One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the indenter.H...One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the indenter.However,this indirect measurement occasionally leads to inaccurate properties of the indented material.The objective of this study is to investigate the effects of E/σr and the strain hardening exponents n of materials on the behaviors of pile-up and sink-in in nano-indentation and to predict n values of materials from the residual indentation impressions.The relations between the residual indentation profile and n value of the indented material were identified by dimensional analysis.Also,they were numerically formulated using FE analysis of nano-indentation for 140 different combinations of elastic-plastic parameters such as E,σy and n.The parameters of hrp/hm,herp/hm,Rr/hm and HO&P/Hreal were introduced as various dimensionless parameters to represent and quantify the residual indentation profile after indentation.They were subsequently characterized as dimensionless functions using n and E/σr values.Finally,the validity of these functions was verified through 3D FE analysis of nano-indentation for Al 6061-T6 and AISI 1010 materials.展开更多
In this paper,three-scale stochastic elastic finite element analyses are made for recycled aggregate concrete (RAC)based on nano-indentation digital images.The elastic property of RAC contains uncertainties across sca...In this paper,three-scale stochastic elastic finite element analyses are made for recycled aggregate concrete (RAC)based on nano-indentation digital images.The elastic property of RAC contains uncertainties across scales.It has both theoretical and practical values to model and predict its mechanical performance.Based on homogenization theory,effective stochastic elastic moduli of RAC at three different scales are obtained using moving window technique,nano-indentation digital images,and Monte-Carlo method.It involves the generation of a large number of random realizations of microstructure geometry based on different volume fraction of the inclusions and other parameters.The mean value,coefficient of variation and probability distribution of the effective elastic moduli are computed considering the material multiscale structure.The microscopic randomness is taken into account,and correlations of RAC among five phases are investigated.The effective elastic properties are used to obtain the global behavior of a composite structure.It is indicated that the response variability can be considerably affected by replacement percentage of recycled aggregates.展开更多
Equiatomic CrMnFeCoNi high entropy alloy prepared by powder metallurgy was remelted by laser.The relative density and microstructure of fusion zone are evaluated.The nanoindentation tests are conducted to reveal the h...Equiatomic CrMnFeCoNi high entropy alloy prepared by powder metallurgy was remelted by laser.The relative density and microstructure of fusion zone are evaluated.The nanoindentation tests are conducted to reveal the hardness difference of dendrite arms and interdendritic areas.Tensile tests are conducted to assess the mechanical properties of remelted HEA.After laser remelting,the number and morphology of voids changed significantly.Dendritic structure with face-centered cubic phase form in the fusion zone.Fe,Cr and Co are enriched in dendrite arm,while Mn and Ni are enriched in interdendritic area.Elements segregation led to a nanohardness difference between dendrite arm and interdendritic area.Local deformation occurs in interdendritic area during tensile tests and results in a fracture with directionality.展开更多
The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete sur...The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.展开更多
Microstructure and mechanical properties of non-equiatomic(CuNi)_(100-x)Co_(x)(x=15,20,25 and 30,at.%)medium-entropy alloys(MEAs)prepared by vacuum arc-melting were investigated.Results show that all the as-cast MEAs ...Microstructure and mechanical properties of non-equiatomic(CuNi)_(100-x)Co_(x)(x=15,20,25 and 30,at.%)medium-entropy alloys(MEAs)prepared by vacuum arc-melting were investigated.Results show that all the as-cast MEAs exhibit dual face-centered cubic(fcc)solid-solution phases with identical lattice constant,showing typical dendrite structure consisting of(Ni,Co)-rich phase in dendrites and Cu-rich phase in inter-dendrites.The positive enthalpy of mixing among Cu and Ni-Co elements is responsible for the segregation of Cu.With the increase of Co content,the volume fraction of(Ni,Co)-rich phase increases while the Cu-rich phase decreases,resulting in an increment of yield strength and a decrement of elongation for the(CuNi)_(100-x)Co_(x) MEAs.Nano-indentation test results show a great difference of microhardness between the two fcc phases of the MEAs.The measured microhardness value of the(Ni,Co)-rich phase is almost twofold as compared to that of the Cu-rich phase in all the(CuNi)_(100-x)Co_(x) MEAs.During the deformation of the MEAs,the Cu-rich phase bears the main plastic strain,whereas the(Ni,Co)-rich phase provides more pronounced strengthening.展开更多
