specimen. It is calculated as the total area under the stress-strain diagram. (Units: Psi or MPa)
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Tension Test on Hot Rolled Plain Steel Bar
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RESIDUAL STRAIN When Material is loaded beyond the elstic limit then after unloading the material does not come back to its origional position and there is a permanent set in the specimen, which is called Residual Strain.
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Tension Test on Hot Rolled Plain Steel Bar
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SPECIFIC STRENGTH Ratio of ultimate/tensile strength to the specific weight (weight per unit volume) is called specific strength. (Units: Length)
SPECIFIC MODULUS Ration of Modulus of Elasticity/Young’s Modulus to the specific weight is called as specific modulus. (Units: Length)
ELASTICITY The ability of material to regain its original shape and size after the removal of load is known as elasticity. The elastic strain is reversible change in the dimensions of body.
PLASTICITY The property of material by virtue of which it retains the shape given to it, is known as plasticity. Plastic strain is deformation or change in dimensions which is irreversible and remains in after the load has been removed.
Ductile Materials Any material that can be subjected to large strains before it rupture is called a ductile materials, e.g. mild steel.
Figure 8 Ductile failure of a specimen strained axially
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Tension Test on Hot Rolled Plain Steel Bar
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MEASUREMENT OF DUCTILITY Ductility is a quantity, subjective property of a material. In general, measurements of ductility are of interest in three ways: 1. To indicate the extent to which a metal can be deformed without fracture in metalworking operation such as rolling and extrusion. 2. To indicate to the designer, in a general way, the ability of the metal to flow plastically before fracture. A high ductility indicates that the material is “forgiving” and likely to deform locally without fracture should the designer err in the stress calculation or the prediction of severe loads. 3. To serve as an indicator of changes in impurity level or processing conditions. Ductility measurements may be specified to assess material quality even though no direct relationship exists between the ductility measurement and performance in service. The conventional measures of ductility that are obtained from the tension test are the strain at fracture (usually called elongation) and the reduction of area at fracture. Both of these properties are obtained after fracture by putting the specimen back together and taking measurement of length and cross sectional area. Because a appreciable fracture of the plastic deformation will be concentrate in the necked region of the tension specimen, the value of rupture strain (elongation) will depend on the gauge length over which the measurement was taken. The smaller the gauge length the greater will be the contribution to the overall elongation from the necked region and the higher will be the value of rupture strain. Therefore, when reporting values of percentage elongation, the gauge length L0 always should be given.
PERCENTAGE ELONGATION “The change in length per unit original length expressed in percentage” % 𝐸𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 =
𝐿𝑂 − 𝐿𝑓 𝑋 100, 𝑤𝑒𝑟𝑒 𝐿𝑂 = 𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡, 𝐿𝑓 = 𝐹𝑖𝑛𝑎𝑙 𝐿𝑒𝑛𝑔𝑡 𝐿𝑂
PERCENTAGE REDUCTION IN AREA “Reduction in cross-sectional area per unit original area expressed in percentage” % 𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑖𝑛 𝑋. 𝐴𝑟𝑒𝑎 =
11
𝐴𝑂 − 𝐴𝑓 𝑋 100, 𝑤𝑒𝑟𝑒 𝐴𝑂 = 𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎, 𝐴𝑓 = 𝐹𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎 𝐴𝑂
Tension Test on Hot Rolled Plain Steel Bar
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Ductile and Brittle Materials Materials having a relatively larger tensile strain up to the point of rupture or failure are called as ductile materials, e.g. Structural Steel, Aluminum, etc. Whereas, the materials having a relatively small tensile strain up to the point of rupture are called as brittle materials, e.g Cast Iron, Concrete, etc.
