Short fiber reinforced cementitious composites (SFRCC) manufactured by the extrusion technique exhibit significant improvements in physical, mechanical and durable properties as compared with the fiber-reinforced cementitious composites made by traditional manufacturing techniques. The constitutive properties of the fresh SFRCC pastes for extrusion, as well as their interactions with the walls of extrusion equipments, are very important for enabling a successive and successful extrusion process. However, very few researches have been done in these areas. Till now, no proper experimental method is available for calibrating the constitutive behavior of the fresh SFRCC pastes for extrusion and no reliable constitutive model has been developed for such pastes. Moreover, numerical simulation...[ Read more ]

Short fiber reinforced cementitious composites (SFRCC) manufactured by the extrusion technique exhibit significant improvements in physical, mechanical and durable properties as compared with the fiber-reinforced cementitious composites made by traditional manufacturing techniques. The constitutive properties of the fresh SFRCC pastes for extrusion, as well as their interactions with the walls of extrusion equipments, are very important for enabling a successive and successful extrusion process. However, very few researches have been done in these areas. Till now, no proper experimental method is available for calibrating the constitutive behavior of the fresh SFRCC pastes for extrusion and no reliable constitutive model has been developed for such pastes. Moreover, numerical simulation, optimization and control of various forming processes of the fresh SFRCC pastes are still challenging.

In the present study, first, various promising rheology and plasticity methods, including ram extrusion, orifice extrusion, capillary extrusion and upsetting, have been examined to investigate constitutive characteristics of the fresh SFRCC pastes for extrusion. In these experimental works, the traditional ram extrusion and orifice extrusion theories have been further developed and the capillary extrusion theory has been modified by taking the rate and the slip effects. The upsetting theory has been corrected to include the effects of boundary friction and strain rate. It has been found that the fresh SFRCC pastes show pseudo-plasticity and significant strain rate hardening behavior. Only by combing rheology and plasticity methods could it give a full description of the constitutive behavior of such pastes.

Second, based on experimental and theoretical investigations, an elasto-viscoplastic constitutive model has been proposed for the fresh SFRCC paste, which considers the von Mises yield criterion, the associated flow rule and nonlinear isotropic strain rate-hardening. The model is formulated by introducing a strain rate-dependent yield function. The associated material parameters in the proposed constitutive model could be identified from material tests without the help of numerical methods. These parameters have been determined for the fresh SFRCC paste for extrusion in this study.

Third, the proposed elasto-viscoplasticy constitutive model has been formulated in a computational form and implemented into the explicit finite element code ANSYS/LS-DYNA for simulation purposes. Various forming processes of the fresh SFRCC pastes, including upsetting and ram extrusion, have been simulated using the ANSYS/LS-DYNA FE package, combined with the calibrated constitutive model and the established boundary conditions. The finite element simulation results, with respect to the forming load versus imposed deformation data, agree well with the pertinent experimental results, which verify the reliability of the proposed constitutive model, boundary interaction description and numerical procedures. The predicted material flow behavior, in light of displacement fields and distributions of some internal state variables, also gives promising interpretations of various forming processes. The present study provides an appropriate method to link materials science and engineering. This research procedure can be used in developing new technique and new products for civil engineering in the future.