Raw Material Data
| Aluminium | Acrylic | Steel | |
|---|---|---|---|
| Width | 1.80 mm | 2.15 mm | 1.85 mm |
| Thickness | 1.00 mm | 1.40 mm | 0.85 mm |
| Gauge Length | 31.00 mm | 31.10 mm | 31.10 mm |
| Final Gauge Length | 33.40 mm | 31.40 mm | 34.90 mm |
Cross-sectional area = width thickness
Dial Indicator Value
| 0.2 mm Cycle | Aluminium (mm) | Acrylic (mm) | Steel (mm) |
|---|---|---|---|
| 1 | 0.000 | 0.000 | 0.000 |
| 2 | 0.150 | 0.080 | 0.210 |
| 3 | 0.340 | 0.170 | 0.380 |
| 4 | 0.510 | 0.265 | 0.570 |
| 5 | 0.710 | 0.380 | 0.760 |
| 6 | 0.890 | 0.450 | 0.950 |
| 7 | 1.080 | 0.555 | 1.155 |
| 8 | 1.265 | 0.655 | 1.330 |
| 9 | 1.410 | 0.740 | 1.515 |
| 10 | 1.490 | 0.835 | 1.720 |
| 11 | 1.560 | 0.915 | 1.890 |
| 12 | 1.665 | 0.965 | 2.100 |
| 13 | 1.750 | 1.050 | 2.275 |
| 14 | 1.765 | 1.085 | 2.450 |
| 15 | 1.770 | 1.095 | 2.665 |
| 16 | 1.750 | - | 2.825 |
| 17 | 1.650* | - | 3.015 |
| 18 | - | - | 3.280 |
| 19 | - | - | 3.470 |
| 20 | - | - | 3.675 |
| 21 | - | - | 3.840 |
| 22 | - | - | 4.040 |
| 23 | - | - | 4.200 |
| 24 | - | - | 4.380 |
| 25 | - | - | 4.540 |
| 26 | - | - | 4.665 |
| 27 | - | - | 4.780 |
| 28 | - | - | 4.840 |
| 29 | - | - | 4.950 |
| 30 | - | - | 5.015 |
| 31 | - | - | 5.110 |
| 32 | - | - | 5.180 |
| 33 | - | - | 5.235 |
| 34 | - | - | 5.310 |
| 35 | - | - | 5.3130 |
| 36 | - | - | 5.340 |
| 37 | - | - | 5.400 |
| 38 | - | - | 5.400 |
| 39 | - | - | 5.400 |
| 40 | - | - | 5.405 |
| 41 | - | - | 5.405 |
| 42 | - | - | 5.410 |
| 43 | - | - | 5.400 |
| *rough reading at time of fracture |
Group Contacts:
21980884 - Tom
24785313 - Smith
Aim
- Obtain stress-strain curves for tested materials
Introduction
In engineering, the mechanical behaviour of materials is fundamental in their selection and use. Tensile testing provides critical insight into how materials perform under loads and allows us to model properties such as toughness, strength and ductility. Material analysis is essential in engineering design to ensure high performance, safety and reliability. In this experiment, the behaviour under stress of three materials- aluminium alloy, mild steel and acrylic (PMMA) were investigated using a tensile testing machine.
This report aims to give insight into the tensile deformation behaviour of these materials, including Young’s modulus, a measure of a material’s ability to resist elastic deformation, and the yield strength, the maximum stress a material can withstand before plastic, non-recoverable deformation. Material property data, such as the data included in this report, helps engineers make informed choices on what materials are suitable for their purpose.
Results
Aluminium:
Points: (0.0016, 8.33), (0.0050, 86)
Intersection (0.0068, 80) → MPa
Ductility:
- Steel: 0.122 = 12.2%
- Aluminium: 0.0774 = 7.7%
- Acrylic: 0.0096 = 1.0%
Modulus:
- Acrylic:
- Point 1: (0.01, 8.5)
- Point 2: (0.031, 27.74)
- E = 916 MPa = 0.916 GPa
Discussion
- What are the main differences among the three materials tested from the stiffness, strength and ductility perspectives based on the stress-strain curves obtained?
- How do the measured Young’s moduli of the three materials compare to the “handbook value” of 69, 210 and 3 GPa for aluminium alloy, steel and PMMA, respectively? Calculate the percent difference. (Note: it is likely that your values for Young’s modulus are significantly different from the reported values for the three materials tested. This does not mean you have done something wrong. The question is what the likely cause is for such measurement errors. I encourage you to think in terms of the likely source of errors in the testing set up we have, particularly in terms if it is more likely from the applied force or the displacement.)
From our results of this experiment, it is observed that mild steel displayed the highest ductility, stiffness (Young’s modulus) and strength (yield and ultimate tensile strength). On the other hand, acrylic had, by a large margin, the lowest ductility, stiffness and strength. This is likely due to the differences in interatomic bonding between steel, aluminium and acrylic. Acrylic is a polymer, which means that it has weaker intermolecular forces, such as Van de Wahl’s and dipole-dipole forces between the long chains that make up its structure. These intermolecular bonds are significantly weaker than the metallic bonding present in steel and aluminium which is what likely caused the acrylic to shatter with less force due to its decreased strength.
Additionally, polymers are less dense than metallic compounds due to their irregular molecular structure (composed of long, branched chains) and the weaker intermolecular forces. This results in a further decrease in their strength, stiffness and ductility. The two metals on the other hand have dense atomic structures with atoms held together by very strong metallic bonds. This results in high strength and stiffness as their atomic structures are difficult to break. Metals are also able to have interatomic bonds break and re-join (i.e. a “slip”) allowing them to plastically deform. Thus, the structure can undergo more deformation without shattering. Steel was observed to have higher values than aluminium which can be explained by its crystalline structure which is even more dense than aluminium’s structure.