The development and supporting technologies of high-strain line pipe steel and pipes used for oil and gas pipeline projects in special geological environments(such as earthquake zone,landslide zone,mine goaf and subsi...The development and supporting technologies of high-strain line pipe steel and pipes used for oil and gas pipeline projects in special geological environments(such as earthquake zone,landslide zone,mine goaf and subsidence zone)is one of the international research hotspots,and it is also a major problem that China's major oil and gas pipeline projects have to solve.Focusing on a series of key technical difficulties in the research&development and application of high-strain line pipe steel and pipes,a number of theoretical and technological innovations have been achieved after more than ten years of joint researches.And the main achievements are as follows.First,the method of applying many different parameters(e.g.stress ratio,yield to tensile ratio and uniform elongation(UEL))to comprehensively characterize and evaluate the deformation behavior of steel pipes is proposed,and a technical index system and standard for the new products of X70HD/X80HD high-strain line pipe steel and pipes are established.Second,a complete set of X70HD/X80HD steel plate manufacturing technology is researched and developed,and the high-strain steel plate with the properties of low yield to tensile ratio,high uniform elongation,high stress ratio and high strength and toughness is worked out.Third,the X70HD/X80HD JCOE and UOE high-strain longitudinal submerged arc welded pipe manufacturing technology is researched and developed,reasonable performance matching between a steel pipe and a welding seam is realized,and the performance deterioration in the process of forming,welding,diameter-expending and thermal coating is solved.Fourth,a full-scale test device of steel pipe internal pressure t bending large deformation is independently developed,and the physical simulation based steel pipe deformation test technology is formed.X70HD/X80HD high-strain line pipe steel and pipes have been applied in the West to East Gas Pipeline,the ChinaeMyanmar Pipeline and other major gas pipeline projects in the large scale,and their application effects are remarkable.To satisfy the new needs of pipeline construction and long-term safe operation under complex geological conditions,some suggestions were put forwarded,such as developing new methods of strain-based pipeline design,and researching and developing or improving the supporting technologies suitable for the higher matching requirements of girth weld,such as welding methods,welding materials,welding processes,and girth weld performance quality and defect control requirements.展开更多
The microstructure evolution and impact-toughness variation of heat-affected zone（HAZ）in X80 highstrain pipeline steel were investigated via a welding thermal-simulation technique,Charpy impact tests,and scanning el...The microstructure evolution and impact-toughness variation of heat-affected zone（HAZ）in X80 highstrain pipeline steel were investigated via a welding thermal-simulation technique,Charpy impact tests,and scanning electron microscopy observations under different welding heat inputs and peak temperatures.The results indicate that when heat input was between 17 and 25kJ·cm^（-1）,the coarse-grained heat-affected zone showed improved impact toughness.When the heat input was increased further,the martensite-austenite（M-A）islands transformed from fine lath into a massive block.Therefore,impact toughness was substantially reduced.When the heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was between 900 and 1300°C,a higher impact toughness was obtained.When heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was 1300°C,the impact toughness value at the second peak temperature of 900°C was higher than that at the second peak temperature of 800°C because of grain refining and uniformly dispersed M-A constituents in the matrix of bainite.展开更多
Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjec...Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope（OM） was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band（ASB） is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.展开更多
An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrica...An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.展开更多
A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the...A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.展开更多
The microstructures in the electroformed copper liners of shapedcharges after high-strain-rate plastic deformation were in-vestigated by transmission electron microscopy(TEM). Meanwhile, theorientation distribution of...The microstructures in the electroformed copper liners of shapedcharges after high-strain-rate plastic deformation were in-vestigated by transmission electron microscopy(TEM). Meanwhile, theorientation distribution of the grains in the recovered slug wasexamined by the electron backscattering Kikuchipattern(EBSP)technique. EBSP analysis illustrated that unlike theas-formed electro- formed copper liners of shaped charges the grainorientations in the recovered slug are distributed along randomly allthe directions after undergoing heavily strain deformation athigh-strain rate. Optical microscopy shows a typicalrecrystallization structure, and TEM exam- ination revealsdislocation cells existed in the thin foil specimen. These resultsindicate that dynamic recovery and recrystallization occur duringthis plastic deformation process, and the associated deformationtemperature is considered to be higher than 0.6 times the meltingpoint of copper.展开更多
