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
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
通过Rockwell C 120°金刚石压头对16种金属材料进行微米划痕测试,研究渐进法向力对材料划痕响应的影响。结果表明:随着法向力从5 mN线性增大到30 N,压入深度和残余深度均线性增加;弹性回复率先迅速增大,然后趋于一个常数。当压入...通过Rockwell C 120°金刚石压头对16种金属材料进行微米划痕测试,研究渐进法向力对材料划痕响应的影响。结果表明:随着法向力从5 mN线性增大到30 N,压入深度和残余深度均线性增加;弹性回复率先迅速增大,然后趋于一个常数。当压入深度小于压头的球锥转变深度时,仅有压头顶端的圆球与材料接触,残余划痕宽度非线性增加;当压头的圆锥部分与材料接触时,残余划痕宽度线性增大。稳定弹性回复率和划痕硬度随屈服强度的增加而线性增大。纯Mo、纯W和40Cr的划痕摩擦系数随法向力的增加始终非线性增大,其余金属的划痕摩擦系数先非线性增加,之后趋于稳定;划痕摩擦系数的变化趋势可通过几何接触模型进行解释。在较大法向力下,QT500的摩擦机制中黏着摩擦和犁沟摩擦起到几乎相同的作用,其余材料的摩擦机制主要为犁沟摩擦。稳定划痕摩擦系数随稳定划痕硬度及其与弹性模量比值的增加而线性减小。展开更多
在恒定的法向载荷下,使用Rockwell C 120°金刚石压头对聚碳酸酯(PC)、熔融石英、紫铜和镁合金AZ31进行微米划痕测试,研究滑动速度对试样划痕响应的影响.压入深度小于压头的球锥转变深度,确保仅有压头顶端的圆球部分与试样接触.结...在恒定的法向载荷下,使用Rockwell C 120°金刚石压头对聚碳酸酯(PC)、熔融石英、紫铜和镁合金AZ31进行微米划痕测试,研究滑动速度对试样划痕响应的影响.压入深度小于压头的球锥转变深度,确保仅有压头顶端的圆球部分与试样接触.结果表明:随着滑动速度的增加,压入深度、残余深度和划痕沟槽的宽度均非线性减小,划痕硬度和弹性恢复率均非线性增大;PC和紫铜的划痕摩擦系数先增大后减小,PC的黏弹性行为对其摩擦响应有显著影响;熔融石英的划痕摩擦系数先增大后减小,最后趋于稳定;镁合金AZ31的划痕摩擦系数先减小后增大.熔融石英、紫铜和镁合金AZ31的划痕摩擦系数的变化趋势可通过几何接触模型进行解释.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
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.
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.
文摘通过Rockwell C 120°金刚石压头对16种金属材料进行微米划痕测试,研究渐进法向力对材料划痕响应的影响。结果表明:随着法向力从5 mN线性增大到30 N,压入深度和残余深度均线性增加;弹性回复率先迅速增大,然后趋于一个常数。当压入深度小于压头的球锥转变深度时,仅有压头顶端的圆球与材料接触,残余划痕宽度非线性增加;当压头的圆锥部分与材料接触时,残余划痕宽度线性增大。稳定弹性回复率和划痕硬度随屈服强度的增加而线性增大。纯Mo、纯W和40Cr的划痕摩擦系数随法向力的增加始终非线性增大,其余金属的划痕摩擦系数先非线性增加,之后趋于稳定;划痕摩擦系数的变化趋势可通过几何接触模型进行解释。在较大法向力下,QT500的摩擦机制中黏着摩擦和犁沟摩擦起到几乎相同的作用,其余材料的摩擦机制主要为犁沟摩擦。稳定划痕摩擦系数随稳定划痕硬度及其与弹性模量比值的增加而线性减小。
文摘在恒定的法向载荷下,使用Rockwell C 120°金刚石压头对聚碳酸酯(PC)、熔融石英、紫铜和镁合金AZ31进行微米划痕测试,研究滑动速度对试样划痕响应的影响.压入深度小于压头的球锥转变深度,确保仅有压头顶端的圆球部分与试样接触.结果表明:随着滑动速度的增加,压入深度、残余深度和划痕沟槽的宽度均非线性减小,划痕硬度和弹性恢复率均非线性增大;PC和紫铜的划痕摩擦系数先增大后减小,PC的黏弹性行为对其摩擦响应有显著影响;熔融石英的划痕摩擦系数先增大后减小,最后趋于稳定;镁合金AZ31的划痕摩擦系数先减小后增大.熔融石英、紫铜和镁合金AZ31的划痕摩擦系数的变化趋势可通过几何接触模型进行解释.
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.
