Hardness of a material is a large factor in selecting engineering materials, to better understand what it means for a material to be hard. I conducted the Brinell Hardness test to better understand the mechanical properties of different materials.
Brinell Hardness tests are used to understand some of the mechanical properties of materials. It’s important to know how hard a material is when using it for certain things. The Brinell Hardness test helps engineers understand the hardness of the material being used, it is essential to understand this mechanical property to accurately design machines, cars, building etc. to suit the requirements demanded of the materials. When conducting the Brinell Hardness tests, it is important to remember that the steel ball that indents the samples cannot indent a steel that has a hardness of 444HB or higher, or if a carbide ball is being used, a sample can have a maximum of 627HB. An assumption for this lab can be that the aluminum sample will indent more than the steel sample. This assumption is based on the fact that steel will be harder than the aluminum, because if the inverse were true, the testing machine would have an indenter made of aluminum rather than steel. Another reason this assumption is made is because aluminum Is known to be a softer material than steel. An example of why this test is useful is it help understand a materials resistance to wear and deformation. This can be useful when selecting a material for a gear or a shaft that undergoes repeated loads or stresses. There are similar tests available such as the Rockwell Hardness Test, Vickers Hardness Test and the Knoop Hardness Test which all measure hardness differently yet are similar to the Brinell Hardness Test[1].
2. Important Data and Needed Sample Calculations
3. Analysis of data
The practical applicability of the hardness test in engineering and some examples are as follows. The practical applicability of the hardness test in engineering is to understand the mechanical property of different materials. In the case of this lab, the Brinell Hardness of the steel and aluminum samples average to be around 178.81 HB and 99.47 HB. The applicability of this is, if I were now to be asked to select a material to design the head of a hammer for example. I would pick steel rather than aluminum as the preferred material. The hammer may be heavier due the difference in densities of the materials, however the point remains that the application of the Brinell Hardness test is essential to do or to have access to the data of the results of this test on multiple different materials, for material selection purposes. There are many other examples, such as a phone screen protector. It must be a material that is hard enough to resist every day wear and tear to avoid scratches on its surface. Another example may be, a skid plate for an off roading car. It must be hard enough to resist intense periods of forces being applied to the skid plate in case of the car being stuck on a large rock.
Other hardness tests for metals currently being used in engineering are the following. The Rockwell Hardness Test. This test measures the depth of penetration of an indenter into the material. This test is the most used one in engineering due to how simple it is and how accurate it is. Another one is the Vickers Hardness Test, this test measures the size of an indentation made on the surface of a sample by a diamond. The Vickers Hardness Test is usually used on thin materials or coatings [1]. Finally, another test used is the Knoop Hardness Test, similar the Vickers Hardness Test, the Knoop Test measures the size of the indentation made of the surface of usually brittle materials or coatings [1].
If an indentation is made to close to the edge of a sample, the material that is being deformed would be pushed outwards over the edge of the sample. The internal resistance to deformation of the sample would be less due to there not being any material, or much material along the perimeter of the hole being formed. This would likely lead to the results of the test being lower than expected therefor indicating a softer hardness than expected. If an indentation were made too close to a previous indentation, the opposite would happen. The results would yield a harder material due to strain hardening. Once the metal is deformed and the hole is formed, the areas close to this hole are significantly harder than an area a couple of centimeters away. This is due to strain hardening happening, when a material is plastically deformed, its surface becomes harder due to crystal structures dislocating. Once this happens the internal resistances are higher than before, therefore increasing the surface hardness.
Some sources of error in this experiment are as follow. The first source of error that can lead to skewed results are that the machine used was not calibrated properly, therefore the actual load applied to the samples were not the ones recorded. This can therefor lead to inaccurate results. A user error could be that of over rotate, or under rotating the sample when measuring the dx and dy . Although it is a circle, this error could lead to inaccurate results. Another source of error could be the miss preparation of the sample surfaces, if there are already scratches on the surface of the material, dirt on its surface, small indentations etc.. These minor details can effect the hardness of the material and since the experiment did not require us to check for these minor flaws, it is possible that they were present and effected the results obtained. There are many sources of error that can effect this lab, the important thing is to remain consistent when conducting the experiments. This will avoid varying results and give consistent data to, if necessary compare with other results found from reliable sources to validate our data found in the lab. If our data is similar to said reliable sources, it can be concluded that the sources of error did not have a large impact on our tests.
The results obtained are as would be expected, in the lab manual on page one there is a table indicating the expected hardness of a material when using a ball diameter of 10mm and different loads. When using a load in Kg between 500 and 1500, the hardness should vary from 48HB to 300 HB which is consistent with the results obtained.
4. Conclusion
In conclusion, it was found that the hardness of the materials is what would be expected. The aluminum sample has a hardness of 99.47 HB 10/5/15 which is smaller than the steel samples hardness of 178.81 HB 10/10/15. Knowing the difference between aluminums hardness and steels hardness is useful when choosing between these two metals for a known application.
5. References
[1] Admin. (2023, April 27). Hardness test – Types, Characteristics & Applications -. EngineeringHulk - Engineering Content. https://engineeringhulk.com/hardness-test-types-characteristics-applications/#google_vignette
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