An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt% Sr and 0.1 wt% La as well as solution treatment was jointly employed.The samples were solution trea...An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt% Sr and 0.1 wt% La as well as solution treatment was jointly employed.The samples were solution treated at 535℃ for 15 min to 12 h.The microstructure,fracture mechanism,and their correlation with the impact properties of the alloy were studied in detail mainly through optical microscopy(OM),scanning electron microscopy(SEM) and oscillography impact test.The results show that the addition of Sr and La refined the eutectic Si particles significantly from~ 2.05 μm(modified with Sr alone) to~ 0.75 μm in as-cast microstructure,leading to a very homogeneous distribution of spheroidized Si particles in the alloy solution treated at 535℃ for 8 h.The alloy exhibits excellent impact toughness up to 75 J·cm^(-2),which is much higher than the maximum impact toughness of the alloys modified by Sr alone(~ 46 J·cm^(-2)).The major reason for this remarkable increase in the impact property is the dramatic increase in crack initiation energy.The dispersoid-free zones(DFZs)near the eutectic regions mainly consist of the ductile Al-matrix,which exhibits excellent ductility.The ductile Al-matrix of the DFZs hinders the crack propagation,resulting in a significant increase in crack propagation energy.展开更多
The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic ...The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.展开更多
The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of...The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.展开更多
The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows su...The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization.展开更多
The impact properties of hot rolled carbon steel （used for the manufacture of reinforcement steel bars） and the quenched ＆ tempered （Q＆T） low alloy steel （used in the pressure vessel industry） were determined....The impact properties of hot rolled carbon steel （used for the manufacture of reinforcement steel bars） and the quenched ＆ tempered （Q＆T） low alloy steel （used in the pressure vessel industry） were determined. The microstructure of the hot rolled carbon steel contained ferrite/pearlite phases, while that of the quenched and tempered low alloy steel contained bainite structure. Impact properties were determined for both steels by instrumented impact testing at temperatures between -150 and 200℃. The impact properties comprised total impact energy, ductile to brittle transition temperature, crack initiation and propagation energy, brittleness transition temperature and cleavage fracture stress. The Q＆T low alloy steel displayed much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was a little higher than that of the hot rolled carbon steel. The results were discussed in relation to the difference in the chemical composition and microstructure for the two steels.展开更多
In this paper an experimental investigation on the impact behaviour of hybrid composites is conducted by instrumental Charpy impact test. The variation of impact strength and impact toughness index of C/K and C/G hybr...In this paper an experimental investigation on the impact behaviour of hybrid composites is conducted by instrumental Charpy impact test. The variation of impact strength and impact toughness index of C/K and C/G hybrid composites of different matrices with hybrid ratio and interface number is revealed. The dynamic hybrid effect is also investigated from different aspects. Meanwhile, the estimating model for impact strength is established and the estimated values are in good agreement with experimented ones. The hybrid effect coefficients based on different definitions are organically related by the model. This provides a basis for the further study of the impact constitutive equation of hybrid composites.展开更多
Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown ...Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown that the mechanical properties satisfy all the standard requirements of the X70 and X80 steels. UFC results in a presence of microstructure containing quasi polygonal（QF）, acicular ferrite（AF） and granular bainite（GB）. The alloying elements and UFC enhance the strengthening contribution caused by solid solution, dispersion, dislocation and precipitation strengthening. The size and distribution of precipitates in the linepipe steels are fine and dispersed. MA is also homogeneously dispersed due to UFC. Average grain size in the X80 steel is finer than that in the X70 steel. The volume fractions of secondary phases in the X80 steel are greater than those in the X70 steel. The X80 steel remains finer and more dispersed precipitates compared to the X70 steel. As a result, the tensile properties of X80 steel are higher than those of X70 steel. The Charpy absorbed energies of X70 and X80 steels at-10 ℃ reached 436 and 460 J, respectively. They reached 433 and 461 J at-15 ℃, respectively. This is mainly attributed to the presence of larger amounts of AFs in the X80 steel. A microstructure of AF for the X80 steel results in combining high strength and high toughness.展开更多
The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material...The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding （CCGTAW）, pulsed current gas tungsten arc welding （PCGTAW）, and plasma arc welding （PAW） joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCG-TAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.展开更多
Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurr...Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy(SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A recently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the underlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in contrast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.展开更多
