Tensile Stress of a Material - Essay Example

The tensile stress of a material is defined as the maximum stress the material can withstand before failing. The tensile strength of aluminum and Plexiglas specimens is determined by conducting a tensile test. The objective of conducting a tensile stress experiment is to establish the modulus of elasticity, tensile strength, or ultimate strength of a material. Tensile test also helps to ascertain the nature of a material (ductile or brittle) as well as the yield strength of a material. In order to establish the fractural behavior of a material or specimen, force or stress is applied to the material to determine its elasticity. The ratio of the extension in length to the original length is referred to as a tensile strain. Consequently, the modulus of elasticity of the material is obtained by finding the ratio between tensile stress and strain. The measurement of the extension of a material before it snaps enables the classification of the material or specimen as ductile or brittle. The yield strength of a ductile material is obtained when the expansion is 0.2 percent.

In order to understand the behavior of materials under high stress or loading rates, an impact test is done. Impact tests are usually done using Izod or Charpy procedures. Impact test on steel and plastic aims at establishing their toughness. Impact test determines the behavior of a material under high-stress levels that include tension/torsion and bending of the material. A specimen in an impact test is broken by a single blow and is a specially designed device. The energy spent in breaking the specimen in a single blow is the quality of the material or specimen. The property of a material varies with variation in temperature, thus conducting the experiment at different temperatures allows for the determination of change in properties of the material as temperature changes.

Expected Value and Measured Value from the Experiment

Steel has a yield value of 43 ksi, which is approximately the same as the expected value. Also, the tensile strength and strain as well as ultimate strength before the material snaps are approximately the same as the measured value. The modulus of elasticity of aluminum measured value tends towards 11 Msi as it approaches power six, which is perceived as an equal value. The measured value for Plexiglas is very close to the expected value as seen in Table 1.

Impact Test

The temperature of the specimen affects the impact test on the specimen. Consequently, in order to determine the effect of temperature on the impact test, a similar specimen is tested under two different temperatures.  The measured value or behavior of the specimen at two different temperatures varies significantly as depicted in Table 2. It is evident that the steel absorbs high energy at room temperature compared to the energy absorbed at extremely low temperatures.

1. Discussion

Conclusion

The comparison of the data (measured and expected values) in table 1 reveals that the expected value of aluminum and Plexiglas is close to the measured value for aluminum and Plexiglas. In this case, aluminum exhibits maximum expansion before rupture is closer to 13 percent, which is higher than 5 percent. Plexiglas exhibits a maximum increase in length before 2.3%. This means that aluminum and Plexiglas are ductile and brittle materials respectively. From table 1, it is clear that ductile material is tougher than brittle material. This can be attributed to the large area covered under the stress-strain curve as a result of high strain at the rupture point. Consequently, we conclude that ductile material is always tougher than brittle material.

Limitations and Experimental Error

The difference between the measured and expected values is a result of an arithmetic error. This is attributed to the machine reading error or inhomogeneous property of the material. Variation in temperature also affects measured value. The sources of error mentioned above could be an explanation for the difference in the measured and expected value from the experiment.