Nondestructive testing technology and its progress

Nondestructive testing technology and its progress of aerospace composites

with the increasing application of composites in aerospace structures, monitoring the internal quality of composite structures has attracted more and more attention in order to ensure flight safety. Therefore, the non-destructive testing technology of aerospace composites is also increasingly used in the whole process of aerospace composite structure molding, assembly, testing, maintenance and use

non destructive testing (NDT) refers to the use of non-destructive means, using acoustic, optical, electrical, thermal, magnetic and ray technologies to detect the pores, inclusions, cracks, delaminations and other defects in materials and components that affect their use and their locations. At present, the nondestructive testing methods of aerospace composites mainly include ultrasonic testing, radiographic testing and so on. Combined with the common defect types, this paper discusses the requirements of aerospace composites for nondestructive testing technology, introduces the current situation and application of several aerospace composites nondestructive testing technology, and prospects the development trend of aerospace composites nondestructive testing technology

nondestructive testing of aerospace composites and defects

composites have the advantages of light weight, high specific strength, high specific stiffness, fatigue resistance, designability and so on, which are conducive to the weight reduction of aviation flight, so they are more and more widely used. Fiber reinforced composites are different from traditional metal materials in terms of nondestructive testing due to their anisotropic physical properties and serious sound attenuation. How to control the internal quality of composites has become a research hotspot. In combination with the common defect types of composites, the technical requirements for nondestructive testing of aerospace composites are briefly described below

the types of defects in composites generally include: cracks, resin cracks, fractures, bonding defects, voids, delaminations, inclusions, glue overflow, degumming, super thick or ultra-thin glue layer, fiber fracture and curl, lean glue, thickness deviation, wear, scratch, resin accumulation, ply wrinkles, pits, bulges, nodules, etc. Among them, cracks, fractures, voids, delaminations, etc. are generally the most important defects in composite materials, which have significantly improved the effective elastic modulus and strength under the extremely low volume fraction of polycarbonate, which is only 0.082%. Common defect types, effects and detection characteristics of aerospace composite components

4 microwave detection

as a high-frequency electromagnetic wave, microwave is characterized by wave length, high frequency and wide frequency band. Its wavelength is between 1mm~1000mm, and the frequency is usually 300mhz~300ghz. Microwave has strong penetration ability and small attenuation in composite materials, which can overcome the shortcomings of other detection methods, such as ultrasonic attenuation in composite materials is large, it is difficult to detect defects in deep internal parts, ray detection sensitivity to planar defects is low, and microwave detection has high sensitivity to defects such as holes, porosity, matrix cracking, delamination and debonding in composite structures

in 1967, the US Air Force combustion control engineering laboratory used microwaves with frequencies of 9.6GHz (X-band) and 35GHz (Ka band) to measure the thickness of plastic sheets by reflection method, with an accuracy of 0.125mm. The laboratory can detect defects with a diameter of 1.02mm~5.8mm by scanning epoxy resin samples; Scanning the filament wound reinforced plastic can detect the debonding between the plastic with the internal area as small as 1.2mm in diameter and the rubber liner with the thickness of 2.5mm~50mm and 4.0mm~75mm respectively; Using the penetration method to measure the energy change of microwave, the density change of 0.02mg/cm3 can be detected. Since the 1970s, the American ad report and NASA report have introduced a lot of microwave nondestructive testing of large solid rocket motors, mainly including standing wave interferometry, reflection method and scattering method. Standing wave method is generally used for thickness measurement; The reflection method can find the pores with a diameter of 25mm at the depth of 600mm inside the solid propellant

to sum up, although it is reported that there are many non-destructive testing technologies for aerospace composites, each technology has its specific application scope, advantages and disadvantages. A single method is difficult to detect all types of defects, and usually requires a combination of multiple methods

prospects for the development of nondestructive testing technology for aerospace composites