The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is ...The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigatio.n, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.展开更多
In the present study,the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy im...In the present study,the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy impact testing machine.The experimental results showed that the impact toughness was remarkably improved by Nb addition in TiVTa to form TiVTaNb alloy.The crack initiation energy and propagation energy of TiVTaNb were 67.3%and 24.9%higher than that of TiVTa,indicating that Nb addition simultaneously reinforced the resistance to crack initiation and propagation.The impact fracture of TiVTaNb exhibited larger bending degree of shear lips,deeper dimples and more secondary cracks which effectively dissipated more impact energy.The deformation mechanism of TiVTa alloy was dominated by dislocation activities.While in TiVTaNb,the deformation mechanism was synergized by dislocation activities and deformation twinning,which were the main contributors for the improved impact properties and the stronger crack resistance of TiVTaNb alloy under impact loading.展开更多
The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were ch...The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscopy(TEM)and energy disperse spectrum(EDS),while the mechanical properties were evaluated according to the impact test.A dispersively distributed spherical and needle-likeη(MgZn2)phase was obtained in the welding seam.The phase composition of the heat-affected zone(HAZ)wasα(Al)+η(MgZn2)+Al6Mn,and there were a large number of dispersively precipitated nanoscale particles.The welded joint zone had the highest impact toughness as compared with the other parts of the joint.The MgZn2 phase in the weld zone contributed to the improved toughness of the joint.Al2 MgCu phase in HAZ was proven to act as a crack source during fracture.展开更多
The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigat...The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.展开更多
A74-mm-diameter Split Hopkinson pressure bar was used to carry out the dynamic compression experiment of concrete made of desert sand.The dynamic failure processes of concrete different in specimen size,impact velocit...A74-mm-diameter Split Hopkinson pressure bar was used to carry out the dynamic compression experiment of concrete made of desert sand.The dynamic failure processes of concrete different in specimen size,impact velocity,desert sand replacement ratio,size and volume content of coarse aggregate were simulated.Research results showed that concrete made of desert sand had size-effect and was rate-dependent.The peak stress of concrete made of desert sand declined with the minimum size of coarse aggregate.However,the peak stress of concrete made of desert sand increased first,and then declined with the volume content and maximum size of coarse aggregate.展开更多
Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration an...Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration and noise,which have a serious influence on the safety and concealment of the equipment.Based on the theory of phononic crystals,this paper studies the vibration transfer properties of a locally resonant(LR)pipe under the condition of fluid–structure interaction.The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method.Further,the different impact excitation and fluid–structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model.The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation,and the vibration reduction frequency range is near the bandgap under the fluid–structure interaction effect.Finally,the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation,and to validate the finite element model.The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.展开更多
The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. ...The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.展开更多
Experimental investigation into impact-resistant behavior of reactive powder concrete (RPC)-filled steel tubular columns was conducted,and dynamic response of the columns under axial impact loading was studied by mean...Experimental investigation into impact-resistant behavior of reactive powder concrete (RPC)-filled steel tubular columns was conducted,and dynamic response of the columns under axial impact loading was studied by means of numerical simulation method.Increase coefficient of load carrying capacity and ratio of load carrying capacity between steel tube and RPC core of col-umns were obtained.展开更多
The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain leve...The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness.With increasing Ti content,the grain size in the steel decreased from 17.7 to 8.9μm.This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations,which act as barriers to hinder crack propagation.The Ti microalloyed steel exhibits a 20%increase in yield strength and a 14%increase in tensile strength.The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%.The low-temperature impact toughness of the steel gradually decreases with increasing Ti content.At low Ti content,the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions.At high Ti content,the low-temperature impact toughness of the steel deteriorates due to several factors.These include the narrower tough–brittle transition zone,grain boundary embrittlement caused by small-sized grains,and the decrease in the solid solution strengthening effect.展开更多