Nano-SiO2 particles strengthened Ni-based composite coating was designed and prepared on steel substrate. The structures and nanoparticle content of the nano-SiO2/Ni composite coating were determined by SEM, EDS and T...Nano-SiO2 particles strengthened Ni-based composite coating was designed and prepared on steel substrate. The structures and nanoparticle content of the nano-SiO2/Ni composite coating were determined by SEM, EDS and TEM; and the micro mechanical properties were tested by nano-indentation technique. The results show that 56% of particles in the solution are dispersed in size of less than 100nm, the content of nanoparticles co-deposited in the coating doubles and structure of the coating is more compact and uniform than that of Ni coating. Nano-SiO2/Ni coating exhibits excellent micro mechanical properties, and the nanohardness and elastic modulus are 7.81GPa and 198GPa, respectively, which are attributed to finer crystal strengthening, dispersion strengthening and high-density dislocation strengthening of nano-SiO2 particles to the composite coatings.展开更多
Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site(Tournemire,CD borehole)for 18 years.In a saturated context and outside the excavation disturbed zone(EDZ),the clays...Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site(Tournemire,CD borehole)for 18 years.In a saturated context and outside the excavation disturbed zone(EDZ),the claystone exhibits a 11.6-mm black rim at the cement/paste interface,which shows a different mechanical behaviour from the rest of the claystone.Three sets of measurements of elastic modulus were performed using:(i)nano-indentation tests with a constant indentation depth of 2 mm,(ii)microindentation tests with a constant indentation depth of 20 mm,and(iii)meso-compression tests with a constant displacement of 200 mm.The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale.Moreover,an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone.In view of the mineralogy and petrographic observations,higher values of modulus of deformability in the black rim are related to carbonate content and its distribution.Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone.展开更多
In this study,Pinus massoniana Lamb at different heights,across the annual rings,and between earlywood and latewood was measured by X-ray diffraction and the chemical composition was analyzed by chemical treatment.Res...In this study,Pinus massoniana Lamb at different heights,across the annual rings,and between earlywood and latewood was measured by X-ray diffraction and the chemical composition was analyzed by chemical treatment.Results indicated that the microfibril angle(MFA)decreased and the chemical composition changed little with the increase in height from 1 m to 9 m.In the radial direction,the MFA decreased and the chemical composition changed little with an increase in annual rings.The cellulose content of latewood was higher than that of early-wood.The viscoelastic changes of wood cell walls at different heights,across the annual rings by the method of quasi-static nanoindentation and dynamic modulus mapping techniques.Results indicated that the wood cell walls’elastic modulus increased,and the creep rate and creep compliance decreased with the increase in height;The elastic modulus and hardness increased with the annual rings.The cell walls’storage modulus increased and the loss modulus gradually decreased with an increase in height;the storage modulus gradually increased and the loss modulus decreased with the annual rings.展开更多
Atomistic simulations are carried out to investigate the nano-indentation of single crystal Cu and the sliding of the Cu-Zn alloy.As the contact zone is extended due to adhesive interaction between the contact atoms,t...Atomistic simulations are carried out to investigate the nano-indentation of single crystal Cu and the sliding of the Cu-Zn alloy.As the contact zone is extended due to adhesive interaction between the contact atoms,the contact area on a nanoscale is redefined.A comparison of contact area and contact force between molecular dynamics(MD)and contact theory based on Greenwood-Williamson(GW)model is made.Lower roughness causes the adhesive interaction to weaken,showing the better consistency between the calculated results by MD and those from the theoretical model.The simulations of the sliding show that the substrate wear decreases with the mol%of Zn increasing,due to the fact that the diffusion movements of Zn atoms in substrate are blocked during the sliding because of the hexagonal close packed(hcp)structure of Zn.展开更多