The as-formed and post-deformed microstructures in both electroformed and spin-formed copper liners of shaped charge were studied by optical microscopy(OM), electron backscattering Kikuchi patterns(EBSP) technique and...The as-formed and post-deformed microstructures in both electroformed and spin-formed copper liners of shaped charge were studied by optical microscopy(OM), electron backscattering Kikuchi patterns(EBSP) technique and transmission electron microscopy(TEM). The deformation was carried out at an ultra-high strain rate. OM analysis shows that the initial grains of the electroformed copper liner are finer than those of the spin-formed copper liners. Meanwhile, EBSP analysis reveals that the fiber texture exists in the electroformed copper liners, whereas there is no texture observed in the spin-formed copper liners before deformation. Having undergone high-strain-rate deformation the grains in the recovered slugs, which are transformed from both the electroformed and spin-formed copper liners, all become small. TEM observations of the above two kinds of post-deformed specimens show the existence of cellular structures characterized by tangled dislocations and subgrain boundaries consisting of dislocation arrays. These experimental results indicate that dynamic recovery and recrystallization play an important role in the high-strain-rate deformation process.展开更多
A fictitious soil pile(FSP)model is developed to simulate the behavior of pipe piles with soil plugs undergoing high-strain dynamic impact loading.The developed model simulates the base soil with a fictitious hollow p...A fictitious soil pile(FSP)model is developed to simulate the behavior of pipe piles with soil plugs undergoing high-strain dynamic impact loading.The developed model simulates the base soil with a fictitious hollow pile fully filled with a soil plug extending at a cone angle from the pile toe to the bedrock.The friction on the outside and inside of the pile walls is distinguished using different shaft models,and the propagation of stress waves in the base soil and soil plug is considered.The motions of the pile—soil system are solved by discretizing them into spring-mass model based on the finite difference method.Comparisons of the predictions of the proposed model and conventional numerical models,as well as measurements for pipe piles in field tests subjected to impact loading,validate the accuracy of the proposed model.A parametric analysis is conducted to illustrate the influence of the model parameters on the pile dynamic response.Finally,the effective length of the FSP is proposed to approximate the affected soil zone below the pipe pile toe,and some guidance is provided for the selection of the model parameters.展开更多
The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-ba...The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-bar) tests of the cylindrical specimens with five different steel fiber volumetric fractions.The properties of wave stress transmission,failure,strength,and energy consumption of RPC with varied fiber volumes and impact strain rates were analyzed.The influences of impact strain rates and fiber volumes on those properties were characterized as well.The general forms of the dynamic stress-strain relationships of RPC were modeled based on the experimental data.The investigations indicate that for the plain RPC the stress response is greater than the strain response,showing strong brittle performance.The RPC with a certain volume of fibers sustains higher strain rate impact and exhibits better deformability as compared with the plain RPC.With a constant fiber fraction,the peak compressive strength,corresponding peak strain and the residual strain of the fiber-reinforced RPC rise by varying amounts when the impact strain rate increases,with the residual strain demonstrating the greatest increment.Elevating the fiber content makes trivial contribution to improving the residual deformability of RPC when the impact strain rate is constant.The tests also show that the fiber content affects the peak compressive strength and the peak deformability of RPC in a different manner.With a constant impact strain rate and the fiber fraction less than 1.75%,the peak compressive strength rises with an increasing fiber volume.The peak compressive strength tends to decrease as the fiber volume exceeds 1.75%.The corresponding peak strain,however,incessantly rises with the increasing fiber volume.The total energy Edisp that RPC consumed during the period from the beginning of impacts to the time of residual strains elevates with the fiber volume increment as long as the fiber fraction is not larger than 2%.It turns to decrease if the fiber volume exceeds 2%.The added fibers make various contributions to enhancing the capability of RPC to consume energy at different loading stages.If the fiber fraction is not larger than 2%,the added fibers make more contribution to enhancing the energy consumption ability of RPC in the period before the peak strain than in the period after the peak strain.The impact strain rate,however,distinctively affects the total energy that RPC consumed and the energy consumed in the different loading periods.The higher the impact strain rate,the more the energy consumed in the stages and therefore the higher the dynamic impact toughness.The empirical relationships of the peak compressive strength,corresponding peak strain,residual strain,total consumed energy and the energy consumed in the varied periods with the impact strain rate and the fiber fraction are derived.Four generalized forms of the dynamic impact stress-strain responses of RPC are formulated by normalizing stresses and strains as the generalized coordinates and by taking account of the influences of impact strain rates and fiber volumetric fractions.展开更多