Procedure for Experiment 1. Note the shape and size of specimen, measure the length of specimen and weight it to find the cross sectional area of specimen, firm this area effective diameter of the bar is found in mm. compare this diameter with nominal size of bar. 2. Mark the gauge length on the specimen throughout the length of the specimen for determination of % elongation after fracture, i.e. Ductility. 3. Fix the Battey extensometer to measure the elongation up to its region and grip the specimen in machine jaws. Note the gauge length of extensometer and its least count. 4. Calculate the expected Yield and Ultimate load and decide suitable load increment and draw a table for recording readings of loads and extensions. 5. Apply the load in desire increment and take readings of extensometer. 6. Remove the Battey extensometer at its limit and record the elongation with a spring divider and steel ruler up to breaking point. 7. Join the two broken pieces together and measure the approximate diameter at failure zones for determination of final cross sectional area. 8. Measure the change in lengths for gauge lengths marked throughout the lengths of specimen for estimation of effect of gauge length on % age elongation (ductility).
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Tension Test on Hot Rolled Plain Steel Bar
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Calculations and Observations L= 613 mm M= .578 Kg = 578 grams Density: 7.850 g/cm3
Marking Length = GL/4 = 50.8 mm = 2” Gauge Length of Extensometer = 50.8 mm
In order to calculate diameter, we will use the relation𝜌 = 𝑚/𝑉, where rho is 7.850 g/m3. 𝑑=
𝑚 7.850 𝑋 𝐿 𝑋 𝜋 4
=
.578 7850 𝑋 .613 𝑋 .7853
Extension = %age strain = Stress = Length of steel bar = Area of steel bar = Mean Fracture Diameter = Reduced Area = % Reduction in Area = True Rupture strength =
13
= 0.01236 𝑚 = 12.36 𝑚𝑚
(R – I.R ) X L.C. X 25.4 (∆L/L) X 100, where L= Gauge Length Load/Area 613 mm m/lρ = 578/(613 X .007850) = 120.11 mm2 8 mm 58.08 mm2 ((120.11-58.08)/120.11)X100 = 51.64% (fracture load/reduced area) = 1076.101 MPa
Tension Test on Hot Rolled Plain Steel Bar
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S.N o
Load (kN)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
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Extensometer/ Extension Spring Divider (mm) reading
%age Strain
1400 1402 1404 1408 1412 1416 1424 1432 1438 1510 1515 1600 1615 1700 1800 1850 1890 2110 2500 54 56 57 62 67 70
0 0.005 0.01 0.02 0.03 0.04 0.06 0.08 0.095 0.275 0.2875 0.5 0.5375 0.75 1 1.125 1.225 1.775 2.75 7.874016 11.81102 13.77953 23.62205 33.46457 39.37008
0 5 10 15 20 25 30 35 40 43.5 43.7 43.7 43.7 43.7 43.7 43.7 45 48 50 52.5 61 65 67.2 63.3 62.5
0 0.00254 0.00508 0.01016 0.01524 0.02032 0.03048 0.04064 0.04826 0.1397 0.14605 0.254 0.27305 0.381 0.508 0.5715 0.6223 0.9017 1.397 4 6 7 12 17 20
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Stress Remarks (MPa) 0 41.62851 83.25701 124.8855 166.514 208.1425 249.771 291.3996 333.0281 362.168 363.8332 363.8332 363.8332 363.8332 363.8332 363.8332 374.6566 399.6337 416.2851 437.0993 507.8678 541.1706 559.4871 527.0169 520.3563
P.L./E.L. Y.P.
U.T.S. N.R.S
Stress Strain Curve
600 500
stress
400 300
200 100 0 0
14
10
20 30 percentage strain
Tension Test on Hot Rolled Plain Steel Bar
40
50
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Sr. no
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Deformed Length
G.L
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Elongation
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% elongation
L-R 1 2 3 4
50 100 150 200
70 126 181 233
20 26 31 33
40 26 20.67 16.5
50 100 150 200
68 126 186 244
18 26 36 44
36 26 24 22
R-L 1 2 3 4
G.L. ~ %Elog. L to R 50 %age Elong.
40 30 20 10
Gauge Length
0 0
50
100
150
200
250
G.L. ~ %Elog. R to L 40
%age Elong.
