Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear...Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear by approximately 80%. However, the performance of these sFTC/NAB composite surface deposits is determined by their residual stress state, and the precise macroscopic and microscopic residual stresses within these composites have yet to be clearly established. To address this gap, we employed neutron diffraction to measure the residual stresses in the sFTC/NAB composite surface deposits and re-melted NAB samples produced via laser melt injection. Significant residual stresses were determined. The maximum tensile macro residual stress appears approximately 1-1.5 mm below the composite layer. Residual stresses accumulate with an increasing number of laser process tracks. The maximum tensile macro residual stress in the three-track samples reaches about 350 MPa. Preheating the base plate significantly reduces the levels of macroscopic residual stress. The WC phase displayed significant compressive thermal misfit residual stress magnitude, while the Cu matrix exhibited tensile thermal misfit residual stress. Preheating the base plate does not reduce microscopic thermal misfit residual stress levels. In addition, a finite element model was built to investigate temperature and residual stresses in the re-melted NAB samples. The predicted temperature history and residual stress agree with the experimental results.展开更多
The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled ...The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.展开更多
The deformation, damage and failure behaviors of 17 vol.% SiCp/2009AI composite were studied by micro- scopic finite element （FE） models based on a representative volume element （RVE） and a unit cell. The RVE havi...The deformation, damage and failure behaviors of 17 vol.% SiCp/2009AI composite were studied by micro- scopic finite element （FE） models based on a representative volume element （RVE） and a unit cell. The RVE having a 3D realistic microstructure was constructed via computational modeling technique, in which an interface phase with an average thickness of 50 nm was generated for assessing the effects of interracial properties. Modeling results showed that the RVE based FE model was more accurate than the unit cell based one. Based on the RVE, the predicted stress-strain curve and the fracture morphology agreed well with the experimental results. Furthermore, lower interface strength resulted in lower flow stress and ductile damage of interface phase, thereby leading to decreased elongation. It was revealed that the stress concentration factor of SiC was -2.0： the average stress in SiC particles reached -1200 MPa, while that of the composite reached -600 MPa.展开更多
One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning...One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited.In this study,in-situ neutron diffraction study on the tensile deformation of the 3 vol.%CNT/2009 Al composite and the unreinforced 2009 Al alloy was conducted.The{311}and{220}diffraction elastic constants(DECs)of the 2009 Al alloy were determined.Using those DECs the average stress in the 2009 Al matrix of the composite was calculated.Then the average stress in the CNTs was separated by using the stress equilibrium condition.Computational homogenization models were also applied to explain the stress evolution in each phase.Predicted results agree with experimental data.In the present case,the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data,which leads to an increment of yield strength by about 37 MPa.As the result of this work,an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites,which can be applied to optimize the mechanical properties of the composites.展开更多
Thermal residual stress and strain(TRSS)in particle reinforced metal matrix composites(PRMMCs)are believed to cause strengthening effects,according to previous studies.Here,the representative volume element(RVE)based ...Thermal residual stress and strain(TRSS)in particle reinforced metal matrix composites(PRMMCs)are believed to cause strengthening effects,according to previous studies.Here,the representative volume element(RVE)based computational homogenization technique was used to study the tensile deformation of PRMMCs with different particle aspect ratios(AR).The influence of TRSS was assessed quantitatively via comparing simulations with or without the cooling process.It was found that the strengthening effect of TRSS was affected by the particle AR.With the average strengthening effect of TRSS,a fast method of introducing the strengthening effect of TRSS to the tensile behavior of PRMMCs was developed.The new method has reduced the computational cost by a factor 2.The effect of TRSS on continuous fiber-reinforced metal matrix composite was found to have a softening-effect during the entire tensile deformation process because of the pre-yield effect caused by the cooling process.展开更多
The hot deformation behaviors of the bimodal carbon nanotube reinforced 2009Al(CNT/2009Al)composite were studied by establishing processing map and characterizing the microstructure evolution.The results indicate that...The hot deformation behaviors of the bimodal carbon nanotube reinforced 2009Al(CNT/2009Al)composite were studied by establishing processing map and characterizing the microstructure evolution.The results indicate that the grain size in the ultra-fine grained zones was stable during hot deformation,while the coarse grained zones were elongated with their long axis directions tending to be perpendicular to the compression direction.Low temperature with high strain rate(LTHR),as well as high temperature with low strain rate(HTLR)could increase the length/width ratio of the coarse grained zones.However,LTHR and HTLR could cause the instable deformation.The instable deformation at LTHR was induced by severe intragranular plastic deformation and the localized shear crack,while the instable deformation at HTLR resulted from the more deformation component at the coarse grained zones,and the micro-pore initiation due to CNT re-agglomeration at the boundaries between the coarse and the ultra-fine grained zones.展开更多
