Symbols	Nomenclature	Definition	Unit
${\sigma }_s^{max}$	The maximum compressive stress	The maximum value of the stress applied to the rubber during compression.	MPa
$P_{c1}^{max}$ and $P_{c2}^{max}$	The maximum contact stress	The maximum value of the stress generated by the contact surface when contacting each other.	MPa
$P_c^{min}$	The small contact stress	The minimum value between $P_{c1}^{max}$ and $P_{c2}^{max}$.	MPa
${\sigma }_{lim}$	Limit stress	The stress value of the rubber in the compression process when the normal working capacity is lost.	MPa
$P_{oil}$	Oil pressure	The pressure of the hydraulic oil on O-ring during hydraulic system work.	MPa
$P_{oil}^{max}$	The maximum oil pressure	The maximum value of oil pressure.	MPa
$\Delta d$	Decrement of O-ring	Decrement of O-ring during compression.	mm
$\overline{\Delta d}$	The mean of $\Delta d$.	The mean of $\Delta d$.	mm
$R_{s1}$	Material reliability	The probability that rubber material does not fail.	/
$R_{s2}$	Seal reliability	The probability of no leakage.	/
$R_s$	System reliability	The probability of O-ring working properly.	/
$\Delta d_{Rs1}$/$\Delta d_U$	The upper limit of decrement	Decrement which satisfies with $R_{s1}$.	mm
$\Delta d_{Rs2}$/$\Delta d_L$	The lower limit of decrement	Decrement which satisfies with $R_{s2}$.	mm
$\Delta d_{Rs}$	The limit of decrement	Decrement which satisfies with both $R_{s1}$ and $R_{s2}$.	mm
/	Contract properties	The properties of the two contact surface in ABAQUS.	/
/	Nephogram	A photograph of a cloud.	/
/	Deviation	The degree of deviation from the initial value.	%