Mineralized tissues are usually constructed of nanosized materials with ordered hierarchical structures. The main reason for their high load-bearing ability is the multi-scale hierarchy. It is important to have a meth...Mineralized tissues are usually constructed of nanosized materials with ordered hierarchical structures. The main reason for their high load-bearing ability is the multi-scale hierarchy. It is important to have a method for measuring the energy absorbed during the nanoscale deformation of mineralized tissues. The objective of this study was to use a combination of nanoindentation and elastic-plastic mechanics techniques to measure the damage resistance of peritubular and intertubular dentin, based on the energy consumed in the plastic deformation regime and the volume created by the indents. The control materials were soda-lime glass, gold, and poly-methyl methacrylate (PMMA). Plastic deformation energy was calculated from the plastic part of load-displacement curves. The mean values of peritubular dentin and intertubular dentin were 3.8 × 10<sup>9</sup>, and 5.2 × 10<sup>9</sup> J/m<sup>3</sup>, respectively, compared to glass, PMMA, and gold which were 3.3 × 10<sup>7</sup>, 1.3 × 10<sup>9</sup>, and 3.1 × 10<sup>9</sup> J/m<sup>3</sup>, respectively. This method can be applied to study the resistance of mineralized tissues or organic/inorganic hybrid materials to deformation at the nanoscale.展开更多
A Co-free as-cast AlCrAlCrFe_(2)Ni_(2)medium entropy alloy(MEA)with multi-phases was remelted by fiber laser in this study.The effect of laser remelting on the microstructure,phase distribution and mechanical properti...A Co-free as-cast AlCrAlCrFe_(2)Ni_(2)medium entropy alloy(MEA)with multi-phases was remelted by fiber laser in this study.The effect of laser remelting on the microstructure,phase distribution and mechanical properties was investigated by characterizing the as-cast and the remelted AlCrAlCrFe_(2)Ni_(2)alloy.The laser remelting process resulted in a significant decrease of grain size from about 780μm to 58.89μm(longitudinal section)and 15.87μm(transverse section)and an increase of hardness from 4.72±0.293 GPa to 6.40±0.147 GPa(longitudinal section)and 7.55±0.360 GPa(transverse section).It was also found that the long side plate-like microstructure composed of FCC phase,ordered B2 phase and disordered BCC phase in the as-cast alloy was transformed into nano-size weave-like microstructure consisting of alternating ordered B2 and disordered BCC phases.The mechanical properties were evaluated by the derived stressstrain relationship obtained from nano-indentation tests data.The results showed that the yield stress increased from 661.9 MPa to 1347.6 MPa(longitudinal section)and 1647.2 MPa(transverse section)after remelting.The individual contribution of four potential strengthening mechanisms to the yield strength of the remelted alloy was quantitatively evaluated,including grain boundary strengthening,dislocation strengthening,solid solution strengthening and precipitation strengthening.The calculation results indicated that dislocation and precipitation are dominant strengthening mechanisms in the laser remelted MEA.展开更多
2219 aluminum alloys welding joints were prepared by Friction stir welding (FSW) and Variable polarity plasma arc welding (VPPAW).The microstructure of joints was characterized by means of OM,SEM,and EDX.Microhardness...2219 aluminum alloys welding joints were prepared by Friction stir welding (FSW) and Variable polarity plasma arc welding (VPPAW).The microstructure of joints was characterized by means of OM,SEM,and EDX.Microhardness measurements was performed to differentiate the joint zones and to evaluate the symmetry level of the joints with the help of nano-indentation experiment.The dissymmetry of microstructure and mechanical properties was found both in FSW joint and VPPAW joint.The dissymmetry in FSW joint can not be suppressed due to the nature of the mixing head,but the symmetry and satisfactory welding joint can be obtained by changing the working pattern of VPPAW.展开更多
Tungsten as a material exhibits broad and increasingly important applications;however,the characterization of its ductile-to-brittle transition(BDT)is currently limited to large-scale scenarios and destructive testing...Tungsten as a material exhibits broad and increasingly important applications;however,the characterization of its ductile-to-brittle transition(BDT)is currently limited to large-scale scenarios and destructive testing.In this study,we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten.In order to predict the failure mode at various temperature ranges,the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with temperature.High temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures,which is required for dislocation activities in an atomic scaled activation volume.On one hand,atomistic simulations have provided the temperature dependence of brittle fracture stress,where the atomic bonds break due to intergranular or intragranular fracture.We considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing,and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data processing.The fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests,which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure tungsten.Based on the BDT estimations by small-scale characterization,we provided further insights into the factors affecting the BDT behavior of tungsten,focusing on the contributions of different types of dislocations.展开更多