30
20 10 0 0
16
Gauge Length 50
100
150
200
Tension Test on Hot Rolled Plain Steel Bar
250
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Results True Rupture strength =
(fracture load/reduced area) = 1076.101 MPa
Modulus of Elasticity = Modulus of Resilience = 𝑈𝑟 =
1 𝜍 𝜖 2 𝑃𝑙 𝑃𝑙
2 1 𝜍𝑃𝑙 = 𝐸
=2
½(333.02*0.04825/50) = 0.1607 MPa
Modulus of Toughness = area of one box = (5/400)*20 = .25, total boxes= 807, total area = 807*.25 = 20.175 Mpa
S.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
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Property Proportional Limit Elastic Limit Yield Strength/Proof Stress Ultimate Strength Nominal Rupture Strength True Rupture Strength %age elongation %age reduction in area Modulus of Elasticity Modulus of Resilience Modulus of Toughness Weight/unit length
Specimen Results 333.02 MPa 333.02 MPa 362.168 MPa 559.4871 MPa 520.35 MPa 1076.101 MPa 40 % 51.64%
Standard Values
12% min. 200 GPa
0.1607 MPa 201 MPa 0.9429 kg/m
Tension Test on Hot Rolled Plain Steel Bar
0.994 kg/m
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Conclusion and Comments
1. Grade of Steel Specimen The yield strength of our steel specimen in 363.8332 MPa which is 52769.53 psi. Thus we can conclude our steel specimen falls in the category of Grade 40 [300]. Steel specimens having yield strength From 40000 psi to 60000 psi are said to be grade 40 steel. Grade 40 is less brittle than grade 60 because it has less about of carbon contents which make it comparatively brittle.
2. Discussion over Failure and Fracture The specimen did not break in a proper cup cone manner. This may be due to impurities present or due to non-uniformity of the specimen. A cup cone manner of the specimen helps us to predict the homogeneity if a material. If the material is made of standard proportions then it will break in perfect manner. More over mild steel is weaker in shear and strong in tension. So it should be noted here that the cup cone manner is only for mild steel i.e. a material strong in tension and weaker in shear. So if we see the breaking or fracture pattern of a cast iron then it would be cleared that cast iron is weak in tension because it does not fracture in a cup cone manner.
3. Discussion over Weight/Unit Length The specimen results gives us the value of mass/unit length as 0.8429 kg/m, while the standard value of it as ASTM-A615/615M 2005, it is 0.994 kg/m. the result gives us value lesser than standard value. This means that for one meter of length the mass is lesser that that of standard. So, it shows that the strength of bar will ultimately be lower than the required one as standard one. Hence it would not be safe to use.
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Tension Test on Hot Rolled Plain Steel Bar
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4. Discussion over Percentage Elongation The percentage elongation in over case is 40 %, while according to ASTM-A615/615M 2005, it must be 12%. It means our specimen has elongated more than it should. This shows that it does not satisfy the standards and more percentage elongation tells us that it is not made up accurate proportions. Moreover it also tells us that or particular value of load our specimen will elongate more that the standard value so it is not suited for the valuable structures.
5. Discussion over Percentage Reduction of Area Percentage reduction of area in specimen is 51% where as in standards it should be less than that It shows that it has elongate more than it should. This can be due to impurities present in the material or the non-homogeneity of the material. It has showed larger reduction in area when the load is applied. From this we can conclude that it can show abnormal behavior in the structure during any unfavorable circumstances.
6. Discussion over True Rupture and Nominal Rupture Strength True rapture is always greater than the nominal rupture strength of the specimen. In our case nominal rupture strength is 520.3536MPa, which is obtained by diving the applied load by the original area of the steel bar, where as we have in our case true rupture strength is 1076 MPa, which is obtained by diving applied load by the reduced area i.e. average area of cup and cone.
19
Tension Test on Hot Rolled Plain Steel Bar
Adil Javed 07-Civil-73
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