Abstract A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and fini...Abstract A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and finite element simulation results. Microstructure and tensile properties of the repaired specimens were studied. The results showed that the entire crack repairing was a solid-phase process and plastic materials tended to flow toward the shoulder center and then resulted in the repairing of cracks. Meanwhile, the coarse grain structures were refined in repaired zone （RZ）, while the grains in thermal-mechanically affected zone and heat-affected zone were elongated and driven to grow up. Meanwhile, large phases are crushed into small particles and dispersed inside the RZ. Finally, the strength of the repaired specimens can be restored dramatically and their ductility can be partially restored. After heat treatment, the tensile properties of the repaired specimens can be further enhanced.展开更多
Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult ...Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult task.To address such inspection and maintenance issues,this study presents a computer-vision-guided semi-autonomous robotic system for identification and repair of concrete cracks,and humans can make repair plans for this system.Concrete cracks are characterized through computer vision,and a crack feature database is established.Furthermore,a trajectory generation and coordinate transformation method is designed to determine the robotic execution coordinates.In addition,a knowledge base repair method is examined to make appropriate decisions on repair technology for concrete cracks,and a robotic arm is designed for crack repair.Finally,simulations and experiments are conducted,proving the feasibility of the repair method proposed.The result of this study can potentially improve the performance of on-site automatic concrete crack repair,while addressing such issues as high accident rate,low efficiency,and big loss of skilled workers.展开更多
Using SiC, Al, Al_2O_3, ZrO_2 and Y_2O_3 as raw materials, based on chemical reactions those can cause expansion effect to compensate for the sintering shrinkage at elevated temperature among them, such as Al oxidizes...Using SiC, Al, Al_2O_3, ZrO_2 and Y_2O_3 as raw materials, based on chemical reactions those can cause expansion effect to compensate for the sintering shrinkage at elevated temperature among them, such as Al oxidizes to Al_2O_3, SiC converts to SiO_2, and their reaction productions react further to form mullite (3Al_2O_3·2SiO_2), a sort of tiny expansion composites were prepared and designed which can be used to repair macroscopic cracks of sintered ceramics. The total expanding extent can be adjusted by proportion of raw materials or control of sintering temperature. Filling this expandable ceramic ingredient in cracks of real ceramic part in a designed paste state, cracks could be repaired by a re-sintering process.展开更多
This study focused on testing the possibility of formation of alumina ceramic phase using aluminum/alumina mixture with other low content sintered at high temperature. It was found from XRD and SEM that aluminium is o...This study focused on testing the possibility of formation of alumina ceramic phase using aluminum/alumina mixture with other low content sintered at high temperature. It was found from XRD and SEM that aluminium is oxidized to alumina completely and the samples formatted ceramic phase accompanying minute expansion. This research supplies a new method of repairing macroscopic cracking of ceramic.展开更多
Surface crack of components of the cast nickel base superalloy was repaired with twin laser beams under proper technological conditions. One laser beam was used to melt the substrate material of crack, and the other t...Surface crack of components of the cast nickel base superalloy was repaired with twin laser beams under proper technological conditions. One laser beam was used to melt the substrate material of crack, and the other to fill in powder material to the crack region. The experimental results show that the surface crack with the width of 0.1 ～ 0.3?mm could be repaired under the laser power of 3?kW and the scanning speed of 6 ～ 8?mm/s. The repaired deepness of crack region is below 6.5?mm. The microstructure of repaired region is the cellular crystal, columnar crystal dendrite crystal from the transition region to the top filled layer. The phases in repaired region mainly consisted of supersaturated α Co with plenty of Ni, some Cr and Al, Cr 23 C 6, Co 2B, Co Ni Mo, Ni 4B 3, TiSi and VSi. The hardness of filled layer in repaired region ranged from HV 0.2 450 to HV 0.2 500, and the hardness decreases gradually from the filled layer to joined zone.展开更多
Transverse cracks occur usually in repair welding for thick plate of high strength steel. It needs multiple times of repair welding. The quality of production and deliver deadline will be influenced. Therefore, it is ...Transverse cracks occur usually in repair welding for thick plate of high strength steel. It needs multiple times of repair welding. The quality of production and deliver deadline will be influenced. Therefore, it is very significant to investigate the cause and control of transverse crack in repair welding. In this paper, both ends restraint crack experiment is developed to produce delay transverse crack for high strength steel. Metallographic results show that four types of cracks are found in repair welding metal zone and heat affected zone. Large chevron transverse cracks are found in repair welding zone. Lots of micro transverse cracks are found in inter-layer repair welding metal zone, root HAZ and two ends of repair welding individually. The distribution character and formation mechanism of the transverse crack are further analyzed through hardness testing and residual stress measurement.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51405309)the Natural Science Foundation of Liaoning Province(Grant No. 2015020183)
文摘Abstract A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and finite element simulation results. Microstructure and tensile properties of the repaired specimens were studied. The results showed that the entire crack repairing was a solid-phase process and plastic materials tended to flow toward the shoulder center and then resulted in the repairing of cracks. Meanwhile, the coarse grain structures were refined in repaired zone （RZ）, while the grains in thermal-mechanically affected zone and heat-affected zone were elongated and driven to grow up. Meanwhile, large phases are crushed into small particles and dispersed inside the RZ. Finally, the strength of the repaired specimens can be restored dramatically and their ductility can be partially restored. After heat treatment, the tensile properties of the repaired specimens can be further enhanced.
