Microstructure of transient liquid phase( TLP) diffusion bonded a third generation single crystal superalloy joint was investigated using scanning electron microscopy( SEM),and mechanical properties test of joint was ...Microstructure of transient liquid phase( TLP) diffusion bonded a third generation single crystal superalloy joint was investigated using scanning electron microscopy( SEM),and mechanical properties test of joint was carried out,for obtaining relationship between microstructure and mechanical properties of joint. The results showed that the joint contained bonding zone and base metal. The diffusion zone was obviously observed. When it was not finished for isothermal solidification process,the bonding zone would contain isothermal solidification zone and rapid solidification zone. Metallographic examination revealed that isothermal solidification zone was consisted of γ and γ' phase. Rapid solidification zone was consisted of two different structures,which were ternary eutectic of borides,γ and γ' phase developing at the edge of joint,binary eutectic of γ and γ' phase appearing in the portion of joint. When it was not enough for homogenization process under the condition of finishing isothermal solidification process,the bonding zone would contain isothermal solidification zone and borides at the interface. Under the conditions of relatively high welding temperature and long welding time,average tensile strength of joint was equivalent to that of parent material.展开更多
Thermally responsive liquid crystal elastomers (LCEs) hold great promise in applications of soft robots and actuators because of the induced size and shape change with temperature. Experiments have successfully demons...Thermally responsive liquid crystal elastomers (LCEs) hold great promise in applications of soft robots and actuators because of the induced size and shape change with temperature. Experiments have successfully demonstrated that the LCE based bimorphs can be effective soft robots once integrated with soft sensors and thermal actuators. Here, we present an analytical transient thermo-mechanical model for a bimorph structure based soft robot, which consists of a strip of LCE and a thermal inert polymer actuated by an ultra-thin stretchable open-mesh shaped heater to mimic the unique locomotion behaviors of an inchworm. The coupled mechanical and thermal analysis based on the thermo-mechanical theory is carried out to underpin the transient bending behavior, and a systematic understanding is therefore achieved. The key analytical results reveal that the thickness and the modulus ratio of the LCE and the inert polymer layer dominate the transient bending deformation. The analytical results will not only render fundamental understanding of the actuation of bimorph structures, but also facilitate the rational design of soft robotics.展开更多
A new numerical model is developed using a Cellular Automata (CA) method to study the liquid-phase dissolution behavior of gap-filler powder particles in interlayer powder mixture during transient liquid phase (TLP) b...A new numerical model is developed using a Cellular Automata (CA) method to study the liquid-phase dissolution behavior of gap-filler powder particles in interlayer powder mixture during transient liquid phase (TLP) bonding process. The model prediction of microstructural evolution in TLP joint between single crystal substrates show that formation of misoriented stray-grains results from incomplete liquation of the gap-filler powder particles. In contrast to what is generally assumed and reported, numerical calculations coupled with experimental verification show that under properly selected process parameters, complete melting of the gap-filler powder particles is possible. This is imperative to prevent the formation of misoriented stray-grains and maintain single crystallinity during TLP bonding of single crystal materials. The dependence of complete melting of the gap-filler particles on salient TLP bonding parameters are analyzed and discussed.展开更多
Thermochromic liquid crystals (TLC) and true-colour digital image processing have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. Thin coatings of TLC at surfaces...Thermochromic liquid crystals (TLC) and true-colour digital image processing have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. Thin coatings of TLC at surfaces are utilized to obtain detailed temperature distributions and heat transfer rates for steady or transient processes. Liquid crystals also can be used to make the temperature and velocity fields in liquids visible by the simple expedient of directly mixing the liquid crystal material into the liquid (water, glycerol, glycol, and silicone oils) in very small quantities to use as thermal and hydrodynamic tracers. In biomedical situations, e.g., skin diseases, breast cancer, blood circulation and other medical application, TLC and image processing are successfully used as an additional non-invasive diagnostic method especially useful for screening large groups of potential patients. The history of this technique is reviewed, principal methods and tools are described and some examples are presented. Also steady-state and transient liquid crystal thermography (LCT) is used to measure local heat transfer on a plate equipped with transverse vortex generators. Automated evaluation allows determining the heat transfer coefficient without arbitrary influence of human interpretation.展开更多
文摘Microstructure of transient liquid phase( TLP) diffusion bonded a third generation single crystal superalloy joint was investigated using scanning electron microscopy( SEM),and mechanical properties test of joint was carried out,for obtaining relationship between microstructure and mechanical properties of joint. The results showed that the joint contained bonding zone and base metal. The diffusion zone was obviously observed. When it was not finished for isothermal solidification process,the bonding zone would contain isothermal solidification zone and rapid solidification zone. Metallographic examination revealed that isothermal solidification zone was consisted of γ and γ' phase. Rapid solidification zone was consisted of two different structures,which were ternary eutectic of borides,γ and γ' phase developing at the edge of joint,binary eutectic of γ and γ' phase appearing in the portion of joint. When it was not enough for homogenization process under the condition of finishing isothermal solidification process,the bonding zone would contain isothermal solidification zone and borides at the interface. Under the conditions of relatively high welding temperature and long welding time,average tensile strength of joint was equivalent to that of parent material.
基金Project supported by the National Basic Research Program(No.2015CB351901)the National Natural Science Foundation of China(Nos.11372272,11622221,11621062,11502009,and 11772030)+2 种基金the Doctoral New Investigator Grant from American Chemical Society Petroleum Research Fund of the National Science Foundation(Nos.1509763 and 1554499)the Opening Fund of State Key Laboratory for Strength and Vibration of Mechanical Structures,Xi’an Jiaotong University(No.SV2018-KF-13)the Fundamental Research Funds for the Central Universities(No.2017XZZX002-11)
文摘Thermally responsive liquid crystal elastomers (LCEs) hold great promise in applications of soft robots and actuators because of the induced size and shape change with temperature. Experiments have successfully demonstrated that the LCE based bimorphs can be effective soft robots once integrated with soft sensors and thermal actuators. Here, we present an analytical transient thermo-mechanical model for a bimorph structure based soft robot, which consists of a strip of LCE and a thermal inert polymer actuated by an ultra-thin stretchable open-mesh shaped heater to mimic the unique locomotion behaviors of an inchworm. The coupled mechanical and thermal analysis based on the thermo-mechanical theory is carried out to underpin the transient bending behavior, and a systematic understanding is therefore achieved. The key analytical results reveal that the thickness and the modulus ratio of the LCE and the inert polymer layer dominate the transient bending deformation. The analytical results will not only render fundamental understanding of the actuation of bimorph structures, but also facilitate the rational design of soft robotics.
文摘A new numerical model is developed using a Cellular Automata (CA) method to study the liquid-phase dissolution behavior of gap-filler powder particles in interlayer powder mixture during transient liquid phase (TLP) bonding process. The model prediction of microstructural evolution in TLP joint between single crystal substrates show that formation of misoriented stray-grains results from incomplete liquation of the gap-filler powder particles. In contrast to what is generally assumed and reported, numerical calculations coupled with experimental verification show that under properly selected process parameters, complete melting of the gap-filler powder particles is possible. This is imperative to prevent the formation of misoriented stray-grains and maintain single crystallinity during TLP bonding of single crystal materials. The dependence of complete melting of the gap-filler particles on salient TLP bonding parameters are analyzed and discussed.
文摘Thermochromic liquid crystals (TLC) and true-colour digital image processing have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. Thin coatings of TLC at surfaces are utilized to obtain detailed temperature distributions and heat transfer rates for steady or transient processes. Liquid crystals also can be used to make the temperature and velocity fields in liquids visible by the simple expedient of directly mixing the liquid crystal material into the liquid (water, glycerol, glycol, and silicone oils) in very small quantities to use as thermal and hydrodynamic tracers. In biomedical situations, e.g., skin diseases, breast cancer, blood circulation and other medical application, TLC and image processing are successfully used as an additional non-invasive diagnostic method especially useful for screening large groups of potential patients. The history of this technique is reviewed, principal methods and tools are described and some examples are presented. Also steady-state and transient liquid crystal thermography (LCT) is used to measure local heat transfer on a plate equipped with transverse vortex generators. Automated evaluation allows determining the heat transfer coefficient without arbitrary influence of human interpretation.
