Nine square concrete columns including 6 CFRP/ECCs and 3 concrete columns are prepared,which have cross-section of 200 mm×200 mm and height of 600 mm.The CFRP tubes with fibers oriented at hoop direction were man...Nine square concrete columns including 6 CFRP/ECCs and 3 concrete columns are prepared,which have cross-section of 200 mm×200 mm and height of 600 mm.The CFRP tubes with fibers oriented at hoop direction were manufactured to have 3 or 5 layers of CFRP with 10 mm, 20 mm,or 40 mm rounding corner radii at vertical edges.A 100 mm overlap in the direction of fibers was provided to ensure proper bond.Uniaxial compression tests were conducted to investigate the compressive behavior.It is evident that the CFRP t...展开更多
In this study,interconnected porous Mg-2Zn-xY alloys with different phase compositions were prepared by various Y additions(x=0.4,3,and 6 wt.%)to adjust the compressive properties and energy absorption characteristics...In this study,interconnected porous Mg-2Zn-xY alloys with different phase compositions were prepared by various Y additions(x=0.4,3,and 6 wt.%)to adjust the compressive properties and energy absorption characteristics.Several characterization methods were then applied to identify the microstructure of the porous Mg-Zn-Y and describe the details of the second phase.Compressive tests were performed at room temperature(RT),200℃,and 300℃to study the impact of the Y addition and testing temperature on the compressive properties of the porous Mg-Zn-Y.The experimental results showed that a high Y content promotes a microstructure refinement and increases the volume fraction of the second phase.When the Y content increases,different Mg-Zn-Y ternary phases appear:I-phase(Mg_(3)Zn_(6)Y),W-phase(Mg_(3)Zn_(3)Y_(2)),and LPSO phase(Mg_(12)ZnY).When the Y content ranges between 0.4%and 6%,the compressive strength increases from 6.30MPa to 9.23 MPa,and the energy absorption capacity increases from 7.33 MJ/m^(3)to 10.97 MJ/m^(3)at RT,which is mainly attributed to the phase composition and volume fraction of the second phase.However,the average energy absorption efficiency is independent of the Y content.In addition,the compressive deformation behaviors of the porous Mg-Zn-Y are altered by the testing temperature.The compressive strength and energy absorption capacity of the porous Mg-Zn-Y decrease due to the softening effect of the high temperature on the struts.The deformation behaviors at different temperatures are finally observed to reflect the failure mechanisms of the struts.展开更多
In this work, porous Ti6Al4V alloys with 30%–70% porosity for biomedical applications were fabricated by diffusion bonding of alloy meshes. Pore structure was characterized by Micro-CT and SEM. Compressive behavior i...In this work, porous Ti6Al4V alloys with 30%–70% porosity for biomedical applications were fabricated by diffusion bonding of alloy meshes. Pore structure was characterized by Micro-CT and SEM. Compressive behavior in the out-of-plane direction and biocompatibility with cortical bone were studied. The results reveal that the fabricated porous Ti6Al4V alloys possess anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The average pore size of porous Ti6Al4V alloys with 30%–70% porosity is in the range of 240–360 μm. By tailoring diffusion bonding temperature, aspect ratio of alloy meshes and porosity, porous Ti6Al4V alloys with different compressive properties can be obtained, for instance, Young's modulus and yield stress in the ranges of 4–40 GPa and70–500 MPa, respectively. Yield stress of porous Ti6Al4V alloys fabricated by diffusion bonding is close to that of alloys fabricated by rapid prototyping, but higher than that of fabricated by powder sintering and space-holder method. Diffusion bonding temperature has some effects on the yield stress of porous Ti6Al4V alloys, but has a minor effect on the Young's modulus. The relationship between compressive properties and relative density conforms well to the Gibson–Ashby model. The Young's modulus is linear with the aspect ratio, while the yield stress is linear with the square of aspect ratio of alloy meshes. Porous Ti6Al4V alloys with 60%–70% porosity have potential for cortical bone implant applications.展开更多
Lattice structures have numerous outstanding characteristics,such as light weight,high strength,excellent shock resistance,and highly efficient heat dissipation.In this work,by combining experimental and numerical met...Lattice structures have numerous outstanding characteristics,such as light weight,high strength,excellent shock resistance,and highly efficient heat dissipation.In this work,by combining experimental and numerical methods,we investigate the compressive behavior and energy absorption of lattices made through the stereolithography apparatus process.Four types of lattice structures are considered:(i)Uniform bodycentered-cubic(U-BCC);(ii)graded body-centered-cubic(G-BCC);(iii)uniform body-centered-cubic with z-axis reinforcement(U-BCCz);and(iv)graded body-centeredcubic with z-axis reinforcement(G-BCCz).We conduct compressive tests on these four lattices and numerically simulate the compression process through the finite element method.Analysis results show that BCCz has higher modulus and strength than BCC.In addition,uniform lattices show better energy absorption capabilities at small compression distances,while graded lattices absorb more energy at large compression distances.The good correlation between the simulation results and the experimental phenomena demonstrates the validity and accuracy of the present investigation method.展开更多
