Viscoelastic properties of plant cell walls. IV. Physical meaning of parameter K in mathematical formulation for stress-relaxation and load-extension processes

When the function ϕ(K, A; B) is defined by the equation ϕ ( K , A ; B ) = B ( 1 + A B ) 1 + B − K A the stress-relaxation process at a fixed strain has been represented in the previous papers of this series as follows: S = b k · ln ϕ ( K , t p ; t + T mk ) ϕ ( K , t p ; t + T ok ) + c k where S is stress, t_p is pre-extension time, and the parameters T_ok, T_mk, b_k, c_k, and K are constants. As we have reported, the parameters T_ok, T_mk, b_k, and c_k can be defined physically. However, the physical meaning of the parameter K has remained unclear. This study leads to the conclusion that parameter K can be defined as being equal to the pre-extension time, t_p, in the stress-relaxation experiment. Thus, the stress-relaxation curve and the effect of auxin pretreatment on a hysteresis loop in a stress-strain curve at a constant rate could be represented well by the calculated values.