We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73....We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73.2%.Our ab initio calculations reveal that such pathway cannot work in covalent systems like graphene and BN;for monolayer with metallic bonds like stanene,stanane and In Bi that have all been synthesized,however,such pathway can be feasible with a low switching barrier(<0.15 eV)and stress(<graphene upon 1%tensile strain),also with the highest energy/stress point in the elastic region.Their distinct behaviors are attributed to the different feature of covalent bonds and metallic bonds:the former is rigid with directionality,while the latter is malleable with ductility.A general trend of linear decrease in switching barrier with uprising metallicity for the same group compounds is revealed.Similar behaviors can be extended to bulk zinc-blended or wurtzite structure that can be deemed as multilayer stacking of buckled monolayer.Binary compounds like In Bi monolayer are even multiferroics with both in-plane and vertical ferroelectricity as well as nontrivial topological properties.展开更多
基金Project supported by the National Key R&D Program of China“Research and Development of High-strain Marine Line Pipes”(No.2018YFC03010300)PetroChina's Major Science&Technology Project“Research on Key Technologies for Controlling Pipe Fracture and Deformation in the Second West-East Gas Pipeline”(No.2009E-0105)+1 种基金“Research and Development of Special Welded Pipes for the Second West-East Gas Pipeline”(No.2009E-0104)CNPC's Science&Technology Infrastructure Program“CNPC Infrastructure Construction of Key Laboratory for Petroleum Tubular Engineering”(No.07H611).
文摘The development and supporting technologies of high-strain line pipe steel and pipes used for oil and gas pipeline projects in special geological environments(such as earthquake zone,landslide zone,mine goaf and subsidence zone)is one of the international research hotspots,and it is also a major problem that China's major oil and gas pipeline projects have to solve.Focusing on a series of key technical difficulties in the research&development and application of high-strain line pipe steel and pipes,a number of theoretical and technological innovations have been achieved after more than ten years of joint researches.And the main achievements are as follows.First,the method of applying many different parameters(e.g.stress ratio,yield to tensile ratio and uniform elongation(UEL))to comprehensively characterize and evaluate the deformation behavior of steel pipes is proposed,and a technical index system and standard for the new products of X70HD/X80HD high-strain line pipe steel and pipes are established.Second,a complete set of X70HD/X80HD steel plate manufacturing technology is researched and developed,and the high-strain steel plate with the properties of low yield to tensile ratio,high uniform elongation,high stress ratio and high strength and toughness is worked out.Third,the X70HD/X80HD JCOE and UOE high-strain longitudinal submerged arc welded pipe manufacturing technology is researched and developed,reasonable performance matching between a steel pipe and a welding seam is realized,and the performance deterioration in the process of forming,welding,diameter-expending and thermal coating is solved.Fourth,a full-scale test device of steel pipe internal pressure t bending large deformation is independently developed,and the physical simulation based steel pipe deformation test technology is formed.X70HD/X80HD high-strain line pipe steel and pipes have been applied in the West to East Gas Pipeline,the ChinaeMyanmar Pipeline and other major gas pipeline projects in the large scale,and their application effects are remarkable.To satisfy the new needs of pipeline construction and long-term safe operation under complex geological conditions,some suggestions were put forwarded,such as developing new methods of strain-based pipeline design,and researching and developing or improving the supporting technologies suitable for the higher matching requirements of girth weld,such as welding methods,welding materials,welding processes,and girth weld performance quality and defect control requirements.
文摘The microstructure evolution and impact-toughness variation of heat-affected zone（HAZ）in X80 highstrain pipeline steel were investigated via a welding thermal-simulation technique,Charpy impact tests,and scanning electron microscopy observations under different welding heat inputs and peak temperatures.The results indicate that when heat input was between 17 and 25kJ·cm^（-1）,the coarse-grained heat-affected zone showed improved impact toughness.When the heat input was increased further,the martensite-austenite（M-A）islands transformed from fine lath into a massive block.Therefore,impact toughness was substantially reduced.When the heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was between 900 and 1300°C,a higher impact toughness was obtained.When heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was 1300°C,the impact toughness value at the second peak temperature of 900°C was higher than that at the second peak temperature of 800°C because of grain refining and uniformly dispersed M-A constituents in the matrix of bainite.
