Exploitation of oxygen evolution reaction(OER)and urea oxidation reaction(UOR)catalysts with high activity and stability at large current density is a major challenge for energy-saving H_(2) production in water electr...Exploitation of oxygen evolution reaction(OER)and urea oxidation reaction(UOR)catalysts with high activity and stability at large current density is a major challenge for energy-saving H_(2) production in water electrolysis.Herein,we use the pyridinic-N doping carbon layers coupled with tensile strain of FeNi alloy activated by NiFe_(2)O_(4)(FeNi/NiFe_(2)O_(4)@NC)for efficiently increasing the performance of water and urea oxidation.Due to the tensile strain effect on FeNi/NiFe_(2)O_(4)@NC,it provides a favorable modulation on the electronic properties of the active center,thus enabling amazing OER(η_(100)=196 mV)and UOR(E_(10)=1.32 V)intrinsic activity.Besides,the carbon-coated layers can be used as armor to prevent FeNi alloy from being corroded by the electrolyte for enhancing the OER/UOR stability at large current density,showing high industrial practicability.This work thus provides a simple way to prepare high-efficiency catalyst for activating water and urea oxidation.展开更多
In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to c...In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to create the hollow centers of the tapering tubes,with and without corrugations.The results demonstrate that the energy absorption(EA)and specific energy absorption(SEA)of the single corrugated tapered tube sandwich are 51.6% and 19.8% higher,respectively,than those of the conical tube sandwich.Furthermore,the results demonstrate that energy absorbers can benefit from corrugation in order to increase their efficiency.Additionally,the tapered corrugated tubes'resistance to oblique impacts was studied.Compared to a straight tube,the tapered tube is more resistant to oblique loads and has a lower initial peak crushing force(PCF),according to numerical simulations.After conducting a parametric study,it was discovered that the energy absorption performance of the sandwich construction is significantly affected by the amplitude,number of corrugations,and wall thickness.EA and SEA of DTS with corrugation number of 8 increased by 17.4%and 29.6%,respectively,while PCF decreased by 9.2% compared to DTS with corrugation number of 10.展开更多
This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact behaviour.Menger cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensi...This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact behaviour.Menger cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensions of 40 mm×40 mm×40 mm.Three different orders of Menger cubes with different void ratios were considered,namely M1 with a void ratio of 0.26,M2 with a void ratio of 0.45,and M3with a void ratio of 0.60.Quasi-static Compression tests were conducted using a universal testing machine,while the drop hammer was used to observe the behaviour under impact loading.The fracture mechanism,energy efficiency and force-time histories were studied.With the structured nature of the void formation and predictability of the failure modes,the Menger geometry showed some promise compared to other alternatives,such as foams and honeycombs.With the increasing void ratio,the Menger geometries show force-displacement behaviour similar to hyper-elastic materials such as rubber and polymers.The third-order Menger cubes showed the highest energy absorption efficiency compared to the other two geometries in this study.The findings of the present work reveal the possibility of using additively manufactured Menger geometries as an energy-efficient system capable of reducing the transmitting force in applications such as crash barriers.展开更多
The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and...The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.展开更多
There is limited applicability to the current method for testing the direct tensile strength of rocks because it places stringent requirements on the testing equipment.This work suggests a universal method based on th...There is limited applicability to the current method for testing the direct tensile strength of rocks because it places stringent requirements on the testing equipment.This work suggests a universal method based on the‘‘compression-to-tensiono idea in response to these difficulties.By applying pressure,this technique makes it possible to test the tensile strength of rocks directly with any conventional compression test machines.Granite was utilized as the test material in order to validate this suggested testing method,and the results showed what follows.Upon determining the true fracture area through digital reconstruction,an average calculated tensile strength of 5.97 MPa with a Cvof 0.04 was obtained.There is a positive correlation between tensile strength and the joint roughness coefficient(JRC)of the failure surface.The aggregation mode of AE events with the loading process conforms to the damage characteristics of rock tensile failure.The direct tensile testing method proposed in this study not only has high universality but also produces test results with outstanding consistency.Additionally,factors influencing the results of the tensile test are pointed out,and recommendations for optimizing the suggested testing method are offered.展开更多
