The presence of residual stresses in materials or engineering structures can significantly influence their mechanical per-formance.Accurate measurement of residual stresses is of great importance to ensure their in-se...The presence of residual stresses in materials or engineering structures can significantly influence their mechanical per-formance.Accurate measurement of residual stresses is of great importance to ensure their in-service reliability.Although numerous instrumented indentation methods have been proposed to evaluate residual stresses,the majority of them require a stress-free reference sample as a comparison benchmark,thereby limiting their applicability in scenarios where obtaining stress-free reference samples is challenging.In this work,through a number of finite element simulations,it was found that the loading exponent of the loading load-depth curve and the recovered depth during unloading are insensitive to residual stresses.The loading curve of the stress-free specimen was virtually reconstructed using such stress-insensitive parameters extracted from the load-depth curves of the stressed state,thus eliminating the requirement for stress-free reference samples.The residual stress was then correlated with the fractional change in loading work between stressed and stress-free loading curves through dimensional analysis and finite element simulations.Based on this correlation,an instrumented sharp indentation method for measuring equibiaxial residual stress without requiring a stress-free specimen was established.Both numerical and experimental verifications were carried out to demonstrate the accuracy and reliability of the newly proposed method.The maximum relative error and absolute error in measured residual stresses are typically within±20%and±20 MPa,respectively.展开更多
We study the axisymmetric frictionless indentation problem of a piezoelectric semiconductor(PSC)thin film perfectly bonded to a semi-infinite isotropic elastic substrate by a rigid and insulating spherical indenter.Th...We study the axisymmetric frictionless indentation problem of a piezoelectric semiconductor(PSC)thin film perfectly bonded to a semi-infinite isotropic elastic substrate by a rigid and insulating spherical indenter.The Hankel integral transformation is first employed to derive the general solutions for the governing differential equations of the PSC film and elastic substrate.Then,using the boundary and interface conditions,the complicated indentation problem is reduced to numerically solve a Fredholm integral equation of the second kind.Numerical results are given to demonstrate the effects of semiconducting property,film thickness as well as Young’s modulus and Poisson’s ratio of the substrate on the indentation responses.The obtained findings will contribute to the establishment of indentation experiments for PSC film/substrate systems.展开更多
The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redu...The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redundant tensile testing on specimens prepared along diverse directions,this study proposes an instrumented indentation-based inverse identification method for the efficient characterization of additively manufactured materials.In the present work,a 3D finite element model of indentation test is first established for the printed material,for which an anisotropic material constitutive model is incorporated.We have demonstrated that the indentation responses are information-rich,and material anisotropy along different directions can be interpreted by a single indentation imprint.Subsequently,an inverse identification framework is built,in which an Euclidean error norm between simulated and experimental indentation responses is minimized via optimization algorithms such as the Globally Convergent Method of Moving Asymptotes(GCMMA).The developed method has been verified on diverse printed materials referring to either the indentation curve or the residual imprint,and the superiority of this latter over the former is confirmed by a better and faster convergence of inverse identification.Experimental validations on 3D printed materials(including stainless steel 316L,aluminum alloy AlSi10Mg,and titanium alloy TC4)reveal that the developed method is both accurate and reliable when compared with material constitutive behaviors obtained from uni-axial tensile tests,regardless of the degree of anisotropy among different materials.展开更多
This work investigates the indentation response of an elastic plate resting upon a thin,transversely isotropic elastic layer supported by a rigid substrate.Such a scenario is encountered across a range of length scale...This work investigates the indentation response of an elastic plate resting upon a thin,transversely isotropic elastic layer supported by a rigid substrate.Such a scenario is encountered across a range of length scales from piezoresistive tests on graphite nanoflakes to the bending of floating ice shelves atop seabed,where the elastic layer commonly exhibits certain anisotropy.We first develop an approximate model to describe the elastic response of a transversely isotropic layer by exploiting the slenderness of the layer.We show that this approximate model can be reduced to the classic compressible Winkler foundation model as the elastic constants of the layer are set isotropic.We then investigate the combined response of an elastic plate on the transversely isotropic elastic layer.Facilitated by the simplicity of our proposed approximate model,we can derive simple analytical solutions for the cases of small and large indenter radi.The analytical results agree well with numerical calculations obtained via finite element methods,as long as the system is sufficiently slender in a mechanical sense.These results offer quantitative insights into the mechanical behavior of numerous semiconductor materials characterized by transverse isotropy and employed with slender geometries in various practical applications where the thin layer works as conductive and functional layers.展开更多
Some factors that affect the experimental results in nanoindentation tests such as the contact depth,contact area,load and loading duration are analyzed in this article. Combining with the results of finite element nu...Some factors that affect the experimental results in nanoindentation tests such as the contact depth,contact area,load and loading duration are analyzed in this article. Combining with the results of finite element numerical simulation,we find that the creep property of the tested material is one of the important factors causing the micron indentation hardness descending with the increase of indentation depth. The analysis of experimental results with different indentation depths demonstrates that the hardn...展开更多
