engineering materials lap report
Page 6 of 8
Engineering
Materials Science
Metals Lab
LEEDS BECKETT UNIVERSITY
SCHOOL OF THE BUILT ENVIRONMENT & ENGINEERING
Course: BSc (Hons) Civil Engineering
BEng (Hons) Civil Engineering
HND Civil Engineering
Laboratory Experiment:
Stress-Strain Behaviour of Mild Steel and High Yield Steel bars.
Associated Module(s)
Level 4 Engineering Materials Science
Object of Experiment
To investigate the stress-strain behaviour of the above materials.
Theory/Analysis
A knowledge of the behaviour of structural steel under load is essential to ensure structural collapse does not occur and that serviceability requirements are achieved. In these respects the following mechanical properties of a material are required:-
1. The yield stress, σy (or 0.2% proof stress)
2. The Elastic (or Young’s) Modulus, E
3. The maximum tensile strength, σmax
4. The stress at failure, ie the fracture stress, σf
5. The % elongation at failure
Apparatus
1. 500kN Denison Testing Machine
2. Extensometer and Denison extension gauge (measures cross head movement)
3. Grade 250 plain round mild steel bar, 20mm diameter
Characteristic strength = 250 N/mm²
Conforms to BS 4449.
4. Grade 460 deformed high yield steel.
Reinforcing bar, T16, 16mm diameter.
Characteristic strength = 460 N/mm²
Conforms to BS 4449.
Method
Each of the bars in turn is placed in the jaws of the testing machine.
The 50mm extensometer is attached to the bar and zeroed.
Load is applied and recorded in increments up to failure. For each load increment, extension readings from the extensometer and the Denison extension gauge are noted.
At the yield point, the extensometer is removed to prevent damage to it and readings continue on the Denison extension gauge.
The load at failure and the manner of failure are noted.
See the Figure below showing the Test Setup.
( L G values; L G = 100 mm for the plain round bar, and L G = 80 mm for the deformed high yield bar ) ( L G , gauge length of the samples ) ( P = the tensile force applied to bars from Dennison testing machine ) ( P ) ( Extension of the sample bars is measured by: the Dennison (on-board) extension gauge which monitors cross-head movement . This effectively gives sample extension readings from the start of the test (P = 0) through to failure. An extensometer gauge. This is accurate only over the initial linear-elastic phase of the test. ) ( P ) Each student should prepare and submit a laboratory report, the results and discussion sections are outlined below:
a) Results and Calculations
Readings of load (P), against extension (e), have been recorded for each specimen tested and provided to you (appended at the end of this laboratory briefing document).
Knowing the original bar diameters (d), load data can converted to stress (σ) by dividing each load reading by the appropriate cross sectional area.
Strain values are determined by dividing the extension (e) data by the appropriate gauge length for each bar (LG); the gauge length is the original length.
(1) Plot load, P (kN), against extension, e (mm), for each of the samples; extension here being measured by the Denison extension gauge,
(2) Convert the load and extension data in (1) to stress and strain values respectively and plot stress, σ (N/mm²), against strain, ε (dimensionless), for each of the samples.
NB extension and strain values must be plotted on the x-axis.
From the graphs determine:
(3) The yield stress, σy (N/mm²), and 0.2% proof stress (ie the stress at which the stress-strain curve intersects a straight line drawn parallel to the initial linear part of the stress-strain curve, from the value of 0.2% strain (ie 0.002).
(4) The elastic modulus, E (kN/mm²), over the initial linear-elastic part of the stress-strain (σ vs ε) graph produced in (2) above. E is determined as the slope of the σ vs ε graph in this initial linear-elastic range.
Also, determine E from the Load and Extensometer readings over the elastic region (any point between 0 – 85 kN). Note, you must convert load to stress, and extension to strain, in order to determine the elastic modulus.
(5) The maximum tensile strength (N/mm²)
(6) The stress at failure (N/mm²).
b) Discussion
(This part of the report should include a discussion of results and comments/deductions on the properties of the materials tested as directed below)
In approximately one side of A4 (word processed):
(i) Compare the stress and strain values calculated from your test data with typical or expected values. Refer to standard texts or relevant web based sources. You must cite/quote the source(s) used.
(ii) Describe the mode of failure of the two samples and comment on their ductility, noting the strain values at both yield and failure. State why ductility is an important property of these materials.
(iii) From your data and calculated stress values, comment on the relative strength properties of the two steels, using the theory of steels / metals discuss why the samples have different strengths – please note this part contributes to at least 20% of the total mark.
(iv) Discuss what this means in terms of the suitability of the respective steels for use in the construction industry. Why is the yield stress an important material property in the design of steel structures? Why is the 0.2% proof stress sometimes used? How do the properties of the two steels compare with that of the other major construction material concrete? Marks will be allocated for including metallurgical theory presented in lectures on material properties, ferrous / non-ferrous metals and crystal structures.
(v) Identify the main sources of experimental error which may have affected the accuracy and precision of the data obtained.
(vi) Include briefly, any additional relevant observations or findings.
c) Conclusion
Here, summarise in a very short paragraph what was done and the main findings of the experiment.
d) Introduction
This section should be a minimum of 4 pages and should address the following:
· Main mechanical properties of materials
· Different types of metals, i.e. ferrous and non-ferrous
· What is steel
· What is steel made of, i.e. chemical constituents
· Manufacturing process of steel
· Properties of steel / different types of steel
· Application of steel in civil engineering including two examples
Indicative Reading
Ash Ahmed & John Sturges’ text: Material Science in Construction –
An Introduction (2014), Routledge.
