Papers by Keyword: Dynamic Mechanical Behaviour

Abstract: This study highlighted the effect of incorporation of rice husk silica (RHS) on the tensile properties and dynamic mechanical behaviour of natural rubber (NR) compounds. High purity RHS was synthesised by solvent-thermal extraction method, which was inspired by TAPPI T204 cm-97 and TAPPI T264 cm-97 standards with some modifications. The extraction method had successfully produced RHS with 99.9% of silica content and surface area of 234.25 m²/g. The incorporation of RHS in NR showed increment in tensile properties compared to unfilled NR. Further improvement was recorded by surface modification of RHS with 1 wt. % bis (triethoxysilylpropyl) tetrasulfide (TESPT). The modification of RHS with TESPT increased the rubber-filler interaction between RHS and NR matrix, hence enhancing the strength-related properties. The modified RHS-NR also recorded highest storage modulus, and the presence of RHS in the NR compound had slightly shifted the glass transition temperature (T_g) to a higher value. This confirmed that the strong rubber-filler interaction had increased the rigidity of the compounds and restricted the mobility of the rubber chains.

Abstract: The simulation system between smooth rigid wheel and lunar soil by Discrete Element Method (DEM) was established and validated. Three section structures of smooth rigid wheel, including flat, concave and convex structures were designed. The effects of these three different wheel section structures on dynamic mechanical behaviors of lunar soil simulant were simulated by PFC2D^®. The simulation results indicated that the concave section structure of smooth rigid wheel has the best anti-sinkage ability, the convex section structure has the good anti-sinkage ability, and the flat section structure has the worst anti-sinkage ability.

Abstract: The continuum/discontinuum multiscale analytical system of the interaction between rigid wheel and lunar soil by coupling discrete elements and matrix module was established. The DEM parameter of lunar soil particles was confirmed by the biax-test. The mesoscopic dynamic behaviors of lunar soil simulant subjected to rigid lugged wheel with different structures were simulanted and analysized by the multiscale method. Comparing the simulation results with the soil-bin test results, the multiscale model not only satisfied the computation accuracy, but also had the much higher computation efficiency.

Abstract: An experimental system is designed by combining the split Hopkinson pressure bar (SHPB) with microwave heating device, based on stress wave theory, availability of the experiment technique is analyzed. Tests of concrete whose temperature changes from room temperature to 650°C and impact velocity from 5m/s to 12m/s are completed and for the first time high-temperature dynamical damaging phenomena of concrete are obtained. Based on data analysis, the dynamical mechanical behavior of concrete with high temperature is affected by not only the strain rate effect whose influence keeps on decreasing with temperature increasing, but also the high temperature weakening effect. And the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Abstract: One new kind of epoxy resin toughening agent defined as liquid crystalline polyurethane elastomers (LCPUE) containing mesogenic ester groups and trithylene glycol flexible chain was synthesized and its nematic structure was observed by POM and XRD. The LCPUE was to modify the epoxy resin (E-51). The mechanical properties, fracture surface morphology, and thermal properties of the E-51/LCPUE curing system were systematically investigated. Experimental results revealed that the impact strength of the epoxy resin modified with LCPU is 1.9 times higher than that of the unmodified system, enhanced the thermal decomposition temperature by about 12 °C, and the fracture surfaces all modified systems display tough fracture feature.

Abstract: An experimental system of high-temperature split Hopkinson pressure bar (SHPB) was developed by combination of the split Hopkinson pressure bar (SHPB) and microwave heating system, then tests of concrete whose temperature changed from room temperature to 650°С and impact velocity from 5m/s to 12m/s were completed. Based on the test results, the dynamic strength of concrete increases with increasing impact velocity whether with high temperature or room temperature, meanwhile the dynamic strength of concrete with high temperature has the strain rate effect, but the effect keeps decreasing with temperature increasing, even at temperature above 500°С , compressive strength will not have strain rate sensitive effect any longer when strain rate surpasses a certain value. In the meantime, the strain rate hardening effect is coupled with high temperature weakening effect, but the latter has greater influence.

Abstract: The high-strain-rate response of ultra-fine-grained (UFG) copper fabricated by equal channel angular pressing (ECAP) has been characterized by Split Hopkinson Pressure Bar (SHPB) test and quasi-static compression test has also been performed for comparison here. In the result of quasi-static tests a maximum yield stress equal to 432 MPa has been reached, at the same time the corresponding value turned out to be 995 MPa after a dynamic loading with the strain rate equal to 1700 s-1. It has been demonstrated that the strain rate sensitivity coefficient (m) has enhanced from 0.026 (coarse-grained copper) to 0.037 (UFG copper). Microstructure has indicated a high dislocation density and deformation twins inside the grains formed after a high-strain-rate deformation, which resulted in a high flow stress. The occurrence of a dynamic recrystallization has also been observed in the UFG copper subjected to high-strain-rate deformation. This has become apparent as an accelerated thermal softening and inherent instability typical for the UFG structure. Absence of adiabatic shear bands pointed out that UFG copper can be subjected to a dynamic impact without any fracture.

Abstract: The dynamic compression experiments of reinforced concrete are carried out by one-stage light gas gun apparatus which subjects the reinforced concrete to deformation at strain rates of the order of 104/s with confining pressures of 1~1.5GPa. The stress-strain curves of reinforced concrete with different impact velocities are obtained using Lagrangian analysis method. Experimental results indicate that reinforced concrete is non-linear, rate-sensitive and pressure-dependent.

Abstract: In this paper, the dynamic macroscopical properties of reactive powder concrete (RPC) are studied by using the split Hopkinson pressure bar (SHPB) system. The effect on dynamic properties of RPC material with different water binder ratio (W/B) and steel fiber influence under high temperature burnt is discussed. And scanning electron microscope (SEM) technology is also used to investigate the micro-structure change under high temperature burnt. The experiment result shows: without high temperature burnt, the higher water binder ratio, the lower dynamic compression strength of RPC material. With high temperature burnt, strength decreases exquisite. However, steel fiber can prevent micro-crack from generating, the toughness effect still alive after high temperature burnt. From SEM analysis: the inner part of RPC will have a series of physical chemistry changing, such as: micro-crack generation, C-S-H gel damage. This essential change is the basic reason for dynamic properties degrade.

Abstract: The cure kinetics of Derakane 411-350, a kind of vinyl ester resin, and its suspensions containing multi-walled carbon nanotubes( MWCNTs) were investigated via non-isothermal dynamic scanning calorimetry (DSC) measurements. The results showed that incorporation of MWCNTs into vinyl ester resin excessively reduces polymerization degree and crosslinking density of vinyl ester resin. For suppressing the negative effect caused by nanotubes, the higher temperature initiator combined with the initiator MEKP was used. Dynamic-mechanical Behavior testing was then carried out on the cured sample in order to relate the curing behavior of MWCNTs modified resin suspensions to mechanical response of their resulting nanocomposites. It was revealed that nanocomposites containing MWCNTs possessed larger storage modulus values as well as higher glass transition temperatures (Tg) as compared to those without MWCNTs after using mixed intiators system to improve the degree of cure.