The effect of micro-void on transverse stiffness and strength for fiber-reinforced composites subjected to load perpendicular to fiber is studied using the state-based peridynamic(PD)theory.The heterogeneous microstru...The effect of micro-void on transverse stiffness and strength for fiber-reinforced composites subjected to load perpendicular to fiber is studied using the state-based peridynamic(PD)theory.The heterogeneous microstructure with micro-voids are discretized with irregular and non-uniform grids on mesoscale.The PD representative volume element with randomly distributed and sized micro-voids has been established with periodic boundary conditions.A parametric study was performed to evaluate the effects of void fraction and void size on transverse properties.It was found that the transverse modulus decreases with the void fraction in the range of 0.5–2%.A smaller void has a greater impact on the transverse modulus than a larger void under the same void content.The crack growth path for the multi-fiber model subjected to transverse tension was analyzed.The PD predictions show that cracks initiate at the interface between fiber and matrix,then deflect to the micro-voids nearby.The PD predictions match well with the analytical and experimental observations available in the literature.展开更多
Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using pure Nb or Mo interlayer at 950 ~C with a total reduction ratio of 86.7%. Interfacial microstructure...Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using pure Nb or Mo interlayer at 950 ~C with a total reduction ratio of 86.7%. Interfacial microstructure and bonding properties of titanium clad steel plates were investigated by electron microscopy and mechanical tests. The results showed β-Ti, TiC and Fe2Ti reaction phases were generated at Ti/steel interface for the clad plates with no interlayer. Inserting Nb or Mo interlayer can effectively suppress the formation of brittle phases, while the weak bonding joint transferred to Nb/steel or Mo/steel interface. And some micro-voids were found at the interface of Nb/steel and Mo/steel. The improved shear strength of clad plates with Nb interlayer might be attributed to the elimination of brittle phases at bonding interface. The small size and little quantities of the micro-voids at Nb/steel interface had a relatively weak effect on shear strength. However, the large number and big size of micro-voids were responsible for the degradation of shear strength for the clad plates with Mo interlayer.展开更多
Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, bu...Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface charac- teristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.11902197 and 11972234is sponsored by Shanghai Sailing Program under Contract No.19YF1421700.
文摘The effect of micro-void on transverse stiffness and strength for fiber-reinforced composites subjected to load perpendicular to fiber is studied using the state-based peridynamic(PD)theory.The heterogeneous microstructure with micro-voids are discretized with irregular and non-uniform grids on mesoscale.The PD representative volume element with randomly distributed and sized micro-voids has been established with periodic boundary conditions.A parametric study was performed to evaluate the effects of void fraction and void size on transverse properties.It was found that the transverse modulus decreases with the void fraction in the range of 0.5–2%.A smaller void has a greater impact on the transverse modulus than a larger void under the same void content.The crack growth path for the multi-fiber model subjected to transverse tension was analyzed.The PD predictions show that cracks initiate at the interface between fiber and matrix,then deflect to the micro-voids nearby.The PD predictions match well with the analytical and experimental observations available in the literature.
文摘Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using pure Nb or Mo interlayer at 950 ~C with a total reduction ratio of 86.7%. Interfacial microstructure and bonding properties of titanium clad steel plates were investigated by electron microscopy and mechanical tests. The results showed β-Ti, TiC and Fe2Ti reaction phases were generated at Ti/steel interface for the clad plates with no interlayer. Inserting Nb or Mo interlayer can effectively suppress the formation of brittle phases, while the weak bonding joint transferred to Nb/steel or Mo/steel interface. And some micro-voids were found at the interface of Nb/steel and Mo/steel. The improved shear strength of clad plates with Nb interlayer might be attributed to the elimination of brittle phases at bonding interface. The small size and little quantities of the micro-voids at Nb/steel interface had a relatively weak effect on shear strength. However, the large number and big size of micro-voids were responsible for the degradation of shear strength for the clad plates with Mo interlayer.
基金financially supported by the National Natural Science Foundation of China (Nos.51505386 and 51275416)the Fundamental Research funds for the Central Universities (No.3102017GX06003)
文摘Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via experiments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to examine the interface charac- teristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.
