Experimental and numerical studies of ferritic stainless steel tubular cross sections under combined compression and bending

An experimental and numerical study of ferritic stainless steel tubular cross sections under combined loading is presented in this paper. Two square hollow section (SHS) sizes—SHS 40×40×240×40×2 and SHS 50×50×250×50×2 made of Grade EN 1.4509 (AISI 441) stainless steel—were considered in the experimental program, which included 2 concentrically loaded stub column tests, 2 four-point bending tests, and 14 eccentrically loaded stub column tests. In parallel with the experimental investigation, a finite-element (FE) study was also conducted. Following validation of the FE models against the test results, parametric analyses were carried out to generate further structural performance data. The experimental and numerical results were analyzed and compared with the design strengths predicted by the current European stainless steel design code EN 1993-1-4 and American stainless steel design specification SEI/ASCE-8. The comparisons revealed that the codified capacity predictions for ferritic stainless steel cross sections under combined loading are unduly conservative. The deformation-based continuous strength method (CSM) has been extended to cover the case of combined loading. The applicability of CSM to the design of ferritic stainless steel cross sections under combined loading was also evaluated. The CSM was shown to offer substantial improvements in design efficiency over existing codified methods. Finally, the reliability of the proposals was confirmed by means of statistical analyses according to both the SEI/ASCE-8 requirements and those of EN 1990

Effect of Dependent Scattering on Light Absorption in Highly Scattering Random Media

The approximate nature of radiative transfer equation (RTE) leads to a bunch of considerations on the effect of "dependent scattering" in random media, especially particulate media composed of discrete scatterers, in the last a few decades, which usually indicates those deviations RTE (combined with ISA) lead to from experimental and exact numerical results due to electromagnetic wave interference. Here we theoretically and numerically demonstrate the effect of dependent scattering on absorption in disordered media consisting of highly scattering scatterers. By making comparison between the independent scattering approximation-radiative transfer equation (ISA-RTE) and the full-wave coupled dipole method (CDM), we find that deviations between the two methods increase as scatterer density in the media increases. The discrepancy also grows with optical thickness. To quantitatively take dependent scattering effect into account, we develop a theoretical model using quasi-crystalline approximation (QCA) to derive dependent-scattering corrected radiative properties, based on the path-integral diagrammatic technique in multiple scattering theory. The model results in a more reasonable agreement with numerical simulations. The present work has profound implications for the coherent scattering physics in random media with absorption, correctly modeling light absorptance in random media and interpreting the experimental observations in various applications for random media such as solar energy concentration, micro/nanofluids, structural color generation, etc.Comment: 30 pages, 8 figures, submitte

The heavy-element abundances of AGB stars and the angular momentum conservation model of wind accretion for barium stars

Adpoting new s-process nucleosynthesis scenario and branch s-process path, we calculate the heavy-element abundances and C/O ratio of solar metallicity 3M_sun TP-AGB stars. The evolutionary sequence from M to S to C stars of AGB stars is explained naturally by the calculated results. Then combining the angular momentum conservation model of wind accretion with the heavy-element abundances on the surface of TP-AGB stars, we calculate the heavy-element overabundances of barium stars via successive pulsed accreting and mixing. Our results support that the barium stars with longer orbital period, P>1600 days, form through wind accretion scenario.Comment: 14 pages, LaTex, 17 PS figures included, accepted for publication in A &

Visualization of the homogeneous charge compression ignition/controlled autoignition combustion process using two-dimensional planar laser-induced fluorescence imaging of formaldehyde

The paper reports an investigation into the HCCI/CAI combustion process using the two-dimensional PLIF technique. The PLIF of formaldehyde formed during the low-temperature reactions of HCCI/CAI combustion was exciting by a tunable dye laser at 355nm wavelength and detected by a gated ICCD camera. Times and locations of the two-stage autoignition of HCCI/CAI combustion were observed in a single cylinder optical engine for several fuel blends mixed with n-heptane and iso-octane. The results show, when pure n-heptane was used, the initial formation of formaldehyde and its subsequent burning were closely related to the start of the low temperature heat release stage and the start of the main heat release stage of HCCI combustion respectively. Meanwhile, it was found that the formation of formaldehyde was more affected by the charge temperature than by the fuel concentration. But its subsequent burning or the start of main heat release combustion toke place at those areas where both the fuel concentration and the charge temperature were sufficient high. As a result, it was found that the presence of stratified residual gases affected both the spatial location and the temporal site of autoignition in a HCCI/CAI combustion engine. All studied fuels were found having similar formaldehyde formation timings with n-heptane. This means that the presence of iso-octane did not affect the start of low temperature reactions apparently. However, the heat release during low temperature reaction was significantly reduced with the presence of iso-octane in the studied fuels. In addition, the presence of iso-octane retarded the start of the main combustion stage