Table 2.

Parameters of Plackett–Burman test.

Symbol	Parameters	Low level (−1)	High level (−1)
A	MM coefficient of restitution	0.05	0.1
B	MM rolling friction factor	0.1	0.2
C	MM static friction factor	0.4	0.8
D	MS coefficient of restitution	0.15	0.3
E	MS rolling friction factor	0.1	0.2
F	MS static friction factor	0.3	0.6
G	JKR surface energy/(J/m2)	0.1	0.2