Tensile Test Laboratory Report

Introduction

In mechanical testing, one of the common properties widely used is the strength of materials. In this lab report, tensile testing was used to determine these strengths. The experiment provides details on the mechanical behavior or strength of a material. The foundational idea is to place the material specimen between fixtures known as grips which clamp the specimens. For comparison purposes, these materials should have equal dimensions of initial measurements such as lengths, and cross-sectional areas (Callister & Rethwisch, 2007). After confirming these dimensions, we can then begin to apply the loads or forces or weights while at the same time recording the change in lengths as the weights are steadily increased.

A very simple test requires one to hang some materials on an immovable grip and the weights on hooked end. To ensure the change in the consecutive lengths, add the weights to keep the material to stretch until the point of breakage. The experiment gives a result of a graph of force (N) against extension (mm), and because the force required in stretching the materials depends on the strength of the materials, a comparison between the specimens can be easily obtained. The various abilities of the materials can be very crucial to a structural designer who must ensure that the materials withstand certain forces. This mechanical strengths and behavioral properties of materials can only be found when these materials are tested and pulled until breakage. In this experiment, the three materials which were brass, aluminum, steel and stainless steel were used as specimens. The strength properties were used to determine their tensile strengths and Young’s modulus.

Objectives

The experiment is to examine the behavior of four material specimens under the tensile test. The materials under the test are brass, steel, aluminum and stainless steel. From the tensile test, the properties that will be determined are the tensile strengths, 0.2% proof stress and Young’s modulus (Yoshida, Uemori & Fujiwara, 2002). This experiment is used to establish materials properties. Moreover, it can be used in diverse industries. An example where the tensile test can be applied is to decide the Ultimate Tensile Stress required for building structures, railways, shopping bags, et cetera (Hosford & Caddell, 2011).

Equipment and Methodology

Four composite specimens of brass, stainless steel, steel, and aluminum, and which have equal dimensions. The test was performed by putting the specimens under a test machine that contain grips to hold the specimens (Meyers & Chawla, 2009). The machine then was allowed to exert tensile forces, causing the specimen to extend. As was read from the machine, the load per increment and the specimen extensions were written down for analysis. The loads and lengths of all the materials were recorded and then compared with each other.

Results and Analyses

Load (N)-Extension (mm) Curve for Brass, Stainless steel, steel, and Aluminum

Calculations

Given the materials with equal dimensions, in this experiments case 10mm diameter and 60mm material length. We can perform the following calculations;

Tensile strength = (Maximum Load)/(Cross Sectional Area)

At the maximum load of 7665N, Stainless Steel Yields a tensile strength of

Tensile strength = 7665/78.57

= 97.55 N/mm2 Or 0.098kN/mm2

At the maximum load of 3769N, Brass Yields a tensile strength of

Tensile strength = 3769/78.57

= 47.97 N/mm2 Or 0.048kN/mm2

At the maximum load of 3652N, Steel Yields a tensile strength of

Tensile strength = 3652/78.57

= 46.48 N/mm2 Or 0.04648kN/mm2

At the maximum load of 811N, Aluminum Yields a tensile strength of

Tensile strength = 811/78.57

= 10.322 N/mm2 Or 0.0103kN/mm2

The Proof Stress at 0.2% of these materials can be calculated as follows;

0.2% of 60mm is equal to 12mm. Therefore, at 12 mm, by reading this value against the corresponding load, we get the proof load of Stainless steel as 0.06216kN, Brass as 0.034kN, and Steel as 0.03350kN. The aluminum breaks before attaining the 0.2% proof Load.

The 0.2% proof Stress is therefore given as;

Stainless Steel, Proof Load = 0.0621kN/78.57mm2

Proof Load= 0.00079kN/mm2

Brass, Proof Load = 0.034kN/78.57mm2

Proof Load= 0.000433kN/mm2

Steel, Proof Load = 0.0335kN/78.57mm2

Proof Load= 0.000424kN/mm2

Young’s Modulus

From an elastic curve region in the diagram, we can obtain Young’s Modulus (Chen, Gandhi, Lee, & Wagoner, 2016).

In stainless Steel experiment, Young^’ s Modulus = Stress/Strain

Stress= Load/(Cross Sectional Area)

Strain= Extension/(Original Length)

For Stainless Steel,

Stress= 3.384kN/78.57mm2

Strain= 0.3mm/60mm

Young^’ s Modulus = 0.04307/0.005

Young^’ s Modulus = 8.614kN/mm2

For Brass,

Stress= 2.168kN/78.57mm2

Strain= 0.3mm/60mm

Young^’ s Modulus = 5.519kN/mm2

For Steel,

Stress= 1.318kN/78.57mm2

Strain= 0.17mm/60mm

Young^’ s Modulus = 0.01677/0.002833

Young^’ s Modulus = 5.92kN/mm2

For Aluminum,

Stress= 0.569kN/78.57mm2

Strain= 0.17mm/60mm

Young^’ s Modulus = 0.00724/0.002833

Young^’ s Modulus = 2.56kN/mm2

Discussions

These graphical analyses were conducted from the data that was obtained from the specimens after the experimentations. From the load-extension curves, the tensile strengths, 0.2% proof stress and Young’s modulus for the four specimens are as calculated below.

The first phase of each graph is the elastic region. This is where the specimens extend uniformly with the load added. The second stage when the curve begins to bend is known as the offset yield strength; in this lab, calculated at 0.2%. After the materials extend up to the maximum reachable stress, they fail to hold any more loads and; therefore, break. This point of breakage is known as the Fracture point. The elasticity limits of brass, stainless steel, steel, and aluminum differ with their respective tensile strengths obtained from the calculations. From our analysis, stainless steel is found to have the highest tensile strength, followed by the brass, steel and finally the aluminum is the weakest (Ross, Irvin, & Roth, 2007). This means that in structural engineering, stainless steel can be the most preferred where stronger tensile forces are needed.

Conclusion

The tensile tests on stainless steel, brass, steel, and aluminum identify stainless steel to be having the highest tensile strength followed by brass, steel and finally aluminum in the above order. These results also mean that the structures made from these materials have the ability to carry heavy loads in that order starting from the stainless steel, the strongest material. By knowing the strengths of particular materials, an engineer is able to identify their suitability in coming up with rails, buildings, shopping bags and other structures. To avoid fractures and breakages, the carrying capacity of these materials must not be surpassed (Callister & Rethwisch, 2007).

References

Callister, W. D., & Rethwisch, D. G. (2007). Materials science and engineering: an introduction (Vol. 7, pp. 665-715). New York: Wiley.

Chen, Z., Gandhi, U., Lee, J., & Wagoner, R. H. (2016). Variation and consistency of Young’s modulus in steel. Journal of Materials Processing Technology, 227, 227-243.

Hosford, W. F., & Caddell, R. M. (2011). Metal forming: mechanics and metallurgy. Cambridge University Press.

Meyers, M. A., & Chawla, K. K. (2009). Mechanical behavior of materials (Vol. 2, pp. 420-425). Cambridge: Cambridge university press.

Ross, C. D., Irvin, D. B., & Roth, J. T. (2007). Manufacturing aspects relating to the effects of direct current on the tensile properties of metals. Journal of engineering materials and technology, 129(2), 342-347.

Yoshida, F., Uemori, T., & Fujiwara, K. (2002). Elastic–plastic behavior of steel sheets under in-plane cyclic tension–compression at large strain. International Journal of Plasticity, 18(5), 633-659.