In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relativ...In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relatively small field of view of FAST makes the search for new FRBs challenging,but its high sensitivity significantly improves the accuracy of FRB localization and enables the detection of high-precision neutral hydrogen absorption lines generated by FRBs.Our goal is to develop an FRB searching system capable of realtime detection of FRBs that allows high-time resolution spectro-temporal studies among the repeated bursts,as well as detailed investigations of these bursts and exploration of FRB progenitor models.The data from each beam of the 19-beam receiver are fed into a high-performance computing node server,which performs real-time searches for pulses with a wide dispersion measure(DM)range of 20–10,000 pc cm^(-3) with step efficiency of 25%in real time.Then,the head node server aggregates all the candidate signals from each beam within a given time,determining their authenticity based on various criteria,including arrival time,pulse width,signal-to-noise ratio and coincidence patterns among the 19 beams.Within the 1.05–1.45 GHz operating bandwidth of the FAST 19beam receiver,the system achieves a frequency resolution of 122.07 kHz and a time resolution of 270.336μs.Subsequently,our team detected a series of bursts with a DM of 566 on 2019 August 30 confirming them as FRB121102.The FRB searching system enables the 19-beam receiver of FAST to detect repeated/one-off pulses/bursts in real time.展开更多
文摘Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear by approximately 80%. However, the performance of these sFTC/NAB composite surface deposits is determined by their residual stress state, and the precise macroscopic and microscopic residual stresses within these composites have yet to be clearly established. To address this gap, we employed neutron diffraction to measure the residual stresses in the sFTC/NAB composite surface deposits and re-melted NAB samples produced via laser melt injection. Significant residual stresses were determined. The maximum tensile macro residual stress appears approximately 1-1.5 mm below the composite layer. Residual stresses accumulate with an increasing number of laser process tracks. The maximum tensile macro residual stress in the three-track samples reaches about 350 MPa. Preheating the base plate significantly reduces the levels of macroscopic residual stress. The WC phase displayed significant compressive thermal misfit residual stress magnitude, while the Cu matrix exhibited tensile thermal misfit residual stress. Preheating the base plate does not reduce microscopic thermal misfit residual stress levels. In addition, a finite element model was built to investigate temperature and residual stresses in the re-melted NAB samples. The predicted temperature history and residual stress agree with the experimental results.
基金supported financially by the National Key R&D Program of China (No. 2017YFB0703104)the National Natural Science Foundation of China (No. 51401219)
文摘The effects of welding speed on the macroscopic and microscopic residual stresses(RSes) in friction stir welded 17 vol.% SiCp/2009 Al-T4 composite plates were studied via neutron diffraction and an improved decoupled hierarchical multiscale modeling methods. Measurements showed that the macroscopic and total RSes had the largest variations in the longitudinal direction(LD). Increasing the welding speed led to higher values of measured LD macroscopic and total RSes in the matrix. The welding speed also significantly influenced the distributions and magnitudes of the microscopic RSes. The RSes were predicted via an improved hierarchical multiscale model, which includes a constant coefficient of friction based thermal model. The RSes in the composite plates before friction stir welding(FSW) were computed and then set as the initial states of the FSW process during modeling. This improved decoupled multiscale model provided improved predictions of the temperature and RSes compared with our previous model.
基金supported financially by the National Key R&D Program of China(No.2017YFB0703104)the National Natural Science Foundation of China(Nos.51671191 and 51401219)
文摘The deformation, damage and failure behaviors of 17 vol.% SiCp/2009AI composite were studied by micro- scopic finite element （FE） models based on a representative volume element （RVE） and a unit cell. The RVE having a 3D realistic microstructure was constructed via computational modeling technique, in which an interface phase with an average thickness of 50 nm was generated for assessing the effects of interracial properties. Modeling results showed that the RVE based FE model was more accurate than the unit cell based one. Based on the RVE, the predicted stress-strain curve and the fracture morphology agreed well with the experimental results. Furthermore, lower interface strength resulted in lower flow stress and ductile damage of interface phase, thereby leading to decreased elongation. It was revealed that the stress concentration factor of SiC was -2.0： the average stress in SiC particles reached -1200 MPa, while that of the composite reached -600 MPa.