Rock macro-indentation plays a fundamental role in mechanical rock breaking for various rock engineering application,such as drilling,tunneling,cutting,and sawing.Over the past decades,extensive research has been cond...Rock macro-indentation plays a fundamental role in mechanical rock breaking for various rock engineering application,such as drilling,tunneling,cutting,and sawing.Over the past decades,extensive research has been conducted to understand the indentation mechanisms and responses through various approaches.This review aims to provide an overview of the current status and recent advancements in theories,experiments,numerical simulations,and applications of macro-indentation in rock engineering.It starts with elaborating on the mechanisms of macro-indentation,followed by a discussion of the merits and limitations of commonly used models.Influence factors and their effects on indentation test results are then summarized.Various numerical simulation methods for rock macro-indentation are highlighted,along with their advantages and disadvantages.Subsequently,the applications of indentation tests and indentation indices in characterizing rock properties are explored.It reveals that compression-tension,compression-shear,and composite models are widely employed in rock macroindentation.While the compression-tension model is straightforward to use,it may overlook the anisotropic properties of rocks.On the other hand,the composite model provides a more comprehensive description of rock indentation but requires complex calculations.Additionally,factors,such as indentation rate,indenter geometry,rock type,specimen size,and confining pressure,can significantly influence the indentation results.Simulation methods for macro-indentation encompass continuous medium,discontinuous medium,and continuous-discontinuous medium methods,with selection based on their differences in principle.Furthermore,rock macro-indentation can be practically applied to mining engineering,tunneling engineering,and petroleum drilling engineering.Indentation indices serve as valuable tools for characterizing rock strength,brittleness,and drillability.This review sheds light on the development of rock macro-indentation and its extensive application in engineering practice.Specialists in the field can gain a comprehensive understanding of the indentation process and its potential in various rock engineering endeavors.展开更多
Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect a...Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect and indentation size effect were explored.The indentation hardness was fitted using the Nix-Gao model by considering the scaling factor.The results show that the scaling factor is barely correlated with the grain/sub-grain size.The interaction between the plastically deformed zone（PDZ） boundary and the grain/sub-grain boundary is believed to be the reason that leads to an increase of the measured hardness at the specific depths.Results also indicate that the area of the PDZ is barely correlated with the grain/sub-grain size,and the indentation hardness starts to stabilize once the PDZ expands to the dimension of an individual grain/sub-grain.展开更多
The indentation method is useful in determining the residual stress according to the elastic-plastic properties of materials.So the effect of the residual stress on the elastic-plastic indentation properties of materi...The indentation method is useful in determining the residual stress according to the elastic-plastic properties of materials.So the effect of the residual stress on the elastic-plastic indentation properties of materials was studied by using the finite element method to find better indentation parameters which are strongly induced by the residual stress.The results show that load-depth curve,plastic pile-up,indentation shape,indentation contact stress and indentation residual stress are affected by different residual stress,and these parameters can be used to deduce the residual stress.Also,a special indentation equipment was developed to analyze the elastic-plastic properties of materials with different residual stress,and the experimental results show a good agreement with the FEM results.For practical application,the elastic-plastic indentation properties of materials with unknown residual stress could be obtained by the developed equipment to deduce the residual stress comprehensively.展开更多
Cr/CrN multilayer coatings with bilayer periods in the range from 1351 to 260 nm were prepared on 304 stainless steel substrates by arc ion plating to study the microstructure and properties of multilayer coatings and...Cr/CrN multilayer coatings with bilayer periods in the range from 1351 to 260 nm were prepared on 304 stainless steel substrates by arc ion plating to study the microstructure and properties of multilayer coatings and stimulate their application.SEM results confirm the clear periodicity of the Cr/CrN multilayer coatings and the clear interface between individual layers.XRD patterns reveal that these multilayer coatings contain Cr,CrN and Cr_2N phases.Because Cr layer is softer than its nitride layer,the hardness decreases with the shortening of the bilayer period(or increasing volume fraction of Cr layer).The Cr/CrN multilayer coating with 862 nm period possesses the highest indentation toughness due to a proper individual Cr and nitride layer thickness.However,for the Cr/CrN multilayer with the bilayer period of 1351 nm,it possesses the lowest toughness due to more nitride phase.The indentation toughness of Cr/CrN multilayer coatings is related with their bilayer period.A coating with a proper individual Cr and nitride layer thickness possesses the highest indentation toughness.展开更多
The quasi-static indentation behavior of sandwich beams with a metal foam core was investigated. An analytical model was developed to predict the large deflections of indention of the sandwich beams with a metal foam ...The quasi-static indentation behavior of sandwich beams with a metal foam core was investigated. An analytical model was developed to predict the large deflections of indention of the sandwich beams with a metal foam core subjected to a concentrated loading. The interaction of plastic bending and stretching in the local deformation regions of the face sheet was considered in the analytical model. Moreover, the effects of the shear strength of the foam core on the indentation behavior were discussed in detail. The finite element simulations were preformed to validate the theoretical model. Comparisons between the analytical predictions and finite element results were conducted and good agreement was achieved. The results show that the membrane force dominates indentation behavior of the sandwich beams when the maximum deflection exceeds the thickness of the face sheet.展开更多