Effects of alloying processing on tensile test properties of Fe 3Al based alloys have been studied. Results show that microalloying of cerium is very effective on increasing the room temperature ductility of Fe 3Al...Effects of alloying processing on tensile test properties of Fe 3Al based alloys have been studied. Results show that microalloying of cerium is very effective on increasing the room temperature ductility of Fe 3Al based alloys. Surface analysis by XPS demonstrates that cerium addition causes the change in the oxide chemistry and provides rapid passivation of the specimen surface. The high temperature strength and creep resistance of Fe 3Al based alloys can be significantly enhanced by alloying additions of tungsten, niobium or molybdenum, especially when combined additions of tungsten with niobium or molybdenum are used. The additions of tungsten, niobium or molybdenum also result in the significant microstructural refinement and the formation of fine precipitates which are identified as M 6C type carbide in the alloys containing tungsten.展开更多
A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineeri...A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineering hi-materials. In the stable growth stage, stress and strain have the same singularity, ie （σ, ε） ∝ r^-1/（n-1）. The variable-separable asymptotic solutions of stress and strain at the crack tip were obtained by adopting Airy＇s stress function and the numerical results of stress and strain in the crack-tip field were obtained by the shooting method. The results showed that the near-tip fields are mainly governed by the power-hardening exponent n and the Poisson ratio v of the pressure-sensitive material. The fracture criterion of mode I quasi-static crack growth in pressure-sensitive materials, according to the asymptotic analyses of the crack-tip field, can be viewed from the perspective of strain.展开更多
In this paper, the fabrication and investigation of flexible impedance and capacitive tensile load sensors based on carbon nanotube（CNT） composite are reported. On thin rubber substrates, CNTs are deposited from sus...In this paper, the fabrication and investigation of flexible impedance and capacitive tensile load sensors based on carbon nanotube（CNT） composite are reported. On thin rubber substrates, CNTs are deposited from suspension in water and pressed at elevated temperature. It is found that the fabricated load cells are highly sensitive to the applied mechanical force with good repeatability. The increase in impedance of the cells is observed to be 2.0 times while the decrease in the capacitance is found to be 2.1 times as applied force increases up to 0.3 N. The average impedance and capacitive sensitivity of the cell are equal to 3.4 N^（-1） and 1.8 N^（-1）, respectively. Experimental results are compared with the simulated values,and they show that they are in reasonable agreement with each other.展开更多
This paper employs a first-principles total-energy method to investigate the theoretical tensile strengths of bcc and fcc Fe systemically. It indicates that the theoretical tensile strengths are shown to be 12.4, 32.7...This paper employs a first-principles total-energy method to investigate the theoretical tensile strengths of bcc and fcc Fe systemically. It indicates that the theoretical tensile strengths are shown to be 12.4, 32.7, 27.5 GPa for bcc Fe, and 48.1, 34.6, 51.2 GPa for fcc Fe in the [001], [110] and [111] directions, respectively. For bcc Fe, the [001] direction is shown to be the weakest direction due to the occurrence of a phase transition from ferromagnetic bcc Fe to high spin ferromagnetic fcc Fe. For fcc Fe, the [110] direction is the weakest direction due to the formation of an instable saddle-point ＇bct structure＇ in the tensile process. Furthermore, it demonstrates that a magnetic instability will occur under a tensile strain of 14%, characterized by the transition of ferromagnetic bcc Fe to paramagnetic fcc Fe. The results provide a good reference to understand the intrinsic mechanical properties of Fe as a potential structural material in the nuclear fusion Tokamak.展开更多
AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the...AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.展开更多
Biomechanical characteristics of the root system of hornbeam （Carpinus betulus） were assessed by measuring Root Area Ratio （RAR） values and tensile strength of root specimens of eight hornbeam trees growing on hil...Biomechanical characteristics of the root system of hornbeam （Carpinus betulus） were assessed by measuring Root Area Ratio （RAR） values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman＇s bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength.展开更多