Understanding the mechanical behavior of hybrid fiber-reinforced concrete(HFRC),a composite material,is crucial for the design of HFRC and HFRC structures.In this study,a series of compression experiments were perform...Understanding the mechanical behavior of hybrid fiber-reinforced concrete(HFRC),a composite material,is crucial for the design of HFRC and HFRC structures.In this study,a series of compression experiments were performed on hybrid steelpolyvinyl alcohol(PVA)fiber-reinforced concrete containing fly ash and slag powder,with a focus on the fiber content/ratio effect on its compressive behavior;a new approach was built to model the compression behavior of HFRC by using an artificial neural network(ANN)method.The proposed ANN model incorporated two new developments:the prediction of the compressive stress-strain curve and consideration of 23 features of components of HFRC.To build a database for the ANN model,relevant published data were also collected.Three indices were used to train and evaluate the ANN model.To highlight the performance of the ANN model,it was compared with a traditional equation-based model.The results revealed that the relative errors of the predicted compressive strength and strain corresponding to compressive strength of the ANN model were close to 0,while the corresponding values from the equation-based model were higher.Therefore,the ANN model is better able to consider the effect of different components on the compressive behavior of HFRC in terms of compressive strength,the strain corresponding to compressive strength,and the compressive stress-strain curve.Such an ANN model could also be a good tool to predict the mechanical behavior of other composite materials.展开更多
In order to optimize the out-of-plane compression performance of the wood structure,wood-based 2-D lattice structures were designed and manufactured with oriented strand board as the panel and birch round stick as the...In order to optimize the out-of-plane compression performance of the wood structure,wood-based 2-D lattice structures were designed and manufactured with oriented strand board as the panel and birch round stick as the core by using a simple insert-glue method.In this experiment,the different thicknesses of the upper and lower panels,the different shavings arrangement directions of the upper and lower panels and the different configurations of the specimens were used to analyze the compression performance of the specimens under multivariable conditions.Through the combination of experimental test and theoretical analysis,we analyzed and compared different failure types of the structure and multiple compression parameters.The results showed that the shavings arrangement direction of the panel has a more important influence on the whole specimen than the thickness of the panel,especially the transverse shavings of the panel can withstand greater shear stress than the longitudinal shavings for a specimen.展开更多
The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinso...The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.展开更多
As a new type of lightweight structure,metallic lattice structure has higher stiffness and strength to weight ratio.To freely obtain 316L lattice structures with designed cell structure and adjustable porosity,additiv...As a new type of lightweight structure,metallic lattice structure has higher stiffness and strength to weight ratio.To freely obtain 316L lattice structures with designed cell structure and adjustable porosity,additive manufacturing combined with investment casting was conducted to fabricate the 316L lattice structures with Kelvin cell.The compression simulation of 316L lattice structures with different porosities was carried out by using the finite element method.The numerical simulation results were verified by compression experiment,and the simulated results were consistent with the compression tests.The compressive mechanical properties of 316L lattice structures are directly related to porosity and independent of strut diameters.The 316L lattice structures with Kelvin cell have a smooth stress-strain curve and obvious plastic platform,and the hump stress-strain curves are avoided.展开更多
Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coati...Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400℃using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.展开更多
Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads.In this study,a reference UHPCC mixture with no fiber reinforcement and...Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads.In this study,a reference UHPCC mixture with no fiber reinforcement and four mixtures with a single type of fiber reinforcement or hybrid fiber reinforcements of straight smooth and end hook type of steel fibers were prepared.Split Hopkinson pressure bar (SHPB) was performed to investigate the dynamic compression behavior of UHPCC and X-CT test and 3D reconstruction technology were used to indicate the failure process of UHPCC under impact loading.Results show that UHPCC with 1% straight smooth fiber and 2% end hook fiber reinforcements demonstrated the best static and dynamic mechanical properties.When the hybrid steel fiber reinforcements are added in the concrete,it may need more impact energy to break the matrix and to pull out the fiber reinforcements,thus,the mixture with hybrid steel fiber reinforcements demonstrates excellent dynamic compressive performance.展开更多
