Chemical vapor deposition zinc sulfide （CVD ZnS） is widely used as an infrared window material to transmit infrared signals, keep the aerodynamic shape and protect its imaging system, which often suffers high temper...Chemical vapor deposition zinc sulfide （CVD ZnS） is widely used as an infrared window material to transmit infrared signals, keep the aerodynamic shape and protect its imaging system, which often suffers high temperature and complicated thermal stresses. The purpose of this paper is to investigate the thermal shock damage of CVD ZnS through a finite element method and oxygen propane flame experiments. The finite element model is developed to simulate the temperature and thermal stress fields by an oxygen propane flame. Then, the thermal shock experiments are performed to investigate the thermal shock damage behavior. The results show that the temperature rising rate of the shock surface is fast during the initial heating stage resulting in high thermal stress. After the thermal shock experiment, the scanning electron microscope （SEM） photographs shows that the shock surface of the specimen becomes rough and the microcracks occur in the thermal shock zone. Good agreements are achieved between the numerical solutions and the experimental results.展开更多
RDX/Al mixtures are widely utilized in energetic materials,yet their hybrid dust generated during production and application poses potential explosion hazards.Moreover,the synergistic explosion mechanisms remain poorl...RDX/Al mixtures are widely utilized in energetic materials,yet their hybrid dust generated during production and application poses potential explosion hazards.Moreover,the synergistic explosion mechanisms remain poorly understood,particularly at varying dust concentrations.This study systematically investigates the effects of different aluminum powder mass percentages and dust concentrations(300 g/m^(3),600 g/m^(3),900 g/m^(3))on RDX dust explosion severity,flame propagation behavior,and gaseous products.The results indicate that the maximum explosion pressure peaks at 35%RDX,65%RDX,and 80%RDX at 300 g/m^(3),600 g/m^(3),and 900 g/m^(3),respectively.Concurrently,the time for the flame to propagate to the wall(t1)reaches minimum values of 34.8 ms,25.66 ms,and 23.93 ms.The maximum rate of pressure rise is observed for pure RDX at 900 g/m^(3).Aluminum powder enhances flame propagation velocity and combustion duration,as validated by the flame propagation system.Overall,the concentrations of carbon oxides(CO+CO_(2))decrease significantly with increasing aluminum mass percentage.At 20%RDX,the concentrations decreased by 51.64%,72.31%,and 79.55%compared to pure RDX at 300 g/m^(3),600 g/m^(3),and 900 g/m^(3),respectively.Notably,N_(2)O concentration only at 300 g/m^(3)showed such a trend.It rises first and then falls at 35%RDX at 600 g/m^(3)and 900 g/m^(3).These findings elucidate the synergistic explosion mechanisms and provide critical guidelines for safe production and handling.展开更多
The seismic behavior of steel reinforced high strength and high performance concrete （SRHC） frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios, axial ...The seismic behavior of steel reinforced high strength and high performance concrete （SRHC） frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios, axial compression ratios, concrete strengths, steel ratios and stirrup ratios. Three kinds of failure mechanisms are presented and the characteristics of experimental hysteretic curves and skeleton curves with different design parameters are discussed. The columns＇ ductility and energy dissipation were quantitatively evaluated based on seismic resistance. The research results indicate that SRHC frame columns can withstand extreme bearing capacity, but the abilities of ductility and energy dissipation are inferior because of SRHC＇s natural brittleness. As a result, the axial load ratio should be restricted and some construction measures adopted, such as increasing the stirrup ratio. This research established effect factors on the bearing capacity of SPHC columns. Finally, an algorithm for obtaining ultimate bearing capacity using the flexural failure mode is established based on a modified plane- section assumption. The authors also established equations to determine shearing baroclinic failure and shear bond failure based on the accumulation of the axial load force distribution ratio. The calculated results of shear bearing capacity for different failure modes were in good agreement with the experimental results.展开更多
The curing behavior of diglycidyl ether of bisphenol-A （DGEBA） with different phosphorus containing diamidediimide-tetraamines （DADITAs） was studied by DSC. Eight DADITAs of varying structures were synthesized by ...The curing behavior of diglycidyl ether of bisphenol-A （DGEBA） with different phosphorus containing diamidediimide-tetraamines （DADITAs） was studied by DSC. Eight DADITAs of varying structures were synthesized by reacting 1 mole of pyromellitic anhydride （PMDA）/3,3＇-benzophenone tetracarboxylic dianhydride （BTDA）/1,4,5,8-naphthalene tetraearboxylic dianhydride （NTDA）/4,4＇-oxydiphthalic anhydride （ODPA） with 2 mole of L-tryptophan （T） in a mixture of acetic acid and pyridine （3：2 V/V） followed by activaton with thionyl chloride and then condensation with excess of phosphorus containing triamines tris（3-aminophenyl） phosphine （TAP） and tris（3-aminophenyl） phosphine oxide （TAPO）. DADITAs obtained by reacting PMDA/BTDA/NTDA/ODPA with L-tryptophan followed by condensation with TAP/TAPO were designated as PTAP, PTAPO, BTAP, BTAPO, NTAP, NTAPO, OTAP and OTAPO respectively. The structural characterization of synthesized DADITAs was done by FTIR, ~H-NMR, I3C-NMR, 31p-NMR spectroscopic techniques and elemental analysis. Thermal stability of the isothermally cured epoxy was investigated using dynamic thermogravimetry analysis. The glass transition temperature （Tg） was highest in DGEBA cured using PTAP. All epoxy thermosets exhibited excellent flame retardancy, moderate changes in Tg and thermal stability. Due to presence of phosphorus in curing agents, all epoxy resin systems met the UL-94 V-0 classification and the limiting oxygen index （LOI） reached up to 38.5, probably because of the nitrogen-phosphorus synergistic effect.展开更多
基金supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 51121004)Doctoral Scientific Fund Project of the Ministry of Education of China (No. 20112302110036)the Fundamental Research Funds for the Central Universities of China (No. HIT.BRETIV.201315)
文摘Chemical vapor deposition zinc sulfide （CVD ZnS） is widely used as an infrared window material to transmit infrared signals, keep the aerodynamic shape and protect its imaging system, which often suffers high temperature and complicated thermal stresses. The purpose of this paper is to investigate the thermal shock damage of CVD ZnS through a finite element method and oxygen propane flame experiments. The finite element model is developed to simulate the temperature and thermal stress fields by an oxygen propane flame. Then, the thermal shock experiments are performed to investigate the thermal shock damage behavior. The results show that the temperature rising rate of the shock surface is fast during the initial heating stage resulting in high thermal stress. After the thermal shock experiment, the scanning electron microscope （SEM） photographs shows that the shock surface of the specimen becomes rough and the microcracks occur in the thermal shock zone. Good agreements are achieved between the numerical solutions and the experimental results.
