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Lab Report - tensile test
Materials 1 (AMME1362)
University of Sydney
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Laboratory Report
Aim: Conducting the tensile tests on the three different types of materials was conducted in order to measure the elongation of the specific material with respect to how much load was applied, and to further investigate the mechanical properties of each of the materials.
Background: Although the entire sample material was exposed to the loads applied by the machine, the stress was focused on the gauge length of the material. Carrying out the tensile test required a variation in load on the gauge length of the material, and adversely affected the engineering strain and stress the gauge length of the material was exposed too. The load (F) refers to the quantity of force applied upon the sample material and that can be measured. The gauge length (l) refers to the rectangular portion of the specimen being tested where elongation is measured. Engineering stress (!) is the instantaneous load applied to a specimen divided by its cross sectional area, and engineering strain (ε) is given by the gauge length of the tested specimens divided by the original gauge length, and it measures the elongation within the gauge length of the sample.
Method:
- Obtain the appropriate measurements required from the sample undergoing the tensile test to calculate the cross sectional area.
- Put the sample material in the jaws of the tensile testing machine. Attempt to make sure that there is no angular difference between the placement of the sample material within both jaws of the apparatus. This could have an adverse affect on the accuracy of the results.
- Place the extensometer clips on the gauge length of the material. Note that the extensometer won’t work when testing the nylon samples due to the amount of elongation that nylon experiences.
- Input the appropriate pulling rate for that material within the apparatus’s computer (e. nylon would require a higher pulling rate than the other materials to speed up the process).
- Start the tensile testing machine and gather appropriate data from the computer.
Sketch/ Drawings of specimen:
Specimen dimensions:
Results:
Width (m) Thickness (m) Cross-Sectional Area (m^2)
PMMA 1 0 0 3-
2 0 0 3-
3 0 0 0.
Nylon
1 0 0 0.
2 0 0 0.
3 0 0 2-
AL 1 0 0 3-
2 0 0 3-
3 0 0 3-
AL6061 - T 0 0 3-
Throughout the tensile test specimen, the deformation and stress is uniform throughout the gauge length of the sample. However, at the maximum stress point, typically the middle of the sample for metallic specimens, a small neck begins to form at this point. As more stress is applied over time, the necking point continues to stretch until it reaches its failure point and fracture ultimately occurs at this point.
Discussion:
Using open sources within the internet to obtain literature values for the specimens tested, it is clear that some values match up whilst others do not. According to MIT’s material database, it is shown that the range for the Young’s Modulus of PMMA is between 1339 - 1412 MPa. However the average value of Young’s Modulus from the gathered data is 2752 MPa. Therefore the experimental obtained values don’t match the property values for this specimen. This could be due to an error in calculation of the Young’s Modulus, but it could also be due to any existing slip systems or deformations within the sample used. Furthermore, as polymers and ceramic sample specimens shouldn’t be tested with the same shaped specimen as metallic materials are tested, but our test was done with this incorrect sample, could also provide a reason as to why the experimentally obtained value isn’t within the accepted range.
A reason as to which the experimentally obtained values aren't within an accepted range is due to the fact that what the metal has undergone is a mystery. The conditions under which the materials endured on the online sources are unknown, and hence they could have possibly been annealed and
Young’s Modulus (MPa)
Ductility (%)
Yielding strength (Pa)
Tensile Stress (Pa)
Elongation at failure
Ultimate Tensile Strength (Pa)
PMMA 1 2833 5 83812997 85597011 0 85597011
2 2708 7 79427930 80216245 0 80216245
3 2715 10 81325252 83249999 0 83249999
Nylon
1 3 229 36421941 70147296 218 70147296
2 4 190 37342152 63593706 188 63593706
3 4 387 37436771 80977106 386 80977106
AL
1 5911 10 234596186 226681359 0 226681359
2 7377 10 235391220 241994279 0 241994279 3 7808 11 221419703 226970951 0 226970951
AL6061 - T 5253 20 82858607 146221971 0 146221971
heat treated to remove any possible deformations prior to testing. This also applies to the samples used within the lab. Although the chances of obtaining a sample where majority of the deformations on the sheet metal was is low, it is still a possibility and could adversely affect the observed properties of the specimens used.
Compared to each other, the materials tested all offer different properties and characteristics. AL6061 and AL6061-T contains a much larger modulus of elasticity in comparison to nylon and PMMA. As a higher young’s modulus results in a stiffer material and a lower modulus results in a more ductile material, this high value for AL6061 specimens might be a desired attribute depending on what the material will be used for. Nylon contains the lowest Young’s Modulus and is hence the most ductile material as depicted within the results table in the ductility column. Furthermore, nylon also contains the greatest value for the elongation at failure property, providing further evidence as to its highly ductile property. The heat treated sample for AL6061 contains different properties to its counterpart. It is more flexible and ductile but will plastically deform at a lower stress value compared to AL6061. It however won’t fracture prior to the original samples as it only fractures when its elongation reaches an approximate value of 0. These properties are potentially different to other sources due to any deformations that continue to exist within the sample, as it was only heat treated at 560°C for three hours.
The ceramic material tested, PMMA, contains the average property results of both AL6061 and nylon. It contains a moderately high young’s modulus meaning it isn’t ductile but isn’t completely stiff. It does however have the lowest ductile results meaning it isn’t flexible at all. However, PMMA contains the highest value for yielding strength and compared to the other two materials requires the greatest force before it undergoes plastic deformation and yields. However, as it is a ceramic material, it will experience little to no elastic deformation prior to its yielding point which results in PMMA containing an average value of 0 for its elongation point at fracture. These values highly restrict the use of PMMA, or ceramics in general, in a variety of applications. Although it requires a high stress to yield, upon achieving this stress the material will permanently deform and never recover as it fractures.
Hence, all tested materials pose different properties and aren’t suitable for all projects. It is thus necessary to conduct tests on materials that are going to be used within a project to ensure that it exhibits the desired properties and won’t fracture or deform under high loads of stress.
Lab Report - tensile test
Course: Materials 1 (AMME1362)
University: University of Sydney
