Raindrop impact erosion has been observed since early days of aviation,and can be catastrophic for exposed materials during supersonic flight.A single impact waterjet apparatus is established for mimicking drop impact...Raindrop impact erosion has been observed since early days of aviation,and can be catastrophic for exposed materials during supersonic flight.A single impact waterjet apparatus is established for mimicking drop impacts at the velocities between 350 m/s and 620 m/s.Carbon Fiber Reinforced Polymer(CFRP)laminates with three different surface morphologies and specimen thicknesses are tested here.A central region with no visible damage has been noticed,surrounded by a"failure ring"with common damage patterns including resin removal,matrix cracking,fiber breakage and mass fiber loss.Asymmetric features are presented in the"failure ring"whose whole scope extends larger along the longitudinal direction than the transverse direction of the top layer.The mechanism of the resin removal is related to fiber-matrix debonding,and its onset and propagation can be facilitated by initial surface asperities with the shear action of the lateral jetting.In cases of multiple impact,good surface quality can slow down the evolution of resin removal and fiber exposure on the CFRP surface,reducing the erosion speed and delaying the occurrence of structural damages in the subsequent impacts.Rayleigh wave dominates the occurrence of matrix cracking on the CFRP surface,and subsequently,results in material loss and peeling of the top-layer because of lateral flow.With the increase of the specimen thickness,both the interlaminar and intralaminar failures decrease as the impact damage mechanism changes from plate bending stress to the reflection of stress waves.展开更多
Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of proje...Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of projectile forms and oblique angles on damage formation was particularly discussed by applying different loading conditions such as multiple projectile forms and oblique angles. Additionally, the numerical simulation method was employed to provide further insight into the characteristics of damage and target responses. The Johnson-Cook(J-C)constitutive model with revised failure parameters was used to support the simulations to assess target responses and characteristics of the damage created from different impact conditions. Results show that there is a significant transition in the deformation mode as changes of the projectile form are applied. Moreover, the cracks on the back of the 2618 aluminum alloy plates impacted by the solid plate projectile and the hollow blade projectile tend to locate at different positions, which are supposed to be influenced by local bending and stretching. The work in this paper may provide guidance for the design of fan blade containment systems.展开更多
In the present work, we explore the strain hardening behaviors as well as the effect of temperature on the plastic deformation of ultrafine grained aluminum. The temperature sensitivity is determined and compared with...In the present work, we explore the strain hardening behaviors as well as the effect of temperature on the plastic deformation of ultrafine grained aluminum. The temperature sensitivity is determined and compared with that of coarse grained material. The results indicate that the flow stress of ultrafine grained aluminum displays enhanced sensitivity to temperature. The reduction in activation volume is suggested to be the major reason for the enhanced temperature sensitivity as grain size is refined into the sub-micrometer regime. Finally, a phenomenological constitutive model is proposed to describe the post-yield response of ultrafine grained aluminum.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11832015,12072289 and 12172304).
文摘Raindrop impact erosion has been observed since early days of aviation,and can be catastrophic for exposed materials during supersonic flight.A single impact waterjet apparatus is established for mimicking drop impacts at the velocities between 350 m/s and 620 m/s.Carbon Fiber Reinforced Polymer(CFRP)laminates with three different surface morphologies and specimen thicknesses are tested here.A central region with no visible damage has been noticed,surrounded by a"failure ring"with common damage patterns including resin removal,matrix cracking,fiber breakage and mass fiber loss.Asymmetric features are presented in the"failure ring"whose whole scope extends larger along the longitudinal direction than the transverse direction of the top layer.The mechanism of the resin removal is related to fiber-matrix debonding,and its onset and propagation can be facilitated by initial surface asperities with the shear action of the lateral jetting.In cases of multiple impact,good surface quality can slow down the evolution of resin removal and fiber exposure on the CFRP surface,reducing the erosion speed and delaying the occurrence of structural damages in the subsequent impacts.Rayleigh wave dominates the occurrence of matrix cracking on the CFRP surface,and subsequently,results in material loss and peeling of the top-layer because of lateral flow.With the increase of the specimen thickness,both the interlaminar and intralaminar failures decrease as the impact damage mechanism changes from plate bending stress to the reflection of stress waves.
基金financial support from the National Natural Science Foundation of China (No. 11772268, 11522220, 11627901 and 11527803)
文摘Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of projectile forms and oblique angles on damage formation was particularly discussed by applying different loading conditions such as multiple projectile forms and oblique angles. Additionally, the numerical simulation method was employed to provide further insight into the characteristics of damage and target responses. The Johnson-Cook(J-C)constitutive model with revised failure parameters was used to support the simulations to assess target responses and characteristics of the damage created from different impact conditions. Results show that there is a significant transition in the deformation mode as changes of the projectile form are applied. Moreover, the cracks on the back of the 2618 aluminum alloy plates impacted by the solid plate projectile and the hollow blade projectile tend to locate at different positions, which are supposed to be influenced by local bending and stretching. The work in this paper may provide guidance for the design of fan blade containment systems.
基金supported by the National Natural Science Foundation of China(Nos.11272267,11102168 and 10932008)111 Project(No.B07050)of Northwestern Polytechnical University
文摘In the present work, we explore the strain hardening behaviors as well as the effect of temperature on the plastic deformation of ultrafine grained aluminum. The temperature sensitivity is determined and compared with that of coarse grained material. The results indicate that the flow stress of ultrafine grained aluminum displays enhanced sensitivity to temperature. The reduction in activation volume is suggested to be the major reason for the enhanced temperature sensitivity as grain size is refined into the sub-micrometer regime. Finally, a phenomenological constitutive model is proposed to describe the post-yield response of ultrafine grained aluminum.
