Simulation of Scattering of Bending Characteristics of FRCC based on Bridging Law Considering Fiber Distribution

It is well known that tensile and bending characteristics of fiber-reinforcedcementitious composite (FRCC) are influenced by fiber orientation and distribution. In this study, a visualization simulation is conducted using sodium silicate solution (known as water glass) to observe the flow patterns of the fibers in the beam specimen. The results of the visualization simulation are discussed mainly for the distribution of the position of each single fiber. In this study, based on the visualization results, Poisson distribution for expressing the position of fibers is adopted to calculate the bridging law (tensile stress – crack width relationship), inwhich the pullout properties of the single fiber are considered. The influence of fiber orientation is also considered in the calculation using the elliptic function characterized by the principal orientation angle and the orientation intensity. The scattering of maximum tensile stress (bridging strength) can be confirmed by Monte Carlo simulation (MCS), in which the fiber distribution following Poisson distribution is considered. The calculated bridging law is modeled by trilinear model, and section analysis is conducted to compare with the bending test results using polyvinyl alcohol (PVA) fiber. The possibility to evaluate the variation of bendingstrength can be found out by considering fiber distribution

Observation of elastic anomalies driven by coexisting dynamical spin Jahn-Teller effect and dynamical molecular spin state in paramagnetic phase of the frustrated MgCr2_2O4_4$

Ultrasound velocity measurements of magnesium chromite spinel MgCr$_2$O$_4$ reveal elastic anomalies in the paramagnetic phase that are characterized as due to geometrical frustration. The temperature dependence of the tetragonal shear modulus $(C_{11}-C_{12})/2$ exhibits huge Curie-type softening, which should be the precursor to spin Jahn-Teller distortion in the antiferromagnetic phase. The trigonal shear modulus $C_{44}$ exhibits nonmonotonic temperature dependence with a characteristic minimum at $\sim$50 K, indicating a coupling of the lattice to dynamical molecular spin state. These results strongly suggest the coexistence of dynamical spin Jahn-Teller effect and dynamical molecular spin state in the paramagnetic phase, which is compatible with the coexistence of magnetostructural order and dynamical molecular spin state in the antiferromagnetic phase.Comment: 6 pages, 3 figure

Elastic Instabilities within Antiferromagnetically Ordered Phase in the Orbitally-Frustrated Spinel GeCo2_2O4_4

Ultrasound velocity measurements of the orbitally-frustrated GeCo$_2$O$_4$ reveal unusual elastic instabilities due to the phonon-spin coupling within the antiferromagnetic phase. Shear moduli exhibit anomalies arising from the coupling to short-range ferromagnetic excitations. Diplike anomalies in the magnetic-field dependence of elastic moduli reveal magnetic-field-induced orbital order-order transitions. These results strongly suggest the presence of geometrical orbital frustration which causes novel orbital phenomena within the antiferromagnetic phase.Comment: 5 pages, 3 figure