A non-classical nonlinear detection method for microcracks in variable cross-section members

Abstract

The invention discloses a non-classical nonlinear detection method aiming at micro crack in non-uniform members. The method is as below: an energy-gathered energy transducer is coupled in one end of a non-uniform member, so that the other end of the non-uniform member is in a free state; the energy-gathered energy transducer applies forced periodic vibration force on one end of the non-uniform member to stimulate large strain wave, and the large strain wave stimulates non-classical nonlinear acoustic wave propagation at the microcrack in the non-uniform member, so as to obtain in higher order odd harmonics; and four laser displacement sensors fixed in the length direction of the non-uniform member perform non-contact measurement, and location and width of the micro crack are acquired through computer processing. The method of the invention can effectively identify and locate the micro crack in the non-uniform member, and is high in accuracy and not affected by transmission loss. The invention provides an effective way for early detection and localization of micro cracks in non-uniform member for the engineering field, and has significant practical value.

Description

technical field [0001] The invention relates to a non-classical nonlinear detection method for microcracks in variable cross-section components, and belongs to the technical field of ultrasonic nondestructive testing. Background technique [0002] Variable cross-section members such as tapered rods or exponential beams are widely used in the engineering field to withstand large periodic alternating loads with optimized structures and minimum self-weight. Compared with constant cross-section members, under alternating loads, stress concentration tends to occur inside variable cross-section members. According to the principle of Griffith’s energy balance, when the stress accumulation reaches a certain level, the micro-defects begin to expand and form micro-cracks. These micro-cracks appear to be closed at the beginning, but as the load continues, the micro-cracks widen and then expand into cracks. Therefore, early detection and location of micro-cracks in the body of variable...

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Problems solved by technology

However, the above-mentioned non-linear method to detect microcracks is restricted by various conditions in practical applications, such as the contact non-linear (CAN) method, which requires an external impact device; the time-reversal non-linear method requires a transceiving transducer array group; the nonlinear elastic wave spectral analysis method is only suitable for components with regular cross-sections; at the same time, these methods generally can only find whether there are micro-cracks or micro-holes in the components, but the location of these defects, their width and size cannot be determined. This also limits the application of ultrasonic nonlinear detection methods in industry, especially in the aerospace industry.

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