Issue 45

C. Huang et alii, Frattura ed Integrità Strutturale, 45 (2018) 108-120; DOI: 10.3221/IGF-ESIS.45.09 119 The variations of the creep strain with the fiber content characteristics for 4 loads in unloading phase are plotted in Fig. 10. It can be observed that within 30min after unloading, the greater the stress is, the greater both the damage of the FRAC at creep loading process and residual creep strain is. At the same time, the larger the loading stress is, the greater the elastic deformation is, and as a result, the inertia of the recovery elastic deformation after unloading causes that the recovery creep rate increases with the increase of stress. It should be mentioned that the residual strain of FRAC under the same creep loading stress decreases firstly and then increases with the increase of the fiber content characteristic parameter after unloading, while the creep recovery rate increases firstly and then decreases under the same condition. In addition, when the fiber content characteristic parameter is about 1.13, the residual creep strain of FRAC is at minimum and the creep deformation recovery rate reaches maximum, the FRAC shows better recovery performance of the viscoelastic deformation in this case. It can be concluded from Eqn. (32) that the viscoelastic deformation recovery rate decreases gradually at the beginning with the uninstall time elapsing, and then goes to a stable value, that is consistent with test results. C ONCLUSIONS y adding viscous unit into Burgers model, the new model with five units and eight parameters can effectively present the deformation characteristics of FRAC during the whole creep process in the stage of loading. The rheological time of FRAC calculated from the model is consistent with that from test results, and the curves from the present model coincide well with the curve of tests. The creep tests of FRAC show that with the increase of fiber content and aspect ratio, FRAC beam the curve of bottom flexural tensile strain and time is firstly reduced and then elevated. When the fiber content is 0.35% and its aspect ratio is 324, corresponding curves of creep deformation and time are in the lowest position and FRAC has a larger resistance to deformation, which is consistent with the influence of the fiber content and aspect ratio on the viscoelastic properties of AC obtained from the present model. Fiber content characteristic parameter can comprehensively reflect the effect of fiber content and aspect ratio. The differential constitutive equation of FRAC performed through the present model by considering the influence of fiber content characteristic parameter can be characterized by Eqn. (31) and (32). Both the theoretical analysis and experimental studies show that: the creep strain, creep speed, the damage in FRAC, and the residual strain after unloading increase with the increasing of the loading stress and the loading time. It should be mentioned that under the same condition of load stress, the load creep strain, creep rate, and residual strain after unloading decreases firstly and then increases with the increase of fiber content characteristic parameter, while creep deformation recovery rate increases firstly and then decreases with the increase of fiber content characteristic parameter. When the fiber content characteristic parameter is 1.13, FRAC has better abilities of both anti-deform and creep deformation recovery. A CKNOWLEDGMENTS he authors gratefully acknowledge the financial support of the project from the Colleges and Universities Key Scientific Research Projects of Henan Province (Grant No. 16B580003) and Horizontal Research Project of Xuchang University (Grant No. 2017HX029). R EFERENCES [1] Popoola, A. O., Baoku, I. G. and Olajuwon, B. I., (2016). Heat and mass transfer on MHD viscoelastic fluid flow in the presence of thermal diffusion and chemical reaction, International Journal of Heat and Technology, 34, pp. 15-26. [2] Xu, S. F. (1992). A rheological model representing the deformation behavior of asphalt mixtures, Mechanics and Engineering, pp. 1437-1440. [3] Yang, T. Q. (1990). Viscoelastic mechanics, Central China University of Technology Press, Wuhan. [4] Yang, Y. (2009). Experience study on the visco-elastoplastic constitute model of asphalt mixture, Huazhong University of Science and Technology, Wuhan. [5] Mitra, K., Das, A., Basu, S. (2012). Mechanical behavior of asphalt mix: An experimental and numerical study, Construction and Building Materials, 27, pp. 545-552. B T