The influence of titanium alloy(Ti–5 Al–2.5 Sn) and commercially pure titanium(cp Ti) as fillers on dissimilar pulsed tungsten inert gas weldments of Ti–5 Al–2.5 Sn/cp Ti was investigated in terms of microstructur...The influence of titanium alloy(Ti–5 Al–2.5 Sn) and commercially pure titanium(cp Ti) as fillers on dissimilar pulsed tungsten inert gas weldments of Ti–5 Al–2.5 Sn/cp Ti was investigated in terms of microstructure, mechanical/nano-mechanical properties, and residual stresses. A partial martensitic transformation was observed in the weldments for all the welding conditions due to high heat input. The microstructure evolved in the FZ/cp Ti interfacial region was observed to be the most sensitive to the proportion of α stabilizer in the filler alloy. Furthermore, the addition of filler alloy improved the tensile properties and nano-mechanical response of the weld joint owing to the increased volume of metal in the weld joint. As compared to the Ti–5 Al–2.5 Sn wire, the use of cp Ti filler wire proved to be better in terms of energy absorbed during tensile and impact tests, tensile strength and ductility of the dissimilar welds. An asymmetrical residual stresses profile was observed close to the weld centerline, with high compressive stresses on the Ti–5 Al–2.5 Sn side for both the weldments obtained with and without filler wires. This was attributed to mainly the low thermal conductivity of Ti–5 Al–2.5 Sn. The presence of residual stresses also influenced the nano-hardness profile across the weldments.展开更多
The diamond-like carbon(DLC)film on 316L stainless steel substrate was preparedpulsed plasma-enhanced chemical vapor deposition,and the performance of the films was optimizedregulating the pulse voltage.Microstructure...The diamond-like carbon(DLC)film on 316L stainless steel substrate was preparedpulsed plasma-enhanced chemical vapor deposition,and the performance of the films was optimizedregulating the pulse voltage.Microstructure and properties of DLC film on 316L stainless steel were characterizedatomic force microscopy,field-emission scanning electron microscopy,Raman spectra,nano-indenter and electrochemical workstations.The results showed that DLC films with smooth and dense morphology have a low friction coefficient and high nano-indentation hardness,and the surface hardness of 316L stainless steel substrate was enhancedmore than 3 times.The mechanical properties of DLC films and their bond with 316L stainless steel could be further optimizedincreasing pulse voltage.DLC films on 316L stainless steel substrate increased the self-corrosion potential0.173 V and decreased self-corrosion current99%,which significantly improved the anti-corrosive properties of 316L substrate.展开更多
基金Project(2010-0008-277)supported by the NCRC(National Core Research Center)Program through the National Research Foundation of Koreafunded by the Ministry of Education,Science,and Technology,KoreaProject supported by R&D for Technology Development Program of Ministry of Knowledge Economy,Korea
文摘One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the indenter.However,this indirect measurement occasionally leads to inaccurate properties of the indented material.The objective of this study is to investigate the effects of E/σr and the strain hardening exponents n of materials on the behaviors of pile-up and sink-in in nano-indentation and to predict n values of materials from the residual indentation impressions.The relations between the residual indentation profile and n value of the indented material were identified by dimensional analysis.Also,they were numerically formulated using FE analysis of nano-indentation for 140 different combinations of elastic-plastic parameters such as E,σy and n.The parameters of hrp/hm,herp/hm,Rr/hm and HO&P/Hreal were introduced as various dimensionless parameters to represent and quantify the residual indentation profile after indentation.They were subsequently characterized as dimensionless functions using n and E/σr values.Finally,the validity of these functions was verified through 3D FE analysis of nano-indentation for Al 6061-T6 and AISI 1010 materials.
基金This work is sponsored by the National NaturalScience Foundation of China(Crant Nos.10972162and 51325802).