It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmosp...It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmospheres,and compressive experiments in the ambient and 150℃,were conducted for three kinds of PICA-like materials(CF/PR-Si,CBCF/PR-SiOC and NQF/PR-Si composites).The traditional carbon/phenolic(C/PR)braided composites were also used for comparison.PICA-like materials have the better thermal insulation than traditional C/PR composite,especially for CBCF/PR-SiOC composite.The ablation behavior of CF/PR-Si and CBCF/PR-SiOC PICA-like materials in the CO2 atmosphere can produce a large amount of SiO2 in the form of coatings,oxide layers and skeletons on the ablated surface,which are greatly different from that in the air atmosphere.The compressive behavior of PICA-like material is greatly depended on the fiber fabrics,and exhibits the large discrete characteristics.The longer fiber in the PICA-like materials plays the role in maintaining the material integrity,while it may increase the thermal conductivity.展开更多
In the present research,results of buckling analysis of 384 finite element models,verified using three different test results obtained from three separate experimental investigations,were used to study the effects of ...In the present research,results of buckling analysis of 384 finite element models,verified using three different test results obtained from three separate experimental investigations,were used to study the effects of five parameters such as D/t,L/D,imperfection,mesh size and mesh size ratio.Moreover,proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD,ISO 19902,and NORSOK N-004 have been compared to FE and experimental results.One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of compressive members to properly investigate the interaction of global and local buckling which leads to the correct estimation of performance levels and ductility.Achievement of the proper compressive behavior of tubular members validated by experimental data is the main purpose of this paper.Modeling of compressive braces of offshore jacket platforms by 3D shell or solid elements can consider buckling modes and deformations due to local buckling.ABAQUS FE software is selected for FE modeling.The scope of action of each of elastic buckling,plastic buckling,and compressive yielding for various L/r ratios is described.Furthermore,the most affected part of each parameter on the buckling capacity curve is specified.The pushover results of the Resalat Jacket with proper versus improper modeling of compressive members have been compared as a case study.According to the results,applying improper mesh size for compressive members can under-predict the ductility by 33%and under-estimate the lateral loading capacity by up to 8%.Regarding elastic stiffness and post-buckling strength,the mesh size ratio is introduced as the most effective parameter.Besides,imperfection is significantly the most important parameter in terms of critical buckling load.展开更多
Open cell steel foams were successfully fabricated through the powder metallurgy route using urea granules as the water leachable space holder in the present study.The influence of different amounts of phosphorus(0,0....Open cell steel foams were successfully fabricated through the powder metallurgy route using urea granules as the water leachable space holder in the present study.The influence of different amounts of phosphorus(0,0.5wt%,1wt%,2wt%,and 4wt%)was investigated on the cell morphology,porosity,microstructure of cell walls,and mechanical properties of steel foams.The cell morphology and microstructure of the cell walls were evaluated using an optical microscope equipped with image processing software and a scanning electron microscope equipped with an energy dispersive X-ray spectrometer.In addition,the compression tests were conducted on the steel foams using a universal testing machine.Based on microscopic images,the porous structure consists of spherical cells and irregularly shaped pores that are distributed in the cell walls.The results indicated that by increasing the phosphorus content,the porosity increases from 71.9%to 83.2%.The partially distributed ferrite and fine pearlite was observed in the microstructure of the cell walls,andα-Fe and Fe3P eutectic extended between the boundaries of agglomerated iron particles.Furthermore,elastic and long saw-toothed plateau regions were observed before fracture in the compressional stress–strain curves.According to the results,by increasing the phosphorus content from 0 to 4wt%,the plateau region of the stress–strain curves shifts to the right and upward.Therefore,increasing phosphorus content causes improvement in the mechanical properties of steel foams.展开更多
As a wide-bandgap semiconductor, 4H-SiC is an ideal material for high-power and high-frequency devices, and plays an increasingly important role in developing our country’s future electric vehicles and 5G techniques....As a wide-bandgap semiconductor, 4H-SiC is an ideal material for high-power and high-frequency devices, and plays an increasingly important role in developing our country’s future electric vehicles and 5G techniques. Practical applications of SiCbased devices largely depend on their mechanical performance and reliability at the micro-and nanoscales. In this paper, singlecrystal [0001]-oriented 4H-SiC nanopillars with the diameter ranging from ~200 to 700 nm were microfabricated and then characterized by in situ nanomechanical testing under SEM/TEM at room temperature. Loading-unloading compression tests were performed, and large, fully reversible elastic strain up to ~6.2% was found in nanosized pillars. Brittle fracture still occurred when the max strain reached ~7%, with corresponding compressive strength above 30 GPa, while in situ TEM observation showed few dislocations activated during compression along the [0001] direction. Besides robust microelectromechanical system(MEMS), flexible device and nanocomposite applications, the obtained large elasticity in [0001]-oriented 4H-SiC nanopillars can offer a fertile opportunity to modulate their electron mobility and bandgap structure by nanomechanical straining,the so called "elastic strain engineering", for novel electronic and optoelectronic applications.展开更多
Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature.Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbid...Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature.Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge.In this study,it is proposed that the hightemperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated Ta C nanoparticles,through solid solution strengthening of Ta atoms.Based on the designed experiments and microstructural characterizations combined with finite element simulations,the grain morphology,stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides.The mechanisms of Ta dissolving in WC crystal and strengthening ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale.This study opens a new perspective to modulate hard phases of cemented carbides for improving their hightemperature performance,which will be applicable to a variety of cermet and ceramic-based composite materials.展开更多
The deformation mode of{332}<113>twinning(hereafter called 332T)has often been observed under the plastic flow in metastableβtitanium alloys with body-centered cubic(BCC)structure,which contributes to improving...The deformation mode of{332}<113>twinning(hereafter called 332T)has often been observed under the plastic flow in metastableβtitanium alloys with body-centered cubic(BCC)structure,which contributes to improving the mechanical performance.Herein,we report a structure of compressive deformation-induced primary 332T with hierarchical and/or heterogeneous composite sub-structure in a Twin-Induced Plasticity(TWIP)βTi-alloy under uniaxial compression.The detailed structural characterization after compressive deformation revealed that the sub-structure,including secondary 332T and secondary{112}<111>twinning,formed inside the 332T structure,which constitutes a hierarchical and/or heterogeneous structure at micro-and nano-scale and consequently contributes to the high strength,large ductility and enhanced strain-hardening behavior.展开更多
The goal of this study is to establish relationships between the hot compression deformation behaviors and the fractal dimension of primary phase morphology of TA15 titanium alloy using the analytical methods of metal...The goal of this study is to establish relationships between the hot compression deformation behaviors and the fractal dimension of primary phase morphology of TA15 titanium alloy using the analytical methods of metallurgical microscope and transmission electron microscope coupled with box-counting dimension method. The hot compression deformation behaviors vary with decreasing fractal dimension owing to the change of microstructure caused by different parameters of the hot compressive deformation.The results indicate that TA15 alloy shows dynamic recrystallization characteristics at deformation temperature lower than 850℃while fractal dimension exhibits a moderate decreasing trend with the temperature increasing,and shows dynamic recovery characteristics at deformation temperature higher than 850℃while fractal dimension reduces rapidly with the temperature increasing.The fractal dimension displays non-linear relationship with fraction of primary phase and with aspect ratio of primary phase.展开更多
To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated ...To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading.Subsequently,the failure process and failure modes were observed,and load-displacement curves as well as the strain of various materials were analyzed.The effects on the substitution percentage of recycled coarse aggregate(RCA),width of CFRP strips,spacing of CFRP strips and strength of recycled aggregate concrete(RAC)on the axial compression properties of columns were also analyzed in the experimental investigation.Furthermore,the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study.The results show that the first to reach the yield state was the profile steel in the columns,then the longitudinal rebars and stirrups yielded successively,and finally RAC was crushed as well as the CFRP strips was also broken.The replacement rate of RCA has little effect on the columns,and with the substitution rate of RCA from 0 to 100%,the bearing capacity of columns decreased by only 4.8%.Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns,the maximum increase was 10.5%or 11.4%,and the ductility of columns was significantly enhanced.Obviously,CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns.On this basis,considering the restraint effect of CFRP strips and the adverse effects of RCA,the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed.展开更多
文摘Nine square concrete columns including 6 CFRP/ECCs and 3 concrete columns are prepared,which have cross-section of 200 mm×200 mm and height of 600 mm.The CFRP tubes with fibers oriented at hoop direction were manufactured to have 3 or 5 layers of CFRP with 10 mm, 20 mm,or 40 mm rounding corner radii at vertical edges.A 100 mm overlap in the direction of fibers was provided to ensure proper bond.Uniaxial compression tests were conducted to investigate the compressive behavior.It is evident that the CFRP t...
