The 12th International Conference of the Slovenian Society for Non-Destructive Testing «Application of Contemporary Non-Destructive Testing in Engineering»

September 4-6, 2013, Portorož, Slovenia

NONDESTRUCTIVE TESTING OF FRP BY USING PHASED ARRAY ULTRASONIC TECHNOLOGY

A.S. Boychuk 1, A.S. Generalov and A.V. Stepanov

Federal State Unitary Enterprise “All-Russian Scientific Research Institute of Aviation Materials”

Address: 17, Radio Street, 105005, Moscow, Russia E-mail: bas140185@rambler.ru

ABSTRACT The report is about non-destructive testing (NDT) of fiber reinforced plastics (FRP) by using ultrasonic phased array technique. The main advantages of using phased array technique in comparing with traditional ultrasonic technique are shortly described in this report. The basic defect types are enumerated. CFRP specimens testing results and optimal conditions for detection of the defects equivalent to 5 mm diameter reference reflector with 40 m2/h testing productivity are given. Methods of testing results registration, location and size determination of detected defects are described.

Key words: fiber reinforced plastics (FRP), carbon fiber reinforced plastics (CFRP), non-destructive testing, ultrasonic testing, phased array

1. Introduction Nondestructive testing (NDT) and diagnostic providing on the stages of important parts and structures designing, production and service in aviation and other industries are production quality ensuring prerequisite. Wide application of nondestructive techniques which are do not require specimens cutting or finished structures destruction, allow us to avoid big losses of time and financial expenditures, provide partial or full testing procedures automation and simultaneously guarantee considerable structure quality and reliability increase. New nonmetal materials, their production technologies [2] and wide application become the important modern material science development lines. Nonmetal materials are widely applied in structures of jets, helicopters, space machineries and others. These materials are substitute for metal analogs. Therefore NDT of nonmetal materials, especially fiber reinforced plastics (FRP) is an important problem of the present time. Echo method is widely applied for FRP structures testing now [3]. The method is known to be based on ultrasonic pulses transmitting and echo-signals receiving reflected from different types of testing object discontinuity. Echo method improvement led to phased array technique creation. Many applied problems of defectoscopy turned out to be solvable by phased arrays. It allows us to carry out testing much faster and easier. Phased array application for FRP testing is not an exception.

51

Mor

e in

fo a

bout

this

art

icle

: ht

tp://

ww

w.n

dt.n

et/?

id=

1608

7

Scientific and research work aimed at nondestructive testing of important aircraft FRP (mainly CFRP) parts and structures is carried out in FSUE “VIAM” [4-5]. The main goal of ultrasonic nondestructive testing of CFRP parts and elements of structures technique development is increasing productivity, sensitivity, fullness and reliability of testing. 2. Researching CFRP specimens (based on adhesive prepreg and 0°/90° lay-up scheme) structurally similar to real parts and structures were produced for researching (Fig. 1-2). Special accessories were made with the aim of moulding a stringer panel specimen.

Ŕ-Ŕ

Ŕ Ŕ

Fig. 1: Specimen sketch and photos of the flat panel after production with artificial defects

Fig. 2: CFRP stringer panel specimen with artificial defects

Artificial reflectors (defects) were made in specimens with the aim of defining testing parameters and ability of FRP typical defects detection (Fig. 3). Artificial reflectors were made by: flat bottom hole milling on the surface opposite to transducers location; putting special technological filaments (Teflon® or polyimide with the thickness of 40

μm) between CFRP prepreg layers before molding process; putting preliminary molded RTV-silicone inlays in T-shaped braid zone of stringer and panel joining.

These artificial reflectors types are well imitating main FRP defects (laminations, inclusions and voids in T-shaped zone of stringer and panel joining).

