heating of the alloys. The tensile testing was carried out on the Hounsfield equipment at AUT University and the load- ing rate was 1mm/min in all cases.
Results and discussion
For each experimental response, calculation of S/N ratios and Analysis of Variance (ANOVA) identified the most sig- nificant factors and their corresponding levels at given con- fidence levels. Error terms in an experiment represent the de- gree of inter-experiment error when the degree of freedom is sufficiently large. When the error degree of freedom is small or zero, which is the case when all the columns (factors) in an orthogonal array are occupied, the small column effects are pooled to form a larger error term, which is known as pooling up.30
In the current experimental investigation, the factor contributing the least sum of squares to the total sum
of squares was pooled as the error. In most cases, this may have been higher than the recommended 10% of the maxi- mum factor outlined by Ross.31
tensile strength
The ANOVA calculations with the tensile strength analy- sis are presented in Table 3, and Fig. 2 depicts the S/N ratios calculated for the same. The ANOVA indicates that there are no significant factors at any of the tested confidence levels, suggesting that no single factor from the chosen variables was influencing the UTS (Ultimate Tensile Strength) and the variation observed is due to a combination of effects of all constituent factors. Based on the higher the better S/N ratio, results of Fig. 2 depict that
It may also be noted here
that none of the metal specimens received any heat treatment subsequent to being cast in the prototyped moulds.
Table 3. ANOVA of Ultimate Tensile Strength Figure 2. S/N ratios of tensile strength are shown in four graphs.
30
International Journal of Metalcasting/Summer 2011
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