基金supported by"The National Key Research and Development Program of China(No.2018 YFA0703300)""Science and Technology Project of Education Department of Jilin Province(No.JJKH20231086KJ)"Development Project of Jilin Province(No.2021C038-4)。
文摘In this study,interconnected porous Mg-2Zn-xY alloys with different phase compositions were prepared by various Y additions(x=0.4,3,and 6 wt.%)to adjust the compressive properties and energy absorption characteristics.Several characterization methods were then applied to identify the microstructure of the porous Mg-Zn-Y and describe the details of the second phase.Compressive tests were performed at room temperature(RT),200℃,and 300℃to study the impact of the Y addition and testing temperature on the compressive properties of the porous Mg-Zn-Y.The experimental results showed that a high Y content promotes a microstructure refinement and increases the volume fraction of the second phase.When the Y content increases,different Mg-Zn-Y ternary phases appear:I-phase(Mg_(3)Zn_(6)Y),W-phase(Mg_(3)Zn_(3)Y_(2)),and LPSO phase(Mg_(12)ZnY).When the Y content ranges between 0.4%and 6%,the compressive strength increases from 6.30MPa to 9.23 MPa,and the energy absorption capacity increases from 7.33 MJ/m^(3)to 10.97 MJ/m^(3)at RT,which is mainly attributed to the phase composition and volume fraction of the second phase.However,the average energy absorption efficiency is independent of the Y content.In addition,the compressive deformation behaviors of the porous Mg-Zn-Y are altered by the testing temperature.The compressive strength and energy absorption capacity of the porous Mg-Zn-Y decrease due to the softening effect of the high temperature on the struts.The deformation behaviors at different temperatures are finally observed to reflect the failure mechanisms of the struts.
基金supported by the National Basic Research Program of China (No. 2012CB619101)
文摘In this work, porous Ti6Al4V alloys with 30%–70% porosity for biomedical applications were fabricated by diffusion bonding of alloy meshes. Pore structure was characterized by Micro-CT and SEM. Compressive behavior in the out-of-plane direction and biocompatibility with cortical bone were studied. The results reveal that the fabricated porous Ti6Al4V alloys possess anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The average pore size of porous Ti6Al4V alloys with 30%–70% porosity is in the range of 240–360 μm. By tailoring diffusion bonding temperature, aspect ratio of alloy meshes and porosity, porous Ti6Al4V alloys with different compressive properties can be obtained, for instance, Young's modulus and yield stress in the ranges of 4–40 GPa and70–500 MPa, respectively. Yield stress of porous Ti6Al4V alloys fabricated by diffusion bonding is close to that of alloys fabricated by rapid prototyping, but higher than that of fabricated by powder sintering and space-holder method. Diffusion bonding temperature has some effects on the yield stress of porous Ti6Al4V alloys, but has a minor effect on the Young's modulus. The relationship between compressive properties and relative density conforms well to the Gibson–Ashby model. The Young's modulus is linear with the aspect ratio, while the yield stress is linear with the square of aspect ratio of alloy meshes. Porous Ti6Al4V alloys with 60%–70% porosity have potential for cortical bone implant applications.
基金This work was supported by the National Key Research and Development Program of China(Grant No.2017YFB1102800)the National Natural Science Foundation of China(Grant Nos.11872310 and 5171101743).
文摘Lattice structures have numerous outstanding characteristics,such as light weight,high strength,excellent shock resistance,and highly efficient heat dissipation.In this work,by combining experimental and numerical methods,we investigate the compressive behavior and energy absorption of lattices made through the stereolithography apparatus process.Four types of lattice structures are considered:(i)Uniform bodycentered-cubic(U-BCC);(ii)graded body-centered-cubic(G-BCC);(iii)uniform body-centered-cubic with z-axis reinforcement(U-BCCz);and(iv)graded body-centeredcubic with z-axis reinforcement(G-BCCz).We conduct compressive tests on these four lattices and numerically simulate the compression process through the finite element method.Analysis results show that BCCz has higher modulus and strength than BCC.In addition,uniform lattices show better energy absorption capabilities at small compression distances,while graded lattices absorb more energy at large compression distances.The good correlation between the simulation results and the experimental phenomena demonstrates the validity and accuracy of the present investigation method.
