共晶Si形貌与A356铝合金的动态、准静态压缩变形下的力学性能及抗氢脆性能的影响密切相关。因此文章通过Material Test System(MTS)及霍普金森压杆(SHPB)测试变质前后A356铝合金的动态/准静态压缩力学行为,并采用电化学充氢方法研究合...共晶Si形貌与A356铝合金的动态、准静态压缩变形下的力学性能及抗氢脆性能的影响密切相关。因此文章通过Material Test System(MTS)及霍普金森压杆(SHPB)测试变质前后A356铝合金的动态/准静态压缩力学行为,并采用电化学充氢方法研究合金的抗氢脆性能。结果表明,准静态压缩变形后,合金中板状共晶Si垂直于压缩方向破裂成颗粒状。细化后的共晶Si提高了合金的塑性,延缓了合金的失效。而动态压缩变形后,板状共晶Si变形不均匀,并且碎成块状的共晶Si的尖端在压缩过程中会切割基体,导致其附近出现裂纹等缺陷。随着应变速率增大,铸态A356合金的屈服强度及抗压强度逐渐增大,合金具有一定的应变速率敏感性。变质后,共晶Si得到细化,增大了Al/Si接触面积,共晶Si捕获原子氢后降低了其与基体的连结,导致合金在拉伸变形过程中裂纹更易沿其扩展,并且细化后的共晶Si会进一步降低合金的抗氢脆性能力。其中细化后残存的块状共晶Si在捕获原子氢后会出现脱粘现象,易成为裂纹萌发点。展开更多
The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was e...The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was established to analyze the protection ability and energy absorption by the foam under low velocity impact conditions.For validation,drop hammer experiments were carried out for high porosity closed-cell aluminum foam specimens subjected to low velocity impact loading.The dynamic deformation behavior of the specimen was observed and the velocity attenuation of the drop hammer was measured.The results demonstrated that the aluminum foam had excellent energy absorption capabilities,with its dynamic compressive behavior similar to that obtained under quasi-static loading conditions.Finite element method(FEM) was subsequently employed to obtain stress distributions in the foam specimen.As the propagating period of stress in the specimen was far less than the duration of attenuation,the evolution of the stress was similar to that under quasi-static loading conditions and no obvious stress wave effect was observed,which agreed with the experimental observation.Finally,the predicted velocity attenuation by the ODF-CM was compared with both the experimental measurements and FEM simulation,and good agreements were achieved when the stress distribution was considered to be uniform and the "quasi-static" compressive properties are employed.展开更多
文摘共晶Si形貌与A356铝合金的动态、准静态压缩变形下的力学性能及抗氢脆性能的影响密切相关。因此文章通过Material Test System(MTS)及霍普金森压杆(SHPB)测试变质前后A356铝合金的动态/准静态压缩力学行为,并采用电化学充氢方法研究合金的抗氢脆性能。结果表明,准静态压缩变形后,合金中板状共晶Si垂直于压缩方向破裂成颗粒状。细化后的共晶Si提高了合金的塑性,延缓了合金的失效。而动态压缩变形后,板状共晶Si变形不均匀,并且碎成块状的共晶Si的尖端在压缩过程中会切割基体,导致其附近出现裂纹等缺陷。随着应变速率增大,铸态A356合金的屈服强度及抗压强度逐渐增大,合金具有一定的应变速率敏感性。变质后,共晶Si得到细化,增大了Al/Si接触面积,共晶Si捕获原子氢后降低了其与基体的连结,导致合金在拉伸变形过程中裂纹更易沿其扩展,并且细化后的共晶Si会进一步降低合金的抗氢脆性能力。其中细化后残存的块状共晶Si在捕获原子氢后会出现脱粘现象,易成为裂纹萌发点。
基金supported by the National Basic Research Program of China ("973" Project)(Grant No. 2011CB610305)the National "111" Project of China (Grant No. B06024)the National Natural Science Foundation of China (Grant Nos. 10825210,11072188)
文摘The impact of a rigid body(protected structure) together with cushion material(cellular metal foam) on hard ground from a fixed height was investigated.An analytical one-degree-of-freedom colliding model(ODF-CM) was established to analyze the protection ability and energy absorption by the foam under low velocity impact conditions.For validation,drop hammer experiments were carried out for high porosity closed-cell aluminum foam specimens subjected to low velocity impact loading.The dynamic deformation behavior of the specimen was observed and the velocity attenuation of the drop hammer was measured.The results demonstrated that the aluminum foam had excellent energy absorption capabilities,with its dynamic compressive behavior similar to that obtained under quasi-static loading conditions.Finite element method(FEM) was subsequently employed to obtain stress distributions in the foam specimen.As the propagating period of stress in the specimen was far less than the duration of attenuation,the evolution of the stress was similar to that under quasi-static loading conditions and no obvious stress wave effect was observed,which agreed with the experimental observation.Finally,the predicted velocity attenuation by the ODF-CM was compared with both the experimental measurements and FEM simulation,and good agreements were achieved when the stress distribution was considered to be uniform and the "quasi-static" compressive properties are employed.