In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20...In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.展开更多
Split Hopkinson technique has been developed to test the strength of common concrete and steel fiber reinforced concrete under dynamic tensile stress. Two types of test methods are considered, the splitting tensile te...Split Hopkinson technique has been developed to test the strength of common concrete and steel fiber reinforced concrete under dynamic tensile stress. Two types of test methods are considered, the splitting tensile test and a modified spalling test in which a specimen is loaded under uniaxial stress. The result shows that the dynamic strength enhancement of concrete is remarkable by using the reinforcing fiber. But for the common concrete, the base of compressive strength seems to show little effect on the tensile strength under dynamic loading. The experimental results also show that the resistance to tensile fracture of the steel fiber reinforced concrete for C100-mix is higher than those of C40-mix..展开更多
The effect of microwave treatment on the tensile properties of treated sugar palm fibre with 6% NaOH reinforced thermoplastic polyurethane composites was investigated. Firstly, the sugar palm fibres were treated by 6%...The effect of microwave treatment on the tensile properties of treated sugar palm fibre with 6% NaOH reinforced thermoplastic polyurethane composites was investigated. Firstly, the sugar palm fibres were treated by 6% alkali solution. Then, microwave treatment was used to treat the alkali treated sugar palm fibres. Three types of temperatures(i.e. 70, 80 and 90℃) were applied in microwave treatment. The extruder and hot press machines were used to mixing the sugar palm fibres and polyurethane resin, and fabricate the composites. Tensile properties(i.e. tensile strength, tensile modulus and elongation at break) were studied by following the ASTM D-638 standard. The highest tensile strength was recorded 18.42 MPa with microwave temperature at 70℃ and 6% alkali pre-treatment. Therefore, the temperature 70℃ of microwave treatment may consider the best degree cent grate.展开更多
In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain ...In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.展开更多
Biomechanical characteristics of the root system of hornbeam(Carpinus betulus) were assessed by measuring Root Area Ratio(RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly ter...Biomechanical characteristics of the root system of hornbeam(Carpinus betulus) were assessed by measuring Root Area Ratio(RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran.RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m.In total 123 root specimens were analyzed for tensile strength.Results indicate that in general, RAR decreases with depth, following a power function.The RAR values in up and down slopes have no significant statistical differences.In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m.The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively.The number of roots in the up and down slope trenches was not significantly different.In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function.The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively.Results of Spearman's bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots.The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, follow-ing a power law equation.Using ANCOVA, we found intraspecies variation of tensile strength.展开更多
Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young’s modulus of shotcrete were considered. Six different undulations o...Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young’s modulus of shotcrete were considered. Six different undulations of rock-shotcrete interface were set up. The influences of multiple parameters on the bearing characteristics of the rock-shotcrete interface were studied. The results showed that a better support performance can be obtained by increasing the Young’s modulus of shotcrete rather than the tensile strength of shotcrete. For different tensile strength and Young’s modulus, the increase of sawtooth height has different effects on the support performance. The failure mechanism of the rock-shotcrete interfaces was analysed in detail. The stress shielding effect and stress concentration effect caused by the shape characteristics of rock-shotcrete interface were observed. The influence of these parameters on the overall support performance should be fully considered in a reasonable support design.展开更多
To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tes...To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method(FDM)—discrete element method(DEM)was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to be stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.展开更多
Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp...Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp and wood fiber based composites. In this study, we carried out tensile tests on single mature latewood tracheids of Chi- nese fir （Cunninghamia lanciolata （Lamb.） Hook.）, using three different delignified treatment methods to obtain different amounts of lignin. We applied single fiber tests to study the effect of the amount of lignin on mechanical tensile proper- ties of single wood fibers at the cellular level. The results show that in their dry state, the modulus of elasticity of single fi- bers decreased with the reduction in the amount of Iignin; even their absolute values were not high. The amount of lignin affects the tensile strength and elongation of single fibers considerably. Tensile strength and elongation of single fibers increase with a reduction in the amount of lignin.展开更多
The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field（HPMF） parallel to the axial direction.The effects of magnetic induction in...The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field（HPMF） parallel to the axial direction.The effects of magnetic induction intensity（5 = 0,1 T,3 T,and 5 T） on elongation（5） of TC4 alloy are investigated.At 3 T,the elongation arrives at a maximum value of12.41%,which is enhanced by 23.98%in comparison with that of initial sample.The elongation curve shows that 3 T is a critical point.With B increasing,the volume fraction of α phase is enhanced from 49.7%to 55.9%,which demonstrates that the HPMF can induce the phase transformation from β phase to α phase.Furthermore,the magnetic field not only promotes the orientation preference of crystal plane along the slipping direction,but also has the effect on increasing the dislocation density.The dislocation density increases with the enhancement of magnetic induction intensity and the 3-T parameter is ascertained as a turning point from increase to decrease tendency.When B is larger than 3 T,the dislocation density decreases with the enhancement of B.The influence of magnetic field is analyzed on the basis of magneto-plasticity effect.The high magnetic field will enhance the dislocation strain energy and promote the state conversion of radical pair generated between the dislocation and obstacles from singlet into triplet state,in which is analyzed the phenomenon that the dislocation density is at an utmost with B = 3 T.Finally,the inevitability of optimized 3-T parameter is further discussed on a quantum scale.展开更多
基金supported by the National Natural Science Foundation of China(21872040,22162004)the Excellent Scholars and Innovation Team of Guangxi Universities,the Innovation Project of Guangxi Graduate Education(YCBZ2022038)the High-performance Computing Platform of Guangxi University.
文摘Exploitation of oxygen evolution reaction(OER)and urea oxidation reaction(UOR)catalysts with high activity and stability at large current density is a major challenge for energy-saving H_(2) production in water electrolysis.Herein,we use the pyridinic-N doping carbon layers coupled with tensile strain of FeNi alloy activated by NiFe_(2)O_(4)(FeNi/NiFe_(2)O_(4)@NC)for efficiently increasing the performance of water and urea oxidation.Due to the tensile strain effect on FeNi/NiFe_(2)O_(4)@NC,it provides a favorable modulation on the electronic properties of the active center,thus enabling amazing OER(η_(100)=196 mV)and UOR(E_(10)=1.32 V)intrinsic activity.Besides,the carbon-coated layers can be used as armor to prevent FeNi alloy from being corroded by the electrolyte for enhancing the OER/UOR stability at large current density,showing high industrial practicability.This work thus provides a simple way to prepare high-efficiency catalyst for activating water and urea oxidation.
基金the grants from the National Natural Science Foundation of China(Nos.52078152 and 12002095)Guangzhou Government-University Union Fund(No.202201020532)。
文摘In this article,the experimental and finite element analysis is utilized to investigate the quasi-static compression features of sandwich constructions built with tapered tubes.3D printing technology was utilized to create the hollow centers of the tapering tubes,with and without corrugations.The results demonstrate that the energy absorption(EA)and specific energy absorption(SEA)of the single corrugated tapered tube sandwich are 51.6% and 19.8% higher,respectively,than those of the conical tube sandwich.Furthermore,the results demonstrate that energy absorbers can benefit from corrugation in order to increase their efficiency.Additionally,the tapered corrugated tubes'resistance to oblique impacts was studied.Compared to a straight tube,the tapered tube is more resistant to oblique loads and has a lower initial peak crushing force(PCF),according to numerical simulations.After conducting a parametric study,it was discovered that the energy absorption performance of the sandwich construction is significantly affected by the amplitude,number of corrugations,and wall thickness.EA and SEA of DTS with corrugation number of 8 increased by 17.4%and 29.6%,respectively,while PCF decreased by 9.2% compared to DTS with corrugation number of 10.
