Applied Mechanics and Materials Vols. 152-154

Abstract: The extended finite element method is applied to modeling growth of arbitrary crack with crack surface tractions. Firstly, the extended finite element method is investigated for the stress intensity factor solution of surface traction problems. Secondly, for different water pressure acting on the crack surfaces and different crack length, the variation of the stress intensity factors is investigated. Finally, the process of hydraulic fracturing is simulated with the method. Numerical simulations illustrate that the method can effectively model the fracture problems with surface tractions.

Abstract: Thermal spray technology allows providing wear-resistant coating on the surface of mechanical components. In this study, wear characteristics of thermally sprayed Al/SiC composite coatings were evaluated. These Al/SiC composite coatings reinforced with SiC particles were fabricated on Al 6061 substrate by thermal spray process. Dry sliding wear tests were performed using the varied sliding speeds and applied loads. Wear behavior of these Al/SiC composite coatings were investigated using scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDX) and X-ray diffraction(XRD).

Abstract: RETRACTED ARTICLE: Metal-CO2 propulsion is less known than in-situ resource utilization (ISRU) technologies. This concept, based on using Martian carbon dioxide as an oxidizer in jet or rocket engines, offers the advantage of no chemical processing for CO2 and thus requires less power consumption than ISRU alternatives. In this paper, we study the burning behavior of the Mg in a CO2 atmosphere to assess the feasibility of using Mg/CO2 reactions as an in situ resource utilization technology for rocket propulsion and energy generation on other planets. From the experimental results, we can see that the critical ignition temperature increases with increasing the particle size and decreases with increasing the ambient pressure. In the CO2 atmosphere, we found the complicated sequence of interaction modes including pulsating combustion in a wide range of ambient temperatures. The pulsation frequency is determined by the sample temperature at the phases of slow heterogeneous combustion between the flashes. The combustion mechanisms are discussed with consideration of processes in both a surface film and gas phase.

Abstract: A novel Tin-functionalized integrated rubber of styrene-isoprene-butadiene (St-Ip-Bd) tri-copolymer (Sn-SIBR) was prepared by anionic polymerization using self-made tin-containing organolithium (SnLi) as initiator, tetrahydrofuran (THF) as polar modifier, and cyclohexane as solvent. The microstructure and the glass-transition temperature (Tg) of tri-copolymers were characterized by 1H NMR and differential scanning calorimetry (DSC), respectively. The result shows that the non-1,4-structure content and the Tg of tri-copolymers increased with the increase of THF dosage and the initiator concentration or the decrease of polymerization temperature. We also obtained the relationships between the ln(T/Li)( THF/ SnLi, mole ratio) and the non-1,4-structure content, the non-1,4-structure content and the Tg of copolymers, respectively.

Abstract: The master sintering curve (MSC) of nanocomposite WC-MgO was constructed based on the combined-stage sintering model. Nano-sized WC-4.3wt%MgO powder with average particle size of 35nm was synthesized by high-energy ball milling, and then uniaxially pressed at the pressure of 500MPa to fabricate green compacts. The shrinkage response of the compacts, used to construct the master sintering curve, were studied by dilatometric runs at two constant heating rates of 5°C/min and 10°C/min up to 1900°C. Using the estimated activation energy, the master sintering curves were established and compared to acquire an optimum value (Q=361.8 kJ/mol). The obtained MSC was validated by non-isothermal sintering with the identical green compacts. The results demonstrate that the MSC can be applied successfully to predict and control shrinkage level and final density during heating up regardless of heating rates.

Abstract: Preparation process of new 5XXX series aluminum alloys containing cerium-rich mischmetal wasintroduced .The effects of cerium-rich mischmetal on fracture morphology and mechanical properties of aluminium alloy were investigated in detail by scanning electronic microscope (SEM), and tensile test.The results show that alloys tensile strength and elongation with the increase of the content of mischmetal first increased, then down. When the mischmetal content is increased up to 0.30%, the tensile strength and elongation are 115 MPa and 25.9% respectively, meanwhile, the fractograph exhibited typical ductile dimple fracture pattern. Then the alloy performance is best. Mischmetal added into the alloy can improve the mechanical properties of materials, but too much mischmetal will induce the decrease in the material performance.Becase it may generate more the coarse Al₁₁(Ce ,La)₃ particle.

Abstract: In order to graft β-cyclodextrin onto chitosan fibers as more as possible, amino group of chitosan fibers should be protected by benzaldehyde firstly. Based on the similar structure of chitosan and cellulose fibers, different experimental programs were employed to discuss the possibility of β-cyclodextrin grafted onto chitosan fibers in the similar method. By infrared spectral and UV–visible spectroscopy analysis, the results showed although benzaldehyde could be grafted to chitosan fibers successfully to protect amino group, β-cyclodextrin could not be grafted further.

Abstract: The flow of the molten slag pool determines the temperature distribution and the pool profiles in the electroslag casting process, which impact on the quality of ingot casting. The flow field of the molten slag pool in the electroslag casting process was simulated by the large-scale finite element analysis software ANSYS, the result of which was completely in accordance with the physical simulation results. It was discussed that the influence of the molten slag flow field was caused by the current, the filling scale and the angle of electrode taper, which provided the scientific basis for the produce of the electroslag casting.

Abstract: We issue the theoretical calculation of C7H12O+ excited state, the corresponding vibration mode is given by the Gaussian03 calculation; In the analysis of vibration mode, it gives the possibility of C7H12O+ dissociation into fragments and the corresponding fragment analysis. In order to obtain relevant data of the fragments dissociation mechanism, we take the way analysis of C6H10O+ ion fragmentation as an example, then the bridge of experiment and theoretical calculations will provide a reference basis.

Abstract: WC matrix composites toughened by commercial Al₂O₃composed of AlOOH, χ-Al₂O₃and amorphous Al₂O₃ were prepared by high energy ball milling and then hot pressed at 769°C, 984°C, 1100°C, 1540°C for 90min, respectively, to investigate the phase transformation process. Microstructure and mechanical properties of WC-40vol.%Al₂O₃ composites were studied as well. The results showed that, with the increasing hot pressing temperature, the commercial Al2O3 transformed to α-Al₂O₃ completely through γ-Al₂O₃. WC could be oxidized and decarburized to W, C and W₂C at low temperature when the vacuum degree was very low. The existence of W in the composites sintered at 1540°C for 90min could contribute to a metal particle toughening effect to the composites, resulting in the achievement of an excellent fracture toughness of 10.43MPa•m^1/2, combining a Vickers hardness of 18.65GPa with a relative density of 97.98% for WC-40vol.%Al₂O₃ composites.