The Tensile Strength of Steel - Coursework Example

Experiment number: Title: Name: Id no: Date of experiment: Date of submission: Abstract This report analyses the tensile strength of mild steel, stainless steel, various heat treated aluminium samples and polycarbonate, with the aim of identifying a suitable material for the construction of blackboxes to be used on-board of a new fleet of unmanned aerial vehicles (UAV). Different materials differ in strength and the objective of this experiment was to determine the most suitable material. Each of the specimens was subjected to a tension test. After loading the machine, the changes in length were recorded. Tension test provides basic design properties on the strength of a material which was drawn on a stress – strain curve. These properties include: modulus elasticity (E), Ultimate tensile strength (UTS), and percent elongation (∆L %), It was found that the stainless steel is toughest. Introduction When designing the construction materials, there are two major requirements for the structure. These include: the strength and the stiffness of the material. The material has to be strong enough so that it cannot crack, break or collapse. It should also be stiff such that it cannot bend too much. Stress relates to the strength of the material. Yield stress is the stress at a yielding point of a material and if the material breaks, it has attained an ultimate stress. Modulus of elasticity is the measure of the stiffness of a material (Dowling, 2012). It is obtained from the linear region of the graph as shown in the graph below. Figure 1: Stress – strain curve Strain = Stress = Young’s modulus is the ration of stress and strain as shown below. Tensile test is the basic and universal engineering testing of materials used to find the material parameters like the yield strength, ultimate strength, % area of reduction, and % elongation as well as Young's modulus. The parameters obtained from the standard tensile test are important when selecting engineering materials for any application needed (Davis, 2004: Rees, 2006). The test involves the application of axial or longitudinal load at a given rate of extension to a test specimen till failure. The tensile load applied and the corresponding extensions are recorded during the test to be used in calculation of strain and stress. The ends of the specimens have sufficient length and a surface for gripping the specimen. Specimens can be subjected to heat treatment before machining (Davis, 2004). Aim 1. To obtain the stress-strain diagram 2. To determine the tensile properties of polycarbonate, stainless steel and mild steel, and use it get the engineering performance and the mechanical behavior of the materials. Procedure A universal testing machine was used to conduct the standard tensile test 1 on the three types of materials, which include polycarbonate, mild steel and stainless steel. Before the start of the experiment, the length the diameter and the cross head speed. Then the specimen pieces were set-up, one at a time. Polycarbonate was placed on the grips of the testing machine, while ensuring that the specimen was aligned with the direction of pull and also to ensure that there is no slippage of the specimen during the test. The test began and the load versus extension was recorded. The procedure was repeated for the other three specimens. The results obtained were used to plot stress – strain graph. Figure1: Tensile testing machine Stainless steel and mild steel were also tested using the same procedure. . Results: Table 1: The test results obtained from the experiment Polycarbonate Stainless steel Mild steel Load at Break 1,746.94 N 7,689.80 -1,947.23 Extension at Break 122.6966 mm 46.60147 26.31352 Data point at Break 7363 2799 1586 Tensile strain (Extension) at Break 1.22697 mm/mm 0.46601 0.26314 Tensile extension at Break 122.6966 mm 46.60147 26.31353 Tensile stress at Break (Standard) 174.6943 MPa 768.9801 -194.723 Table 2: The dimensions of polycarbonate, stainless steel and mild steel Sample Polycarbonate Stainless steel Mild steel Length x Width Length x Width Length x Width Sample 1 1.5 x 12.17 1.45 x 12.10 1.6 x 12.39 Sample 2 1.61 x 12.12 1.44 x 12.10 1.6 x 12.30 Sample 3 1.59 x 12.16 1.45 x 12.13 1.60 x 12.32 Sample 4 1.62 x 12.13 1.46 x 12.12 1.60 x 12.33 The dimensions of aluminum subjected to heat treatment for a given amount of time are given below. Table 3: Heat treatment of aluminium 2000 series Sample size heat duration (hrs) Thickness (mm) width (mm) Cross section area (mm2) Sample 1 1 1.6 12.32 19.712 Sample 2 3 1.6 12.32 19.712 Sample 3 6 1.6 12.3 19.68 Sample 4 16 1.6 12.38 19.808 Work hardening samples Changing 10 mm/m Length = 80 mm Different stress