摘要
This study focused on the rate-dependent relaxation time of concrete using the split Hopkinson pressure bar test and the ultrasonic technique.Based on the experimental results,and considering the viscous effect in concrete,the viscoelastic stress-strain relationship was established in terms of the principles of irreversible thermodynamics and the generalized Onsager's principle,providing the convergence of an iterative scheme in terms of the Lipschitz's condition.It was found that the relaxation time of concre te depends on the strain rate.Furt her more,considering the state equations and damage evolution,a nonlinear viscoelastic constitutive model of concrete coupling damage was proposed.Compared with the experimental results,this model could better characterize the strengthening and softening characteristics of concrete prior to and beyond the strength limit.Further analysis indicated that the viscous effect is dominantly caused by the C-S-H in concrete.
基金
the financial support from the National Natural Science Foundation of China(NSFC#11832013,#11772164,#11572163)
the National Basic Research Program of China(973 Program,2009CB623203)
the Key Research Program of Society Development of Ningbo(2013C51007)
the K.C.Wong Magna Fund in Ningbo University.
