Ultrasonic method for determining layer depth of defects in laminar structure of composite

Abstract

The invention belongs to the technical field of non-destructive testing and relates to an ultrasonic method for determining the layer depth of defects in a laminar structure of a composite. According to the method, the time-domain characteristic of a reflection echo signal formed by broadband narrow-pulse ultrasonic waves in the laminar structure of the to-be-detected composite is used, mathematical representation functions between the time-domain characteristic of the echo signal and thickness, layer number, defect depth and the like of the laminar structure of the to-be-detected composite are constructed, a quantitative representation method, a mathematical relation and determination method and an actual measurement method of the layer depth of the ultrasonic detected defects based on the time-domain characteristic of the echo signal are established, different frequency and ultrasonic detection systems can be selected, and quantitative representation of the layer depth of the ultrasonic detected defects in the laminar structure of the composite is realized. Actual detection effects prove that the positioning deviation of the layer depth of the detected defect can reach one layer of the composite, and a very effective ultrasonic detection method is provided for defect and destruction depth setting analysis, process optimization, structure repair and the like of indoor and outdoor composites.

Description

technical field [0001] The invention belongs to the technical field of non-destructive testing and relates to an ultrasonic method for determining the layer depth of a defect in a laminated composite structure. Background technique [0002] Composite materials have been widely used in aerospace, transportation and other industrial fields. It mainly includes resin-based composite materials and metal-matrix composite materials. Among resin-based composite materials, composite laminated structures are currently the most widely used and important In the process of manufacture and use, it is easy to produce defects such as delamination or damage at the laminated layer interface of the composite material laminated structure. Due to quality control and safety reasons, it is not only necessary to conduct 100% non-destructive testing on the composite material laminated structure, Moreover, it is also required to accurately locate the layup depth of the detected defects in the composi...

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Problems solved by technology

[0003] At present, ultrasound is the main method for indoor and outdoor non-destructive testing of composite laminated structures. The depth of detected defects is mainly characterized by relative depth: that is, according to the propagation time t between the surface reflection signal and the bottom surface reflection signal in the ultrasonic echo signal FB and the propagation time t between the surface reflection signal and the defect reflection signal FD The ratio of the ratio gives the relative depth or depth of the detected defect. The main disadvantage is that (1) the deviation is large, especially when the pulse characteristic of the ultrasonic system used is multi-cycle, which will lead to t FB and t FD The estimation is inaccurate, which will lead to inaccurate estimation of the depth of defects detected by ultrasonic, which will affect the judgment of the depth position of detected defects, and it is difficult to accurately obtain the layer depth of detected defects; (2) The depth quantification of detected defects is not enough , especially for the strength and structural force analysis of the detected defects in some key and important composite material laminated structures, and the fine repair of defects / damages, it is often necessary to provide accurate layup depth information for detected defects in order to quantify the strength (3) The lack of quantitative characterization of the ply depth of ultrasonically detected defects is not conducive to the cause analysis of detected defects, process optimization and accurate repair of damage

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