Zirconium alloy cladding materials inevitably undergo hydrogen absorption in the processing and operation process of the reactor,and its static and dynamic mechanical properties are closely related to the hydrogen con...Zirconium alloy cladding materials inevitably undergo hydrogen absorption in the processing and operation process of the reactor,and its static and dynamic mechanical properties are closely related to the hydrogen content.Samples with hydrogen content ranging from 23μg/g to 132μg/g were obtained using the method of gas-phase hydrogen charging,and the influence of hydrogen content on static/dynamic mechanical properties of Zr-Sn-Nb-Fe alloy was studied.The results show that the effect of weak hydrogen charging on the ultimate tensile strength,yield strength,and elongation of zirconium alloy is not obvious.There are a large number of dimples on the fracture surface of the tensile sample before and after hydrogen charging,which is a typical ductile fracture.However,the impact toughness of Zr-Sn-Nb-Fe alloy decreases significantly after trace hydrogen charging.The impact sample without hydrogen charging shows the mixed fracture mechanism of ductile fracture and microcleavage fracture.The increase in hydrogen permeability leads to the emergence of hydride,and the deformation of high strain rate under the impact loading condition leads to secondary cracks in the microstructure.The initiation and expansion of the secondary cracks is the main reason for the reduction of the impact toughness.展开更多
Laser-arc hybrid welding has the characteristics of optimal surface formation and greater penetration;it is extensively used in the welding of plates of medium thickness.However, for hybrid welding of lasers, the weld...Laser-arc hybrid welding has the characteristics of optimal surface formation and greater penetration;it is extensively used in the welding of plates of medium thickness.However, for hybrid welding of lasers, the welding seam cooling rate is rapid;thus, the welding seam has a higher tendency to significantly harden, which has a negative impact on the weld quality of the high-strength low-alloy(HSLA) steel plates of medium thickness.In this study, laser-arc hybrid welding is performed on the BG890 QL HSLA steel produced by Baoshan Iron & Steel Co.,Ltd.,and the quenching tendency of the welded structure is examined.The results demonstrate that the specific growth direction of the columnar crystal structure of the laser-arc hybrid welded joint is obvious.However, at the center and top of the welded seam, there are equiaxed crystals.The impact properties at room temperature and-40 ℃ of the weld area are 58.0 J and 40.0 J,respectively, and those of the heat-affected zone(HAZ) are 147.0 J and 66.5 J,respectively.The impact performance can meet these requirements.Laser-arc hybrid welding of HSLA steel can yield strong and durable welds and the HAZ structure to meet the requirements of engineering applications.展开更多
基金financially supported by Beijing Natural Science Foundation (No.L223001)。
文摘An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt% Sr and 0.1 wt% La as well as solution treatment was jointly employed.The samples were solution treated at 535℃ for 15 min to 12 h.The microstructure,fracture mechanism,and their correlation with the impact properties of the alloy were studied in detail mainly through optical microscopy(OM),scanning electron microscopy(SEM) and oscillography impact test.The results show that the addition of Sr and La refined the eutectic Si particles significantly from~ 2.05 μm(modified with Sr alone) to~ 0.75 μm in as-cast microstructure,leading to a very homogeneous distribution of spheroidized Si particles in the alloy solution treated at 535℃ for 8 h.The alloy exhibits excellent impact toughness up to 75 J·cm^(-2),which is much higher than the maximum impact toughness of the alloys modified by Sr alone(~ 46 J·cm^(-2)).The major reason for this remarkable increase in the impact property is the dramatic increase in crack initiation energy.The dispersoid-free zones(DFZs)near the eutectic regions mainly consist of the ductile Al-matrix,which exhibits excellent ductility.The ductile Al-matrix of the DFZs hinders the crack propagation,resulting in a significant increase in crack propagation energy.
文摘The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.
文摘The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.
基金This work was supported by National Natural Science Foundation of China (No. 59703002).
文摘The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization.
文摘The impact properties of hot rolled carbon steel （used for the manufacture of reinforcement steel bars） and the quenched ＆ tempered （Q＆T） low alloy steel （used in the pressure vessel industry） were determined. The microstructure of the hot rolled carbon steel contained ferrite/pearlite phases, while that of the quenched and tempered low alloy steel contained bainite structure. Impact properties were determined for both steels by instrumented impact testing at temperatures between -150 and 200℃. The impact properties comprised total impact energy, ductile to brittle transition temperature, crack initiation and propagation energy, brittleness transition temperature and cleavage fracture stress. The Q＆T low alloy steel displayed much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was a little higher than that of the hot rolled carbon steel. The results were discussed in relation to the difference in the chemical composition and microstructure for the two steels.
文摘In this paper an experimental investigation on the impact behaviour of hybrid composites is conducted by instrumental Charpy impact test. The variation of impact strength and impact toughness index of C/K and C/G hybrid composites of different matrices with hybrid ratio and interface number is revealed. The dynamic hybrid effect is also investigated from different aspects. Meanwhile, the estimating model for impact strength is established and the estimated values are in good agreement with experimented ones. The hybrid effect coefficients based on different definitions are organically related by the model. This provides a basis for the further study of the impact constitutive equation of hybrid composites.