文摘In this paper,three-scale stochastic elastic finite element analyses are made for recycled aggregate concrete (RAC)based on nano-indentation digital images.The elastic property of RAC contains uncertainties across scales.It has both theoretical and practical values to model and predict its mechanical performance.Based on homogenization theory,effective stochastic elastic moduli of RAC at three different scales are obtained using moving window technique,nano-indentation digital images,and Monte-Carlo method.It involves the generation of a large number of random realizations of microstructure geometry based on different volume fraction of the inclusions and other parameters.The mean value,coefficient of variation and probability distribution of the effective elastic moduli are computed considering the material multiscale structure.The microscopic randomness is taken into account,and correlations of RAC among five phases are investigated.The effective elastic properties are used to obtain the global behavior of a composite structure.It is indicated that the response variability can be considerably affected by replacement percentage of recycled aggregates.
基金This research is supported by the National Key R&D Program of China(Grant No.2017YFB0305005).
文摘Equiatomic CrMnFeCoNi high entropy alloy prepared by powder metallurgy was remelted by laser.The relative density and microstructure of fusion zone are evaluated.The nanoindentation tests are conducted to reveal the hardness difference of dendrite arms and interdendritic areas.Tensile tests are conducted to assess the mechanical properties of remelted HEA.After laser remelting,the number and morphology of voids changed significantly.Dendritic structure with face-centered cubic phase form in the fusion zone.Fe,Cr and Co are enriched in dendrite arm,while Mn and Ni are enriched in interdendritic area.Elements segregation led to a nanohardness difference between dendrite arm and interdendritic area.Local deformation occurs in interdendritic area during tensile tests and results in a fracture with directionality.
基金supported by the National Natural Science Foundation of China (Grant No.41772333)the National Natural Science Foundation of Shaanxi Province, China (Grant No.2018JQ5124)the New-Star Talents Promotion Project of Science and Technology of Shaanxi Province, China (Grant No.2019KJXX049)。
文摘The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed.
基金supported by the Key-Area Research and Development Program of Guangdong Province(Grant No.2018B090905002)the National Natural Science Foundation of China(Grant No.52103360)the Basic Research Foundation of Guangzhou City(Grant No.201804020071).
文摘Microstructure and mechanical properties of non-equiatomic(CuNi)_(100-x)Co_(x)(x=15,20,25 and 30,at.%)medium-entropy alloys(MEAs)prepared by vacuum arc-melting were investigated.Results show that all the as-cast MEAs exhibit dual face-centered cubic(fcc)solid-solution phases with identical lattice constant,showing typical dendrite structure consisting of(Ni,Co)-rich phase in dendrites and Cu-rich phase in inter-dendrites.The positive enthalpy of mixing among Cu and Ni-Co elements is responsible for the segregation of Cu.With the increase of Co content,the volume fraction of(Ni,Co)-rich phase increases while the Cu-rich phase decreases,resulting in an increment of yield strength and a decrement of elongation for the(CuNi)_(100-x)Co_(x) MEAs.Nano-indentation test results show a great difference of microhardness between the two fcc phases of the MEAs.The measured microhardness value of the(Ni,Co)-rich phase is almost twofold as compared to that of the Cu-rich phase in all the(CuNi)_(100-x)Co_(x) MEAs.During the deformation of the MEAs,the Cu-rich phase bears the main plastic strain,whereas the(Ni,Co)-rich phase provides more pronounced strengthening.
文摘Nano-SiO2 particles strengthened Ni-based composite coating was designed and prepared on steel substrate. The structures and nanoparticle content of the nano-SiO2/Ni composite coating were determined by SEM, EDS and TEM; and the micro mechanical properties were tested by nano-indentation technique. The results show that 56% of particles in the solution are dispersed in size of less than 100nm, the content of nanoparticles co-deposited in the coating doubles and structure of the coating is more compact and uniform than that of Ni coating. Nano-SiO2/Ni coating exhibits excellent micro mechanical properties, and the nanohardness and elastic modulus are 7.81GPa and 198GPa, respectively, which are attributed to finer crystal strengthening, dispersion strengthening and high-density dislocation strengthening of nano-SiO2 particles to the composite coatings.
文摘Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site(Tournemire,CD borehole)for 18 years.In a saturated context and outside the excavation disturbed zone(EDZ),the claystone exhibits a 11.6-mm black rim at the cement/paste interface,which shows a different mechanical behaviour from the rest of the claystone.Three sets of measurements of elastic modulus were performed using:(i)nano-indentation tests with a constant indentation depth of 2 mm,(ii)microindentation tests with a constant indentation depth of 20 mm,and(iii)meso-compression tests with a constant displacement of 200 mm.The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale.Moreover,an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone.In view of the mineralogy and petrographic observations,higher values of modulus of deformability in the black rim are related to carbonate content and its distribution.Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone.
