a	Depth of a semi-elliptical surface crack
c	Half-length of a semi-elliptical surface crack
FI	Influence coefficient functions for KI
FII	Influence coefficient functions for KII
FIII	Influence coefficient functions for KIII
fθ	Angle effect correction factor
fμ	Frictional influence correction factor
H1, H2, H3, H4	Sub-curve-fitting functions for FI, FII, FIII
h1, h2, h3, h4	Sub-curve fitting constants for H1, H2, H3, H4
KI	Stress intensity factors for Modes I crack
KII	Stress intensity factors for Modes II crack
KIII	Stress intensity factors for Modes III crack
K0	Normalizing factor for the stress intensity factors
kn	Main normal stiffness of crack front
ks	Sub-normal stiffness of crack front
kt	Tangential stiffness of crack front
l	Length of a pipe
P	Axial pressure of a pipe
P0	External pressure of a pipe
Pn	Main normal pressure of crack front
Q	Shape factor for elliptical crack
Ri,R0	Internal and external radius of a pipe
t	Wall thickness of a pipe
un	Main normal displacement of crack front
us	Sub-normal displacement of crack front
ut	Tangential displacement of crack front
θ	Inclination angle of a surface crack
ξ	Normalized position along the crack front
σ	Far-field compressive stress
τs	Crack front sub-normal shear stress
τt	Crack front tangential shear stress
μ	Friction coefficient of the cracked surface