基金Funded by the National High-Tech Research and Development Program of of China(863 Program)(No.2015AA03A501)Shenyang City Application Basic Research Project(No.F13-316-1-15)the State Key Laboratory Opening Project of Northeastern University(No.12SYS05)
文摘Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown that the mechanical properties satisfy all the standard requirements of the X70 and X80 steels. UFC results in a presence of microstructure containing quasi polygonal（QF）, acicular ferrite（AF） and granular bainite（GB）. The alloying elements and UFC enhance the strengthening contribution caused by solid solution, dispersion, dislocation and precipitation strengthening. The size and distribution of precipitates in the linepipe steels are fine and dispersed. MA is also homogeneously dispersed due to UFC. Average grain size in the X80 steel is finer than that in the X70 steel. The volume fractions of secondary phases in the X80 steel are greater than those in the X70 steel. The X80 steel remains finer and more dispersed precipitates compared to the X70 steel. As a result, the tensile properties of X80 steel are higher than those of X70 steel. The Charpy absorbed energies of X70 and X80 steels at-10 ℃ reached 436 and 460 J, respectively. They reached 433 and 461 J at-15 ℃, respectively. This is mainly attributed to the presence of larger amounts of AFs in the X80 steel. A microstructure of AF for the X80 steel results in combining high strength and high toughness.
文摘The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding （CCGTAW）, pulsed current gas tungsten arc welding （PCGTAW）, and plasma arc welding （PAW） joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCG-TAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.
基金financially supported by the National Research Foundation of Korea(NRF-2020R1C1C1003554)the Creative Materials Discovery Program of the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(NRF2016M3D1A1023384)+1 种基金the Korea Institute for Advancement of Technology(KIAT)grant funded by the Korea Government(MOTIE,P0002019,The Competency Development Program for Industry Specialist)support from the German Research Foundation(Deutsche Forschungsgemeinschaft,DFG)under the priority programme 2006“CCA–HEA"。
文摘Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy(SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A recently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the underlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in contrast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.
文摘The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigatio.n, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.
基金financially supported by the China National Nuclear Corporation(CNNC)Science Fund for Talented Young Scholars(No.FY202307000120)the Continuous Basic Scientific Research Project(No.WDJC-2019-10)the National Natural Science Foundation of China(No.U1867217).
文摘In the present study,the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy impact testing machine.The experimental results showed that the impact toughness was remarkably improved by Nb addition in TiVTa to form TiVTaNb alloy.The crack initiation energy and propagation energy of TiVTaNb were 67.3%and 24.9%higher than that of TiVTa,indicating that Nb addition simultaneously reinforced the resistance to crack initiation and propagation.The impact fracture of TiVTaNb exhibited larger bending degree of shear lips,deeper dimples and more secondary cracks which effectively dissipated more impact energy.The deformation mechanism of TiVTa alloy was dominated by dislocation activities.While in TiVTaNb,the deformation mechanism was synergized by dislocation activities and deformation twinning,which were the main contributors for the improved impact properties and the stronger crack resistance of TiVTaNb alloy under impact loading.
基金Project(ZR2016EEQ03) supported by the Shandong Province Natural Science Foundation,ChinaProject(2018M641822) supported by the China Postdoctoral Science Foundation-General ProgramProject(HIT.NSRIF.201703) supported by the Natural Scientific Research Innovation Foundation in HIT,China
文摘The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscopy(TEM)and energy disperse spectrum(EDS),while the mechanical properties were evaluated according to the impact test.A dispersively distributed spherical and needle-likeη(MgZn2)phase was obtained in the welding seam.The phase composition of the heat-affected zone(HAZ)wasα(Al)+η(MgZn2)+Al6Mn,and there were a large number of dispersively precipitated nanoscale particles.The welded joint zone had the highest impact toughness as compared with the other parts of the joint.The MgZn2 phase in the weld zone contributed to the improved toughness of the joint.Al2 MgCu phase in HAZ was proven to act as a crack source during fracture.
文摘The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.