In this paper,NiCr-Cr3C2 coating was deposited onto AISI 1045 steel substrate by employing supersonic plasma spraying technique.The surface and cross-section morphologies of the NiCr-Cr3C2 coating were observed by SEM...In this paper,NiCr-Cr3C2 coating was deposited onto AISI 1045 steel substrate by employing supersonic plasma spraying technique.The surface and cross-section morphologies of the NiCr-Cr3C2 coating were observed by SEM.The phase constituents of the coating were identified by XRD.The SEM images showed that the coating was very dense,and it had a low porosity structure.The XRD pattern implied that the coating was mainly composed of NiCr,Cr3C2 and Cr7C2.Nanoindentation tests were performed on the coating surface by a Nano indenter.The widely used Oliver-Pharr method was adopted to extract the mechanical properties of the coating.The hardness exhibited a strong peak-load-dependence,i.e.indentation size effect;the elastic modulus was not affected by indentation size effect.展开更多
A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R...A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. <展开更多
Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying...Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying loads in the range of 25-1000μN. Simultaneously, AFM images of the sample surface were recorded before and after indentation process .For type 316 stainless steel, the indentation size effect was found. The results were discussed in the terms of the model of geometrically necessary dislocations proposed to interpret the indentation size effect.It can be seen that the square of the nanohardness, H 2, vs the inverse of indentation depth, 1/h, is linearly dependent on the indented depth in the range of 25-150nm,which is a good qualitative agreement with the predictions of the model. However, for shallow indents, the slope of the line severely changes.Some possible mechanisms for this change were proposed.展开更多
We present a multimodal ferrule-top sensor designed to perform the integrated epidetection of Optical Coberence Tomognphy(OCT)depth-profiles and micron-scale indentation by all-optical detection.By scarning a sample u...We present a multimodal ferrule-top sensor designed to perform the integrated epidetection of Optical Coberence Tomognphy(OCT)depth-profiles and micron-scale indentation by all-optical detection.By scarning a sample under the probe,we can obtain structural crosse soction images and identify a region of interest in a nonhomogencous sample.Then,with the same probe and setup,we can immediately target that area with a series of spherical indentation measurements,in which the applied load is known with aμN precision,the indentation depth with sub-/m precision and a maximum contact radius of 100 pm.Thanks to the visualization of the internal structure of the sample,we can gain a better insi ght into the observed mechanical behavior.The ability to impart a small,confined load,and perfomn OCT A scans at the same time,could lead to an altemative,high transverse resolution,Optical Coherence Elastography(OCE)sensor.展开更多
Indentations onto crystalline silicon and copper with various indenter geometries, loading forces at room temperature belong to the widest interests in the field, because of the physical detection of structural phase ...Indentations onto crystalline silicon and copper with various indenter geometries, loading forces at room temperature belong to the widest interests in the field, because of the physical detection of structural phase transitions. By using the mathematically deduced F<sub>N</sub>h<sup>3/2 </sup>relation for conical and pyramidal indentations we have a toolbox for deciding between faked and experimental loading curves. Four printed silicon indentation loading curves (labelled with 292 K, 260 K, 240 K and 210 K) proved to be faked and not experimental. This is problematic for the AI (artificial intelligence) that will probably not be able to sort faked data out by itself but must be told to do so. High risks arise, when published faked indentation reports remain unidentified and unreported for the mechanics engineers by reading, or via AI. For example, when AI recommends a faked quality such as “no phase changes” of a technical material that is therefore used, it might break down due to an actually present low force, low transition energy phase-change. This paper thus installed a tool box for the distinction of experimental and faked loading curves of indentations. We found experimental and faked loading curves of the same research group with overall 14 authoring co-workers in three publications where valid and faked ones were next to each other and I can thus only report on the experimental ones. The comparison of Si and Cu with W at 20-fold higher physical hardness shows its enormous influence to the energies of phase transition and of their transition energies. Thus, the commonly preferred ISO14577-ASTM hardness values HISO (these violate the energy law and are simulated!) leads to almost blind characterization and use of mechanically stressed technical materials (e.g. airplanes, windmills, bridges, etc). The reasons are carefully detected and reported to disprove that the coincidence or very close coincidence of all of the published loading curves from 150 K to 298 K are constructed but not experimental. A tool-box for distinction of experimental from faked indentation loading curves (simulations must be indicated) is established in view of protecting the AI from faked data, which it might not be able by itself to sort them out, so that technical materials with wrongly attributed mechanical properties might lead to catastrophic accidents such as all of us know of. There is also the risk that false theories might lead to discourage the design of important research projects or for not getting them granted. This might for example hamper or ill-fame new low temperature indentation projects. The various hints for identifying faked claims are thus presented in great detail. The low-temperature instrumental indentations onto silicon have been faked in two consecutive publications and their reporting in the third one, so that these are not available for the calculation of activation energies. Conversely, the same research group published an indentation loading curve of copper as taken at 150 K that could be tested for its validity with the therefore created tools of validity tests. The physical algebraic calculations provided the epochal detection of two highly exothermic phase transitions of copper that created two polymorphs with negative standard energy content. This is world-wide the second case and the first one far above the 77 K of liquid nitrogen. Its existence poses completely new thoughts for physics chemistry and perhaps techniques but all of them are open and unprepared for our comprehension. The first chemical reactions might be in-situ photolysis and the phase transitions can be calculated from experimental curves. But several further reported low temperature indentation loading curves of silicon were tested for their experimental reality. And the results are compared to new analyses with genuine room temperature results. A lot is to be learned from the differences at room and low temperature.展开更多
