Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability as...Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns.To develop a unified model of fatigue initiation and crack propagation,a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments.However,there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy,which is widely used as load-bearing components in aircraft industry.In this paper,strain-controlled uniaxial,torsion,and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air.Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens.Fatigue experiments under the fully reversed shear loading with a static axial stress,proportional axial-torsion loading,and 90°out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens.The experimental results show that the mean stress has a significant influence on the fatigue strength of the material.A tensile mean stress decreases the fatigue life dramatically,while a compressive mean stress increases the fatigue life.The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation.However,two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink.The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.展开更多
分别用搅拌摩擦焊(FSW)和超声辅助搅拌摩擦焊(UAFSW)两种方法对1.8 mm 2024-T4铝合金进行对接焊接,并对焊缝的微观组织和力学性能进行了分析比较。结果表明:FSW和UAFSW两种方法焊接的1.8 mm 2024-T4铝合金均可得到成型美观、内部无缺陷...分别用搅拌摩擦焊(FSW)和超声辅助搅拌摩擦焊(UAFSW)两种方法对1.8 mm 2024-T4铝合金进行对接焊接,并对焊缝的微观组织和力学性能进行了分析比较。结果表明:FSW和UAFSW两种方法焊接的1.8 mm 2024-T4铝合金均可得到成型美观、内部无缺陷的焊缝,但UAFSW的焊缝力学性能优于FSW;在其它条件相同时,FSW的焊接强度达母材的74.14%,UAFSW的焊接强度可达到母材82.83%。金相组织分析表明,UAFSW焊缝区组织比FSW的更均匀,晶粒更细小。展开更多
Friction stir welding (FSW) is a new and promising welding processing that can produce low-cost and high-quality joints of aluminum alloys. 1 mm thick sheets of 2024-T4 aluminum alloys which are always used as buildin...Friction stir welding (FSW) is a new and promising welding processing that can produce low-cost and high-quality joints of aluminum alloys. 1 mm thick sheets of 2024-T4 aluminum alloys which are always used as building and decorating materials were welded by FSW. The microstructure and mechanical properties of friction stir welded 1 mm thick sheets of 2024-T4 aluminum alloy were studied. It was found that the thinner the 2024 aluminum alloy, the larger the FSW technological parameters field. The grains size of weld nugget zone (WNZ) is approximately 10 times smaller than that of the parent material, but the second phase in the material is not refined apparently in the welding. The FS welded joints have about 40% higher yield strength than the parent material, but the elongation of FS welded joints is under about 50% of the parent material. The electron backscattered diffraction (EBSD) results show that there are much more low angle boundaries (LAB) in WNZ than that in parent material, which indicates that FSW causes a number of sub-grain structures in WNZ, and this is also the reason of the increase of yield strength and Vickers hardness of the welded joint.展开更多
基金supported by National Natural Science Foundation of China(Grant No.50975260)Zhejiang Provincial Natural Science Foundation of China(Grant No.Z1091027)
文摘Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns.To develop a unified model of fatigue initiation and crack propagation,a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments.However,there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy,which is widely used as load-bearing components in aircraft industry.In this paper,strain-controlled uniaxial,torsion,and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air.Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens.Fatigue experiments under the fully reversed shear loading with a static axial stress,proportional axial-torsion loading,and 90°out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens.The experimental results show that the mean stress has a significant influence on the fatigue strength of the material.A tensile mean stress decreases the fatigue life dramatically,while a compressive mean stress increases the fatigue life.The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation.However,two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink.The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.
文摘分别用搅拌摩擦焊(FSW)和超声辅助搅拌摩擦焊(UAFSW)两种方法对1.8 mm 2024-T4铝合金进行对接焊接,并对焊缝的微观组织和力学性能进行了分析比较。结果表明:FSW和UAFSW两种方法焊接的1.8 mm 2024-T4铝合金均可得到成型美观、内部无缺陷的焊缝,但UAFSW的焊缝力学性能优于FSW;在其它条件相同时,FSW的焊接强度达母材的74.14%,UAFSW的焊接强度可达到母材82.83%。金相组织分析表明,UAFSW焊缝区组织比FSW的更均匀,晶粒更细小。
文摘Friction stir welding (FSW) is a new and promising welding processing that can produce low-cost and high-quality joints of aluminum alloys. 1 mm thick sheets of 2024-T4 aluminum alloys which are always used as building and decorating materials were welded by FSW. The microstructure and mechanical properties of friction stir welded 1 mm thick sheets of 2024-T4 aluminum alloy were studied. It was found that the thinner the 2024 aluminum alloy, the larger the FSW technological parameters field. The grains size of weld nugget zone (WNZ) is approximately 10 times smaller than that of the parent material, but the second phase in the material is not refined apparently in the welding. The FS welded joints have about 40% higher yield strength than the parent material, but the elongation of FS welded joints is under about 50% of the parent material. The electron backscattered diffraction (EBSD) results show that there are much more low angle boundaries (LAB) in WNZ than that in parent material, which indicates that FSW causes a number of sub-grain structures in WNZ, and this is also the reason of the increase of yield strength and Vickers hardness of the welded joint.
文摘钩状缺陷是影响搅拌摩擦搭接焊接头性能的重要因素.为了尽可能的避免钩状缺陷的产生,利用不扎透上板的方式对2024-T4铝合金进行焊接,重点分析不同转速下的接头横截面形貌及力学性能.结果表明,利用不扎透上板的方式所得搭接界面保持连续且主要呈水平方向分布.由于搅拌针长度较小,焊核区底部的宽度远大于搅拌针尖端直径,使有效连接宽度增加,导致搭接接头在承受拉剪载荷时呈拉伸断裂模式.与转速为500 r/min相比,600 r/min下接头的有效连接宽度与剪切拉伸强度均有小幅度地增加,最大剪切拉伸载荷为17 215.11 N.
