Effects of natural aging and test temperature on the tensile behaviors have been studied for a highperformance cast aluminum alloy Al–10Si–1.2Cu–0.7Mn. Based on self-strengthening mechanism and spheroidization micr...Effects of natural aging and test temperature on the tensile behaviors have been studied for a highperformance cast aluminum alloy Al–10Si–1.2Cu–0.7Mn. Based on self-strengthening mechanism and spheroidization microstructures, the alloy tested at room temperature（RT） exhibits higher 0.2% proof stress（YS） of 206 MPa, ultimate tensile strength（UTS） of 331 MPa and elongation of 10%. Increasing aging time improves the YS and UTS and reduces the ductility of the alloy. Further increasing aging time beyond72 h does not signi？cantly increase the tensile strengths. Increasing test temperature significantly decreases the tensile strengths and increases the ductility of the alloy. The UTS of the alloy can be estimated by using the hardness. The Portevin–Le Chatelier effect occurs at RT due to the interactions between solid solution atoms and dislocations. Similar behaviors occurring at 250℃ are attributed to dynamic strain aging mechanism. Increasing aging time leads to decrease in the strain-hardening exponent（n） value and increase in the strain-hardening coeficient（k） value. Increasing test temperature apparently decreases the n and k values. Eutectic phase particles cracking and debonding determine the fracture mechanism of the alloy. Final failure of the alloy mainly depends on the global instability（high temperature, necking） and local instability（RT, shearing）. Different tensile behaviors of the alloy are mainly attributed to different matrix strengths, phase particle strengths and damage rate.展开更多
Unlike biological materials that can sense mechanical force and actively remodel locally,synthetic polymers typically break down under stress.Molecular-level responses to damage with both stress-reporting and self-str...Unlike biological materials that can sense mechanical force and actively remodel locally,synthetic polymers typically break down under stress.Molecular-level responses to damage with both stress-reporting and self-strengthening functions are significant yet difficult to realize for synthetic polymers.To overcome this challenge,chemo-mechanical coupling into polymers that can simultaneously ameliorate mechanical,optical,or other functional properties of a polymer combined with mechanical treatment will offer a new principle for materials design.Here,we report a kind of elastomer in which destructive forces are channelled into productive and bond-forming reactions by using diselenide(Se–Se)as a mechanophore.Polyurethane has been functionalized with labile Se–Se bonds,whosemechanical activation generates seleno radicals that trigger radical transfer and cross-linking reactions in situ.These reactions are activated efficiently in a mechanical way by compression in bulk materials.The resulting covalent networks possess turn-on mechano-fluorescence and increased moduli,which provide the functions of stress reporting,mechano-healing,and mechano-remodeling for the deformed film.This study not only illuminates themechano-responsive nature of Se–Se bonds in the bulk state but also paves the way for the development of new stress-responsive materials.展开更多
The introduction of Western science in order to change physical and operational aspects of Shanghai＇s Huangpu River had been debated by Qing and Western officials since almost the beginning of its history as a Treaty...The introduction of Western science in order to change physical and operational aspects of Shanghai＇s Huangpu River had been debated by Qing and Western officials since almost the beginning of its history as a Treaty Port. At stake in those debates was the perception of the river＇s proper use： as a natural barrier for military defense, or as a conduit for global trade. After the Western powers unified to militarily suppress the Boxer Uprising in 1900, they attained their long-awaited goal of the right to transform the river for global trade as part of Article 11 of the Boxer Protocol： the Junpuju （or Huangpu Conservancy Board） was created and authorized by the central government to make the Huangpu River navigable for shipping vessels. Although the Junpuju continued the ethos of earlier extra-bureaucratic organizations established during the Self-Strengthening Movement, after 1901 the organization bore the authority of the central government. During the era of the New Policies, Qing officials were intent on revising the original terms of river conservancy so that they would be more favorable to Chinese sovereignty. At the same time, imperialist rivalries among the Western powers ruptured the apparent unity of the earlier alliance during the suppression of the Boxer Uprising. Before long, Western corruption in the Huangpu River dredging was brought to the attention of Qing officials, who deftly used it to recover Qing control over certain parts of the body of the river.展开更多