A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R...A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. 【展开更多
The increasing use of small material components in a wide range of industrial fields necessitates the development of an accurate and robust indentation testing method.To this end,this paper proposes an Energy-density-...The increasing use of small material components in a wide range of industrial fields necessitates the development of an accurate and robust indentation testing method.To this end,this paper proposes an Energy-density-equivalence for a Flat Indentation(E-FI)model based on the energy density equivalent principle.The proposed model describes the relationships among the material parameters of Hollomon's power law(H-law),flat indenter diameter,energy,and indentation displacement.An E-FI Method(E-FIM)that determines the H-law parameters of materials through the indentation test is also developed.The energy-displacement curves forward-predicted by the E-FI model(based on known H-law parameters of materials)and the H-law parameters of materials given by the E-FIM(based on known energy-displacement curves)are consistent with the results of Finite Element Analysis(FEA)and the H-law parameters of materials used as the input for FEA,respectively.Using E-FIM,the goodness of fit for both stress–strain curves with H-law,predicted based on the displacement with 2%signal interference,and that for stress–strain curves without interference is more than 0.98.The stress–strain relations predicted by E-FIM were consistent with the results obtained via uniaxial tensile tests of ten ductile materials.展开更多
The rock indentation tests by a conical pick were conducted to investigate the rock cuttability correlated to confining stress conditions and rock strength.Based on the test results,the regression analyses,support vec...The rock indentation tests by a conical pick were conducted to investigate the rock cuttability correlated to confining stress conditions and rock strength.Based on the test results,the regression analyses,support vector machine(SVM)and generalized regression neural network(GRNN)were used to find the relationship among rock cuttability,uniaxial confining stress applied to rock,uniaxial compressive strength(UCS)and tensile strength of rock material.It was found that the regression and SVM-based models can accurately reflect the variation law of rock cuttability,which presented decreases followed by increases with the increase in uniaxial confining stress and the negative correlation to UCS and tensile strength of rock material.Based on prediction models for revealing the optimal stress condition and determining the cutting parameters,the axial boom roadheader with many conical picks mounted was satisfactorily utilized to perform rock cutting in hard phosphate rock around pillar.展开更多
The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very ＂smoothed＂ surface and investigate the machining-induced ...The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very ＂smoothed＂ surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the influence factors on brittle/ductile transition behavior,the wear of diamond grits in diamond grinding of ultra pure fused silica（UPFS） are investigated by means of micro/nano indentation technique,as well as single grit diamond grinding on an ultra-stiff machine tool,Tetraform ＂C＂.The single grit grinding processes are in-process monitored using acoustic emission（AE） and force dynamometer simultaneously.The wear of diamond grits,morphology and subsurface integrity of the machined groves are examined with atomic force microscope（AFM） and scanning electron microscope（SEM）.The critical brittle/ductile depth of more than 0.5 μm is achieved.When compared to the using roof-like grits,by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters.However,the influence of grit shapes on the critical depth is not significant as supposed.The grinding force increased linearly with depth of cut in the ductile removal regime,but in brittle removal regime,there are large fluctuations instead of forces increase.The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves.Furthermore,The SEM photographs show multi worn patterns of diamond grits,indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels.The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.展开更多
The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In...The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In this paper, mathematical analysis on a reverse algorithm from Dao model （Dao et al., Acta Mater., 2001, 49, 3899） was carried out, which thought that only when 20 ≤E＊/σ0.033≤ 26 and 0.3n≤ 0.5, the reverse algorithm would yield two solutions of n by dimensionless function Π2. It is shown that, however, there are also two solutions of n when 20≤E＊/σ0.033≤ 26 and 0≤n0.1. A unique n can be obtained by dimensionless function Π3 instead of Π2 in these two ranges. E and H can be uniquely determined by a full indentation curve, and σy can be determined if n is unique. Furthermore, sensitivity analysis on obtaining n from dimensionless function Π3 or Π2 has been made.展开更多
基金support from the National Natural Science Foundation of China(Grant Nos.12172332,11727803 and 12072009)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ23A020007)the Fundamental Research Funds for the Provincial Universities of Zhejiang(Grant No.RF-C2022003).
文摘The presence of residual stresses in materials or engineering structures can significantly influence their mechanical per-formance.Accurate measurement of residual stresses is of great importance to ensure their in-service reliability.Although numerous instrumented indentation methods have been proposed to evaluate residual stresses,the majority of them require a stress-free reference sample as a comparison benchmark,thereby limiting their applicability in scenarios where obtaining stress-free reference samples is challenging.In this work,through a number of finite element simulations,it was found that the loading exponent of the loading load-depth curve and the recovered depth during unloading are insensitive to residual stresses.The loading curve of the stress-free specimen was virtually reconstructed using such stress-insensitive parameters extracted from the load-depth curves of the stressed state,thus eliminating the requirement for stress-free reference samples.The residual stress was then correlated with the fractional change in loading work between stressed and stress-free loading curves through dimensional analysis and finite element simulations.Based on this correlation,an instrumented sharp indentation method for measuring equibiaxial residual stress without requiring a stress-free specimen was established.Both numerical and experimental verifications were carried out to demonstrate the accuracy and reliability of the newly proposed method.The maximum relative error and absolute error in measured residual stresses are typically within±20%and±20 MPa,respectively.
