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Hardness is the resistance of a material to plastic deformation caused by indentation. Sometimes, hardness refers to the resistance of the material to abrasion. In some cases, a relatively quick and simple hardness test may substitute for a tensile test. Hardness can be determined from a small sample of the material without actually destroying it. There are many methods for determining hardness, allowing it to be measured onsite. The most important factor in any hardness test method is forcing an indenter into the sample surface followed by measuring the dimensions of the indentation.
Hardness is not a fundamental property, and its value depends on the combination of yield strength, tensile strength, and modulus of elasticity.
The purpose of this report is to carry out Vickers Hardness tests on a selection of ferrous (e.g., normalized plain carbon steels) and non-ferrous metals (e.g., copper and brass) using the applied loads as indicated in the results tables.
To begin this test, I selected a workload to which I would be recording my results.
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The scale after the workload is selected does not automatically change; the change occurs when the indent icon is clicked. I then rotated the manual wheel to bring the test specimen to an appropriate position beneath the turret to allow for more precise results. After this stage, I placed the test specimen in the anvil and rotated the turret slightly to ensure that the specimen does not contact the indenter or the objectives.
Contact of the indenter or objectives with the specimen may damage the instrument or produce inaccurate measurements.
Afterward, I rotated the manual wheel until the image was in sharp focus using the eyepiece and 50X objective. I performed a zero calibration on the digital eyepiece encoder. To reset, I used the knobs on the digital eyepiece to move the base filar line and the filar line together but without overlapping, then clicked the reset icon (zero). From here, we set the dwell time and then pressed the indent icon, and the hardness tester automatically ran the testing cycle through loading, dwelling, and then unloading.
Finally, I selected an appropriate objective for observation and measurement. I measured the lengths of the indent diagonals, both diagonals for a Vickers indent, and the longest diagonal for a Knoop indent. The hardness tester automatically calculated hardness in the scale that had been selected.
| Specimen Material | Test Load (kg) | Ocular No. Reading | Average VHN |
|---|---|---|---|
| 0.1% Carbon steel | 1 | 120.64 | 118.86 | 1.293 |
| 0.1% Carbon steel | 0.5 | 80.52 | 80.24 | 143.5 |
| 0.4% Carbon Steel | 1 | 98.35 | 98.35 | 191.7 |
| 0.4% Carbon Steel | 0.5 | 71.03 | 71.01 | 183.8 |
The results for the hardness test are shown in the table above. To calculate the Vickers number (HV), we can use the formula:
[HV = 1.854 cdot frac{F}{D^2}]
Where (F) is the applied load in kg and (D) is the length of the impression diagonal in mm. Due to the advanced machine, we can obtain values such as the ocular No. reading and the average VHN.
The Vickers hardness test was established in 1921 as an alternative experiment to discover the hardness of different metals. This experiment tends to be easier to use and more precise, which is why the test is often used in most situations. The required equations involved in this test are also very objective regarding the size of the indenter, and the indenter is suitable for all different materials.
From the table above, I can identify that as the test progressed, we increased the amount of carbon content in each test. This change led to many changes in the results further on. The first change we can see from the table is that the ocular reading decreases significantly as we increase the carbon content. Another change I can identify is that as the carbon content is increased, the average VHN increases.
Following the completion of the laboratory practical sessions where the tensile and hardness properties of various steel samples were examined, this report outlines how these properties were tested and relates the results from both tests to determine any relationships (e.g., graphical trends) between the two tests and/or amongst the samples.
The objective of this section in my report is to determine the yield strength, ultimate tensile strength, and modulus of elasticity (MOE) for three samples of steel samples containing different amounts of carbon (0.1%, 0.4%, 0.8%), in addition to calculating the percentage reduction in area and percentage elongation at fracture for each sample.
To perform this test, we conducted a tensile test to examine the strength and mechanical behavior of the materials.
First, each specimen was measured using callipers to establish the true diameter of the section. A gage length was then measured to determine the distance between the two sections after the tensile test was performed. The load cell was set to 0 to ensure that the system only recorded the tensile force applied to the specimen. The specimen was placed into the jaws of the Instron frame ready to begin the test. The test began, and the specimen was loaded, allowing for measurable strain calculations. Data from this test were processed using software and loaded onto a spreadsheet. The test continued until the sample fractured, at which point the software stopped and finished gathering all the necessary information. The sample was then removed, and the system was reset, and the process was repeated for each sample.
| Carbon Content (%) | Modulus of Elasticity (GPa) | Yield / Proof Stress (N/mm^2) | Ultimate Tensile Strength (MPa) | Reduction in Area (%) | Percentage Elongation (%) |
|---|---|---|---|---|---|
| 0.1 | 198.058 | 348.64 | 58.5 | 29.5 | |
| 0.4 | 205.973 | 497.77 | 43.2 | 25.5 | |
| 0.8 | 201.69 | 616.51 | 28.6 | 12.8 |
Regarding the tensile test, there were notable differences in the results due to the varying carbon content in the experiment. The modulus of elasticity (GPa) did not show a continuous increase as it increased in the second test; however, in the third test, it dropped again. However, the yield stress had a significant increase from test 1 to test 3, with a difference of 267.87 N/mm^2. Finally, the reduction in area and percentage elongation both had a substantial decrease in percentage.
Metals Lab Report – Tensile and Hardness. (2024, Jan 02). Retrieved from https://studymoose.com/document/metals-lab-report-tensile-and-hardness
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