基金Project supported by the National Natural Science Foundation of China(Nos.51978515 and 52090083)the Shanghai Sailing Program(No.19YF1451400)the Shanghai Municipal Science and Technology Major Project(No.2017SHZDZX02),China。
文摘Understanding the mechanical behavior of hybrid fiber-reinforced concrete(HFRC),a composite material,is crucial for the design of HFRC and HFRC structures.In this study,a series of compression experiments were performed on hybrid steelpolyvinyl alcohol(PVA)fiber-reinforced concrete containing fly ash and slag powder,with a focus on the fiber content/ratio effect on its compressive behavior;a new approach was built to model the compression behavior of HFRC by using an artificial neural network(ANN)method.The proposed ANN model incorporated two new developments:the prediction of the compressive stress-strain curve and consideration of 23 features of components of HFRC.To build a database for the ANN model,relevant published data were also collected.Three indices were used to train and evaluate the ANN model.To highlight the performance of the ANN model,it was compared with a traditional equation-based model.The results revealed that the relative errors of the predicted compressive strength and strain corresponding to compressive strength of the ANN model were close to 0,while the corresponding values from the equation-based model were higher.Therefore,the ANN model is better able to consider the effect of different components on the compressive behavior of HFRC in terms of compressive strength,the strain corresponding to compressive strength,and the compressive stress-strain curve.Such an ANN model could also be a good tool to predict the mechanical behavior of other composite materials.
基金Supports of National Natural Science Foundation of China(No.31470581)Fundamental Research Funds for the Central Universities(No.2572016EBJ1)Northeast Forestry University College-level Innovative Training Program Project Funding(No.CL201802)are gratefully acknowledged.
文摘In order to optimize the out-of-plane compression performance of the wood structure,wood-based 2-D lattice structures were designed and manufactured with oriented strand board as the panel and birch round stick as the core by using a simple insert-glue method.In this experiment,the different thicknesses of the upper and lower panels,the different shavings arrangement directions of the upper and lower panels and the different configurations of the specimens were used to analyze the compression performance of the specimens under multivariable conditions.Through the combination of experimental test and theoretical analysis,we analyzed and compared different failure types of the structure and multiple compression parameters.The results showed that the shavings arrangement direction of the panel has a more important influence on the whole specimen than the thickness of the panel,especially the transverse shavings of the panel can withstand greater shear stress than the longitudinal shavings for a specimen.
基金supported by the National Key R&D Program of China(No.2017YFC0602902)the National Natural Scienceof China(Nos.41807259 and 51874350)+2 种基金the Fundamental Research Funds for the Central Universities of Central South University(No.2016zztx096)The support provided by the China Scholarship Council(CSC)during the visit of the first author toécole Polytechnique de Montréal(Student ID:201706370039)the materials supply by Fan Kou lead-zinc mine of Shenzhen Zhongjin Lingnan Non-ferrous metal Company Limited。
文摘The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.
基金supported by the Technology Development Fund of the China Academy of Machinery Science and Technology(No.170221ZY01).
文摘As a new type of lightweight structure,metallic lattice structure has higher stiffness and strength to weight ratio.To freely obtain 316L lattice structures with designed cell structure and adjustable porosity,additive manufacturing combined with investment casting was conducted to fabricate the 316L lattice structures with Kelvin cell.The compression simulation of 316L lattice structures with different porosities was carried out by using the finite element method.The numerical simulation results were verified by compression experiment,and the simulated results were consistent with the compression tests.The compressive mechanical properties of 316L lattice structures are directly related to porosity and independent of strut diameters.The 316L lattice structures with Kelvin cell have a smooth stress-strain curve and obvious plastic platform,and the hump stress-strain curves are avoided.
基金Funded by the National Natural Science Foundation of China(Nos.51874093,51174060,and 51661031)the Fundamental Research Funds for the Central Universities(N182504015)the Liaoning Province Key r&d Project(No.2019JH2/10100008)。
文摘Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400℃using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.
基金Funded by the National Key Research and Development Program of China(No.2018YFC0705400)National Natural Science Foundation of China(No.51678142)the Fundamental Research Funds for the Central Universities。
文摘Ultra-high performance cement-based composites (UHPCC) is promising in construction of concrete structures that suffer impact and explosive loads.In this study,a reference UHPCC mixture with no fiber reinforcement and four mixtures with a single type of fiber reinforcement or hybrid fiber reinforcements of straight smooth and end hook type of steel fibers were prepared.Split Hopkinson pressure bar (SHPB) was performed to investigate the dynamic compression behavior of UHPCC and X-CT test and 3D reconstruction technology were used to indicate the failure process of UHPCC under impact loading.Results show that UHPCC with 1% straight smooth fiber and 2% end hook fiber reinforcements demonstrated the best static and dynamic mechanical properties.When the hybrid steel fiber reinforcements are added in the concrete,it may need more impact energy to break the matrix and to pull out the fiber reinforcements,thus,the mixture with hybrid steel fiber reinforcements demonstrates excellent dynamic compressive performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672089,11732002&11902333)。
文摘It is significant to compare the ablative and compressive mechanical behavior of different PICA-like materials in the engineering applications.The plasma wind tunnel ablation tests with high-entropy air and CO2 atmospheres,and compressive experiments in the ambient and 150℃,were conducted for three kinds of PICA-like materials(CF/PR-Si,CBCF/PR-SiOC and NQF/PR-Si composites).The traditional carbon/phenolic(C/PR)braided composites were also used for comparison.PICA-like materials have the better thermal insulation than traditional C/PR composite,especially for CBCF/PR-SiOC composite.The ablation behavior of CF/PR-Si and CBCF/PR-SiOC PICA-like materials in the CO2 atmosphere can produce a large amount of SiO2 in the form of coatings,oxide layers and skeletons on the ablated surface,which are greatly different from that in the air atmosphere.The compressive behavior of PICA-like material is greatly depended on the fiber fabrics,and exhibits the large discrete characteristics.The longer fiber in the PICA-like materials plays the role in maintaining the material integrity,while it may increase the thermal conductivity.