基金the National Key R&D Program of China(No.2017YFB0703104)the National Natural Science Foundation of China(Nos.51871214 and 51931009)the“Key Research Program of Frontier Sciences,CAS”(No.QYZDJ-SSWJSC015)。
文摘One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites(CNT/Al)composites is the load transfer strengthening mechanism(LTSM).However,a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited.In this study,in-situ neutron diffraction study on the tensile deformation of the 3 vol.%CNT/2009 Al composite and the unreinforced 2009 Al alloy was conducted.The{311}and{220}diffraction elastic constants(DECs)of the 2009 Al alloy were determined.Using those DECs the average stress in the 2009 Al matrix of the composite was calculated.Then the average stress in the CNTs was separated by using the stress equilibrium condition.Computational homogenization models were also applied to explain the stress evolution in each phase.Predicted results agree with experimental data.In the present case,the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data,which leads to an increment of yield strength by about 37 MPa.As the result of this work,an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites,which can be applied to optimize the mechanical properties of the composites.
基金financially supported by the National Key R&D Program of China(No.2017YFB0703104)the Key Research Program of Frontier Sciences,CAS(No.QYZDJ-SSW-JSC015)+1 种基金the National Natural Science Foundation of China(Nos.51931009,51871214 and 51871215)the Youth Innovation Promotion Association CAS(No.2020197)。
文摘Thermal residual stress and strain(TRSS)in particle reinforced metal matrix composites(PRMMCs)are believed to cause strengthening effects,according to previous studies.Here,the representative volume element(RVE)based computational homogenization technique was used to study the tensile deformation of PRMMCs with different particle aspect ratios(AR).The influence of TRSS was assessed quantitatively via comparing simulations with or without the cooling process.It was found that the strengthening effect of TRSS was affected by the particle AR.With the average strengthening effect of TRSS,a fast method of introducing the strengthening effect of TRSS to the tensile behavior of PRMMCs was developed.The new method has reduced the computational cost by a factor 2.The effect of TRSS on continuous fiber-reinforced metal matrix composite was found to have a softening-effect during the entire tensile deformation process because of the pre-yield effect caused by the cooling process.
基金financially supported by the National Key R&D Program of China(No.2017YFB0703104)the Key Research Program of Frontier Sciences,CAS(No.QYZDJ-SSW-JSC015)+2 种基金the project of manned spaceflight(No.040103)the National Natural Science Foundation of China(Nos.51931009,51871214 and 51871215)the Youth Innovation Promotion Association CAS(No.2020197)。
文摘The hot deformation behaviors of the bimodal carbon nanotube reinforced 2009Al(CNT/2009Al)composite were studied by establishing processing map and characterizing the microstructure evolution.The results indicate that the grain size in the ultra-fine grained zones was stable during hot deformation,while the coarse grained zones were elongated with their long axis directions tending to be perpendicular to the compression direction.Low temperature with high strain rate(LTHR),as well as high temperature with low strain rate(HTLR)could increase the length/width ratio of the coarse grained zones.However,LTHR and HTLR could cause the instable deformation.The instable deformation at LTHR was induced by severe intragranular plastic deformation and the localized shear crack,while the instable deformation at HTLR resulted from the more deformation component at the coarse grained zones,and the micro-pore initiation due to CNT re-agglomeration at the boundaries between the coarse and the ultra-fine grained zones.
基金the International Partnership Program of the Chinese Academy of Sciences No.114A11-KYSB20200029the National Natural Science Foundation of China(NSFC,Grant No.12041301)the National Key R&D Program of China No.2020YC2201700。
文摘In this paper,we report a real-time Fast Radio Burst(FRB)searching system that has been successfully implemented with the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The relatively small field of view of FAST makes the search for new FRBs challenging,but its high sensitivity significantly improves the accuracy of FRB localization and enables the detection of high-precision neutral hydrogen absorption lines generated by FRBs.Our goal is to develop an FRB searching system capable of realtime detection of FRBs that allows high-time resolution spectro-temporal studies among the repeated bursts,as well as detailed investigations of these bursts and exploration of FRB progenitor models.The data from each beam of the 19-beam receiver are fed into a high-performance computing node server,which performs real-time searches for pulses with a wide dispersion measure(DM)range of 20–10,000 pc cm^(-3) with step efficiency of 25%in real time.Then,the head node server aggregates all the candidate signals from each beam within a given time,determining their authenticity based on various criteria,including arrival time,pulse width,signal-to-noise ratio and coincidence patterns among the 19 beams.Within the 1.05–1.45 GHz operating bandwidth of the FAST 19beam receiver,the system achieves a frequency resolution of 122.07 kHz and a time resolution of 270.336μs.Subsequently,our team detected a series of bursts with a DM of 566 on 2019 August 30 confirming them as FRB121102.The FRB searching system enables the 19-beam receiver of FAST to detect repeated/one-off pulses/bursts in real time.
