Table 1 Constitutive parameters used to describe the mechanical behavior of metagreywacke from room temperature to 500 ^∘C under 50 MPa to 320 MPa effective normal stress including a pore-fluid pressure of 30 MPa

Area of contact

 Reference friction coefficient

μ₀

0.5

 Reference microasperity size

d₀

1

μm

 Microasperity size sensitivity

α

0.06

 Normal stress sensitivity

β

0.3

 Reference normal stress

σ₀

165

MPa

Flow law

 Reference velocity

V₀

1

μm/s

 Reference shear strength

τ₀

170

MPa

 Stress power exponent

n₁

60

n₂

35

n₃

23

 Activation energy

Q₁

10

kJ/mol

Q₂

50

kJ/mol

Q₃

90

kJ/mol

 Activation temperature

\({T}_{1}^{0}\)

20

^∘C

\({T}_{2}^{0}\)

280

^∘C

\({T}_{3}^{0}\)

280

^∘C

 Compressibility factor

ζ₁

5

ζ₂

0

ζ₃

0

Evolution law

 Reference strain-rate

f₀

1

1/s

 Active gouge layer thickness

h

1

mm

 Characteristic strain

1/λ

0.02

 Micro-asperity size exponent

p₁

4 αn₁

p₂

0.95 αn₂

 Normal stress power exponent

q₁

10

q₂

1

 Activation energy

H₁

40

kJ/mol

H₂

90

kJ/mol

 Activation temperature

T₁

0

^∘C

T₂

415

^∘C