文摘This paper presents the first-ever investigation of Menger fractal cubes'quasi-static compression and impact behaviour.Menger cubes with different void ratios were 3D printed using polylactic acid(PLA)with dimensions of 40 mm×40 mm×40 mm.Three different orders of Menger cubes with different void ratios were considered,namely M1 with a void ratio of 0.26,M2 with a void ratio of 0.45,and M3with a void ratio of 0.60.Quasi-static Compression tests were conducted using a universal testing machine,while the drop hammer was used to observe the behaviour under impact loading.The fracture mechanism,energy efficiency and force-time histories were studied.With the structured nature of the void formation and predictability of the failure modes,the Menger geometry showed some promise compared to other alternatives,such as foams and honeycombs.With the increasing void ratio,the Menger geometries show force-displacement behaviour similar to hyper-elastic materials such as rubber and polymers.The third-order Menger cubes showed the highest energy absorption efficiency compared to the other two geometries in this study.The findings of the present work reveal the possibility of using additively manufactured Menger geometries as an energy-efficient system capable of reducing the transmitting force in applications such as crash barriers.
基金financially supported by National Natural Science Foundation of China,China (Grant No.52022012)National Key R&D Program for Young Scientists of China,China (Grant No.2022YFC3080900)。
文摘The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.
基金financially supported by the National Natural Science Foundation of China(Nos.U20A20266 and 12302503)the Scientific and Technological Research Projects in Sichuan Province(Nos.2024NSFSC0973,2024YFHZ0286,and 2023YFH0005)。
文摘There is limited applicability to the current method for testing the direct tensile strength of rocks because it places stringent requirements on the testing equipment.This work suggests a universal method based on the‘‘compression-to-tensiono idea in response to these difficulties.By applying pressure,this technique makes it possible to test the tensile strength of rocks directly with any conventional compression test machines.Granite was utilized as the test material in order to validate this suggested testing method,and the results showed what follows.Upon determining the true fracture area through digital reconstruction,an average calculated tensile strength of 5.97 MPa with a Cvof 0.04 was obtained.There is a positive correlation between tensile strength and the joint roughness coefficient(JRC)of the failure surface.The aggregation mode of AE events with the loading process conforms to the damage characteristics of rock tensile failure.The direct tensile testing method proposed in this study not only has high universality but also produces test results with outstanding consistency.Additionally,factors influencing the results of the tensile test are pointed out,and recommendations for optimizing the suggested testing method are offered.
文摘Effects of alloying processing on tensile test properties of Fe 3Al based alloys have been studied. Results show that microalloying of cerium is very effective on increasing the room temperature ductility of Fe 3Al based alloys. Surface analysis by XPS demonstrates that cerium addition causes the change in the oxide chemistry and provides rapid passivation of the specimen surface. The high temperature strength and creep resistance of Fe 3Al based alloys can be significantly enhanced by alloying additions of tungsten, niobium or molybdenum, especially when combined additions of tungsten with niobium or molybdenum are used. The additions of tungsten, niobium or molybdenum also result in the significant microstructural refinement and the formation of fine precipitates which are identified as M 6C type carbide in the alloys containing tungsten.
基金Supported by Heilongjiang Province Foundation under Grant No.LC08C02
文摘A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineering hi-materials. In the stable growth stage, stress and strain have the same singularity, ie （σ, ε） ∝ r^-1/（n-1）. The variable-separable asymptotic solutions of stress and strain at the crack tip were obtained by adopting Airy＇s stress function and the numerical results of stress and strain in the crack-tip field were obtained by the shooting method. The results showed that the near-tip fields are mainly governed by the power-hardening exponent n and the Poisson ratio v of the pressure-sensitive material. The fracture criterion of mode I quasi-static crack growth in pressure-sensitive materials, according to the asymptotic analyses of the crack-tip field, can be viewed from the perspective of strain.
基金Ghulam Ishaq Khan Institute of Engineering Science and Technology, Pakistan for its support
文摘In this paper, the fabrication and investigation of flexible impedance and capacitive tensile load sensors based on carbon nanotube（CNT） composite are reported. On thin rubber substrates, CNTs are deposited from suspension in water and pressed at elevated temperature. It is found that the fabricated load cells are highly sensitive to the applied mechanical force with good repeatability. The increase in impedance of the cells is observed to be 2.0 times while the decrease in the capacitance is found to be 2.1 times as applied force increases up to 0.3 N. The average impedance and capacitive sensitivity of the cell are equal to 3.4 N^（-1） and 1.8 N^（-1）, respectively. Experimental results are compared with the simulated values,and they show that they are in reasonable agreement with each other.
