| The working condition of mechanical components can be indicated by their stress states, whose measurement and evaluation can also improve the security, reliability and stability of the products. As one of the most potential experimental stress measurement, ultrasonic technique was widely developed and applied in recent years. Limited by their own characters, bulk wave and surface wave in ultrasonic frequency are difficult to be used to measure the internal tangent stress condition from the surface of medium. In many occasions, they will not be able to evaluate the working condition of mechanical components effectively.Based on the stress measurement model using the Critically Refracted Longitudinal (LCR) Wave, this paper discussed the key techniques of measuring the stress in accessories, which includes the generation, receiving and afterwards management of LCR wave. An experimental stress measurement system based on time was also designed and constructed in this project, by measuring the travel time of LCR wave in the medium, the stress state of testing object can be well evaluated.Travel time is the key point of system, its measure quality decides the survey precision of the stress. Time to Digital Convertor (TDC) was applied to accomplish the precision time interval measurement. At the same time, One Transmitter-Two Receivers probe arrangement and Zero-Crossing detecting method were also applied to reduce the errors in measurement. Furthermore, change of temperature may affect the measuring system, temperature compensation module is used to monitor the ambient temperature of system and correct the result of stress measurement.The travel time of LCR wave and applied stress showed well linear relationship in the qualitative and quantitative experiments, experimental result matched with the theory, achieved the anticipative requirements. These experiments validated the feasibility of evaluating the stress with LCR wave based on TDC travel time measurement preliminarily. |
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