基金supported by the National Natural Science Foundation of China(Nos.12072209,U21A20430,12192211,12472155)the S&T Program of Hebei(225676162GH).
文摘We study the axisymmetric frictionless indentation problem of a piezoelectric semiconductor(PSC)thin film perfectly bonded to a semi-infinite isotropic elastic substrate by a rigid and insulating spherical indenter.The Hankel integral transformation is first employed to derive the general solutions for the governing differential equations of the PSC film and elastic substrate.Then,using the boundary and interface conditions,the complicated indentation problem is reduced to numerically solve a Fredholm integral equation of the second kind.Numerical results are given to demonstrate the effects of semiconducting property,film thickness as well as Young’s modulus and Poisson’s ratio of the substrate on the indentation responses.The obtained findings will contribute to the establishment of indentation experiments for PSC film/substrate systems.
基金Supported by National Key R&D Program of China(Grant Nos.2022YFB4603101,2022YFB3402200)Key Project of NSFC of China(Grant No.92271205)Sichuan Provincial Science and Technology Program and Fundamental Research Funds for the Central Universities of China(Grant No.D5000230049).
文摘The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redundant tensile testing on specimens prepared along diverse directions,this study proposes an instrumented indentation-based inverse identification method for the efficient characterization of additively manufactured materials.In the present work,a 3D finite element model of indentation test is first established for the printed material,for which an anisotropic material constitutive model is incorporated.We have demonstrated that the indentation responses are information-rich,and material anisotropy along different directions can be interpreted by a single indentation imprint.Subsequently,an inverse identification framework is built,in which an Euclidean error norm between simulated and experimental indentation responses is minimized via optimization algorithms such as the Globally Convergent Method of Moving Asymptotes(GCMMA).The developed method has been verified on diverse printed materials referring to either the indentation curve or the residual imprint,and the superiority of this latter over the former is confirmed by a better and faster convergence of inverse identification.Experimental validations on 3D printed materials(including stainless steel 316L,aluminum alloy AlSi10Mg,and titanium alloy TC4)reveal that the developed method is both accurate and reliable when compared with material constitutive behaviors obtained from uni-axial tensile tests,regardless of the degree of anisotropy among different materials.
基金supported by the National Natural Science Foundation of China(12372103)the Opening Fund of State Key Laboratory of Nonlinear Mechanics(Institute of Mechanics,CAS)the Fundamental Research Funds for Central Universities(Peking University).
文摘This work investigates the indentation response of an elastic plate resting upon a thin,transversely isotropic elastic layer supported by a rigid substrate.Such a scenario is encountered across a range of length scales from piezoresistive tests on graphite nanoflakes to the bending of floating ice shelves atop seabed,where the elastic layer commonly exhibits certain anisotropy.We first develop an approximate model to describe the elastic response of a transversely isotropic layer by exploiting the slenderness of the layer.We show that this approximate model can be reduced to the classic compressible Winkler foundation model as the elastic constants of the layer are set isotropic.We then investigate the combined response of an elastic plate on the transversely isotropic elastic layer.Facilitated by the simplicity of our proposed approximate model,we can derive simple analytical solutions for the cases of small and large indenter radi.The analytical results agree well with numerical calculations obtained via finite element methods,as long as the system is sufficiently slender in a mechanical sense.These results offer quantitative insights into the mechanical behavior of numerous semiconductor materials characterized by transverse isotropy and employed with slender geometries in various practical applications where the thin layer works as conductive and functional layers.
基金National Natural Science Foundation of China (10772183, 10532070)
文摘Some factors that affect the experimental results in nanoindentation tests such as the contact depth,contact area,load and loading duration are analyzed in this article. Combining with the results of finite element numerical simulation,we find that the creep property of the tested material is one of the important factors causing the micron indentation hardness descending with the increase of indentation depth. The analysis of experimental results with different indentation depths demonstrates that the hardn...
基金the Yunlong Lake Laboratory of Deep Underground Science and Engineering(Grant No.104023005)the National Natural Science Foundation of China(Grant No.52308403)China Postdoctoral Science Foundation(Grant No.2023M731998)for funding provided to this work.