基金supported by the Project Funded by China Postdoctoral Science Foundation(No.2015M571562)
文摘Effects of natural aging and test temperature on the tensile behaviors have been studied for a highperformance cast aluminum alloy Al–10Si–1.2Cu–0.7Mn. Based on self-strengthening mechanism and spheroidization microstructures, the alloy tested at room temperature（RT） exhibits higher 0.2% proof stress（YS） of 206 MPa, ultimate tensile strength（UTS） of 331 MPa and elongation of 10%. Increasing aging time improves the YS and UTS and reduces the ductility of the alloy. Further increasing aging time beyond72 h does not signi？cantly increase the tensile strengths. Increasing test temperature significantly decreases the tensile strengths and increases the ductility of the alloy. The UTS of the alloy can be estimated by using the hardness. The Portevin–Le Chatelier effect occurs at RT due to the interactions between solid solution atoms and dislocations. Similar behaviors occurring at 250℃ are attributed to dynamic strain aging mechanism. Increasing aging time leads to decrease in the strain-hardening exponent（n） value and increase in the strain-hardening coeficient（k） value. Increasing test temperature apparently decreases the n and k values. Eutectic phase particles cracking and debonding determine the fracture mechanism of the alloy. Final failure of the alloy mainly depends on the global instability（high temperature, necking） and local instability（RT, shearing）. Different tensile behaviors of the alloy are mainly attributed to different matrix strengths, phase particle strengths and damage rate.
基金support of this research by the National Natural Science Foundation of China(grant nos.21734006 and 21975178)the National Key Research and Development Program of China(grant nos.2017YFA0207800 and 2017YFA0204503)is gratefully acknowledged.
文摘Unlike biological materials that can sense mechanical force and actively remodel locally,synthetic polymers typically break down under stress.Molecular-level responses to damage with both stress-reporting and self-strengthening functions are significant yet difficult to realize for synthetic polymers.To overcome this challenge,chemo-mechanical coupling into polymers that can simultaneously ameliorate mechanical,optical,or other functional properties of a polymer combined with mechanical treatment will offer a new principle for materials design.Here,we report a kind of elastomer in which destructive forces are channelled into productive and bond-forming reactions by using diselenide(Se–Se)as a mechanophore.Polyurethane has been functionalized with labile Se–Se bonds,whosemechanical activation generates seleno radicals that trigger radical transfer and cross-linking reactions in situ.These reactions are activated efficiently in a mechanical way by compression in bulk materials.The resulting covalent networks possess turn-on mechano-fluorescence and increased moduli,which provide the functions of stress reporting,mechano-healing,and mechano-remodeling for the deformed film.This study not only illuminates themechano-responsive nature of Se–Se bonds in the bulk state but also paves the way for the development of new stress-responsive materials.
文摘The introduction of Western science in order to change physical and operational aspects of Shanghai＇s Huangpu River had been debated by Qing and Western officials since almost the beginning of its history as a Treaty Port. At stake in those debates was the perception of the river＇s proper use： as a natural barrier for military defense, or as a conduit for global trade. After the Western powers unified to militarily suppress the Boxer Uprising in 1900, they attained their long-awaited goal of the right to transform the river for global trade as part of Article 11 of the Boxer Protocol： the Junpuju （or Huangpu Conservancy Board） was created and authorized by the central government to make the Huangpu River navigable for shipping vessels. Although the Junpuju continued the ethos of earlier extra-bureaucratic organizations established during the Self-Strengthening Movement, after 1901 the organization bore the authority of the central government. During the era of the New Policies, Qing officials were intent on revising the original terms of river conservancy so that they would be more favorable to Chinese sovereignty. At the same time, imperialist rivalries among the Western powers ruptured the apparent unity of the earlier alliance during the suppression of the Boxer Uprising. Before long, Western corruption in the Huangpu River dredging was brought to the attention of Qing officials, who deftly used it to recover Qing control over certain parts of the body of the river.