1 transformation from qualitative testing to quantitative testing

in order to improve the ability of quantitative testing, the United States, Britain and other developed countries began to vigorously develop and study various imaging technologies, signal processing technologies and new methods of analysis and calculation defects. Taking ultrasonic testing technology as an example, the 17 axis automatic ultrasonic C-scan testing system provided by USL for British aerospace systems can detect about 4mm of composite materials at a scanning line speed of 0.5m/s × 4mm manufacturing defects and up to 2 μ M resolution, and the highest repeatability can also reach 5 μ m. It can accurately mark the location of defects, and improve the ability of quantitative detection of defects and the accuracy of quantitative analysis

domestic research institutions have also made some achievements in quantitative detection. Beijing Institute of Aeronautical Manufacturing Engineering used the ultrasonic automatic detection technology to detect the impact damage of typical RTM composite structures. Through the intuitive image method, the detailed distribution of internal defects of the tested composite structures and the internal quality of the whole structure were reproduced, and then the quantitative distribution of defects was obtained, which could be used for quantitative evaluation of defects

2 further improve the automation level of equipment

automatic detection technology can provide better repeatability and consistency of results than manual operation, reduce the probability of random error and human error, reduce the requirements for the proficiency of detection personnel, and realize complex and comprehensive detection, quickly process detection data, so as to greatly improve work efficiency

as an automatic ultrasonic scanning system with more efficiency and adaptability, MacDonald aircraft company's Auss detection system can draw the data map of the previous part while scanning a part, and the operator can also evaluate some details of the data at the video terminal, thus greatly improving the efficiency. The man hour required to inspect the skin honeycomb core of the torque box of the horizontal tail of F-15 aircraft has been shortened from 72 hours of manual inspection to no more than 2 hours. Airbus in Europe has applied the 128 channel ultrasonic automatic scanning technology to the rapid nondestructive testing of large composite wall panels, thereby significantly improving the testing efficiency. The full-automatic ultrasonic C-scan detection system of USL company is equipped with a high-speed, complex surface tracking system, which has the characteristics of high automation, high intensity, high mechanical accuracy and so on. The maximum scanning rate is as high as 1m/s, which can realize the rapid and effective detection of aerospace composite components. Ultrapac's ultrasonic C-scan imaging system is equipped with a multi axis, multi degree of freedom, high-speed (up to 0.5m/s), high-precision (up to 0.05mm position accuracy) water tank scanning system driven by high-performance CNC motor

Beijing Institute of Aeronautical Manufacturing Engineering has successfully developed different series of composite ultrasonic automatic scanning and testing systems, such as mui-20e ultrasonic automatic nondestructive testing system for planar composite structures, which adopts ultrasonic reflection method, and the maximum scanning area at one time can reach 1500mm × 1500mm, with excellent signal-to-noise ratio, it can realize the A, B, C, t automatic scanning detection of composite structures; Mui-21 ultrasonic automatic nondestructive testing system for non curved composite structures adopts ultrasonic penetration method and reflection method, and the maximum scanning area at one time can reach 4000mm × 2500mm, with good synchronous scanning technology, it can realize the B, C, t automatic scanning detection of composite structures; In addition, there are cus-22 ultrasonic adaptive testing equipment, cus-2f composite winding ultrasonic automatic testing equipment, etc

3 development of multi-functional comprehensive testing system

no matter which nondestructive testing method has its own characteristics, but also has its own shortcomings. No matter which method is not omnipotent. In order to detect and evaluate the quality and performance of materials and products more accurately and reliably, in addition to continuously improving the performance of conventional nondestructive testing instruments and equipment, we should also pay attention to the research and development of multi-functional comprehensive testing system composed of multiple methods

sonic BondMaster bonding quality tester integrates acoustic resistance method, resonance method, guided wave method and acoustic ultrasonic method, which expands the detection range and greatly improves the detection performance. The acoustic impedance method is mainly used to detect debonding, inner core deformation and defects with internal depth of material components exceeding 6.3mm. The small mechanical impedance probe can detect the curved surface; Resonance method is generally used to detect delamination and debonding in plate to plate bonding, fiber braiding and honeycomb structural materials, and can determine the location and depth of defects; 5. The guided wave method for poor contact of electronic components is used to scan deeper debonding, including inner core deformation and internal damage of graphite epoxy materials; Acoustic ultrasonic method is used to detect honeycomb structure

conclusion

with the increasing use of composite materials in aircraft, more abundant 3 The detection means of connector or eliminating poor connector will be used, and the detection ability and scope will be further expanded. Nondestructive testing will no longer be limited to the manufacturing process and ground maintenance, but also can provide real-time structural safety monitoring information. At the same time, the software can use data synthesis technology to process the information sent from the sensor and give real-time detection reports, so as to ensure the safe use of composite material structures to the greatest extent