A novel ultra high performance concrete (UHPC) layer composite orthotropic steel deck was adopted in the construction of a new bridge in China to improve the fatigue performance of the orthotropic steel deck plate and reduce the disease of surface wearing layer. In situ experiments were conducted to study the UHPC layer’s impact on the behavior of the orthotropic steel deck. The test vehicle loads were applied on the deck plate before and after UHPC layer paving, the stresses where fatigue cracks usually occur and the deflections of critical sections were measured. The test results verified that the UHPC composite steel deck system could significantly reduce the stress of the rib-to-deck connection region and the stress at the bottom toe of rib-to-diaphragm weld. In addition, it slightly influenced the performance of U shape rib, girder web-to-deck and diaphragm cutout.
For aero-engines, high-altitude valve is a key component, which is important to the high-altitude performance of ventilation system. However, theoretical researches or experimental tests of high-altitude valve are rare. To define whether the high-altitude valve can work normally during the whole flight envelope and to offer relational information for the improve design, this article focuses on the operation process and characteristic computation of high-altitude valve. Based on operational principle and structural analysis, using mechanics method, the high-altitude characteristic computation of high-altitude valve was done and the flight height where the valve closes was identified. In the same way, we analysed the static characteristic, getting the inner-cavity pressure in high-altitude flying state. Compared with the experimental results, the analytical methods and calculated values are validated to be accurate. The characteristic curves obtained can be directly used in the check and acceptance or further design of high-altitude valve.
Taking South-to-North Water Diversion Bridge, a continuous composite box-girder bridge with corrugated steel webs, as the engineering background, the cantilever beam end’s deflection calculation formulae considering shear deformation were deduced by using energy method. Comparing with finite-element analysis (FEA) values and measured values, the formulae which considered both concentrated force and uniform load have enough accuracy. Results show that, shear deformation’s proportion is more obvious in overall deflection of such box-girders which have smaller span ratio, and it’s more than 30%. For continuous composite box-girder bridge with corrugated steel webs, contribution of shear deformation to overall deflection should not be ignored.
The pressure infiltration process of porous preforms by molten metals was investigated
numerically in this paper. The finite element model of heat and mass transfer of the infiltration in
liquid infiltration extrusion process was founded by the introduction of a new continuum model of
fluid in porous medium and a distribution resistance concept. The proposed model can describe the
transient flow behavior of semisolid materials qualitatively. Numerical simulations were developed in
particular for non-isothermal infiltrations which take into account the thermal aspects (the mould, the
fibres and the metal are initially preheated at different temperatures). The temperature distribution,
infiltration front and infiltration depth in the infiltration area were gained by the simulation of
ANSYS/FLOTRAN code. It is shown that the fiber volume fraction and initial temperature have a
strong effect on the infiltration process. The simulation results of axisymmetric infiltration have a
good agreement with their experimental ones. In addition, the infiltration time was predicted to get the
effective infiltration depth based on the simulation results.
10vol. % Csf/AZ91D composites were fabricated by extrusion following vacuum infiltration process with self-developed experimental device and measuring system. The relationships of load vs displacement during process and surface quality of composites at various extrusion temperatures were investigated. SEM microscope was used to observe the microstructure of fabricated composites. The experimental results showed that the extrusion process can be divided into three deformation stages. The extrusion temperature had a great influence on the maximum extrusion load. Based on proper infiltration parameters, a extruded bar with good surface quality was obtained at extrusion temperature of 420°C.
Extrusion directly following vacuum infiltration is a special forming technique that
combines the advantages of liquid metal infiltration and semisolid extrusion. The major advantages of
this process are elimination of porosity and shrinkage, good surface finish, good dimensional
accuracy, high strength to weight ratio and near net shaping. Magnesium matrix composites are
fabricated usually through stirring casting, powder forming, injecting deposition, liquid metal
infiltration or die casting at present time. However few investigations on magnesium matrix
composite are conducted for the specific characteristics of magnesium alloy, such as high chemical
activity and easy oxidation. The present paper is focused on Csf/Mg composites obtained via
infiltration of porous short carbon fiber preform by liquid Magnesium. The complete experiment
setup is designed and fabricated by ourselves, which include the forming molds, the unit for melting
the magnesium, the unit for vacuuming and the monitoring and collecting system of forming process
parameters. In this method the whole experiment setup is vacuumed firstly. Then the pressurized
nitrogen is used to infiltrate the magnesium melt through a porous preform of short carbon fibers.
After the infiltration completed, the punch of the press extrude the magnesium-infiltrated preform out
of the forming die to form the tubes or bars. X-ray diffraction (XRD), optical and SEM microscopes
were used to characterize the infiltration and the microstructure of fabricated composites. The
compression test was used to characterize the mechanical properties of fabricated composites. The
results show that the preform was infiltrated thoroughly by melt magnesium and the fabricated Csf/Mg
composites have excellent mechanical properties compared with the magnesium alloys. Csf/Mg
composites should be very promising candidates for automobile parts and portable electronic
appliance parts in the future.
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