基金supported by the National Natural Science Foundation of China(Grant No 50771008)New Century Excellent Talents in University of China
文摘This paper employs a first-principles total-energy method to investigate the theoretical tensile strengths of bcc and fcc Fe systemically. It indicates that the theoretical tensile strengths are shown to be 12.4, 32.7, 27.5 GPa for bcc Fe, and 48.1, 34.6, 51.2 GPa for fcc Fe in the [001], [110] and [111] directions, respectively. For bcc Fe, the [001] direction is shown to be the weakest direction due to the occurrence of a phase transition from ferromagnetic bcc Fe to high spin ferromagnetic fcc Fe. For fcc Fe, the [110] direction is the weakest direction due to the formation of an instable saddle-point ＇bct structure＇ in the tensile process. Furthermore, it demonstrates that a magnetic instability will occur under a tensile strain of 14%, characterized by the transition of ferromagnetic bcc Fe to paramagnetic fcc Fe. The results provide a good reference to understand the intrinsic mechanical properties of Fe as a potential structural material in the nuclear fusion Tokamak.
文摘AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.
文摘Biomechanical characteristics of the root system of hornbeam （Carpinus betulus） were assessed by measuring Root Area Ratio （RAR） values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman＇s bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength.
基金supported by the National Natural Science Foundation of China(Grant Nos.51371091,51174099,and 51001054)the Industrial Center of Jiangsu University,China(Grant No.ZXJG201586)
文摘In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.
文摘Split Hopkinson technique has been developed to test the strength of common concrete and steel fiber reinforced concrete under dynamic tensile stress. Two types of test methods are considered, the splitting tensile test and a modified spalling test in which a specimen is loaded under uniaxial stress. The result shows that the dynamic strength enhancement of concrete is remarkable by using the reinforcing fiber. But for the common concrete, the base of compressive strength seems to show little effect on the tensile strength under dynamic loading. The experimental results also show that the resistance to tensile fracture of the steel fiber reinforced concrete for C100-mix is higher than those of C40-mix..
文摘The effect of microwave treatment on the tensile properties of treated sugar palm fibre with 6% NaOH reinforced thermoplastic polyurethane composites was investigated. Firstly, the sugar palm fibres were treated by 6% alkali solution. Then, microwave treatment was used to treat the alkali treated sugar palm fibres. Three types of temperatures(i.e. 70, 80 and 90℃) were applied in microwave treatment. The extruder and hot press machines were used to mixing the sugar palm fibres and polyurethane resin, and fabricate the composites. Tensile properties(i.e. tensile strength, tensile modulus and elongation at break) were studied by following the ASTM D-638 standard. The highest tensile strength was recorded 18.42 MPa with microwave temperature at 70℃ and 6% alkali pre-treatment. Therefore, the temperature 70℃ of microwave treatment may consider the best degree cent grate.
文摘In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.
文摘Biomechanical characteristics of the root system of hornbeam(Carpinus betulus) were assessed by measuring Root Area Ratio(RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran.RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m.In total 123 root specimens were analyzed for tensile strength.Results indicate that in general, RAR decreases with depth, following a power function.The RAR values in up and down slopes have no significant statistical differences.In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m.The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively.The number of roots in the up and down slope trenches was not significantly different.In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function.The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively.Results of Spearman's bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots.The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, follow-ing a power law equation.Using ANCOVA, we found intraspecies variation of tensile strength.
基金We acknowledge the financial supports of the National Natural Science Foundation of China(No.41630642)Project of Innovationdriven Plan in Central South University(No.2018CX020)the Funded by Open Research Fund Program of Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring(Central South University),Ministry of Education(No.2017YSJS14).