文摘Rock macro-indentation plays a fundamental role in mechanical rock breaking for various rock engineering application,such as drilling,tunneling,cutting,and sawing.Over the past decades,extensive research has been conducted to understand the indentation mechanisms and responses through various approaches.This review aims to provide an overview of the current status and recent advancements in theories,experiments,numerical simulations,and applications of macro-indentation in rock engineering.It starts with elaborating on the mechanisms of macro-indentation,followed by a discussion of the merits and limitations of commonly used models.Influence factors and their effects on indentation test results are then summarized.Various numerical simulation methods for rock macro-indentation are highlighted,along with their advantages and disadvantages.Subsequently,the applications of indentation tests and indentation indices in characterizing rock properties are explored.It reveals that compression-tension,compression-shear,and composite models are widely employed in rock macroindentation.While the compression-tension model is straightforward to use,it may overlook the anisotropic properties of rocks.On the other hand,the composite model provides a more comprehensive description of rock indentation but requires complex calculations.Additionally,factors,such as indentation rate,indenter geometry,rock type,specimen size,and confining pressure,can significantly influence the indentation results.Simulation methods for macro-indentation encompass continuous medium,discontinuous medium,and continuous-discontinuous medium methods,with selection based on their differences in principle.Furthermore,rock macro-indentation can be practically applied to mining engineering,tunneling engineering,and petroleum drilling engineering.Indentation indices serve as valuable tools for characterizing rock strength,brittleness,and drillability.This review sheds light on the development of rock macro-indentation and its extensive application in engineering practice.Specialists in the field can gain a comprehensive understanding of the indentation process and its potential in various rock engineering endeavors.
基金Project(51174235)supported by the National Natural Science Foundation of China
文摘Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect and indentation size effect were explored.The indentation hardness was fitted using the Nix-Gao model by considering the scaling factor.The results show that the scaling factor is barely correlated with the grain/sub-grain size.The interaction between the plastically deformed zone（PDZ） boundary and the grain/sub-grain boundary is believed to be the reason that leads to an increase of the measured hardness at the specific depths.Results also indicate that the area of the PDZ is barely correlated with the grain/sub-grain size,and the indentation hardness starts to stabilize once the PDZ expands to the dimension of an individual grain/sub-grain.
基金Supported by the Science Research Fund of Shanghai Education Council(No.06VZ004)
文摘The indentation method is useful in determining the residual stress according to the elastic-plastic properties of materials.So the effect of the residual stress on the elastic-plastic indentation properties of materials was studied by using the finite element method to find better indentation parameters which are strongly induced by the residual stress.The results show that load-depth curve,plastic pile-up,indentation shape,indentation contact stress and indentation residual stress are affected by different residual stress,and these parameters can be used to deduce the residual stress.Also,a special indentation equipment was developed to analyze the elastic-plastic properties of materials with different residual stress,and the experimental results show a good agreement with the FEM results.For practical application,the elastic-plastic indentation properties of materials with unknown residual stress could be obtained by the developed equipment to deduce the residual stress comprehensively.
基金Project(51171118)supported by the National Natural Science Foundation of ChinaProject(2012-4)supported by the Liaoning Provincial Key Laboratory of Advanced Materials,Shenyang University,China
文摘Cr/CrN multilayer coatings with bilayer periods in the range from 1351 to 260 nm were prepared on 304 stainless steel substrates by arc ion plating to study the microstructure and properties of multilayer coatings and stimulate their application.SEM results confirm the clear periodicity of the Cr/CrN multilayer coatings and the clear interface between individual layers.XRD patterns reveal that these multilayer coatings contain Cr,CrN and Cr_2N phases.Because Cr layer is softer than its nitride layer,the hardness decreases with the shortening of the bilayer period(or increasing volume fraction of Cr layer).The Cr/CrN multilayer coating with 862 nm period possesses the highest indentation toughness due to a proper individual Cr and nitride layer thickness.However,for the Cr/CrN multilayer with the bilayer period of 1351 nm,it possesses the lowest toughness due to more nitride phase.The indentation toughness of Cr/CrN multilayer coatings is related with their bilayer period.A coating with a proper individual Cr and nitride layer thickness possesses the highest indentation toughness.
基金Projects(11102146,11372235,11272246,11021202,11002107)supported by the National Natural Science Foundation of ChinaProject(2011CB610301)supported by the National Basic Research Program of ChinaProject supported by the Fundamental Research Funds for the Central Universities,China
文摘The quasi-static indentation behavior of sandwich beams with a metal foam core was investigated. An analytical model was developed to predict the large deflections of indention of the sandwich beams with a metal foam core subjected to a concentrated loading. The interaction of plastic bending and stretching in the local deformation regions of the face sheet was considered in the analytical model. Moreover, the effects of the shear strength of the foam core on the indentation behavior were discussed in detail. The finite element simulations were preformed to validate the theoretical model. Comparisons between the analytical predictions and finite element results were conducted and good agreement was achieved. The results show that the membrane force dominates indentation behavior of the sandwich beams when the maximum deflection exceeds the thickness of the face sheet.
基金Advanced Maintenance Research Project(9140A270304090C8501)National Natural Science Foundations of China(50975285,50735006)Equipment Research Project,and Fundamental Research Funds for the Central Universities(2009PY08)
文摘In this paper,NiCr-Cr3C2 coating was deposited onto AISI 1045 steel substrate by employing supersonic plasma spraying technique.The surface and cross-section morphologies of the NiCr-Cr3C2 coating were observed by SEM.The phase constituents of the coating were identified by XRD.The SEM images showed that the coating was very dense,and it had a low porosity structure.The XRD pattern implied that the coating was mainly composed of NiCr,Cr3C2 and Cr7C2.Nanoindentation tests were performed on the coating surface by a Nano indenter.The widely used Oliver-Pharr method was adopted to extract the mechanical properties of the coating.The hardness exhibited a strong peak-load-dependence,i.e.indentation size effect;the elastic modulus was not affected by indentation size effect.
