Strain Rate Related Constitutive Models For Polymer And Cement Mortar Materials

Cement concrete and polymer have been the most widely used materials in our world. Polymer is widely used in hydraulic engineering for its low cost and convenient construct. And composite materials have been developed to the present kinds of structural and functional materials from early anti-permeable materials. Plenty of scholars applied polymers to concrete considering the high specific strength, high toughness, and low energy consumption, in order to enhance the toughness and rheological characteristic all the time. Therefore, the research on the mechanical properties of polymers provides reference for the new project. In the present paper, two typical viscoelastic polymers, polypropylene (PP) and high-density polyethylene (HDPE) were studied. Cycle loadings with different strain rate are carried out on these two materials. The rate relativity during the loading and unloading course are analyzed. On the basis of experiments and theoretical analysis, the expression of the relaxation time at the natural logarithm coordinate is established. And the influence of strain rate on the relaxation time is discussed. Then the nonlinear viscoelastic constitutive relation during the loading and unloading course is established. Based on this, the unloading experiments of nylon unloaded at different strain value are carried out. From the fitting results, it is founded that the plastic strain value doesn't make evident difference to the unloading law.It is an effective way to enhance toughness of polymer by particle reinforcing. The interfacial debonding of particulate-reinforced polymeric material is studied in this paper. Firstly, a nonlinear viscoelastic model is proposed to describe the constitutive relation of the polymeric matrix. Then the interfacial debonding of a particle embedded polymeric matrix material is analyzed, and the equation for solving the critical debonding time is derived. The expression of the debonding time under the condition oflinear loading history is obtained from the equation. Finally, the numerical calculation is carried out, and the numerical results indicate that the debonding time is significantly influenced by the particle size, loading rate, interfacial adhesive energy and nonlinear viscosity parameter.With the development of science and technology, the structure of concrete and its working condition and the loading styles are increasingly complicated. Consequently, many new mechanic phenomena appeared. Therefore, research on the constitutive relation of concrete and the damage theory are still paid closely attention recently. In this paper, the uniaxial compression test for cement mortars of three kinds of mixed proportions are processed with different strain rate. The results show that the mechanical parameters such as the strain-stress curves are strain rate related. The mechanical parameters such as apparent modulus and the peak stress are closely correlated with the strain rate and the loading history. According to the experimental results and theoretical analysis, a non-linear viscoelastic constitutive relation for cement mortar materials is established by adopting standard linear solid model with considering the evolution of the damage internal variable.It is known that concrete has its superiorities. However, when we choose construction materials, we should consider not only the attraction of technology and economy, but also the essence of ecology and energy-save. As the addition of concrete, for the one hand, fly ash can save some cement, for the other, it can improve the performance of concrete. In the present paper, the ESEM photographs of cement mortar mixed with fly ash at sections are taken. It's found that the fly ash particles of different diameters fill into the pores, and their dispersion states are fine, therefore, the uniformity and meso-scope pore structure are improved, then the compaction is enhanced. Hence, it's benefit to strengthen the anti-permeability and durability.