and strain were obtained from different samples. Young’s modulus is the ratio of stress to strain. The table below shows the Young’s modulus for different materials. Table 4: Young’s modulus Specimen Stress Strain Young’s modulus Polycarbonate 174.694 1.22697 142.3784 Stainless steel 769.980 0.46601 1652.282 Mild steel 194.723 0.26313 740.0258 Young’s Modulus of Elasticity Polycarbonate Young’s Modulus of Elasticity MPa Stainless steel MPa Mild steel MPa Percent elongation = Polycarbonate =153.7% Stainless steel = 58.25% Mild steel = 32.89% Ultimate Tensile Strength (UTS) is the maximum load initial cross-sectional area. This is not a true stress because the cross-sectional area has uniformly reduced and the necking is about to start. The results obtained for different treatment of aluminium were used to plot stress vs strain curves as shown below. Figure 2: Stress vs strain for aluminium treated for 1hr Figure 3:Stress vs strain for aluminium treated for 3hrs Figure 4: Stress vs strain for aluminium treated for 6hrs Figure 5: Stress vs strain for aluminium treated for 16hrs From the curves it can be seen that heat treatment for different time duration tends to affect stress verses strain for a material. A short time of heat treatment tend to result in higher strength. Comparison of stress vs strain for different materials The curves obtained for Comparison of stress vs strain for different materials are shown below. Figure 6: The stress vs strain curve for polycarbonate Figure 7: Stress Vs strain curve for stainless steel Figure 8: Stress Vs strain for mild steel Stainless steel and mild steel exhibit a better strength compared to polycarbonate material. Stainless steel has the highest value of Young’s modulus. Thus it is recommended to be used to produce black boxes. Mild steel can also be used as it has higher value of Young’s modulus compared to polycarbonate. Discussion The curves for stress verses strain obtained indicate different strength for the materials. The straight part of the curve shows the young’s modulus of the material. Polycarbonate has the least strength and stainless steel ahs the highest strength. Heat treatment of aluminium tends to lower the strength of aluminium as it weakens the structure. The important mechanical properties that influence toughness of materials include: Including microstructure, Material’s thickness and constraint, Strain rate, Environment and temperature. For steels, temperature influences the transition in fracture behaviour from the ductile upper-shelf at higher temperatures to brittle lower-shelf behavior at lower temperature (Punmia, 2007). Ductility is the ability of a material structure to go through deflections and deformations under load. It the material cannot withstand deflections and deformations under load, then it may experience brittle failure. The experiment shows the different mechanical properties of aluminium, polycarbonate, stainless steel and mild steel. Comparing the three materials it is clearly visible that polycarbonate is weaker compared to the stainless steel and mild steel. The steel also has less elongation and lower percentage of the cross section area. However it higher yield point and is harder. The elasticity of the steel, which is one of the best advantages, is also high. For these reasons, stainless steel best material to be used in the construction of the black box. Conclusion This report has analysed different properties of different materials, which include stress, strain and Young’s modulus. It has been shown that stainless steel has the highest strength compared to mild steel and polycarbonate. It was also found that heat treatment for a long duration weakens the structure of the material. Stainless steel was found to be the best material to be used in the construction of the black box. Reference Dowling N. E., (2012). Mechanical Behavior of Materials: Engineering Methods for Deformation, Fracture, and Fatigue, Pearson Education, Limited Davis J. R., (2004). Tensile testing, Materials Park, Ohio: ASM International Punmia B C, Jain A K and Jain K.A., (2007). Limit state design of reinforced concrete, New Delhi: Laxmi Publications, pp 46. Read More

Aim 1. To obtain the stress-strain diagram 2. To determine the tensile properties of polycarbonate, stainless steel and mild steel, and use it get the engineering performance and the mechanical behavior of the materials. Procedure A universal testing machine was used to conduct the standard tensile test 1 on the three types of materials, which include polycarbonate, mild steel and stainless steel. Before the start of the experiment, the length the diameter and the cross head speed. Then the specimen pieces were set-up, one at a time.

