Assignment Task: Testing materials using scientific method
LO1 Examine scientific data using both quantitative and computational methods
LO3 Explore the characteristics and properties of engineering materials
Purpose of this assignment
Assess the ability of trainees to examine scientific data using computational methods.
Scenario:
You work as a materials engineer and have been tasked with investigating issues with products manufactured by your company. These products are made from polymer, composite and metal components.
Materials are failing in service, but your manager is not sure of the reason for this and has hypothesised that this could be due to degradation caused by fatigue, creep or other means. It has been suggested that types of hysteresis should be considered and/or that there are issues with the specification of materials being used.
Section 1:
In a tensile test on a polycarbonate strip, the following was the procedure.
The initial length, width and thickness of the strip was measured and then the strip was put into the machine. The strip was observed to increase in its length proportionally to the applied force during the elastic phase of the experiment. Following the elastic phase, elongation was observed in the strip without any additional force. Thereafter the strip continued to increase in length when the force was decreased. This phase continued for a long while till the strip got destroyed in a fracture.
The following data outlines the readings obtained before and after the experiment.
Material for test specimen: Polycarbonate strip
Dimensions before test:
Length: 75 mm Width: 10 mm Thickness: 4 mm
Dimensions after test:
Length: 126.6 mm Width: 8.3 mm Thickness: 3.2 mm
The following is the data recorded in the experiment where F is the force on polycarbonate strip in KN and x is its extension in mm.
|
Extension (x) (mm)
|
Force (F) (kN)
|
Extension (x) (mm)
|
Force (F) (kN)
|
Extension (x) (mm)
|
Force (F) (kN)
|
| |
|
|
|
|
|
|
0
|
0.15
|
0.279772
|
2.23
|
0.559544
|
1.84
|
|
0.012164
|
0.31
|
0.291936
|
2.15
|
0.571708
|
1.86
|
|
0.024328
|
0.48
|
0.3041
|
2.08
|
0.583872
|
1.88
|
|
0.036492
|
0.62
|
0.316264
|
1.87
|
0.6082
|
1.82
|
|
0.048656
|
0.78
|
0.328428
|
1.77
|
|
|
|
0.06082
|
0.87
|
0.340592
|
1.73
|
|
|
|
0.072984
|
0.96
|
0.352756
|
1.72
|
|
|
|
0.085148
|
1.07
|
0.36492
|
1.73
|
|
|
|
0.097312
|
1.23
|
0.377084
|
1.74
|
|
|
|
0.109476
|
1.41
|
0.389248
|
1.73
|
|
|
|
0.12164
|
1.55
|
0.401412
|
1.74
|
|
|
|
0.133804
|
1.65
|
0.413576
|
1.73
|
|
|
|
0.145968
|
1.76
|
0.42574
|
1.72
|
|
|
|
0.158132
|
1.76
|
0.437904
|
1.73
|
|
|
|
0.170296
|
1.83
|
0.450068
|
1.75
|
|
|
|
0.18246
|
1.94
|
0.462232
|
1.76
|
|
|
|
0.194624
|
2.02
|
0.474396
|
1.75
|
|
|
|
0.206788
|
2.13
|
0.48656
|
1.77
|
|
|
|
0.218952
|
2.2
|
0.498724
|
1.78
|
|
|
0.231116
|
2.28
|
0.510888
|
1.79
|
|
|
0.24328
|
2.3
|
0.523052
|
1.8
|
|
|
0.255444
|
2.31
|
0.535216
|
1.81
|
|
|
0.267608
|
2.32
|
0.54738
|
1.82
|
|
Use the data above to plot the graph of force vs. extension. Use the graph to locate the elastic region.
Calculate the stress vs. strain for the strip and write your values in the table. Use the values to plot a different graph showing the stress vs. strain for the elastic region. Fit a straight line to the stress vs. strain curve and use the line to calculate Young's modulus Y for the strip.
Write the dimensions of force, extension, stress, strain and Young's modulus.
Use the force-extension graph to calculate the yield stress (σ_Y ), the ultimate stress (σ_U ) and the ductility.
Fit a quadratic curve to the force-extension graph. Use the curve to calculate the error in the last and the middle readings and comment whether the quadratic fit is appropriate to the data.
Section 2:
Your site manager wants you to write a formal report on the major differences in the structural properties of metals and non-metals as observed by the following tests carried out on them : (a) Destructive test on metals (bend test and/or tensile test) (b) Destructive test on non-metals (tensile test) and (c) Non-destructive test on metals. Your report should describe the salient aspects of each of the tests mentioned and proceed to differentiate between the structural properties between metals and non-metals.
You should ensure that your report contains the following :
At least two differences (toughness and ductility) between metals and non-metals backed by numerical data from the tests.
Any three additional differences between metals and non-metals independent or derived from the tests carried out on them.
Section 3:
Your site manager wants you to write a formal report on the types of degradation and failures observed in metals and non-metals. Your report should include the following elements :
An explanation and comparison of the types of degradation and failures observed in metals and non-metals.
Ensure that your report contains a reflection of the scientific method (as shown in your laboratory report) for the testing that was carried out.
A description of the phenomenon of hysteresis observed in the domain of electrical, magnetic and elastic applications.