基金Project supported by the National Natural Science Foundation of China(Nos.51368048 and 11162015)
文摘A74-mm-diameter Split Hopkinson pressure bar was used to carry out the dynamic compression experiment of concrete made of desert sand.The dynamic failure processes of concrete different in specimen size,impact velocity,desert sand replacement ratio,size and volume content of coarse aggregate were simulated.Research results showed that concrete made of desert sand had size-effect and was rate-dependent.The peak stress of concrete made of desert sand declined with the minimum size of coarse aggregate.However,the peak stress of concrete made of desert sand increased first,and then declined with the volume content and maximum size of coarse aggregate.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872371)Major Program of the National Natural Science Foundation of China(Grant Nos.11991032 and 11991034).
文摘Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration and noise,which have a serious influence on the safety and concealment of the equipment.Based on the theory of phononic crystals,this paper studies the vibration transfer properties of a locally resonant(LR)pipe under the condition of fluid–structure interaction.The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method.Further,the different impact excitation and fluid–structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model.The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation,and the vibration reduction frequency range is near the bandgap under the fluid–structure interaction effect.Finally,the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation,and to validate the finite element model.The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.
基金Supported by the National Natural Science Foundation of China under Grant No 11004142the Program for New Century Excellent Talents in University under Grant No 11-035the Project Sponsored by the Scientific Research Foundation for ROCS of the Ministry of Education of China
文摘The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.
基金Supported by National Natural Science Foundation of China(No.50778174).
文摘Experimental investigation into impact-resistant behavior of reactive powder concrete (RPC)-filled steel tubular columns was conducted,and dynamic response of the columns under axial impact loading was studied by means of numerical simulation method.Increase coefficient of load carrying capacity and ratio of load carrying capacity between steel tube and RPC core of col-umns were obtained.
基金supported by the National Natural Science Foundation of China(Nos.52174311 and 51974020).
文摘The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.%was investigated.By adding 0.13 wt.%Ti,the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness.With increasing Ti content,the grain size in the steel decreased from 17.7 to 8.9μm.This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations,which act as barriers to hinder crack propagation.The Ti microalloyed steel exhibits a 20%increase in yield strength and a 14%increase in tensile strength.The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%.The low-temperature impact toughness of the steel gradually decreases with increasing Ti content.At low Ti content,the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions.At high Ti content,the low-temperature impact toughness of the steel deteriorates due to several factors.These include the narrower tough–brittle transition zone,grain boundary embrittlement caused by small-sized grains,and the decrease in the solid solution strengthening effect.
文摘Zirconium alloy cladding materials inevitably undergo hydrogen absorption in the processing and operation process of the reactor,and its static and dynamic mechanical properties are closely related to the hydrogen content.Samples with hydrogen content ranging from 23μg/g to 132μg/g were obtained using the method of gas-phase hydrogen charging,and the influence of hydrogen content on static/dynamic mechanical properties of Zr-Sn-Nb-Fe alloy was studied.The results show that the effect of weak hydrogen charging on the ultimate tensile strength,yield strength,and elongation of zirconium alloy is not obvious.There are a large number of dimples on the fracture surface of the tensile sample before and after hydrogen charging,which is a typical ductile fracture.However,the impact toughness of Zr-Sn-Nb-Fe alloy decreases significantly after trace hydrogen charging.The impact sample without hydrogen charging shows the mixed fracture mechanism of ductile fracture and microcleavage fracture.The increase in hydrogen permeability leads to the emergence of hydride,and the deformation of high strain rate under the impact loading condition leads to secondary cracks in the microstructure.The initiation and expansion of the secondary cracks is the main reason for the reduction of the impact toughness.
文摘Laser-arc hybrid welding has the characteristics of optimal surface formation and greater penetration;it is extensively used in the welding of plates of medium thickness.However, for hybrid welding of lasers, the welding seam cooling rate is rapid;thus, the welding seam has a higher tendency to significantly harden, which has a negative impact on the weld quality of the high-strength low-alloy(HSLA) steel plates of medium thickness.In this study, laser-arc hybrid welding is performed on the BG890 QL HSLA steel produced by Baoshan Iron & Steel Co.,Ltd.,and the quenching tendency of the welded structure is examined.The results demonstrate that the specific growth direction of the columnar crystal structure of the laser-arc hybrid welded joint is obvious.However, at the center and top of the welded seam, there are equiaxed crystals.The impact properties at room temperature and-40 ℃ of the weld area are 58.0 J and 40.0 J,respectively, and those of the heat-affected zone(HAZ) are 147.0 J and 66.5 J,respectively.The impact performance can meet these requirements.Laser-arc hybrid welding of HSLA steel can yield strong and durable welds and the HAZ structure to meet the requirements of engineering applications.