文摘In the present research,results of buckling analysis of 384 finite element models,verified using three different test results obtained from three separate experimental investigations,were used to study the effects of five parameters such as D/t,L/D,imperfection,mesh size and mesh size ratio.Moreover,proposed equations by offshore structural standards concerning global and local buckling capacity of tubular members including former API RP 2A WSD and recent API RP 2A LRFD,ISO 19902,and NORSOK N-004 have been compared to FE and experimental results.One of the most crucial parts in the estimation of the capacity curve of offshore jacket structures is the correct modeling of compressive members to properly investigate the interaction of global and local buckling which leads to the correct estimation of performance levels and ductility.Achievement of the proper compressive behavior of tubular members validated by experimental data is the main purpose of this paper.Modeling of compressive braces of offshore jacket platforms by 3D shell or solid elements can consider buckling modes and deformations due to local buckling.ABAQUS FE software is selected for FE modeling.The scope of action of each of elastic buckling,plastic buckling,and compressive yielding for various L/r ratios is described.Furthermore,the most affected part of each parameter on the buckling capacity curve is specified.The pushover results of the Resalat Jacket with proper versus improper modeling of compressive members have been compared as a case study.According to the results,applying improper mesh size for compressive members can under-predict the ductility by 33%and under-estimate the lateral loading capacity by up to 8%.Regarding elastic stiffness and post-buckling strength,the mesh size ratio is introduced as the most effective parameter.Besides,imperfection is significantly the most important parameter in terms of critical buckling load.
文摘Open cell steel foams were successfully fabricated through the powder metallurgy route using urea granules as the water leachable space holder in the present study.The influence of different amounts of phosphorus(0,0.5wt%,1wt%,2wt%,and 4wt%)was investigated on the cell morphology,porosity,microstructure of cell walls,and mechanical properties of steel foams.The cell morphology and microstructure of the cell walls were evaluated using an optical microscope equipped with image processing software and a scanning electron microscope equipped with an energy dispersive X-ray spectrometer.In addition,the compression tests were conducted on the steel foams using a universal testing machine.Based on microscopic images,the porous structure consists of spherical cells and irregularly shaped pores that are distributed in the cell walls.The results indicated that by increasing the phosphorus content,the porosity increases from 71.9%to 83.2%.The partially distributed ferrite and fine pearlite was observed in the microstructure of the cell walls,andα-Fe and Fe3P eutectic extended between the boundaries of agglomerated iron particles.Furthermore,elastic and long saw-toothed plateau regions were observed before fracture in the compressional stress–strain curves.According to the results,by increasing the phosphorus content from 0 to 4wt%,the plateau region of the stress–strain curves shifts to the right and upward.Therefore,increasing phosphorus content causes improvement in the mechanical properties of steel foams.
基金supported by Hong Kong Research Grant Council (RGC)(Grant No. U11207416)City University of Hong Kong (Grant No.7005234)National Natural Science Foundation of China under the Excellent Young Scientists Fund (Grant No. 11922215)。
文摘As a wide-bandgap semiconductor, 4H-SiC is an ideal material for high-power and high-frequency devices, and plays an increasingly important role in developing our country’s future electric vehicles and 5G techniques. Practical applications of SiCbased devices largely depend on their mechanical performance and reliability at the micro-and nanoscales. In this paper, singlecrystal [0001]-oriented 4H-SiC nanopillars with the diameter ranging from ~200 to 700 nm were microfabricated and then characterized by in situ nanomechanical testing under SEM/TEM at room temperature. Loading-unloading compression tests were performed, and large, fully reversible elastic strain up to ~6.2% was found in nanosized pillars. Brittle fracture still occurred when the max strain reached ~7%, with corresponding compressive strength above 30 GPa, while in situ TEM observation showed few dislocations activated during compression along the [0001] direction. Besides robust microelectromechanical system(MEMS), flexible device and nanocomposite applications, the obtained large elasticity in [0001]-oriented 4H-SiC nanopillars can offer a fertile opportunity to modulate their electron mobility and bandgap structure by nanomechanical straining,the so called "elastic strain engineering", for novel electronic and optoelectronic applications.
