The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values...The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals.The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition.The variations of penetration depth,residual depth,and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions.A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity.A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness.The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter.It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.展开更多
Mechanical characterization of dielectric ceramics,which have drawn extensive attention in wireless communication,remains challenging.The micromechanical properties with the microstructures of dielectric ceramic BaO-S...Mechanical characterization of dielectric ceramics,which have drawn extensive attention in wireless communication,remains challenging.The micromechanical properties with the microstructures of dielectric ceramic BaO-Sm_(2)O_(3)-5TiO_(2)(BST)were assessed by nanoindentation,microhardness,and microscratch tests under different indenters,along with the X-ray diffraction(XRD),scanning electron microscopy(SEM),and Raman spectroscopy.Accurate determination of elastic modulus(Err)(i.e.,260 GPa)and indentation hardness(Hrr)(i.e.,16.2 GPa)of brittle BST ceramic by the instrumented indentation technique requires low loads with little indentation-induced damage.The elastic modulus and indentation hardness were analyzed by different methodologies such as energy-based approach,displacement-based approach,and elastic recovery of Knoop imprint.Consistent values(about 3.1 MPa·m^(1/2))of fracture toughness(Kc)of BST ceramic were obtained by different methods such as the Vickers indenter-induced cracking method,energy-based nanoindentation approaches,and linear elastic fracture mechanics(LEFM)-based scratch approach with a spherical indenter,demonstrating successful applications of indentation and scratch methods in characterizing fracture properties of brittle solids.The deterioration of elastic modulus or indentation hardness with the increase in indentation load(F)is caused by indentation-induced damage and can be used to determine the fracture toughness of material by energy-based nanoindentation approaches,and the critical void volume fraction(f^(*))is 0.27(or 0.18)if elastic modulus(or indentation hardness)of the brittle BST ceramic is used.The fracture work at the critical load corresponding to the initial decrease in elastic modulus or indentation hardness can also be used to assess the fracture toughness of brittle solids,opening new venues of the application of nanoindentation test as a means to characterize the fracture toughness of brittle ceramics.展开更多
This study compares micro-abrasive wear in two kinds of grey cast iron.Classical lamellar cast iron with fully pearlitic matrix(FGL1)and lamellar micro-alloyed cast iron with phosphorus and boron(FGL2)are used.FGL2 ha...This study compares micro-abrasive wear in two kinds of grey cast iron.Classical lamellar cast iron with fully pearlitic matrix(FGL1)and lamellar micro-alloyed cast iron with phosphorus and boron(FGL2)are used.FGL2 has a fully pearlitic matrix reinforced by the hard phosphorus eutectic phase.The microstructures of these two types of iron are mechanically characterized using nanoindentation tests.Vickers microindentation and microscratch tests are also performed on these iron samples.The indent and scratch images obtained via scanning electron microscopy were used to compare the scratch damage to the two kinds of iron.The friction coefficient is discussed in terms of applied load,indenter attack angle,and scratch damage.Nanoindentation tests show an improvement in graphite’s mechanical properties and an increase in the matrix hardness of the FGL2,relatively to FGL1.The same damage forms for both microindentation and microscratch testing were observed for the two iron samples.However,cracking of the hard phase is observed in FGL2.The results show that the scratching of the micro-alloyed iron(FGL2)leads to less matrix damage and to an extended microploughing wear mechanism.However,at low normal load,the reinforcement of the matrix can increase the friction coefficient.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.51705082)the Engineering Research Center for CAD/CAM of Fujian Provincial Colleges and Universities(No.K201705)+1 种基金the Development Center of Scientific and Educational Park of Fuzhou University in the City of Jinjiang(No.2019-JJFDKY-11)Fuzhou University Testing Fund of Precious Apparatus(No.2020T017).
文摘The scratch test is used for quality control mostly in phenomenological ways,and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation.In this paper,values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals.The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition.The variations of penetration depth,residual depth,and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions.A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity.A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness.The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter.It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.
基金supported by the National Natural Science Foundation of China(51705082)Fujian Provincial Minjiang Scholar Program(0020-510759)+1 种基金Development Center of Scientific and Educational Park of Fuzhou University in the city of Jinjiang(2019-JJFDKY-11)Fujian Provincial Collaborative Innovation Center for High-end Equipment Manufacturing(0020-50006103).
文摘Mechanical characterization of dielectric ceramics,which have drawn extensive attention in wireless communication,remains challenging.The micromechanical properties with the microstructures of dielectric ceramic BaO-Sm_(2)O_(3)-5TiO_(2)(BST)were assessed by nanoindentation,microhardness,and microscratch tests under different indenters,along with the X-ray diffraction(XRD),scanning electron microscopy(SEM),and Raman spectroscopy.Accurate determination of elastic modulus(Err)(i.e.,260 GPa)and indentation hardness(Hrr)(i.e.,16.2 GPa)of brittle BST ceramic by the instrumented indentation technique requires low loads with little indentation-induced damage.The elastic modulus and indentation hardness were analyzed by different methodologies such as energy-based approach,displacement-based approach,and elastic recovery of Knoop imprint.Consistent values(about 3.1 MPa·m^(1/2))of fracture toughness(Kc)of BST ceramic were obtained by different methods such as the Vickers indenter-induced cracking method,energy-based nanoindentation approaches,and linear elastic fracture mechanics(LEFM)-based scratch approach with a spherical indenter,demonstrating successful applications of indentation and scratch methods in characterizing fracture properties of brittle solids.The deterioration of elastic modulus or indentation hardness with the increase in indentation load(F)is caused by indentation-induced damage and can be used to determine the fracture toughness of material by energy-based nanoindentation approaches,and the critical void volume fraction(f^(*))is 0.27(or 0.18)if elastic modulus(or indentation hardness)of the brittle BST ceramic is used.The fracture work at the critical load corresponding to the initial decrease in elastic modulus or indentation hardness can also be used to assess the fracture toughness of brittle solids,opening new venues of the application of nanoindentation test as a means to characterize the fracture toughness of brittle ceramics.
文摘This study compares micro-abrasive wear in two kinds of grey cast iron.Classical lamellar cast iron with fully pearlitic matrix(FGL1)and lamellar micro-alloyed cast iron with phosphorus and boron(FGL2)are used.FGL2 has a fully pearlitic matrix reinforced by the hard phosphorus eutectic phase.The microstructures of these two types of iron are mechanically characterized using nanoindentation tests.Vickers microindentation and microscratch tests are also performed on these iron samples.The indent and scratch images obtained via scanning electron microscopy were used to compare the scratch damage to the two kinds of iron.The friction coefficient is discussed in terms of applied load,indenter attack angle,and scratch damage.Nanoindentation tests show an improvement in graphite’s mechanical properties and an increase in the matrix hardness of the FGL2,relatively to FGL1.The same damage forms for both microindentation and microscratch testing were observed for the two iron samples.However,cracking of the hard phase is observed in FGL2.The results show that the scratching of the micro-alloyed iron(FGL2)leads to less matrix damage and to an extended microploughing wear mechanism.However,at low normal load,the reinforcement of the matrix can increase the friction coefficient.