Askeland, D.R., (2007) The Science and Engineering of Materials , Fourth Ed.,
Callister, (2010) Materials Science & Engineering, Wiley.
The marking scheme for the lab report is outlined below:
Each section will be elaborated on by Ash Ahmed during Lecture.
TYPICAL LOAD EXTENSION DATA for the 20mm PLAIN BAR and 16mm REINFORCING BAR (use this data for your Laboratory Report)
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LOAD vs EXTENSION DATA |
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LOAD vs EXTENSION DATA |
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for 20mm PLAIN ROUND BAR |
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for 16mm REINFORCING BAR |
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Load |
Dennison |
Extensometer |
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Load |
Dennison |
Extensometer |
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(kN) |
Extension |
Extension |
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(kN) |
Extension |
Extension |
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Gauge |
(mm) |
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Gauge |
(mm) |
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(mm) |
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(mm) |
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9.6 |
0.011 |
0.0021 |
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11.0 |
0.027 |
0.0089 |
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20.3 |
0.043 |
0.0169 |
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20.0 |
0.069 |
0.0285 |
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30.4 |
0.064 |
0.0310 |
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30.0 |
0.107 |
0.0483 |
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39.0 |
0.077 |
0.0431 |
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40.9 |
0.141 |
0.0714 |
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51.9 |
0.099 |
0.0608 |
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50.5 |
0.168 |
0.0897 |
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61.0 |
0.115 |
0.0743 |
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59.6 |
0.192 |
0.1045 |
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71.2 |
0.128 |
0.0899 |
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69.4 |
0.219 |
0.1235 |
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82.2 |
0.144 |
0.1077 |
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80.3 |
0.243 |
0.1425 |
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89.6 |
0.155 |
0.1197 |
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88.9 |
0.261 |
0.1577 |
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99.9 |
0.171 |
0.1444 |
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100.0 |
0.288 |
0.1815 |
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109.3 |
0.187 |
0.1729 |
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102.7 |
0.296 |
0.2244 |
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112.2 |
0.195 |
0.1815 |
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104.4 |
0.301 |
0.2516 |
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115.0 |
0.203 |
0.1889 |
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106.2 |
0.306 |
0.2675 |
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116.7 |
0.211 |
0.1923 |
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107.2 |
0.312 |
0.2823 |
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116.9 |
0.221 |
0.1921 |
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107.8 |
0.317 |
0.2892 |
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116.9 |
0.232 |
0.1934 |
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108.0 |
0.328 |
0.2953 |
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117.2 |
0.243 |
0.1940 |
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108.0 |
0.336 |
0.2968 |
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116.7 |
0.256 |
0.2111 |
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108.1 |
0.344 |
0.3143 |
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116.5 |
0.400 |
0.3555 |
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108.2 |
0.352 |
0.4144 |
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116.1 |
0.505 |
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107.5 |
0.357 |
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117.9 |
0.721 |
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109.1 |
0.365 |
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120.2 |
1.090 |
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109.0 |
0.710 |
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124.4 |
1.392 |
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110.3 |
2.072 |
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128.1 |
1.750 |
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112.9 |
4.158 |
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131.7 |
2.394 |
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114.5 |
5.184 |
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141.7 |
4.082 |
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116.0 |
5.712 |
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149.7 |
5.973 |
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117.3 |
6.125 |
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160.1 |
9.200 |
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118.6 |
6.552 |
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162.5 |
10.086 |
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119.8 |
7.144 |
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164.3 |
10.742 |
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120.8 |
7.410 |
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165.7 |
11.439 |
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122.6 |
8.569 |
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166.3 |
11.767 |
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124.0 |
9.143 |
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167.4 |
12.423 |
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126.3 |
10.783 |
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167.9 |
12.751 |
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126.5 |
11.070 |
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168.9 |
13.735 |
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126.7 |
11.890 |
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169.2 |
14.063 |
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126.6 |
12.177 |
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169.7 |
15.047 |
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126.3 |
13.020 |
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169.9 |
16.086 |
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126.1 |
13.948 |
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169.7 |
18.304 |
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125.8 |
14.212 |
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169.4 |
18.656 |
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125.3 |
15.888 |
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168.9 |
21.120 |
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124.7 |
16.850 |
NB continued overleaf |
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166.5 |
23.250 |
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123.6 |
17.200 |
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162.1 |
25.064 |
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122.0 |
17.550 |
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158.6 |
26.460 |
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119.9 |
17.850 |
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154.3 |
27.888 |
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117.1 |
18.200 |
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143.4 |
29.812 |
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113.9 |
18.550 |
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136.7 |
31.380 |
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109.9 |
18.950 |
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129.0 |
32.922 |
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103.0 |
19.250 |
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Lab Report First lab report on steels
Format:
Abstract
Introduction (25%)
Experimental / Methodology (10%)
Results & Discussion (20% Results & 30% Discussion)
Conclusion
References / Bibliography
Abstract, Conclusion & References = 15%
Deadline: 4 weeks to submit after completion of lab & metals tutorial (week 8)
46Monday, 16 January 17
Lab ReportFirst lab report on steelsFormat:
Abstract
Introduction (25%)
Experimental / Methodology (10%)
Results & Discussion (20% Results & 30% Discussion)
Conclusion
References / Bibliography
Abstract, Conclusion & References = 15%
Deadline: 4 weeks to submit after completion of lab & metals tutorial (week 8)
46Monday, 16 January 17