Observe that the new parameters included in the model are: δ δ ν ν > 0 , δ δ A > 0 , δ δ η η > 0 , ν ν 0 , A 0 , η η 0 , ψ ψ 0 , δ δ ψ ψ , λ λ , p and ς ς , where ς ς , p, q, ψ ψ , δ δ and λ λ are the pinching parameters. When δ δ ν ν = 0 , δ δ η η = 0 or h ( z ) = 1 no strength degradation, stiffness degradation or pinching effect is included in the model.