Slump Test: A New Empirical Model for High Yield Stress Materials

In order to decrease the fitting deviation between rheometrical measurements and empirical parameters using slump test, this paper proposes a new analytical method to evaluate the high yield stress of materials (cement pastes).In doing so, an experimental study was performed for measuring the empirical characteristics by cylindrical mold with different water to binder ratios (w/b) by aiming to increase the yield stress. Parallelly, experimental observations showed clearly the unyielded zone at flow stoppage of high yield stress samples. Based on these results, an idea was formed to applied metallic element at inlet of mold in order to push the spreading of paste. The obtained results of the model proposed in this paper were compared with the yield stress evaluated from shear flow curves using AR2000-rheometer with plate-plate geometry at rate-controlled. In fact, this study demonstrates the applicability and novelty of the present model in the process of relating the empirical parameters to yield stress.

Strong Electrorheological Performance of Smart Fluids Based on TiO2 Particles at Relatively Low Electric Field

Electrorheological (ER) fluids are a type of smart material with adjustable rheological properties. Generally, the high yield stress (>100 kPa) requires high electric field strength (>4 kV/mm). Herein, the TiO2 nanoparticles were synthesized via the sol–gel method. Interestingly, the ER fluid-based TiO2 nanoparticles give superior high yield stress of 144.0 kPa at only 2.5 kV/mm. By exploring the characteristic structure and dielectric property of TiO2 nanoparticles and ER fluid, the surface polar molecules on samples were assumed to play a crucial role for their giant electrorheological effect, while interfacial polarization was assumed to be dominated and induces large yield stress at the low electric field, which gives the advantage in low power consumption, sufficient shear stress, low leaking current, and security.

Deformation Behavior of Fe-Al Single Crystals Containing Fe2AlTi Precipitates

Fe-20Al-5Ti (at.%) single crystals composed of the bcc Fe-Al matrix and the Fe2AlTi precipitates with the L21 structure was examined. In the single crystals furnace-cooled (FC) from 1373 K to room temperature, coarse Fe2AlTi phase about 300 nm in diameter were precipitated in the bcc matrix. A misfit strain and a dissolution temperature of the L21 precipitates are +0.59% and 1151 K, respectively. The single crystals exhibited high yield stress above 600 MPa up to 973 K while further increase in temperature resulted in a decrease in yield stress due to the dissolution of the precipitates. In the FC crystals, 1/2<111> dislocations in the bcc matrix bypassed the coarse L21 precipitates due to their large misfit strain, resulting in high strength. In contrast, the fine L21 precipitates about 30 nm in diameter were observed in the crystals after solutionization and annealing at 873 K. The crystals with the fine L21 precipitates demonstrated high yield stress above 1100 MPa at and below 773 K. Uncoupled or paired 1/2<111> dislocations cut the fine L21 precipitates, leaving an anti-phase boundary (APB) inside the precipitates. The APB inside the precipitates was considered to be responsible for strong precipitation hardening.

Deformation Behavior of Fe-Al-Co-Ti Single Crystals Containing Co2AlTi Precipitates

Deformation behavior of Fe-15Al-18Co-3Ti (at.%) single crystals containing the Co2AlTi precipitates was examined. In the single crystals furnace-cooled (FC) from 1373 K to room temperature, coarse Co2AlTi phase with the L21 structure was precipitated in the bcc matrix. The L21 phase showed a cuboidal shape with a misfit strain of 0.59%. It is also noted that large amount of Fe substituted for Co in the Co2AlTi precipitates. The FC single crystals exhibited high yield stress above 600 MPa up to 823 K while further increase in temperature resulted in a decrease in yield stress. In the FC crystals, 1/2<111> dislocations in the bcc matrix bypassed the coarse L21 precipitates due to their large misfit strain, resulting in high strength. In contrast, the fine L21 precipitates about 30 nm in diameter were observed in the crystals after solutionization and annealing at 823 K. The crystals with the fine L21 precipitates demonstrated high yield stress above 1400 MPa at room temperature. Paired 1/2<111> dislocations cut the fine L21 precipitates, which led to high strength. The dependence of the yield stress on the precipitate size was also discussed.