Shrinkage cavity may be detrimental to mechanical performances of casting parts.As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative...Shrinkage cavity may be detrimental to mechanical performances of casting parts.As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects.In this paper,process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects.Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography),the shrinkage cavity defects were modeled with SSM (Shape Simplification Method),which reconstructs shrinkage cavity defects to hollow spheroid primitives.After the impact simulation was conducted,the results show that under impact test condition,the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.展开更多
The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate aff...The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.展开更多
Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied. An improved plane expansion method combined with the supercell technique is used to calculate the band ...Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied. An improved plane expansion method combined with the supercell technique is used to calculate the band gaps and the pressure distribution at the defect position. The sonic pressure of defect modes shows that the waves are localized at or near the defect. As the filing fraction increases, more defect modes appear in the band gaps.展开更多
文摘Shrinkage cavity may be detrimental to mechanical performances of casting parts.As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects.In this paper,process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects.Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography),the shrinkage cavity defects were modeled with SSM (Shape Simplification Method),which reconstructs shrinkage cavity defects to hollow spheroid primitives.After the impact simulation was conducted,the results show that under impact test condition,the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.
基金supported by the National Natural Science Foundation of China(Grant No.12132008)the Key Research Project of Zhejiang Laboratory(Grant No.2021PE0AC02)。
文摘The frictional behavior of supported graphene is known to be influenced by the physical properties and surface morphologies of the underlying substrate. However, it is unclear how a surface defect on the substrate affects the friction of supported graphene,and it is even unknown how to define the defect-induced friction force in this context. Here we conduct molecular dynamics(MD) simulations to investigate the friction between a square diamond slider and a graphene sheet supported by a copper substrate with a surface cavity defect. Our results demonstrate that the defect-induced friction exhibits a nonlinear increase with cavity size, while it decreases nonlinearly with slider size. We propose that the definition of defect-induced friction can be linked to the increase in friction work over the length of the slider, and is closely correlated to the defect-induced relative change in indentation depth and the ratio of the cavity area to the contact area. These findings provide a comprehensive evaluation of the impact of a substrate cavity defect on the friction of supported graphene and offer insights that may have broader implications for understanding defect-induced friction in other two-dimensional materials.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10864009)the Natural Science Foundation of Yunnan Province,China (Grant No. 2008CD109)the State Key Program of the National Natural Science of China (Grant No. 50734007)
文摘Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied. An improved plane expansion method combined with the supercell technique is used to calculate the band gaps and the pressure distribution at the defect position. The sonic pressure of defect modes shows that the waves are localized at or near the defect. As the filing fraction increases, more defect modes appear in the band gaps.