基金financially supported by the Ministry of Science and Technology of China (No. 2012DFG51540)
文摘Split Hopkinson pressure bar test system was used to investigate the plastic deformation behavior and dynamic response character of a-type Ti–5Al–2.5Sn ELI and near a-type Ti–8Al–1Mo–1V titanium alloy when subjected to dynamic loading. In the present work, stress–strain curves at strain rate from 1.5 9 103to 5.0 9 103s-1were analyzed, and optical microscope（OM） was used to reveal adiabatic shearing behavior of recovered samples. Results show that both the two alloys manifest significant strain hardening effects. Critical damage strain rate of the two alloys is about 4.3 9 103s-1, under which the impact absorbs energy of Ti–5Al–2.5Sn ELI and Ti–8Al–1Mo–1V are 560 and 470 MJ m-3, respectively. Both of them fracture along the maximum shearing strength orientation, an angle of 45° to the compression axis. No adiabatic shear band（ASB） is found in Ti–5Al–2.5Sn ELI alloy, whereas several ASBs with different widths exist without regular direction in Ti–8Al–1Mo–1V alloy.
文摘An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.
基金support from the Exploring Youth Project of Zhejiang Natural Science Foundation (Grant No.LQ24E080009)the Key Project of Natural Science Foundation of Zhejiang Province (Grant No.LXZ22E080001)the National Natural Science Foundation of China (Grant No.52108347).
文摘A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.
基金financially supported by the National Natural Science Foundation of China (No.59971008).
文摘The microstructures in the electroformed copper liners of shapedcharges after high-strain-rate plastic deformation were in-vestigated by transmission electron microscopy(TEM). Meanwhile, theorientation distribution of the grains in the recovered slug wasexamined by the electron backscattering Kikuchipattern(EBSP)technique. EBSP analysis illustrated that unlike theas-formed electro- formed copper liners of shaped charges the grainorientations in the recovered slug are distributed along randomly allthe directions after undergoing heavily strain deformation athigh-strain rate. Optical microscopy shows a typicalrecrystallization structure, and TEM exam- ination revealsdislocation cells existed in the thin foil specimen. These resultsindicate that dynamic recovery and recrystallization occur duringthis plastic deformation process, and the associated deformationtemperature is considered to be higher than 0.6 times the meltingpoint of copper.
基金Project(571014569) supported by the National Natural Science Foundation of China
文摘The as-formed and post-deformed microstructures in both electroformed and spin-formed copper liners of shaped charge were studied by optical microscopy(OM), electron backscattering Kikuchi patterns(EBSP) technique and transmission electron microscopy(TEM). The deformation was carried out at an ultra-high strain rate. OM analysis shows that the initial grains of the electroformed copper liner are finer than those of the spin-formed copper liners. Meanwhile, EBSP analysis reveals that the fiber texture exists in the electroformed copper liners, whereas there is no texture observed in the spin-formed copper liners before deformation. Having undergone high-strain-rate deformation the grains in the recovered slugs, which are transformed from both the electroformed and spin-formed copper liners, all become small. TEM observations of the above two kinds of post-deformed specimens show the existence of cellular structures characterized by tangled dislocations and subgrain boundaries consisting of dislocation arrays. These experimental results indicate that dynamic recovery and recrystallization play an important role in the high-strain-rate deformation process.
基金This work was supported by the Key Project of Natural Science Foundation of Zhejiang Province(No.LXZ22E080001)National Natural Science Foundation of China(Grant Nos.51779217,52178358,and 52108349)China Scholarship Council(No.202006320262).We gratefully acknowledge this support.
