Issue 45

C. Huang et alii, Frattura ed Integrità Strutturale, 45 (2018) 108-120; DOI: 10.3221/IGF-ESIS.45.09 117 2 ( ) 0 .0016 0.0118 0.005 f f f b    = + − (19) 2 ( ) 2.88 5.32 2.18 f f f c    = + − (20) 9 9 9 2 0 ( ) 1.11 10 5.92 10 2.7 10 f f f     =  +  −  (21) The relationship between model parameters of Eqn. (10) and the fiber content characteristic parameter are as follow: 2 2 ( ) 0.615 0.884 0.401 f f f     = + − (22) 2 1 ( ) 97153.9 675179.3 305297 f f f     = + − (23) 2 2 ( ) 232.1 559.4 256.2 f f f     = + − (24) 4 4 4 2 ( ) 4.5 10 5.9 10 2.37 10 f f f a    − − − =  −  +  (25) 2 ( ) 0.89 5.74 2.64 f f f b    = + − (26) 2 ( ) 191.1 1027 391.6 f f f c    = + − (27) 7 8 7 2 0 ( ) 4.01 10 1.75 10 8 10 f f f     =  +  −  (28) By substituting Eqn. (14)-(21) and (22)-(28) into (9) and (10) respectively, the creep equations of present model of FRAC with consideration of fiber content characteristic parameter effect can be obtained: Load phase: 3 2 0 1 1 2 0 ( ) ( ) ( ) 1 1 3 2 ( , ) ( ) ( ) ( ) ( ) f f t f f f f f f a b t t c t t e t              −   − +   − = + + +           (29) Unload phase: 3 2 ( ) 0 0 0 0 0 0 0 1 2 0 ( ) ( ) ( ) (1 ) 3 2 ( , ) ( ) ( ) ( ) f f t t t f f f f f a b t t c t t e e t              − − −   − +   − = + +          (30) where, 2 2 ( ) ( ) f f E     = . Taking derivative of t in Eqn. (29) and (30), differential constitutive equation of FRAC can be obtained, which is characterized by the present model and considered the influence of fiber content characteristic parameter: Load phase: