The aim is to propose and design a kind of novel impact absorption devices using constant-force elements made from Ni Ti shape memory alloy( SMA) strips for safety protection.The availability evaluation results indica...The aim is to propose and design a kind of novel impact absorption devices using constant-force elements made from Ni Ti shape memory alloy( SMA) strips for safety protection.The availability evaluation results indicate that the constant-force elements can absorb over one half of the impact energy for its martensite transformation and thus the maximum impact force is reduced by nearly 80%.Compared with the ordinary cylindrical compression spring,the device's maximum impact force is reduced by nearly 50%,otherwise it has a very compact structure and insensitivity to the varying impact,and thus it is especially suitable for narrow space and safety purpose.展开更多
The automobile industry has been searching for vehicles that use less energy and emit fewer pollutants, which has resulted in a high demand for fuel-efficient vehicles. Because of their higher strength-to-weight ratio...The automobile industry has been searching for vehicles that use less energy and emit fewer pollutants, which has resulted in a high demand for fuel-efficient vehicles. Because of their higher strength-to-weight ratio compared to traditional steel, using fiber-reinforcement composite materials in automobile bodies has emerged as the most effective strategy for improving fuel efficiency while maintaining safety standards. This research paper examined the utilization of fiber-reinforced composite materials in car bodies to meet the increasing consumer demand for fuel-efficient and eco-friendly vehicles. It particularly focused on a carbon-aramid fiber-reinforced composite impact beam for passenger car side door impact protection. Despite the encouraging prospects of the carbon-aramid fiber-reinforced beam, the research uncovered substantial defects in the fabrication process, resulting in diminished load-bearing capacity and energy absorption. As a result, the beam was un-successful in three-point bending tests. This was accomplished by using an I cross-section design with varying thickness because of the higher area moment of inertia. Vacuum-assisted resin transfer molding (VARTM) manufacturing process was used and the finished beam underwent to three-point bending tests.展开更多
Taking the excellent energy absorption performances of cellular structures into consideration,three beam-column steel joints are proposed to analyze the effect of cellular metallic fillers on impact mechanical respons...Taking the excellent energy absorption performances of cellular structures into consideration,three beam-column steel joints are proposed to analyze the effect of cellular metallic fillers on impact mechanical responses of beam-column joints.Based on the existing experimental results,the finite element models of the associated joints are established by using finite element method software.The deformation mode,the bearing capacity and energy absorption performance of various joints subjected to impact loadings with the loading velocities from 10 to 100 m/s are analyzed,respectively.The dynamic responses of cellular metal-filled beamcolumn joints are quantitatively analyzed by means of displacements of central region,nominal impacting stress and energy absorption efficiency.The results can be concluded that the filling of cellular filler weakens the stress concentration on joints,alleviates the occurrence of tearing in connection region among column and beam,and reduces the displacement caused by impact loading.Energy absorption efficiency of filled joints subjected to impact loading increases as the impacting velocity increases,and the cellular metallic filler improves their impact resistance of beam-column joints.The energy absorption efficiency of fully filled joints is superior to that of others.This study can provide a reference for steel structural design and post-disaster repair under extreme working conditions.展开更多
In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure...In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.展开更多
In soccer, the bicycle kick has provided view- ers moments of breathtaking spectacle that seem virtuosic in scope. The novelty of such moments is underscored by the rarity with which players have performed this comple...In soccer, the bicycle kick has provided view- ers moments of breathtaking spectacle that seem virtuosic in scope. The novelty of such moments is underscored by the rarity with which players have performed this complex skill during national or international tournaments. The rarity of these occurrences is both a product of perceptions that it is a high-risk, low return skill and by the fact that there is a dearth of scientific research on the biomechanics of the technique. Two genera can be discerned based on starting position： 1） back-facing the goal, and 2） side-fac- ing the goal. The current study, using 3D motion capture technology and full-body biomechanical modeling, identi- fies elements that govern entrainment of the technique by examining jumping, kicking and falling phases of the skill execution. Motor sequencing during the first two phases can be characterized by analyzing the following pa- rameters： 1） angle between the player＇s thighs （humerus bones） upon take-off, 2） the whip-like control of the kicking leg, 3） timing between ball motion and joint co- ordination and, for the side-facing bicycle kick, 4） rotation of the player＇s trunk during the jumping phase. Dispersion of energy during falling after the kick is accomplished by sharing the load using a sequence of partial landings. Collectively, this information could help entrainment of the skill. Virtuosic in appearance, more frequent use of the kick can only enhance the excitement of the game.展开更多
文摘The aim is to propose and design a kind of novel impact absorption devices using constant-force elements made from Ni Ti shape memory alloy( SMA) strips for safety protection.The availability evaluation results indicate that the constant-force elements can absorb over one half of the impact energy for its martensite transformation and thus the maximum impact force is reduced by nearly 80%.Compared with the ordinary cylindrical compression spring,the device's maximum impact force is reduced by nearly 50%,otherwise it has a very compact structure and insensitivity to the varying impact,and thus it is especially suitable for narrow space and safety purpose.
