Universal Tensile Test on Mild Steel and Brass Specimens

Questions:

1. What is the significance of the values of percentage of elongation and percentage of reduction in area?

The values of percentage of elongation and percentage of reduction in area indicate the ductility of the material. It comes from the final length and cross-sectional area of the specimen used after the fracture.

Elongation at failure of a tensile specimen as an indication of ductility. Elongation around the point of fracture is very high in low-carbon steels.

2. What is the significance of the area under the stress-strain curve for the two specimens?

Stress-strain curves for mild steel reached very high strains before failure. And the stress-strain curves for brass has a lower strain before it failure.  

3. Determine the yield stress (points) of both the specimens. What will happen if the specimens are stressed beyond these yield points?

The yield stress points for mild steel fall on 615MPa, while the brass is fall on 380MPa. For stress above the yield point, the deformation is not recoverable, and the material for will not return to its initial shape. The unrecoverable deformation is known as plastic deformation. For many applications plastic deformation is unacceptable, and the yield strength is used as the design limitation.

4. Which of the two materials tested is the strongest, which is more ductile?

Mild steel will be the material which is strongest and more ductile compared to brass. This properties is mostly due to it is one type of the low carbon steel which contain only 0.15 to 0.25% of carbon. The lower the contain of the carbon inside the steel, the higher the ductility. They are strong and can be easily worked and welded for various applications. However, brass is an alloy of copper and zinc, and the hardness of brass are depends upon the amount of zinc present in it. Therefore, mild steel will be stronger and more ductile if compared to brass.

Discussion        :

The graph above shows the tensile test for Brass Specimen and Mild steel. The graph are generate through universal tensile tester. Through the graph obtain, it can determine the yield point and maximum load for each specimen.

The yield point is the point where the graph stops being linear which mean it passes from the elastic region, where load is proportional to extension, into the non-linear plastic region where additional load produces increasingly larger extensions.

This is, literally, the maximum value of the load. Note that the graph dips down after this before fracture actually occurs (at the end point of the graph). This occurs because of the local narrowing, known as necking, of the specimen on application of the maximum load. Since stress is load divided by area, if the area is decreased, then so is the load required to produce the same stress, which is already sufficient to break the specimen.

From the brass tensile graph, the yield point will be approximately around 1000N when the material starting to be extend. Until the load reaches approximately 4100N, fracture occurs. This determine the maximum load of the material.

While observing the mild steel tensile graph, there are two yield points - yield-point run-out. The first yield point (or upper yield point) is higher than the second and the yield drops after the upper yield point. The first yield point is approximately 3000N and the second will be around 2950N. However, this value show it's hardness are above brass. The maximum load is approximately 4500N which slightly higher than brass.

Conclusion        :

As conclusion, the characteristic of mild steel enable it to use as structural steel as compare with brass. The hardness of mild steel is much more higher compare with brass as shown in the test.