文摘A fictitious soil pile(FSP)model is developed to simulate the behavior of pipe piles with soil plugs undergoing high-strain dynamic impact loading.The developed model simulates the base soil with a fictitious hollow pile fully filled with a soil plug extending at a cone angle from the pile toe to the bedrock.The friction on the outside and inside of the pile walls is distinguished using different shaft models,and the propagation of stress waves in the base soil and soil plug is considered.The motions of the pile—soil system are solved by discretizing them into spring-mass model based on the finite difference method.Comparisons of the predictions of the proposed model and conventional numerical models,as well as measurements for pipe piles in field tests subjected to impact loading,validate the accuracy of the proposed model.A parametric analysis is conducted to illustrate the influence of the model parameters on the pile dynamic response.Finally,the effective length of the FSP is proposed to approximate the affected soil zone below the pipe pile toe,and some guidance is provided for the selection of the model parameters.
基金supported by the National Natural Science Foundation of China (Grant No. 50974125)the National Basic Research Project of China ("973" Project) (Grant Nos. 2010CB226804, 2002CB412705)the Natural Sciences and Engineering Research Council of Canada (PGS-D2-2006) and the Beijing Key Laboratory Projects
文摘The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-bar) tests of the cylindrical specimens with five different steel fiber volumetric fractions.The properties of wave stress transmission,failure,strength,and energy consumption of RPC with varied fiber volumes and impact strain rates were analyzed.The influences of impact strain rates and fiber volumes on those properties were characterized as well.The general forms of the dynamic stress-strain relationships of RPC were modeled based on the experimental data.The investigations indicate that for the plain RPC the stress response is greater than the strain response,showing strong brittle performance.The RPC with a certain volume of fibers sustains higher strain rate impact and exhibits better deformability as compared with the plain RPC.With a constant fiber fraction,the peak compressive strength,corresponding peak strain and the residual strain of the fiber-reinforced RPC rise by varying amounts when the impact strain rate increases,with the residual strain demonstrating the greatest increment.Elevating the fiber content makes trivial contribution to improving the residual deformability of RPC when the impact strain rate is constant.The tests also show that the fiber content affects the peak compressive strength and the peak deformability of RPC in a different manner.With a constant impact strain rate and the fiber fraction less than 1.75%,the peak compressive strength rises with an increasing fiber volume.The peak compressive strength tends to decrease as the fiber volume exceeds 1.75%.The corresponding peak strain,however,incessantly rises with the increasing fiber volume.The total energy Edisp that RPC consumed during the period from the beginning of impacts to the time of residual strains elevates with the fiber volume increment as long as the fiber fraction is not larger than 2%.It turns to decrease if the fiber volume exceeds 2%.The added fibers make various contributions to enhancing the capability of RPC to consume energy at different loading stages.If the fiber fraction is not larger than 2%,the added fibers make more contribution to enhancing the energy consumption ability of RPC in the period before the peak strain than in the period after the peak strain.The impact strain rate,however,distinctively affects the total energy that RPC consumed and the energy consumed in the different loading periods.The higher the impact strain rate,the more the energy consumed in the stages and therefore the higher the dynamic impact toughness.The empirical relationships of the peak compressive strength,corresponding peak strain,residual strain,total consumed energy and the energy consumed in the varied periods with the impact strain rate and the fiber fraction are derived.Four generalized forms of the dynamic impact stress-strain responses of RPC are formulated by normalizing stresses and strains as the generalized coordinates and by taking account of the influences of impact strain rates and fiber volumetric fractions.
基金supported by the National Natural Science Foundation of China(21573084).
文摘We propose a possible ferroelastic switching pathway of two-dimensional(2 D)honeycomb lattice(including graphene,BN,stanene,etc.)that may swap its armchair and zigzag direction,reversing an unprecedented strain of 73.2%.Our ab initio calculations reveal that such pathway cannot work in covalent systems like graphene and BN;for monolayer with metallic bonds like stanene,stanane and In Bi that have all been synthesized,however,such pathway can be feasible with a low switching barrier(<0.15 eV)and stress(<graphene upon 1%tensile strain),also with the highest energy/stress point in the elastic region.Their distinct behaviors are attributed to the different feature of covalent bonds and metallic bonds:the former is rigid with directionality,while the latter is malleable with ductility.A general trend of linear decrease in switching barrier with uprising metallicity for the same group compounds is revealed.Similar behaviors can be extended to bulk zinc-blended or wurtzite structure that can be deemed as multilayer stacking of buckled monolayer.Binary compounds like In Bi monolayer are even multiferroics with both in-plane and vertical ferroelectricity as well as nontrivial topological properties.
