The dynamic fracture behaviors of the extruded 2024-T4 and 7075-T6 aluminum alloys are investigated by using an instrumented drop tower machine.The specimens are made from a 25 mm diameter extruded circular rod.The dy...The dynamic fracture behaviors of the extruded 2024-T4 and 7075-T6 aluminum alloys are investigated by using an instrumented drop tower machine.The specimens are made from a 25 mm diameter extruded circular rod.The dynamic three-point bending tests of each alloy are carried out at different impact velocities.The initiation fracture toughness and average propagation fracture toughness of 2024-T4 and 7075-T6 are determined at different loading rates.The results show that both the initiation toughness and the propagation toughness increase with the loading rate.Further,the difference between the fracture toughness behaviors of 2024-T4 and 7075-T6 is found to be dependent on the variation of fracture mechanism.The comprehensive fractographic investigations of the fracture surfaces clearly demonstrate that the fracture mode of 2024-T4 is predominantly transgranular fracture with high density small-sized dimples,and the fracture mode of 7075-T6 is mainly intergranular fracture with many intermetallic particles in the bottom of voids located in the fracture surface.展开更多
The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in wh...The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.展开更多
High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package （POP） is a promising three-dimensi...High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package （POP） is a promising three-dimensional high- density packaging method that integrates a chip scale package （CSP） in the top package and a fine-pitch ball grid array （FBGA） in the bottom package. In this paper, in-situ scanning electron microscopy （SEM） observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis and the theoretical analysis results are found to be in good agreement with the experimental results.展开更多
Transformation-induced plasticity(TRIP)steel possesses high strength and formability,enabling the use of a thinner gauge material and allowing for the fabrication of complex shapes.In this research,we measured the eff...Transformation-induced plasticity(TRIP)steel possesses high strength and formability,enabling the use of a thinner gauge material and allowing for the fabrication of complex shapes.In this research,we measured the effect of bending temperatures on the microstructure and air-bending springback angle of TRIP steel at temperatures from 25 to 600C.Real-time in situ X-ray diffraction and scanning electron microscopy were used for pre-and postbending analysis.As the prebending temperature increased from 25C to 600C,the retained austenite(RA)volume fraction decreased,and the RA transformed to bainite at temperatures above 400C.The springback angle was positively correlated with the prebending RA volume fraction,with the smallest springback angle achieved at 400C.Additionally,the springback angle was positively correlated with the bending angle,because the RA transformation ratio contributed to increased strain hardening.Further microstructure analysis revealed that the RA became elongated in the tension direction as the bending temperatures increased.展开更多
基金supported by the NatiS100onal Science Foundation of China under Grant No.11072119the Defense Industrial Technology Development Program under Grant No.B1520110003+2 种基金the K.C.Wong Magna Foundation of Ningbo University,Chinaa grant from the Department of Education of Zhejiang Province through the Impact and Safety of Costal Engineering Initiativea COE Program at Ningbo University
文摘The dynamic fracture behaviors of the extruded 2024-T4 and 7075-T6 aluminum alloys are investigated by using an instrumented drop tower machine.The specimens are made from a 25 mm diameter extruded circular rod.The dynamic three-point bending tests of each alloy are carried out at different impact velocities.The initiation fracture toughness and average propagation fracture toughness of 2024-T4 and 7075-T6 are determined at different loading rates.The results show that both the initiation toughness and the propagation toughness increase with the loading rate.Further,the difference between the fracture toughness behaviors of 2024-T4 and 7075-T6 is found to be dependent on the variation of fracture mechanism.The comprehensive fractographic investigations of the fracture surfaces clearly demonstrate that the fracture mode of 2024-T4 is predominantly transgranular fracture with high density small-sized dimples,and the fracture mode of 7075-T6 is mainly intergranular fracture with many intermetallic particles in the bottom of voids located in the fracture surface.
基金Supported by the National Natural Science Foundation of China(5137520151775227)。
文摘The effects of forming damage are analyzed,which occur during hot stamping process,on the load-carrying capacity and failure mode of hot stamped beams.A damage-coupled pre-forming constitutive model was proposed,in which the damage during hot stamping process was introduced into the service response.The constitutive model was applied into the three-point bending simulation of a hot stamped beam,and then the influences of forming damage on the load-carrying capacity and cracks propagation were investigated.The results show that the forming damage reduces the maximum load capacity of the hot stamped beam by 7.5%.It also causes the crack to occur earlier and promotes crack to propagate along the radial direction of the punch.
基金Projects supported by the National Natural Science Foundation of China(Grant Nos.11072124 and 11272173)the National Basic Research Program of China(Grant No.2010CB631006)the State Key Laboratory of Advanced Metals and Materials, China(Grant No.2010ZD-04)
文摘High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package （POP） is a promising three-dimensional high- density packaging method that integrates a chip scale package （CSP） in the top package and a fine-pitch ball grid array （FBGA） in the bottom package. In this paper, in-situ scanning electron microscopy （SEM） observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis and the theoretical analysis results are found to be in good agreement with the experimental results.
基金This research was funded by Faculty of Engineering,King Mongkut’s Institute of Technology Ladkrabang.
文摘Transformation-induced plasticity(TRIP)steel possesses high strength and formability,enabling the use of a thinner gauge material and allowing for the fabrication of complex shapes.In this research,we measured the effect of bending temperatures on the microstructure and air-bending springback angle of TRIP steel at temperatures from 25 to 600C.Real-time in situ X-ray diffraction and scanning electron microscopy were used for pre-and postbending analysis.As the prebending temperature increased from 25C to 600C,the retained austenite(RA)volume fraction decreased,and the RA transformed to bainite at temperatures above 400C.The springback angle was positively correlated with the prebending RA volume fraction,with the smallest springback angle achieved at 400C.Additionally,the springback angle was positively correlated with the bending angle,because the RA transformation ratio contributed to increased strain hardening.Further microstructure analysis revealed that the RA became elongated in the tension direction as the bending temperatures increased.