文摘The automobile industry has been searching for vehicles that use less energy and emit fewer pollutants, which has resulted in a high demand for fuel-efficient vehicles. Because of their higher strength-to-weight ratio compared to traditional steel, using fiber-reinforcement composite materials in automobile bodies has emerged as the most effective strategy for improving fuel efficiency while maintaining safety standards. This research paper examined the utilization of fiber-reinforced composite materials in car bodies to meet the increasing consumer demand for fuel-efficient and eco-friendly vehicles. It particularly focused on a carbon-aramid fiber-reinforced composite impact beam for passenger car side door impact protection. Despite the encouraging prospects of the carbon-aramid fiber-reinforced beam, the research uncovered substantial defects in the fabrication process, resulting in diminished load-bearing capacity and energy absorption. As a result, the beam was un-successful in three-point bending tests. This was accomplished by using an I cross-section design with varying thickness because of the higher area moment of inertia. Vacuum-assisted resin transfer molding (VARTM) manufacturing process was used and the finished beam underwent to three-point bending tests.
基金the National Natural Science Foundation of China(No.11472005)the National Key Research and Development Project(No.2016YFC0701507-2)the Natural Science Foundation of Anhui Province(No.1908085ME173)。
文摘Taking the excellent energy absorption performances of cellular structures into consideration,three beam-column steel joints are proposed to analyze the effect of cellular metallic fillers on impact mechanical responses of beam-column joints.Based on the existing experimental results,the finite element models of the associated joints are established by using finite element method software.The deformation mode,the bearing capacity and energy absorption performance of various joints subjected to impact loadings with the loading velocities from 10 to 100 m/s are analyzed,respectively.The dynamic responses of cellular metal-filled beamcolumn joints are quantitatively analyzed by means of displacements of central region,nominal impacting stress and energy absorption efficiency.The results can be concluded that the filling of cellular filler weakens the stress concentration on joints,alleviates the occurrence of tearing in connection region among column and beam,and reduces the displacement caused by impact loading.Energy absorption efficiency of filled joints subjected to impact loading increases as the impacting velocity increases,and the cellular metallic filler improves their impact resistance of beam-column joints.The energy absorption efficiency of fully filled joints is superior to that of others.This study can provide a reference for steel structural design and post-disaster repair under extreme working conditions.
基金This work was financially supported by the National Natural Science Foundation of China （No. 51775102）, Open Research Fund from the State Key Laboratory of Roiling and Automation, Northeastern University （No. 2016005） and Project Funded by China Postdoctoral Science Foundation （No. 2016M601877）.
文摘In order to further optimize welding process of Nb-Ti-Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone （CGHAZ） of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time ts/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% （3 s） to 3.0% （60 s）. The fraction of martensite/austenite （M/A） constituent increased from 2.2% （3 s） to 39.0% （60 s）, its shape changed from granular to strip, and the maximum length increased from 2.4 μm （3 s） to 7.0 μm （60 s）. As cooling time increased, the prior austenite grain size increased from 34.0 μm （3 s） to 49.0 gm （60 s）, the impact absorption energy reduced from 101.8 J （5 s） to 7.2 J （60 s）, and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.
基金supported by National Sciences and Engineering Research Council of Canada
文摘In soccer, the bicycle kick has provided view- ers moments of breathtaking spectacle that seem virtuosic in scope. The novelty of such moments is underscored by the rarity with which players have performed this complex skill during national or international tournaments. The rarity of these occurrences is both a product of perceptions that it is a high-risk, low return skill and by the fact that there is a dearth of scientific research on the biomechanics of the technique. Two genera can be discerned based on starting position： 1） back-facing the goal, and 2） side-fac- ing the goal. The current study, using 3D motion capture technology and full-body biomechanical modeling, identi- fies elements that govern entrainment of the technique by examining jumping, kicking and falling phases of the skill execution. Motor sequencing during the first two phases can be characterized by analyzing the following pa- rameters： 1） angle between the player＇s thighs （humerus bones） upon take-off, 2） the whip-like control of the kicking leg, 3） timing between ball motion and joint co- ordination and, for the side-facing bicycle kick, 4） rotation of the player＇s trunk during the jumping phase. Dispersion of energy during falling after the kick is accomplished by sharing the load using a sequence of partial landings. Collectively, this information could help entrainment of the skill. Virtuosic in appearance, more frequent use of the kick can only enhance the excitement of the game.
