L, <sub> The Cr </ Sub> Ultrasonic Measurement Of The Tangential Stress Related Factors Research

The stress state of material and components,which can indicate the working condition of mechanical components, is the key indicator to measure the safety and reliability of products. Besides, it has an important effect to the performance of products especially the accuracy and stability of precision mechanical systems. As one of the most potential non-destructive stress measurement techniques, ultrasonic method has been widely developed and applied in recent years due to its own unique superiority.Limited by their own characters, the applying range of bulk wave method and surface wave method are less. Based on the stress measurement model, the Critically Refracted Longitudinal (LCR) Wave using peculiar measurement theory and method, can be used to measure the internal tangent stress condition from the surface of medium, this method also provides a new way of studying ultrasonic stress measurement.Ultrasonic transducer is a key element of ultrasound transmitting and receiving. Its performance has an important impact to the working characteristics of the whole system. It is necessary to develop special transducers for more efficiency transmitting and receiving LCR Wave. In this paper, the design of LCR transducer has been analyzed and studied from Mason mechanical and electrical equivalent circuit, impedance matching and backing material,Travel time is the key point of system, its measure quality decides the survey precision of the stress. Because of little change of time arosed by stress, the way of using Time to Digital Convertor (TDC) chip based on the absolute transmitting delay of logic gate was applied to accomplish the precision time interval measurement. At the same time, the functional moduals in the hardware system are intergrated together. This can minish the size of the whole system and facilitate in the field measuring.The waveforms of stress measurement are very complicated, which are caused by many factors. According to the experiments in this paper, the effects of waveform mechanism, the related coupling material, thickness and wedge materials, angle, were analyzed from the transmission path of time. From the results of qualitative and quantitative experiments, it is found that the travel time of LCR wave showed well linear relation with applied stress, which is basicly in accordant with the acoustoelastic theory. These experiments validate the feasibility of evaluating the stress with LCR wave based on TDC travel time measurement preliminarily.