| 摘要 |
The machine for performing the tests of ultrasonic fatigue strength in a very high cycle fatigue regime (giga-cycle regime) in metallic alloys and highly resistant plastics, comprises the following elements and systems: a system for generating an electronic signal at a high frequency (20KHz) and a transducer from the electronic vibration to the mechanical vibration of the same frequency, a system for fastening the transducer and displacing multipliers, as well as the multipliers, a system for calibrating the displacements in the free portion of the test tube, a refrigeration system for controlling the temperature in the testing tube, a process for obtaining the natural frequency of oscillation of the test tube and a start-up, stop systems, and systems for counting the cycles and monitoring the temperature. The process for performing a test in ultrasonic fatigue starts with the calculation by numerical simulation of the natural frequency of oscillation of the test tube, adjusting the d imensions thereof for satisfying the resonance condition, fastening the test tube over the test column so as to perform the displacement calibration with the inductive sensor and the associated software. The distribution of the strength in the test tube is subsequently obtained by numerical simulation for a displacement applied in the end portions, with the purpose of obtaining the ratio of applied voltage-displacement-induced strength, then the air flow being adjusted so as to control the temperature in the test tube and the laser thermometer for finally performing the start up and the control of the experimental test by means of a software in the LabVIEW platform. The fatigue life is determined at the end of the test, this being displayed in the screen of the control software, then the required analysis and studies being performed by optic and electronic microscopy with the purpose of studying the causes of fault by fatigue.
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