The Structure Design And Experimental Reseacrh On In-situ Fatigue Testing Instrument Based On Piezoelectric Actuators

As we all know, the metal is a major national material of industry, agriculture andnational defense and military equipment. Affected by the load and environment in theservice, materials would produce a variety of failure modes which likely cause significanteconomic losses and even catastrophic accidents. Fatigue failure as a failure of the mainmetal material form is totally different from simple stretching/compression, bending andshearing under static load. Since it is a potential failure with great sudden, if it happens, thelosses are often disastrous. Therefore, the study of fatigue failure has caused more and moreattention of scientists. However, the fatigue failure is a complex issue which involves manydisciplines, including applied mathematics, mechanics, materials science, metal physics, etc.,but it hasn’t established a specific mathematical model yet. Thus, only through the fatiguetest can we research fatigue failure. Fatigue machine is a essential equipment for the study ofthe fatigue properties of the material. However, the traditional fatigue testing machine isdesigned based on the macroscopic specimen to obtain the fatigue life curve. Micro-fracturemorphology need to wait until the end of the test and the specimen can not be observed allthe time. So the analysis of natural essence of fatigue failure can not be accurate andcomprehensive. There are shortcomings such as long test period, high energy consumptionand without in-situ observationsBased on the analysis of domestic and foreign fatigue testing equipment and testingmethods, combining with the size requirements of in-situ micro fatigue tester andpiezoelectric ceramics as a driver, the author developed a set of piezoelectric actuators insitu micro fatigue testing device which was small, structured and compatible with a varietyof observation apparatus. They can be used in millimeter specimens under micro loads or insitu observation of contain metallic inclusions specimens. The paper analyzes the law of fatigue failure from the micro aspect to solve the the problem of long test period and highenergy consumption caused by traditional fatigue testing equipment which mainly test thelife curve. At the same time this device can be used in conjunction with a metalloscope forfatigue testing of materials in situ observations by analysis of microscopic deformationmechanism of material and research the law of fatigue failure to solve the issue that thetraditional material fatigue unit can not achieve real-time observation of specimens.The main contents of this paper are: the design of a piezoelectric actuator in situ microfatigue testing equipment; the establishment of a three-dimensional model of the machinewhich includes preloaded unit, fatigue loading unit, clamping unit and signal detection unit;the analysis of work principle and calculation and selection of the size; the entire apparatusof the finite element simulation has been the inherent frequency and strain distributionequipment; key components were further analyzed to optimize their structure and size;processed parts and components were assembled and regulated; selecting of the appropriateamplifier according to the model of the force sensor, acquisition card and the correspondingparameters and complete wiring and electrical connections; test the output characteristics ofthe device and, including the piezoelectric hysteresis, effective stroke and speed of responseand other flexible hinge tests; test the material in the elastic stage, neck shrink plastic stagephase load spectrum, verify the availability of the device, and with means for AZ31Bmagnesium alloy,6061aluminum alloy, copper and aluminum composite panels wererepetitive in-situ fatigue tests obtained material fatigue fracture under tensile fatiguemicroscopic processes and the corresponding fracture morphology and found out laws oftheir internal structural changes of different materials under cyclic loading: fatigue fractureAZ31B magnesium alloy by alternating load occurs at room temperature, a clear brittlefracture characteristics, fracture of6061aluminum alloy still showed plastically deformed,copper and aluminum composite panels were serious not synchronous, a plasticity andoverall presentation of features. A series of experimental results show that the presentapparatus can perform in-situ fatigue testing and stable performance.