Es	energy stored in the material a cycle [J/m3]
Ed	energy dissipated as heat in the material a cycle [J/m3]
N	actual number of cycles
N/Nf	ratio between actual cycles and cycles at failure
Q	energy exchanged between material and environment in a cycle [J/m3]
UTS	ultimate tensile strength of the material [MPa]
R	loading ratio
$S$	thermal signal
S2_m	processed value of the second harmonic amplitude of the thermal signal: mean value in the gage length
S 0	mean temperature signal
S 1	amplitude of the first harmonic amplitude of the thermal signal
S 2	the second harmonic amplitude of the thermal signal
S 2_M	mean value in the steady state condition of the S2_m data series [Unit Signal]
W	total energy input per unit volume in a cycle [J/m3]
Wmech	mean value in the steady state condition of the W data series [J/m3]
Wtherm	total energy input obtained by means of the calibration between Wmech and S2_M [J/m3]
ΔU	internal energy changes of the material a cycle [J/m3]
Δσ	is the stress amplitude
ε	actual strain of the hysteresis loop
σ	actual stress of the hysteresis loop
σWmech	stresses obtained by using Ellyn’s model and W data series [MPa]
σWtherm	stresses obtained by using Ellyn’s model and Wtherm data series [MPa]
φi	phase shifts of the harmonics (i = 1,2).