基金The authors would like to gratefully acknowledge Natural Science Foundation of China(31570552).
文摘In this study,Pinus massoniana Lamb at different heights,across the annual rings,and between earlywood and latewood was measured by X-ray diffraction and the chemical composition was analyzed by chemical treatment.Results indicated that the microfibril angle(MFA)decreased and the chemical composition changed little with the increase in height from 1 m to 9 m.In the radial direction,the MFA decreased and the chemical composition changed little with an increase in annual rings.The cellulose content of latewood was higher than that of early-wood.The viscoelastic changes of wood cell walls at different heights,across the annual rings by the method of quasi-static nanoindentation and dynamic modulus mapping techniques.Results indicated that the wood cell walls’elastic modulus increased,and the creep rate and creep compliance decreased with the increase in height;The elastic modulus and hardness increased with the annual rings.The cell walls’storage modulus increased and the loss modulus gradually decreased with an increase in height;the storage modulus gradually increased and the loss modulus decreased with the annual rings.
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFC0808800)the Natural Science Foundation of Jiangsu Higher Education Institutions,China(Grant No.17KJA460002)the“Six Talent Peaks”of Jiangsu Province,China(Grant No.GDZB-002)。
文摘Atomistic simulations are carried out to investigate the nano-indentation of single crystal Cu and the sliding of the Cu-Zn alloy.As the contact zone is extended due to adhesive interaction between the contact atoms,the contact area on a nanoscale is redefined.A comparison of contact area and contact force between molecular dynamics(MD)and contact theory based on Greenwood-Williamson(GW)model is made.Lower roughness causes the adhesive interaction to weaken,showing the better consistency between the calculated results by MD and those from the theoretical model.The simulations of the sliding show that the substrate wear decreases with the mol%of Zn increasing,due to the fact that the diffusion movements of Zn atoms in substrate are blocked during the sliding because of the hexagonal close packed(hcp)structure of Zn.
文摘Mineralized tissues are usually constructed of nanosized materials with ordered hierarchical structures. The main reason for their high load-bearing ability is the multi-scale hierarchy. It is important to have a method for measuring the energy absorbed during the nanoscale deformation of mineralized tissues. The objective of this study was to use a combination of nanoindentation and elastic-plastic mechanics techniques to measure the damage resistance of peritubular and intertubular dentin, based on the energy consumed in the plastic deformation regime and the volume created by the indents. The control materials were soda-lime glass, gold, and poly-methyl methacrylate (PMMA). Plastic deformation energy was calculated from the plastic part of load-displacement curves. The mean values of peritubular dentin and intertubular dentin were 3.8 × 10<sup>9</sup>, and 5.2 × 10<sup>9</sup> J/m<sup>3</sup>, respectively, compared to glass, PMMA, and gold which were 3.3 × 10<sup>7</sup>, 1.3 × 10<sup>9</sup>, and 3.1 × 10<sup>9</sup> J/m<sup>3</sup>, respectively. This method can be applied to study the resistance of mineralized tissues or organic/inorganic hybrid materials to deformation at the nanoscale.
文摘A Co-free as-cast AlCrAlCrFe_(2)Ni_(2)medium entropy alloy(MEA)with multi-phases was remelted by fiber laser in this study.The effect of laser remelting on the microstructure,phase distribution and mechanical properties was investigated by characterizing the as-cast and the remelted AlCrAlCrFe_(2)Ni_(2)alloy.The laser remelting process resulted in a significant decrease of grain size from about 780μm to 58.89μm(longitudinal section)and 15.87μm(transverse section)and an increase of hardness from 4.72±0.293 GPa to 6.40±0.147 GPa(longitudinal section)and 7.55±0.360 GPa(transverse section).It was also found that the long side plate-like microstructure composed of FCC phase,ordered B2 phase and disordered BCC phase in the as-cast alloy was transformed into nano-size weave-like microstructure consisting of alternating ordered B2 and disordered BCC phases.The mechanical properties were evaluated by the derived stressstrain relationship obtained from nano-indentation tests data.The results showed that the yield stress increased from 661.9 MPa to 1347.6 MPa(longitudinal section)and 1647.2 MPa(transverse section)after remelting.The individual contribution of four potential strengthening mechanisms to the yield strength of the remelted alloy was quantitatively evaluated,including grain boundary strengthening,dislocation strengthening,solid solution strengthening and precipitation strengthening.The calculation results indicated that dislocation and precipitation are dominant strengthening mechanisms in the laser remelted MEA.
