Research On The Effects Of The Verticality Error Between Indenter And Specimen On Tests Of Nanoindentation And Nanoscratch

At present, the technology of the nano indentation/scratch has been welldevelopped in aspects such as theoretical, instrument research and application. Butdue to the measurement scale of nano indentation/scratch technology is very small,the requirements of environment and precision of instrument are very high, so thereinevitably exists many factors that affect the test result during the entire test. Duringthe process of design and assembly of the nanoindentation instrument, it was foundthat it is difficult to assure the verticality between indenter and specimen because ofthe errors of machining and assembly. Besides, many factors will lead to the tiltbetween the indenter and specimen during the nanoindentation and nanoscratch test,such as the machining defects of the indenter, the flexibility of overall frame, theuniformity of specimen’s thickness and material composition. Therefore, start fromthe perspective of verticality, this research will focus on the influence of this factoron the test results of nanoindentation and nanoscratch.Firstly, the tilt cases of nanoindentation and nanoscrach were systematicallystudied from theoretical and points. Analysis results show that, the effects of indentertilt on the projected contact area are significantly, and it increases with the tilt angles.Therefore, in order to ensure the error of projection area within the range ofpermissible error, the absolute value of tilt angle should be small enough. During theprocess of nanoscratch, when the indenter tilts different angles around each axis, theprojected contact area varies a lot, some change significantly and some nearly haveno effect.The finite element software Abaqus was used to build the model of nanoindentation, and in the model, the verticality between the indenter and specimenwas used as control parameter to conduct the simulation. Result showed that, the tiltbetween the indenter and specimen could influence the shapes of the residual contactarea and the tendency of the force-displacement curves to some extent. At the samemaximum depth, the loads of tilt indentation are higher than untilted indentation, andthis phenomenon is more obvious when the tilt angle is larger. At the same time, theelastic modulus and hardness of the specimen calculated according to theforce-displacement curves present a certain degree of difference. Results ofnanoscratch simulation showed that, the tilt of the indenter could also influence theshapes of the residual scratch profile, which deviates from the vertical scratch shape.By calculating the friction coefficient, it can be obtained that, compared with verticalscratch, when the indenter tilts around different axes, the friction coefficients varywidely.Once tilt phenomenon happens during the test, we can use AFM, SEM andother techniques to the measured residual outlines, use different functions to estimatethe direction and value of tilt. Using the direction and tilt value, we could correct thevalues of projected area, elastic modulus and hardness to reduce the error of tiltnanoindentation and nanoscratch test results.