The Development And Experimental Research On In Situ Three-point Bending Instrument

With the development of science and technology, some new processes,new theories and new phenomena come out continually which promote thedevelopment on testing technology of materials. The testing method ofmechanical properties in situ emerges at the right time, which can provide us anew approach to observe and record the process of micro-structure in situ. As abranch of the testing methods in situ, the whole process of micro deformation,damage and break of the specimen can be observed by in situ three-pointbending test, as well as the curve of force-deflection. It has a great influence onrevealing the micro damage mechanism of materials.After studying the current situation of in situ three point bending test homeand abroad, it can be found that most in situ three point bending tests areconducted relying on the commercial miniature bending test devices.Meanwhile, the effective methods of evaluating the accuracy and performancesof the test device are reported rarely. In addition, the current method of in situthree point bending test has not involved the device which can satisfy themulti-loads test in situ.Aiming at the above issues about the in situ three point bending test, an insitu three point bending test device was proposed which can be compatible withsome microscopic imaging component such as laser scanning confocalmicroscope, super depth of field microscope and so on. In this paper, the wholedesign scheme, the structure and the working principles were describedspecifically.In this paper, the measuring error of the deflection is analysed and acalibration method is proposed. The modulus of K9glass,7075aluminum andred copper are measured using the test device which is calibrated. Comparing tothe results with modulus which are measured by commercial nanoindentation, it can be seen that all of the errors are less than5%. The calibration method isverified to be correct and universal.The in situ three point bending test of red copper with pre-crack isperformed. Using the laser scanning confocal microscope, we observed themicroscopic behaviors of the specimen simultaneously.In addition, the structure design of three point bending module which isone component in the multiple load in situ mechanical properties testinginstruments is proposed. The question of not contacting well between indenterand supports was solved during the designing scheme.