基金the financial support of the Shanxi Fire&Explosion-Proofing Safety Engineering and Technology Research Center,North University of China。
文摘RDX/Al mixtures are widely utilized in energetic materials,yet their hybrid dust generated during production and application poses potential explosion hazards.Moreover,the synergistic explosion mechanisms remain poorly understood,particularly at varying dust concentrations.This study systematically investigates the effects of different aluminum powder mass percentages and dust concentrations(300 g/m^(3),600 g/m^(3),900 g/m^(3))on RDX dust explosion severity,flame propagation behavior,and gaseous products.The results indicate that the maximum explosion pressure peaks at 35%RDX,65%RDX,and 80%RDX at 300 g/m^(3),600 g/m^(3),and 900 g/m^(3),respectively.Concurrently,the time for the flame to propagate to the wall(t1)reaches minimum values of 34.8 ms,25.66 ms,and 23.93 ms.The maximum rate of pressure rise is observed for pure RDX at 900 g/m^(3).Aluminum powder enhances flame propagation velocity and combustion duration,as validated by the flame propagation system.Overall,the concentrations of carbon oxides(CO+CO_(2))decrease significantly with increasing aluminum mass percentage.At 20%RDX,the concentrations decreased by 51.64%,72.31%,and 79.55%compared to pure RDX at 300 g/m^(3),600 g/m^(3),and 900 g/m^(3),respectively.Notably,N_(2)O concentration only at 300 g/m^(3)showed such a trend.It rises first and then falls at 35%RDX at 600 g/m^(3)and 900 g/m^(3).These findings elucidate the synergistic explosion mechanisms and provide critical guidelines for safe production and handling.
基金National Key Technology R&D Program under Grant No.2013BAJ08B00the Natural Science Foundation of China under Grant Nos.50978218 and 51108376
文摘The seismic behavior of steel reinforced high strength and high performance concrete （SRHC） frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios, axial compression ratios, concrete strengths, steel ratios and stirrup ratios. Three kinds of failure mechanisms are presented and the characteristics of experimental hysteretic curves and skeleton curves with different design parameters are discussed. The columns＇ ductility and energy dissipation were quantitatively evaluated based on seismic resistance. The research results indicate that SRHC frame columns can withstand extreme bearing capacity, but the abilities of ductility and energy dissipation are inferior because of SRHC＇s natural brittleness. As a result, the axial load ratio should be restricted and some construction measures adopted, such as increasing the stirrup ratio. This research established effect factors on the bearing capacity of SPHC columns. Finally, an algorithm for obtaining ultimate bearing capacity using the flexural failure mode is established based on a modified plane- section assumption. The authors also established equations to determine shearing baroclinic failure and shear bond failure based on the accumulation of the axial load force distribution ratio. The calculated results of shear bearing capacity for different failure modes were in good agreement with the experimental results.
文摘The curing behavior of diglycidyl ether of bisphenol-A （DGEBA） with different phosphorus containing diamidediimide-tetraamines （DADITAs） was studied by DSC. Eight DADITAs of varying structures were synthesized by reacting 1 mole of pyromellitic anhydride （PMDA）/3,3＇-benzophenone tetracarboxylic dianhydride （BTDA）/1,4,5,8-naphthalene tetraearboxylic dianhydride （NTDA）/4,4＇-oxydiphthalic anhydride （ODPA） with 2 mole of L-tryptophan （T） in a mixture of acetic acid and pyridine （3：2 V/V） followed by activaton with thionyl chloride and then condensation with excess of phosphorus containing triamines tris（3-aminophenyl） phosphine （TAP） and tris（3-aminophenyl） phosphine oxide （TAPO）. DADITAs obtained by reacting PMDA/BTDA/NTDA/ODPA with L-tryptophan followed by condensation with TAP/TAPO were designated as PTAP, PTAPO, BTAP, BTAPO, NTAP, NTAPO, OTAP and OTAPO respectively. The structural characterization of synthesized DADITAs was done by FTIR, ~H-NMR, I3C-NMR, 31p-NMR spectroscopic techniques and elemental analysis. Thermal stability of the isothermally cured epoxy was investigated using dynamic thermogravimetry analysis. The glass transition temperature （Tg） was highest in DGEBA cured using PTAP. All epoxy thermosets exhibited excellent flame retardancy, moderate changes in Tg and thermal stability. Due to presence of phosphorus in curing agents, all epoxy resin systems met the UL-94 V-0 classification and the limiting oxygen index （LOI） reached up to 38.5, probably because of the nitrogen-phosphorus synergistic effect.
