Applied Mechanics and Materials Vol. 576

Abstract: Magnesium slag is a kind of industrial waste during the silicothermic process for magnesium reduction which has potential hydration activity. By adding 20% to 50% of magnesium slag into Portland cement, the influence principle of the additive amount of magnesium slag on the pozzolanic activity is investigated through performance testing and hydration products analysis. During the early period of hydration process, the strength of pozzolanic effectiveness ratio weakens with the increasing additive amount of magnesium slag, while during the later period of hydration process with the additive amount of magnesium slag less than 40%, the strength of pozzolanic effectiveness ratio increases with increasing additive amount of magnesium slag. The activity index of magnesium slag increases with the increase of period and additive amount, and the strength brought by hydration of magnesium slag is a key source of the strength improvement of Portland cement with magnesium slag.

Abstract: Recent development of polybenzoxazines focuses primarily on broadening their thermal and mechanical properties such as their glass transition temperature, thermal degradation temperature as well as their flexibility and toughness. In this work, we have demonstrated that the incorporation of mono-or dianhydrides can improve both properties of polybenzoxazines but with different manner. Polybenzoxazine property enhancement by phthalic anhydride, PA, (monofunction) and pyromellitic dianhydride, PMDA, (bifunction) are systematically investigated and compared. It was observed that both mono-and dianhydrides can form covalent bonds through ester linkages with benzoxazine resin as confirmed by Fourier transform infrared spectroscopic technique. From thermogravimetric studies, degradation temperature of both anhydrides modified polybenzoxazines shows substantial improvement with increasing the amount of the anhydrides. Furthermore, char formation of the polybenzoxazine copolymers exhibits synergistic behavior with an addition of the dianhydride whereas that of monoanhydride-modified system shows a linear increase. On the other hand, it was found that tensile strength and elongation at break of monoanhydride modified polybenzoxazine are significantly greater than those of dianhydride-modified system comparing at the same mole fraction of the modifiers. However, tensile moduli of PA-and PMDA-modified polybenzoxazines are about the same and reveal an increasing trend with an addition of both types of anhydrides. The above results suggest effective methods to improve thermal properties of the polybenzoxazine with an incorporation of the dianhydride while better mechanical properties require monoanhydride as a polybenzoxazine modifier. The resulting copolymers can be used as high temperature matrix for carbon or glass fiber reinforced composite products.

Abstract: In order to solve reliability-based optimization design of composite transmission shaft, the parametric finite element model of composite transmission shaft was built by secondary development of ABAQUS. The reliability analysis of composite transmission shaft was carried out with the first order reliability method (FORM). Using python language, the finite element program and reliability analysis program are combined. The reliability-based optimization model of composite transmission shaft was obtained. The feasibility and effectiveness of the optimization model was verified by the results of an example application.

Abstract: Bisphenol-A/aniline based polybenzoxazine (PBZ) modified with amine terminated butadiene–acrylonitrile (ATBN) were prepared. The tribological and thermomechanical properties as well as thermal stability of the PBZ/ATBN copolymers were investigated by ball-on-disc tribometer, dynamic mechanical analysis (DMA), universal test machine and thermogravimetric analysis (TGA). The inclusion of ATBN at a mass fraction of 5% was found to greatly increase friction coefficient and wear resistance of the copolymers. DMA measurements showed that the storage modulus and the glass transition temperature of the PBZ can be maintained with an addition of ATBN in the range of 1-5wt%. Moreover, flexural property measurements indicated that the flexural strength of the copolymer increased with increasing of ATBN content up to 10wt% whereas TGA results revealed that an increase of the PBZ content can help improve thermal stability of the copolymers.

Abstract: The whole quality, stiffness and damping of the structure have changed a lot after retrofitting with steel adding layer. It should make seismic response analysis for the overall structure. Use finite element analysis software SATWE to set up finite element models for a three-layer masonry structure with steel top-adding layer. Bottom layer shear, bottom layer axial force and the horizontal displacement of Y direction are obtained by using response spectrum analysis method and time history analysis method. Analysis results indicate that the stories with sudden change in stiffness show less resistance against the earthquake and require special attention in design. Under earthquakes, the analysis to determine the integrated performance of the structure is necessary.

Abstract: Thermally induced vibration (TIV) of composite laminate subjected to suddenly applied heating is studied using finite element (FE) method in this paper. Some Python programs written by the authors are used to process the data of the analysis flow, and complete the pre- and post-process of FE models used in the four analyses. An equivalent displacement method is proposed to calculate equivalent temperature load. Dynamic responses of six composite laminates with different sizes are analyzed with solid FE models and shell FE models. The results gotten by FE method are in close proximity to that gotten by classic theory and shear theory under certain conditions. It is proved that the TIV analysis method proposed in this paper is reliable and efficient. The TIV analysis with FE method based on equivalent displacement method can solve the dynamic response of a structure due to sudden changes of temperature or suddenly applied heating.

Abstract: Discrete element method is applied to investigate the rules of particle flowing by using mesoscopic simulation in the process of compaction. The strain processes,the deformation differences of the particles in typical positions, and the porosities change in different areas under various Die-wall friction coefficients were investigated. The results showed that Die-wall interface friction causes diagonal flow of particles from upper surface edges to the center of compact, which has a significant influence on deformation and density uniformity of powder particles.

Abstract: Abstract: In order to study the weak point and influence factor on creep rupture properties of dissimilar joint, a simulation joint which contains a transition layer has been built with the same welding parameters, the same base and weld materials as the real structure, providing theoretical principle for weld material selection and welding process optimization. In the creep rupture test of the simulation joint, most fractures are found at the fusion zone of transition layer. The existence of a softened layer at fusion zone of transition layer has been proved with metallographic observation, micro hardness test, chemical composition analysis and scanning electron microscope (SEM). The softened layer causes strain concentration and makes it much easier to fracture. A great Cr gradient between transition layers is considered as the reason of soften layer formation, since it leads carbon distribution and decreases the hardness where lack C element. In addition, some features of crystallization direction of fusion zone in transition layer have been found, which could be harmful on creep rupture properties too.

Abstract: Fatigue crack propagation threshold is an important property for the structures with long life, such as nuclear turbine welded rotor. The fatigue crack propagation thresholds of multi-layer, multi-pass SAW weld metal of nuclear turbine rotor simulate are tested. But a big dispersion is found among test values, even at the same stress ratio . The dispersion of critical points between stable propagation zone and near-threshold zone is confirmed as an important reason. After the observation of microstructures around the critical points by backward inference method in different specimens, a good correspondence between the sizes of prior austenite grains and the maximum sizes of monotonic plastic zone at the crack tip is established. The inhomogeneous microstructures in SAW weld metal are the basic cause to dispersion of fatigue crack propagation thresholds at the same stress ratio.

Abstract: A concise model for disk-shaped solid oxide fuel cell (SOFC) with proton conductor electrolyte was developed by concerning relevant polarizations. Sm_0.5Sr_0.5CoO_3-δ - Sm_0.2Ce_0.8O_2-δ was taken as an example for cathode material. Proportions of each polarization were identified separately. Two important capacities, namely max power density and limit current density were discussed. Some suggestions to improve the cell performance were made. Comparison between proton and oxygen conductor electrolyte was discussed.