文摘A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. <
基金FundedbytheNationalNaturalScienceFoundationofChi na (No .5 0 1710 13)andtheSpecialFoundationfortheNationalStateBasicResearchProject(No.G19990 6 5 0 )
文摘Nanoindentation size effect was investigated under very low loads on type 316 stainless steel. Nanoindentation measurements were carried out on the samples surfaces with a Berkovich pyramidal diamond indenter applying loads in the range of 25-1000μN. Simultaneously, AFM images of the sample surface were recorded before and after indentation process .For type 316 stainless steel, the indentation size effect was found. The results were discussed in the terms of the model of geometrically necessary dislocations proposed to interpret the indentation size effect.It can be seen that the square of the nanohardness, H 2, vs the inverse of indentation depth, 1/h, is linearly dependent on the indented depth in the range of 25-150nm,which is a good qualitative agreement with the predictions of the model. However, for shallow indents, the slope of the line severely changes.Some possible mechanisms for this change were proposed.
基金supported by the Dutch Technology Foundation (STW) under the OMNE program (13183)funding from LASERLABEUROPE under the EC's Seventh Framework Program (Grant agreement No.284464)the European Research Council (615170).
文摘We present a multimodal ferrule-top sensor designed to perform the integrated epidetection of Optical Coberence Tomognphy(OCT)depth-profiles and micron-scale indentation by all-optical detection.By scarning a sample under the probe,we can obtain structural crosse soction images and identify a region of interest in a nonhomogencous sample.Then,with the same probe and setup,we can immediately target that area with a series of spherical indentation measurements,in which the applied load is known with aμN precision,the indentation depth with sub-/m precision and a maximum contact radius of 100 pm.Thanks to the visualization of the internal structure of the sample,we can gain a better insi ght into the observed mechanical behavior.The ability to impart a small,confined load,and perfomn OCT A scans at the same time,could lead to an altemative,high transverse resolution,Optical Coherence Elastography(OCE)sensor.
文摘Indentations onto crystalline silicon and copper with various indenter geometries, loading forces at room temperature belong to the widest interests in the field, because of the physical detection of structural phase transitions. By using the mathematically deduced F<sub>N</sub>h<sup>3/2 </sup>relation for conical and pyramidal indentations we have a toolbox for deciding between faked and experimental loading curves. Four printed silicon indentation loading curves (labelled with 292 K, 260 K, 240 K and 210 K) proved to be faked and not experimental. This is problematic for the AI (artificial intelligence) that will probably not be able to sort faked data out by itself but must be told to do so. High risks arise, when published faked indentation reports remain unidentified and unreported for the mechanics engineers by reading, or via AI. For example, when AI recommends a faked quality such as “no phase changes” of a technical material that is therefore used, it might break down due to an actually present low force, low transition energy phase-change. This paper thus installed a tool box for the distinction of experimental and faked loading curves of indentations. We found experimental and faked loading curves of the same research group with overall 14 authoring co-workers in three publications where valid and faked ones were next to each other and I can thus only report on the experimental ones. The comparison of Si and Cu with W at 20-fold higher physical hardness shows its enormous influence to the energies of phase transition and of their transition energies. Thus, the commonly preferred ISO14577-ASTM hardness values HISO (these violate the energy law and are simulated!) leads to almost blind characterization and use of mechanically stressed technical materials (e.g. airplanes, windmills, bridges, etc). The reasons are carefully detected and reported to disprove that the coincidence or very close coincidence of all of the published loading curves from 150 K to 298 K are constructed but not experimental. A tool-box for distinction of experimental from faked indentation loading curves (simulations must be indicated) is established in view of protecting the AI from faked data, which it might not be able by itself to sort them out, so that technical materials with wrongly attributed mechanical properties might lead to catastrophic accidents such as all of us know of. There is also the risk that false theories might lead to discourage the design of important research projects or for not getting them granted. This might for example hamper or ill-fame new low temperature indentation projects. The various hints for identifying faked claims are thus presented in great detail. The low-temperature instrumental indentations onto silicon have been faked in two consecutive publications and their reporting in the third one, so that these are not available for the calculation of activation energies. Conversely, the same research group published an indentation loading curve of copper as taken at 150 K that could be tested for its validity with the therefore created tools of validity tests. The physical algebraic calculations provided the epochal detection of two highly exothermic phase transitions of copper that created two polymorphs with negative standard energy content. This is world-wide the second case and the first one far above the 77 K of liquid nitrogen. Its existence poses completely new thoughts for physics chemistry and perhaps techniques but all of them are open and unprepared for our comprehension. The first chemical reactions might be in-situ photolysis and the phase transitions can be calculated from experimental curves. But several further reported low temperature indentation loading curves of silicon were tested for their experimental reality. And the results are compared to new analyses with genuine room temperature results. A lot is to be learned from the differences at room and low temperature.