文摘2219 aluminum alloys welding joints were prepared by Friction stir welding (FSW) and Variable polarity plasma arc welding (VPPAW).The microstructure of joints was characterized by means of OM,SEM,and EDX.Microhardness measurements was performed to differentiate the joint zones and to evaluate the symmetry level of the joints with the help of nano-indentation experiment.The dissymmetry of microstructure and mechanical properties was found both in FSW joint and VPPAW joint.The dissymmetry in FSW joint can not be suppressed due to the nature of the mixing head,but the symmetry and satisfactory welding joint can be obtained by changing the working pattern of VPPAW.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Ministry of Science,ICT(MSIT)[NRF-2020R1A5A6017701,NRF-2019M3D1A1079214,and NRF-2020R1A6A3A13076748]the ITER Technology R&D Programme。
文摘Tungsten as a material exhibits broad and increasingly important applications;however,the characterization of its ductile-to-brittle transition(BDT)is currently limited to large-scale scenarios and destructive testing.In this study,we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure tungsten.In order to predict the failure mode at various temperature ranges,the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with temperature.High temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures,which is required for dislocation activities in an atomic scaled activation volume.On one hand,atomistic simulations have provided the temperature dependence of brittle fracture stress,where the atomic bonds break due to intergranular or intragranular fracture.We considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing,and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data processing.The fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests,which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure tungsten.Based on the BDT estimations by small-scale characterization,we provided further insights into the factors affecting the BDT behavior of tungsten,focusing on the contributions of different types of dislocations.
文摘The influence of titanium alloy(Ti–5 Al–2.5 Sn) and commercially pure titanium(cp Ti) as fillers on dissimilar pulsed tungsten inert gas weldments of Ti–5 Al–2.5 Sn/cp Ti was investigated in terms of microstructure, mechanical/nano-mechanical properties, and residual stresses. A partial martensitic transformation was observed in the weldments for all the welding conditions due to high heat input. The microstructure evolved in the FZ/cp Ti interfacial region was observed to be the most sensitive to the proportion of α stabilizer in the filler alloy. Furthermore, the addition of filler alloy improved the tensile properties and nano-mechanical response of the weld joint owing to the increased volume of metal in the weld joint. As compared to the Ti–5 Al–2.5 Sn wire, the use of cp Ti filler wire proved to be better in terms of energy absorbed during tensile and impact tests, tensile strength and ductility of the dissimilar welds. An asymmetrical residual stresses profile was observed close to the weld centerline, with high compressive stresses on the Ti–5 Al–2.5 Sn side for both the weldments obtained with and without filler wires. This was attributed to mainly the low thermal conductivity of Ti–5 Al–2.5 Sn. The presence of residual stresses also influenced the nano-hardness profile across the weldments.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51502126 and 51672119)the Natural Science Foundation of Liaoning Province(No.20180550802).
文摘The diamond-like carbon(DLC)film on 316L stainless steel substrate was preparedpulsed plasma-enhanced chemical vapor deposition,and the performance of the films was optimizedregulating the pulse voltage.Microstructure and properties of DLC film on 316L stainless steel were characterizedatomic force microscopy,field-emission scanning electron microscopy,Raman spectra,nano-indenter and electrochemical workstations.The results showed that DLC films with smooth and dense morphology have a low friction coefficient and high nano-indentation hardness,and the surface hardness of 316L stainless steel substrate was enhancedmore than 3 times.The mechanical properties of DLC films and their bond with 316L stainless steel could be further optimizedincreasing pulse voltage.DLC films on 316L stainless steel substrate increased the self-corrosion potential0.173 V and decreased self-corrosion current99%,which significantly improved the anti-corrosive properties of 316L substrate.
