Mechanical Properties Optimization of Friction Stir Welded Lap Joints in Aluminium Alloy

Table 6

Results of ultimate strength analysis of variability.

Regression estimated effects and coefficients for natural log of std. US ratio (coded units)
Term	Effect	Effect	Coef.	SE coef.	T
Constant	—	—	3.2266	0.0909	35.48	0.0
rpm	0.6428	1.902	0.3214	0.1317	2.44	0.059
s/mm	1.2221	3.394	0.6111	0.1317	6.64	0.006
rpm ∗ s/mm	0.3041	1.355	0.1520	0.1317	1.15	0.301
	R^2 = 87.80%		R^2(adj) = 80.48%
Analysis of variance for natural log of std. US
Source	DF	Seq. SS	Adj. SS	Adj. MS	F
Main effects	2	6.6109	5.8970	2.9485	15.46	0.007
2-Way interactions	1	0.2540	0.2540	0.2540	1.33	0.301
Residual error	5	0.9537	0.9537	0.1907	—	—
Curvature	1	0.0037	0.0037	0.0037	0.02	0.907
Pure error	4	0.9500	0.9500	0.2375	—	—
Total	8	7.8187	—	—	—	—