基金supported by the National Natural Science Foundation of China (Grants nos.71732001 and 71821001)the major science and technology project in Hubei Province,China:Key Technologies and Applications of Intelligent Construction (2020ACA006).
文摘Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult task.To address such inspection and maintenance issues,this study presents a computer-vision-guided semi-autonomous robotic system for identification and repair of concrete cracks,and humans can make repair plans for this system.Concrete cracks are characterized through computer vision,and a crack feature database is established.Furthermore,a trajectory generation and coordinate transformation method is designed to determine the robotic execution coordinates.In addition,a knowledge base repair method is examined to make appropriate decisions on repair technology for concrete cracks,and a robotic arm is designed for crack repair.Finally,simulations and experiments are conducted,proving the feasibility of the repair method proposed.The result of this study can potentially improve the performance of on-site automatic concrete crack repair,while addressing such issues as high accident rate,low efficiency,and big loss of skilled workers.
文摘Using SiC, Al, Al_2O_3, ZrO_2 and Y_2O_3 as raw materials, based on chemical reactions those can cause expansion effect to compensate for the sintering shrinkage at elevated temperature among them, such as Al oxidizes to Al_2O_3, SiC converts to SiO_2, and their reaction productions react further to form mullite (3Al_2O_3·2SiO_2), a sort of tiny expansion composites were prepared and designed which can be used to repair macroscopic cracks of sintered ceramics. The total expanding extent can be adjusted by proportion of raw materials or control of sintering temperature. Filling this expandable ceramic ingredient in cracks of real ceramic part in a designed paste state, cracks could be repaired by a re-sintering process.
文摘This study focused on testing the possibility of formation of alumina ceramic phase using aluminum/alumina mixture with other low content sintered at high temperature. It was found from XRD and SEM that aluminium is oxidized to alumina completely and the samples formatted ceramic phase accompanying minute expansion. This research supplies a new method of repairing macroscopic cracking of ceramic.
文摘Surface crack of components of the cast nickel base superalloy was repaired with twin laser beams under proper technological conditions. One laser beam was used to melt the substrate material of crack, and the other to fill in powder material to the crack region. The experimental results show that the surface crack with the width of 0.1 ～ 0.3?mm could be repaired under the laser power of 3?kW and the scanning speed of 6 ～ 8?mm/s. The repaired deepness of crack region is below 6.5?mm. The microstructure of repaired region is the cellular crystal, columnar crystal dendrite crystal from the transition region to the top filled layer. The phases in repaired region mainly consisted of supersaturated α Co with plenty of Ni, some Cr and Al, Cr 23 C 6, Co 2B, Co Ni Mo, Ni 4B 3, TiSi and VSi. The hardness of filled layer in repaired region ranged from HV 0.2 450 to HV 0.2 500, and the hardness decreases gradually from the filled layer to joined zone.
基金Tbis research is supported by National Science Foundation （No. 51105252） and by Harbin Creative Talent Tec, hnology Foundation （No. 2010RFQXGO05） and by Heilongjiang Province Education Foundation （No. 20100503066）.
文摘Transverse cracks occur usually in repair welding for thick plate of high strength steel. It needs multiple times of repair welding. The quality of production and deliver deadline will be influenced. Therefore, it is very significant to investigate the cause and control of transverse crack in repair welding. In this paper, both ends restraint crack experiment is developed to produce delay transverse crack for high strength steel. Metallographic results show that four types of cracks are found in repair welding metal zone and heat affected zone. Large chevron transverse cracks are found in repair welding zone. Lots of micro transverse cracks are found in inter-layer repair welding metal zone, root HAZ and two ends of repair welding individually. The distribution character and formation mechanism of the transverse crack are further analyzed through hardness testing and residual stress measurement.
