shaped’ curve. A single ±σ (sigma) represents 68% of the true scatter of results and ±3σ represents 99.73%. How- ever, the true scatter of tensile test result data sets are not symmetrically Gaussian, but rather are skewed.14-16
The
skewed distribution can arise due to the fact that a tensile test sample can have a low elongation or UTS due to a large defect, while the test sample which is essentially
defect free may represent the highest result possible. As a result, the method of Weibull Statistics has been used which can determine a single number (modulus) repre- senting the reproducibility of data. This method has been growing in use in the metal casting industry. Weibull Sta- tistics are used in this manuscript and are discussed in more detail in the experimental procedure.
G–Gauge Length: D–Diameter:
R–Radius of Fillet: A–Length of Reduced Section:
45.0 ± 0.1 9.0 ± 0.1 8.0 ± 0.1 54.0 ± 0.1
Figure 1. Dimensions of the cylindrical tensile test samples used in this study. They are in accordance with ASTM-577 standard. All dimensions are in millimeters.
Figure 2. The cast structure which under went chilling and the resulting λ2 condition, while the red dashed line reflects the wrap around of chill #2.
32
array. The dark grey reflects chill #1 International Journal of Metalcasting/Winter 10
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