文摘A new experimental measurement of residual stresses around Vickers′ indentations on the surface of the SiC/Al 2O 3 nanocomposites is proposed with the aid of a Raman microprobe. Results s how that the shifts of R lines in the fluorescence spectra va ry with the distance from the centre of indentation. The magnitude of load appli ed on the surface of the materials through the indenter influences the shifts of R lines to great extent. The luminescence of R lines of the materials before indenting is used to determine the residual stresses around the indentation in the materials, assuming that the stress tensor is transversely isotropic. Final ly, the term of hydrostatic stress is adopted to explain and compare different residual stresses around indentations with the increase of the indenting load an d the distance from the centre of indentations. 【
基金co-supported by the National Natural Science Foundation of China(No.11872320)。
文摘The increasing use of small material components in a wide range of industrial fields necessitates the development of an accurate and robust indentation testing method.To this end,this paper proposes an Energy-density-equivalence for a Flat Indentation(E-FI)model based on the energy density equivalent principle.The proposed model describes the relationships among the material parameters of Hollomon's power law(H-law),flat indenter diameter,energy,and indentation displacement.An E-FI Method(E-FIM)that determines the H-law parameters of materials through the indentation test is also developed.The energy-displacement curves forward-predicted by the E-FI model(based on known H-law parameters of materials)and the H-law parameters of materials given by the E-FIM(based on known energy-displacement curves)are consistent with the results of Finite Element Analysis(FEA)and the H-law parameters of materials used as the input for FEA,respectively.Using E-FIM,the goodness of fit for both stress–strain curves with H-law,predicted based on the displacement with 2%signal interference,and that for stress–strain curves without interference is more than 0.98.The stress–strain relations predicted by E-FIM were consistent with the results obtained via uniaxial tensile tests of ten ductile materials.
基金financial supports from the National Natural Science Foundation of China(Nos.51904333,51774326)。
文摘The rock indentation tests by a conical pick were conducted to investigate the rock cuttability correlated to confining stress conditions and rock strength.Based on the test results,the regression analyses,support vector machine(SVM)and generalized regression neural network(GRNN)were used to find the relationship among rock cuttability,uniaxial confining stress applied to rock,uniaxial compressive strength(UCS)and tensile strength of rock material.It was found that the regression and SVM-based models can accurately reflect the variation law of rock cuttability,which presented decreases followed by increases with the increase in uniaxial confining stress and the negative correlation to UCS and tensile strength of rock material.Based on prediction models for revealing the optimal stress condition and determining the cutting parameters,the axial boom roadheader with many conical picks mounted was satisfactorily utilized to perform rock cutting in hard phosphate rock around pillar.
基金supported by National Key Science and Technology Projects of China (Grant No. 2009ZX04001-101, Grant No. 2009ZX01001-151)New Century Excellent Talents in University,China (GrantNo. NCET-07-0246)National Natural Science Foundation of China(Grant No. 50675051)
文摘The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very ＂smoothed＂ surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the influence factors on brittle/ductile transition behavior,the wear of diamond grits in diamond grinding of ultra pure fused silica（UPFS） are investigated by means of micro/nano indentation technique,as well as single grit diamond grinding on an ultra-stiff machine tool,Tetraform ＂C＂.The single grit grinding processes are in-process monitored using acoustic emission（AE） and force dynamometer simultaneously.The wear of diamond grits,morphology and subsurface integrity of the machined groves are examined with atomic force microscope（AFM） and scanning electron microscope（SEM）.The critical brittle/ductile depth of more than 0.5 μm is achieved.When compared to the using roof-like grits,by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters.However,the influence of grit shapes on the critical depth is not significant as supposed.The grinding force increased linearly with depth of cut in the ductile removal regime,but in brittle removal regime,there are large fluctuations instead of forces increase.The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves.Furthermore,The SEM photographs show multi worn patterns of diamond grits,indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels.The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.
基金supported by the National Natural Science Foundation of China (Nos. 11002121, 11002122,and 10828205)the Natural Science Foundation of Hu-nan Province for Innovation Group (No. 09JJ7004)+2 种基金the Key Special Program for Science and Technology of Hu-nan Province (No. 2009FJ1002)and the Natural Science Foundation of Xiangtan University (No. 09XZX04)One of the authors (C. Lu) is also grateful to the support from the Australian Research Council (No. DP0985450)
文摘The reverse analysis provides a convenient method to determine four elastic-plastic parameters through an indentation curve such as Young s modulus E, hardness H, yield strength σy and strain hardening exponent n. In this paper, mathematical analysis on a reverse algorithm from Dao model （Dao et al., Acta Mater., 2001, 49, 3899） was carried out, which thought that only when 20 ≤E＊/σ0.033≤ 26 and 0.3n≤ 0.5, the reverse algorithm would yield two solutions of n by dimensionless function Π2. It is shown that, however, there are also two solutions of n when 20≤E＊/σ0.033≤ 26 and 0≤n0.1. A unique n can be obtained by dimensionless function Π3 instead of Π2 in these two ranges. E and H can be uniquely determined by a full indentation curve, and σy can be determined if n is unique. Furthermore, sensitivity analysis on obtaining n from dimensionless function Π3 or Π2 has been made.
