Multi-objective optimization of functionally graded thickness tubes under external inversion over circular dies

Journal of Materials Science: Materials in Engineering

Table 3 Accuracy of different polynomial RSM models based on (a) CCD and (b) LHD

RS model	R ²	R _adj ²	RMSE	RE interval (%)
(a)
Quadratic polynomial	0.9957	0.9942	0.0921	[−2.18,2.24]
Cubic polynomial	0.9966	0.9956	0.0723	[−1.03,2.31]
Quartic polynomial	0.9984	0.9977	0.0316	[−0.78,1.17]
(b)
Quadratic polynomial	0.9990	0.9990	0.0893	[−1.76,2.04]
Cubic polynomial	0.9992	0.9990	0.0714	[−0.74,1.58]
Quartic polynomial	0.9999	0.9997	0.0292	[−0.39,1.08]