Polycarbonate was placed on the grips of the testing machine, while ensuring that the specimen was aligned with the direction of pull and also to ensure that there is no slippage of the specimen during the test. The test began and the load versus extension was recorded. The procedure was repeated for the other three specimens. The results obtained were used to plot stress – strain graph. Figure1: Tensile testing machine Stainless steel and mild steel were also tested using the same procedure. . Results: Table 1: The test results obtained from the experiment Polycarbonate Stainless steel Mild steel Load at Break 1,746.

94 N 7,689.80 -1,947.23 Extension at Break 122.6966 mm 46.60147 26.31352 Data point at Break 7363 2799 1586 Tensile strain (Extension) at Break 1.22697 mm/mm 0.46601 0.26314 Tensile extension at Break 122.6966 mm 46.60147 26.31353 Tensile stress at Break (Standard) 174.6943 MPa 768.9801 -194.723 Table 2: The dimensions of polycarbonate, stainless steel and mild steel Sample Polycarbonate Stainless steel Mild steel Length x Width Length x Width Length x Width Sample 1 1.5 x 12.17 1.45 x 12.10 1.6 x 12.

39 Sample 2 1.61 x 12.12 1.44 x 12.10 1.6 x 12.30 Sample 3 1.59 x 12.16 1.45 x 12.13 1.60 x 12.32 Sample 4 1.62 x 12.13 1.46 x 12.12 1.60 x 12.33 The dimensions of aluminum subjected to heat treatment for a given amount of time are given below. Table 3: Heat treatment of aluminium 2000 series Sample size heat duration (hrs) Thickness (mm) width (mm) Cross section area (mm2) Sample 1 1 1.6 12.32 19.712 Sample 2 3 1.6 12.32 19.712 Sample 3 6 1.6 12.3 19.68 Sample 4 16 1.6 12.38 19.808 Work hardening samples Changing 10 mm/m Length = 80 mm Different stress and strain were obtained from different samples.

Young’s modulus is the ratio of stress to strain. The table below shows the Young’s modulus for different materials. Table 4: Young’s modulus Specimen Stress Strain Young’s modulus Polycarbonate 174.694 1.22697 142.3784 Stainless steel 769.980 0.46601 1652.282 Mild steel 194.723 0.26313 740.0258 Young’s Modulus of Elasticity Polycarbonate Young’s Modulus of Elasticity MPa Stainless steel MPa Mild steel MPa Percent elongation = Polycarbonate =153.7% Stainless steel = 58.

25% Mild steel = 32.89% Ultimate Tensile Strength (UTS) is the maximum load initial cross-sectional area. This is not a true stress because the cross-sectional area has uniformly reduced and the necking is about to start. The results obtained for different treatment of aluminium were used to plot stress vs strain curves as shown below. Figure 2: Stress vs strain for aluminium treated for 1hr Figure 3:Stress vs strain for aluminium treated for 3hrs Figure 4: Stress vs strain for aluminium treated for 6hrs Figure 5: Stress vs strain for aluminium treated for 16hrs From the curves it can be seen that heat treatment for different time duration tends to affect stress verses strain for a material.

A short time of heat treatment tend to result in higher strength. Comparison of stress vs strain for different materials The curves obtained for Comparison of stress vs strain for different materials are shown below. Figure 6: The stress vs strain curve for polycarbonate Figure 7: Stress Vs strain curve for stainless steel Figure 8: Stress Vs strain for mild steel Stainless steel and mild steel exhibit a better strength compared to polycarbonate material. Stainless steel has the highest value of Young’s modulus.

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