基金supported by the National Key Program of Research and Development(No.2018YFB0703902)the National Natural Science Foundation of China(Nos.51631002,51621003,52101003,52171061,U20A20236)。
文摘Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature.Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge.In this study,it is proposed that the hightemperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated Ta C nanoparticles,through solid solution strengthening of Ta atoms.Based on the designed experiments and microstructural characterizations combined with finite element simulations,the grain morphology,stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides.The mechanisms of Ta dissolving in WC crystal and strengthening ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale.This study opens a new perspective to modulate hard phases of cemented carbides for improving their hightemperature performance,which will be applicable to a variety of cermet and ceramic-based composite materials.
基金supported by the Fund of State Key Lab of Advanced Metals and Materials,University of Science and Technology Beijing(No.2019-ZD03)the Fund of the State Key Laboratory of Solidification Processing,Northwestern Polytechnical University(No.SKLSP201501)+2 种基金the National Natural Science Foundation of China(Nos.51601216 and 51901193)the Fundamental Research Funds for the Central Universities(Nos.2017XKQY009 and 2018GF13)sponsored by China Scholarship Council。
文摘The deformation mode of{332}<113>twinning(hereafter called 332T)has often been observed under the plastic flow in metastableβtitanium alloys with body-centered cubic(BCC)structure,which contributes to improving the mechanical performance.Herein,we report a structure of compressive deformation-induced primary 332T with hierarchical and/or heterogeneous composite sub-structure in a Twin-Induced Plasticity(TWIP)βTi-alloy under uniaxial compression.The detailed structural characterization after compressive deformation revealed that the sub-structure,including secondary 332T and secondary{112}<111>twinning,formed inside the 332T structure,which constitutes a hierarchical and/or heterogeneous structure at micro-and nano-scale and consequently contributes to the high strength,large ductility and enhanced strain-hardening behavior.
文摘The goal of this study is to establish relationships between the hot compression deformation behaviors and the fractal dimension of primary phase morphology of TA15 titanium alloy using the analytical methods of metallurgical microscope and transmission electron microscope coupled with box-counting dimension method. The hot compression deformation behaviors vary with decreasing fractal dimension owing to the change of microstructure caused by different parameters of the hot compressive deformation.The results indicate that TA15 alloy shows dynamic recrystallization characteristics at deformation temperature lower than 850℃while fractal dimension exhibits a moderate decreasing trend with the temperature increasing,and shows dynamic recovery characteristics at deformation temperature higher than 850℃while fractal dimension reduces rapidly with the temperature increasing.The fractal dimension displays non-linear relationship with fraction of primary phase and with aspect ratio of primary phase.
基金The financial support of this work came from the project of National Natural Science Foundation of China(Grant No.51408485)the Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2022JM-258 and 2021JM-332)+1 种基金the Open Fund Project of Qinghai Provincial Key Laboratory of Plateau Green Building and Eco-community(KLKF-2021-001)thanks a lot for the financial support of the above institutions.
文摘To research the axial compression behavior of steel reinforced recycled concrete(SRRC)short columns confined by carbon fiber reinforced plastics(CFRP)strips,nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading.Subsequently,the failure process and failure modes were observed,and load-displacement curves as well as the strain of various materials were analyzed.The effects on the substitution percentage of recycled coarse aggregate(RCA),width of CFRP strips,spacing of CFRP strips and strength of recycled aggregate concrete(RAC)on the axial compression properties of columns were also analyzed in the experimental investigation.Furthermore,the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study.The results show that the first to reach the yield state was the profile steel in the columns,then the longitudinal rebars and stirrups yielded successively,and finally RAC was crushed as well as the CFRP strips was also broken.The replacement rate of RCA has little effect on the columns,and with the substitution rate of RCA from 0 to 100%,the bearing capacity of columns decreased by only 4.8%.Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns,the maximum increase was 10.5%or 11.4%,and the ductility of columns was significantly enhanced.Obviously,CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns.On this basis,considering the restraint effect of CFRP strips and the adverse effects of RCA,the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed.
