Thin-walled long stringer made of aluminum alloy 7050-T7451 is prone to deformation during transportation,so a research of residual stress relaxation was launched in this paper.The transport resonance stress of long s...Thin-walled long stringer made of aluminum alloy 7050-T7451 is prone to deformation during transportation,so a research of residual stress relaxation was launched in this paper.The transport resonance stress of long stringer was analyzed based on the power spectral density of road transport acceleration.The residual stress relaxation experiment of aluminum alloy 7050-T7451 under different equivalent stress levels was designed and carried out.According to the amount of residual stress relaxation in the experiment,an analytical model was established with the equivalent stress level coefficient.The deflection range of long stringer was evaluated under different damping ratios.The results show that when the equivalent stress exceeds 0.8σ0.2,the residual stress relaxation of the thin-walled samples occurs.The residual stress relaxation increases linearly with the equivalent stress,which is logarithmically related to the loading cycle.The deformation caused by residual stress relaxation of the long stringer is proportional to the square of the length and the bending moment caused by stress rebalance,and inversely proportional to the moment of inertia of the structure.As the damping ratio decreases from 0.03 to 0.01,the total deflection of the long stringer increases from 0 to above 1.55 mm.展开更多
The stress corrosion cracking(SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests(SSRTs) and electrochemical tests were used to study the ...The stress corrosion cracking(SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests(SSRTs) and electrochemical tests were used to study the effects of dry/wet ratio(DWR) and pre-immersion on SCC.Fracture and side surface characterizations were observed by scanning electron microscopy(SEM).The results demonstrate that SCC susceptibility decreases with an increase of the DWR. With an increase of the pre-immersion time, both continuous pre-immersion(CP) and wet-dry cyclic preimmersion(WDP) samples are more sensitive to SCC, and the cracking mode in the SCC fracture region is intergranular. Furthermore, the effect of WDP on SCC is greater than that of CP when the total time immersed in solution before an SSRT is the same with each other. In fact, each single wetdry cycle can be divided into three processes with respect to the change of solution on samples' surface. Volatilization of water on the surface results in an increase in solute concentration, thus accelerating corrosion.展开更多
Aluminum alloy 7050 is widely used in the aeronautical industries.However,owing to their highly ductile property,chips created during high-speed machining cannot be naturally broken,and long continuous chips are unavo...Aluminum alloy 7050 is widely used in the aeronautical industries.However,owing to their highly ductile property,chips created during high-speed machining cannot be naturally broken,and long continuous chips are unavoidably formed,impacting the machining stability and quality of the parts.Because a smaller cutting allowance is required compared with conventional machining operations,the behavior of the chips during reaming operation may be more complex and different from those determined in previous investigations.Therefore,studying the characteristics of chip formation and hole quality during the reaming process is essential to improve the machinability of aluminum alloy 7050.In this study,three different cooling conditions were applied to reaming aluminum alloy 7050-T7451 with polycrystalline diamond(PCD)reamers.The finite element models(FEMs)were established to simulate the chip formation.The macro-and micro-morphologies of chips under the three cooling conditions were compared to analyze the chip behaviors.The diameter,surface roughness,and micro-morphologies of the reamed holes were also analyzed to evaluate the hole quality.The results showed that the chip morphology was strongly influenced by the cutting parameters and cooling strategies.It was found that the desired chip morphologies satisfactory geometrical accuracy and surface quality during the reaming of aluminum alloy 7050-T7451 could be achieved using internal cooling at a spindle speed of 8000 r/min and a feed rate of 0.0l mm/z.This study also demonstrates the feasibility of an internal cooling strategy for breaking chips when reaming aluminum alloy 7050-T7451,which opens new possibilities for improving the chip-snarling that occurs during hole machining.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51405226).
文摘Thin-walled long stringer made of aluminum alloy 7050-T7451 is prone to deformation during transportation,so a research of residual stress relaxation was launched in this paper.The transport resonance stress of long stringer was analyzed based on the power spectral density of road transport acceleration.The residual stress relaxation experiment of aluminum alloy 7050-T7451 under different equivalent stress levels was designed and carried out.According to the amount of residual stress relaxation in the experiment,an analytical model was established with the equivalent stress level coefficient.The deflection range of long stringer was evaluated under different damping ratios.The results show that when the equivalent stress exceeds 0.8σ0.2,the residual stress relaxation of the thin-walled samples occurs.The residual stress relaxation increases linearly with the equivalent stress,which is logarithmically related to the loading cycle.The deformation caused by residual stress relaxation of the long stringer is proportional to the square of the length and the bending moment caused by stress rebalance,and inversely proportional to the moment of inertia of the structure.As the damping ratio decreases from 0.03 to 0.01,the total deflection of the long stringer increases from 0 to above 1.55 mm.
基金co-supported by the National Natural Science Foundation of China (No. 51671013)the Beijing Nova Program of China (No. Z161100004916061)
文摘The stress corrosion cracking(SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests(SSRTs) and electrochemical tests were used to study the effects of dry/wet ratio(DWR) and pre-immersion on SCC.Fracture and side surface characterizations were observed by scanning electron microscopy(SEM).The results demonstrate that SCC susceptibility decreases with an increase of the DWR. With an increase of the pre-immersion time, both continuous pre-immersion(CP) and wet-dry cyclic preimmersion(WDP) samples are more sensitive to SCC, and the cracking mode in the SCC fracture region is intergranular. Furthermore, the effect of WDP on SCC is greater than that of CP when the total time immersed in solution before an SSRT is the same with each other. In fact, each single wetdry cycle can be divided into three processes with respect to the change of solution on samples' surface. Volatilization of water on the surface results in an increase in solute concentration, thus accelerating corrosion.
文摘Aluminum alloy 7050 is widely used in the aeronautical industries.However,owing to their highly ductile property,chips created during high-speed machining cannot be naturally broken,and long continuous chips are unavoidably formed,impacting the machining stability and quality of the parts.Because a smaller cutting allowance is required compared with conventional machining operations,the behavior of the chips during reaming operation may be more complex and different from those determined in previous investigations.Therefore,studying the characteristics of chip formation and hole quality during the reaming process is essential to improve the machinability of aluminum alloy 7050.In this study,three different cooling conditions were applied to reaming aluminum alloy 7050-T7451 with polycrystalline diamond(PCD)reamers.The finite element models(FEMs)were established to simulate the chip formation.The macro-and micro-morphologies of chips under the three cooling conditions were compared to analyze the chip behaviors.The diameter,surface roughness,and micro-morphologies of the reamed holes were also analyzed to evaluate the hole quality.The results showed that the chip morphology was strongly influenced by the cutting parameters and cooling strategies.It was found that the desired chip morphologies satisfactory geometrical accuracy and surface quality during the reaming of aluminum alloy 7050-T7451 could be achieved using internal cooling at a spindle speed of 8000 r/min and a feed rate of 0.0l mm/z.This study also demonstrates the feasibility of an internal cooling strategy for breaking chips when reaming aluminum alloy 7050-T7451,which opens new possibilities for improving the chip-snarling that occurs during hole machining.
