ULTRASOUND EXAMINATION OF FIBER GLASS POLYESTER COMPOSITE

Transcription

1 ULTRASOUND EXAMINATION OF FIBER GLASS POLYESTER COMPOSITE Janez Grum 1, Roman Šturm 1, Paul Barsanescu 2, Adriana Savin 3, Rozina Steigmann 3 Raimond Grimberg 3 1 University of Ljubljana, Ljubljana, Slovenia 2 Technical University Gh.Asachi Iasi, Romania 3 National Institute of Research and Development for Technical Physics, Iasi, Romania

2 ABSTRACT This paper presents the possibility to determine the components of the compliance tensor of the Glass Reinforced Polyester (GRP) composite plates using ultrasound procedures. The values of propagation speed for longitudinal and transversal waves are used for the out-of-plane parameters. For in plane parameters we have used the values of phase velocity of fundamental modes of Lamb waves generated and received with air-coupling ultrasound transducers. The results obtained by the proposed nondestructive tests are in good correlation with those obtained by classical destructive tests.

3 EXPERIMENTAL PROCEDURE Samples of GRP plates have composition of: reinforcement of 5 and 6 sheets of ravings with 250±50 gm -2 density, matrix from different types of unsaturated polyester resins. Sample name Matrix components Phtalic anhydride / maleic anhydride Number of reinf. layers Fiber volume ratio Density of GRP [kg/m 3 ] Polyester synthesis l 1 / ±20 2 steps l 1 / ±20 2 steps l 1 / ±20 In-situ l 1 / ±20 2 steps

4 EXPERIMENTAL PROCEDURE For a better characterization of studied GRP samples, the temperature of glass transition has been determined using Dynamical Mechanical Analyzer. Sample name Tg ( C) l l l l 105.7

5 EXPERIMENTAL PROCEDURE The five coefficients which characterize the material are: two Young (or extensional) modulus E x and E z two shear modulus G xz and G xy two Poisson s ratios xz and xy The coordinate system attached to GRP plate.

6 EXPERIMENTAL PROCEDURE destructive testing The measurement of Young modulus along the three directions was made with a Dynamic Mechanical Analyzer DMA 242C Netzsch with a 3 points bending fixture. (*) The measurement of shear modulus G xy and G xz as well as the Poisson s ratio were made on universal testing machine INSTRON E 1000, having hydraulic fixture for samples. (**) Composite E x =E y * [GPa] E z * [GPa] xy * xz ** G xy ** [GPa] G xz ** [GPa] l l l l Average value of 5 samples.

7 EXPERIMENTAL PROCEDURE ultrasound testing Air-coupled ultrasound pitch-catch configuration for generation and reception of Lamb waves and SH 0 mode. =10.2 different distances L

8 EXPERIMENTAL PROCEDURE ultrasound testing The experimental set-up for determination of Lamb waves propagation speed using air-coupled US transducer.

9 EXPERIMENTAL PROCEDURE ultrasound testing The experimental set-up for determination of Lamb waves propagation speed using air-coupled US transducer.

10 EXPERIMENTAL PROCEDURE ultrasound examination The Young modulus E z, shear modulus G xz and Poisson s ratio xz can be determined by measuring the velocities of longitudinal waves c pz and of transversal waves c sz that propagate along Z direction. c c p s z z G Ez1xz 1 12 xz xz Equations can be expressed in function on Lamé coefficients and µ z z G z xz 1 12 xz xz xz E xz

11 EXPERIMENTAL PROCEDURE ultrasound examination For the fundamental symmetric Lamb mode, S 0, the phase speed is c s E x xy The phase speed for the fundamental Lamb anti-symmetric mode, A 0, is c A 0 D p 2h 1/4 Where D p is the flexural rigidity of the plate 1/2 D p 8 x x x 3 2 x x h 3

12 EXPERIMENTAL PROCEDURE ultrasound examination The incident angle,, is chosen so the SH 0 modes horizontally polarized shear waves shall appear, that is c air arcsin c sz where c air = 340 m/s is the ultrasound speed in air, = The determination of phase velocity of fundamental modes S 0 and A 0 was made using the phase spectrum method. The phase velocity of Lamb waves is given by c p 2 fl where is the difference in the phase spectrum of two signals that were collected with a different distance between them of L, and f is the frequency.

13 EXPERIMENTAL RESULTS The signal received by the reception transducer at the examination of l composite, where the modes A 0 (anti-symetric),s 0 (symetric) and SH 0 (horizontally polarized shear waves) can be distinguished.

14 EXPERIMENTAL RESULTS The amplitude spectrum.

15 EXPERIMENTAL RESULTS The spectrogram.

16 EXPERIMENTAL RESULTS E z, xz and G xz were determined from the measurement of propagation speed of the ultrasound along the direction Z, the other mechanical properties being determined from the propagation speed of the Lamb waves, the fundamental symetric and anti-symetric modes S 0 and A 0. Using spectrum phase method, the phase velocity of A 0 and S 0 were determined, and, using the eqs. for C S0 and C A0, the other measures can be determined.

17 EXPERIMENTAL RESULTS In the case of transverse isotropy only five elastic coefficients can be independent 1 xy xz Ex Ex Ex xy 1 xz x E x x Ex E x y 1 y xz xz z Ex Ex E z z xy 1 xy xy yz E x yz xz xz 2G xz G xz where is the strain vector, is the stress vector and A represents the tensor of elastic compliance. or A

18 EXPERIMENTAL RESULTS The mechanical properties determined from the measurement of propagation speed of the ultrasound: Comp osite C p [ms -1 ] C s [ms -1 ] C A0 [ms -1 ] C S0 [ms -1 ] E x =E y [GPa] E z [GPa] xy xz G xy [GPa] G xz [GPa] l l l l

19 SUMMARY A method for generation and reception of Lamb waves in plates of composite materials is represented by the using of air-coupling low frequency ultrasound transducers in pitch catch configuration. The measurement of propagation speed of longitudinal and transversal waves can be used with good results for the determination of elastic modulus E z, the shear modulus G xz and Poisson s ratio xz. For the determination of elastic modulus E x, shear modulus G xy and Poisson s ratio xy, the use of Lamb waves is required, the phase velocity of fundamental modes being directly connected with mechanical parameters.

20 SUMMARY The results of nondestructive measurements proposed in this paper are in good concordance with those obtained by classical destructive tests. Acknowledgements This paper is partially supported by The National Authority for Scientific Research of Romania (ANCS) under Romanian Slovenian Bilateral Cooperation Program-Contract No.371/2009 ende RO-SI and Slovenian Research Agency for the Republic of Slovenia (SRA) under Romanian Slovenian Bilateral Cooperation Program-Contract No.: BI-RO/