文摘Four groups of numerical models of Brazilian tests on rock-shotcrete interfaces were successfully conducted by PFC2D. The tensile strength and Young’s modulus of shotcrete were considered. Six different undulations of rock-shotcrete interface were set up. The influences of multiple parameters on the bearing characteristics of the rock-shotcrete interface were studied. The results showed that a better support performance can be obtained by increasing the Young’s modulus of shotcrete rather than the tensile strength of shotcrete. For different tensile strength and Young’s modulus, the increase of sawtooth height has different effects on the support performance. The failure mechanism of the rock-shotcrete interfaces was analysed in detail. The stress shielding effect and stress concentration effect caused by the shape characteristics of rock-shotcrete interface were observed. The influence of these parameters on the overall support performance should be fully considered in a reasonable support design.
基金financial support of the International Science and Technology Cooperation Plan of Jiangsu Province,China(No.BZ2020066)the National Natural Science Foundation of China(Nos.52179118,42077240 and 52074269)。
文摘To investigate the degradation mechanism of static tensile mechanical behaviors of marble containing dynamic damage,multiple impact loading tests were performed on the disc marble samples,and then static Brazilian tests were conducted for the damaged samples.Besides,coupling modeling technology of finite difference method(FDM)—discrete element method(DEM)was used to carry out the numerical investigation.The results show that after multiple impacts,more white patches appear on the surface,and some microcracks,macro-fractures as well as pulverized grains are found by optical microscopic.The static tensile strength decreases with the increase of the dynamic damage variable characterized by the ultrasonic wave velocity of sample.The interaction between grains in the damaged sample becomes intense in the subsequent static loading process,causing a relatively large strain.The volume of the fragments falling off around the loading points becomes larger as impact number increases.As the dynamic damage increases,the absorbed energy of sample during the static loading first decreases and then tends to be stable.Both the stress concentration and the breakage of the force chains are the root causes of the degradation of the static tensile strength.
基金supported by the Key Program of the National Natural Science Foundation of China (Grant No. 30730076)
文摘Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp and wood fiber based composites. In this study, we carried out tensile tests on single mature latewood tracheids of Chi- nese fir （Cunninghamia lanciolata （Lamb.） Hook.）, using three different delignified treatment methods to obtain different amounts of lignin. We applied single fiber tests to study the effect of the amount of lignin on mechanical tensile proper- ties of single wood fibers at the cellular level. The results show that in their dry state, the modulus of elasticity of single fi- bers decreased with the reduction in the amount of Iignin; even their absolute values were not high. The amount of lignin affects the tensile strength and elongation of single fibers considerably. Tensile strength and elongation of single fibers increase with a reduction in the amount of lignin.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51371091,51174099,and 51001054)the Industrial Center of Jiangsu University,China(Grant No.ZXJG201585)
文摘The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field（HPMF） parallel to the axial direction.The effects of magnetic induction intensity（5 = 0,1 T,3 T,and 5 T） on elongation（5） of TC4 alloy are investigated.At 3 T,the elongation arrives at a maximum value of12.41%,which is enhanced by 23.98%in comparison with that of initial sample.The elongation curve shows that 3 T is a critical point.With B increasing,the volume fraction of α phase is enhanced from 49.7%to 55.9%,which demonstrates that the HPMF can induce the phase transformation from β phase to α phase.Furthermore,the magnetic field not only promotes the orientation preference of crystal plane along the slipping direction,but also has the effect on increasing the dislocation density.The dislocation density increases with the enhancement of magnetic induction intensity and the 3-T parameter is ascertained as a turning point from increase to decrease tendency.When B is larger than 3 T,the dislocation density decreases with the enhancement of B.The influence of magnetic field is analyzed on the basis of magneto-plasticity effect.The high magnetic field will enhance the dislocation strain energy and promote the state conversion of radical pair generated between the dislocation and obstacles from singlet into triplet state,in which is analyzed the phenomenon that the dislocation density is at an utmost with B = 3 T.Finally,the inevitability of optimized 3-T parameter is further discussed on a quantum scale.