52

Fig. 3: Artificial reflectors (defects) High extent of anisotropy is typical for CFRP. Acoustic properties are heterogeneous in different directions due to it. However unlike metal testing objects typical defects of laminated composites have orientation mainly along the layers location, and consequently parallel to entry surface. Therefore it is enough to use longitudinal waves only for CFRP parts and structures ultrasonic testing. Ultrasonic flow detector Omniscan MX (Olympus NDT), linear phased arrays Olympus NDT 3.5L-64-NW1 with 3.5 MHz operation frequency, Olympus NDT 5L-128-13 with 5 MHz operation frequency and Olympus NDT 5L-64-NW1 with 5 MHz operation frequency, sector phased array 5СС10.2-16-R1 with 5 MHz operation frequency, encoder and 2D Glider were used in the research.

Fig.4 Flat panel contained artificial defects testing results (C-scan)

Molded RTV-silicone inlay

Technological filaments fragments which are put between CFRP prepreg layers during laying out

Flat bottom hole

53

Different equipment operation conditions and scanning methods were tested in the research. Optimal conditions and methods, which ensure sensitivity equivalent to assured detection of 5 mm flat bottom hole and productivity up to 40 m2/h, are established.

Test results (C-scan) of a flat panel containing artificial defects (flat bottom holes and inclusions) are illustrated in Fig.4. As it is shown in Fig.4, all flat panel artificial defects were detected and presented visually in graphic image. Results analysis was carried out by using TomoView software. The size and depth of each artificial defect detected were determined. It was found out that the data on sizes and depths of artificial defects are equal to their true values with high accuracy. Phased array 5СС10.2-16-R1 was used for stringer panel radius testing. Special plexiglass and aqualen device (Fig. 5) was designed for stable acoustic contact. It allows testing such zones without waterbox using or eliminating part immersion in the water.

Fig. 5 Special device for stringer panel radius testing

Fig. 6 Test results for radius zones containing artificial defects

54

Setting for radius testing as well as for flat zones is realized by 5 mm flat bottom holes in flat specimen. Test results for radius zones containing artificial defects are shown in Fig. 6. Testing results and data analysis by TomoView software have shown that all radius artificial defects were detected and their sizes and depths were determined with high accuracy. 3. Conclusions CFRP specimens ultrasonic research using phased array has shown that this technique allows us to detect all typical FRP defects and determine their sizes and location with high accuracy. Productivity of large-size panels testing is considerably increasing in comparison with traditional testing technique (10…15 times). Besides that both testing fullness that is the possibility of testing stringer panel radii by using sector phased array and testing results reliability are increasing [6]. 4. References [1] Generalov A.S., Murashov V.V., Dalin M.A., Boychuk A.S.: FRP diagnosis by acousto-

ultrasonic technique, Aviation materials and technology journal, No.1, 2012, p. 42-47. [2] Khrulkov A.V., Dushin M.I., Popov Y.O., Kogan D.I.: Autoclave and without autoclave

FRP formation techniques researching and development, Aviation materials and technology: Anniversary edition (Appendix to aviation materials and technology journal), 2012, p. 292-301.

[3] Klyev V.V.: Non-destructive testing: Handbook in 7 Vol., Vol.3, Ermolov I.N., Lange Y.V.: Ultrasonic testing, Moscow, 2004. p. 473-555.

[4] A.S. Boychuk, A.S. Generalov, A.V. Stepanov, O.V. Yukhatskova: Nondestructive Testing of FRP by Using Phased Array Ultrasonic Technology, Industrial automatic control systems and controllers. 2013. № 2, p. 54-58.

[5] Boychuk A.S., Generalov A.S., Dalin M.A., Stepanov A.V.: Nondestructive testing of T-shaped zone FRP integrated structure technological discontinuities by ultrasonic phased array, All materials. Encyclopaedic handbook, № 10, 2012, p. 38-43.

[6] Boychuk A.S., Stepanov A.V., Dalin M.A., Generalov A.S., Lozhkova D.S.: Probability estimation of FRP structures ultrasonic nondestructive testing results by phased array, XX anniversary conference materials “Modern methods and tools of nondestructive testing and technical diagnosis”, 2012, p. 84-85.

55