Design And Experimental Research On In-situ Fatigue Testing Device Of Force-Thermal Coupling

Elasto-plastic deformation inevitably occurs during the use of the material,resulting in fatigue,fracture,and failure.According to statistics,the loss caused by fatigue failure accounts for more than 80% of all kinds of material destruction.The traditional fatigue tester is mainly used to test the fatigue damage of large-scale engineering structures.Its loading mode is single,and it cannot perform real-time dynamic observation of the entire fatigue failure process,and cannot simulate the actual working conditions of the material.Based on the above issues,the paper reviewed the status of fatigue testing technology at home and abroad.Based on this,A high-temperature fatigue test device was designed and the device was composited to a multi-physics multi-force field-coupled material in-situ property testing instrument to realize fatigue testing of different functional materials and structural materials coupled in physical fields such as temperature field and magnetic field.The tester achieves low-cycle fatigue testing under pre-tension loading,and can test different notched specimens,greatly reducing the fatigue testing time.It is compound in-situ observation device,observes the three stages of fatigue damage,and describes fatigue Destructive mechanism.After test,the device can achieve the maximum temperature of 500 °C,the maximum pre-stretch load force is 2000 N,and it can control the fatigue loading force amplitude changes within 0-300 N,the loading frequency up to 10 Hz.It has different fatigue wave loading,like sine wave,triangle wave and sawtooth wave.The paper uses ANSYS Workbench software to perform modal analysis on the fatigue output module to verify the rationality of the machine design.The integration of the high-temperature fatigue device and the whole testing instrument is completed,the control strategy of the system is formulated,and the debugging is completed.On this basis,the fatigue cyclic force loading under force control and the fatigue no-load displacement output under displacement control were tested repeatedly.Through analyzing the test results,it was found that the force sensor is not suitable for dynamic test,and then the piezoelectric force sensor was reselected for the testing of dynamic fatigue force.Based on the sensor's dynamic stable output characteristics,a dynamic calibration method for force sensor was designed.The calibrated force sensor was used as a standard force sensor in series with the piezoelectric force sensor.By inputting a sine wave voltage to the piezoelectric stack and changing the voltage amplitude,the relationship between the amplitudes of the cyclic force of the two force sensors was determined.The calibration of the pressure sensor's test amplitude was completed.Through these jobs,the test results have been greatly improved,and the dynamic response is also fast at frequencies up to 10 Hz.The calibration of the thermocouple was completed,and the thermal field test was debugged to achieve the maximum temperature loading to 500°C.The relevant experimental study was carried out using the designed high temperature fatigue tester.The change of the performance parameters of the twin steel induced TWIP steel under high temperature conditions was investigated.It was found that the high temperature increased the plasticity,but the tensile strength decreased greatly.When the temperature is lower than 500°C,the Young's modulus has almost no effect.Through the combined use of the indentation module,the cyclic hardening of the AZ31 B wrought magnesium alloy under low cycle fatigue was tested.It was found that with 50000 fatigue life conditions,there was a lot of solidification when the cycle load reached 16,000 times.Great influence.The paper also combined with an in situ observation device,firstly observed the fatigue failure process of the specimen in real time and explored the influence of the notch morphology on the fatigue characteristics.It was found that the arc-shaped defect specimen fatigue failure is faster than the rectangular defect specimen;the change of grain structure in the vicinity of the crack before and after fatigue was observed using a metallographic microscope,and it was found that the grain damage near the crack propagation zone is the most serious.