Tensile Test Results for Non-heat treated Specimens

Stress strain graphs of all the specimens for 1mm, 2mm, 3mm, and solid are shown in Figure 6-5 and Figure 6-6. In addition, Figure 6-7 shows the specimen of each section thickness after tensile test. The tensile test results for different thickness of section, closed and opened hollow structure and solid section in non-heat treated specimens are shown in Figure 6-8 to Figure 6-13.

(a) (b)

(c) (d)

Figure 6-5 Stress-strain graphs for each of the tensile tests non-heat treated specimens for closed hollow with section thickness (a) 1mm, (b) 2mm, (c) 3mm and (d) solid

Figure 6-6 Stress-strain graphs for each of the tensile tests non-heat treated specimens for open hollow with 2mm section thickness

1mm Thickness 0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Strain Stre ss ( M Pa) 2mm Thickness 0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Strain Stre ss ( M Pa) 3mm Thickness 0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Strain Stre ss ( M Pa) Solid 0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Strain Stre ss ( M Pa)

2mm Thickness (open hollow)

0 10 20 30 40 50 60 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Strain Stre ss ( MPa)

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Figure 6-7 Tensile test specimens (after testing) for closed hollow structure with 1mm, 2mm and 3 mm section thickness

Figure 6-8 Tensile strength result of different section thickness of closed hollow and solid non-heat treated specimens. Error bars are at 95% confidence interval

Based on Figure 6-5 and Figure 6-6 all the specimens displayed a linear elastic behaviour within the same region of strain values between 0.0 and 0.02. It can be observed Figure 6-8 that the smaller thickness section created a lower average tensile strength and the solid specimens promoted the highest average tensile strength. The ANOVA confirms that the average tensile strength on each different section thickness and solid specimens increased significantly, in which the p value was smaller than 0.05. This indication confirmed that section thickness have effect on average tensile strength significantly.

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The tensile modulus for each specimen with different wall thickness and solid samples were then determined from the initial slope of the straight line on the stress- strain curves as explained in section 3.5.1.b. Tensile modulus results for all specimens then are shown in Figure 6-9.

Figure 6-9 Tensile modulus result of different section thickness of closed hollow and solid non-heat treated specimens. Error bars are at 95% confidence interval

It was clear that the solid specimens promoted the highest average tensile modulus, while the smaller section thickness specimens created a lower average tensile modulus, in which the smallest average tensile modulus occurred when the smallest thickness of 1mm section specimens were used. The ANOVA confirmed that the p value was smaller than 0.05 when the average tensile modulus on each different section thickness and solid specimens increased significantly. This indication showed that the outline/cross-section thickness and solid have an effect on average tensile modulus significantly.

The elongation at break for each specimen with different section thickness and solid were then determined as described in section 3.5.1.b. Elongation at break results for all specimens are illustrated in Figure 6-10.

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Figure 6-10 Elongation at break results of different section thickness of closed hollow and solid non-heat treated specimens. Error bars are at 95% confidence

interval

The smaller the sections thickness, the lower the average elongation at break obtained. While the solid specimens promoted highest average elongation at break. However, for section thickness 1mm and 2mm, there was not significantly difference, whereas for the 3mm section thickness and solid, it was significantly different.

The results of tensile properties of opened end hollow structure were obtained and shown in Figure 6-11 to Figure 6-13. As described in previous section 6.2, these result then compare to the closed hollow structure to observe if there is any different impact of closed and opened end hollow structure.

Figure 6-11 Summaries of test results: average tensile strength of closed and open hollow structure specimens. Error bars are at 95% confidence interval

Figure 6-11 illustrates the tensile strength for 2mm section thickness of open hollow specimens. From Figure 6-11 and Figure 6-8 It can be seen that there was no

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significant change in the average tensile strength between closed and open hollow 2mm section thickness specimens, as it was also confirmed by ANOVA in which the p value was greater than 0.05.

Figure 6-12 Summaries of test results: average tensile modulus of closed and open hollow structure specimens. Error bars are at 95% confidence interval

Figure 6-12 shows the average tensile modulus results of open hollow specimens with 2mm section thickness. From these evidences, it can be observed that there were no significant changes between the average tensile modulus of open hollow specimen and closed specimen. This was confirmed by ANOVA for a p value that was greater than 0.05.

Figure 6-13 Summaries of test results: average elongation at break of closed and open hollow structure specimens. Error bars are at 95% confidence interval

Figure 6-13 shows the average elongation at break of closed and open hollow specimens with 2mm section thickness. it can be seen that there was no changes of elongation at break for open hollow structure, although there were small differences

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of average at around 0.16 %, but not significant enough at a 95 % confidence level. The ANOVA confirmed this by showing a p value that was greater than 0.05.

Figure 6-11 to Figure 6-13 show that there were no differences in the tensile properties of the specimens with closed and open hollow structure. Even though there were slight different in average tensile strength by 2.24 MPa, average tensile modulus by 115.62MPa and average elongation at break by 0.16%, but they were not significant at 95% confidence level. Therefore, it can be summarised that whether the structure of the specimen were open or closed hollow, it had no effect on the mechanical characteristics. These differences possibly occurred due to the fact that both specimens of closed and open structure were manufactured in different batch of production, as it was confirmed by Zarringhalam et al. [2006] in their research.

6.4.2 Crystallinity Characterisation Results for Non-heat treated Specimens