Investigation of Woven Fiber Reinforced Laminated Composites Using a Through Transmission Ultrasonic Technique

Transcription

1 Photos placed in horizontal position with even amount of white space between photos and header Photos placed in horizontal position with even amount of white space between photos and header Investigation of Woven Fiber Reinforced Laminated Composites Using a Through Transmission Ultrasonic Technique Sarah L. Stair 1, David A. Jack 1, and David G. Moore 2 1 Baylor University Mechanical Engineering Department Waco, Texas, USA 2 Sandia National Laboratories Nondestructive Evaluation Department Albuquerque, New Mexico, USA This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation. SAND C Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.

2 Carbon Fiber Reinforced Laminated Composites: Background Applications Aerospace Marine Automotive [1] [2] Fibrous composites are extremely strong in the fiber s longitudinal direction, however provide little support in transverse directions. Strength in the transverse direction is added by changing ply orientation. For applications where more than one fiber orientation is required, a fabric combining 0 and 90 degrees fiber orientation is useful. Woven product are interlaced with warp 0, and weft, 90 fibers in a regular pattern or weave style. [1] [2] Image courtesy of Russ Mailen

3 Carbon Fiber Reinforced Laminated Composites: Background The fabric s integrity is maintained by the mechanical interlocking of the fibers weave styles. While using a woven fabric, the type of weave and the orientation of each lamina ultimately effect the properties of the bulk laminate. Several ASTM standards exist for determining the final part properties, but many of these permanently damage the part. Furthermore, these standards are intended for coupons, not the full production part. Need NDE method for evaluating the fabricated part properties Goal: Determine part stiffness using ultrasound technology

4 Ultrasound Methods for Evaluating Elastic Constants (1 of 2) Markham [1] Evaluated elastic constants of unidirectional composite Used a through transmission, immersion technique Searched for longitudinal and shear wave, one at a time Part was rotated on turn table to obtain additional wave velocities at oblique incident angles [1] [1] Markham, M.F., Measurement of the Elastic Constants of Fibre Composites by Ultrasonics, Division of Molecular Science, National Physical Laboratory, Teddington, Middlesex, England, Composites, March, 1970.

5 Ultrasound Methods for Evaluating Elastic Constants (2 of 2) Rokhlin and Wang [2,3] Applied a double through transmission, immersion technique Placed the unidirectional sample in the middle of a reflective cylinder with reflector plate located behind the sample What about woven fiber reinforced laminates? [3] [2] Rokhlin, S.I. and W. Wang, Ultrasonic Evaluation of In-Plane and Out-of-Plane Elastic Properties of Composite Materials, Review of Progress in Quantitative Nondestructive Evaluation, 8B, D.O. Thompson and D.E. Chimenti (Eds.), Plenum, New York, [3] Rokhlin, S.I. and W. Wang, Double Through-Transmission Bulk Wave Method for Ultrasonic Phase Velocity Measurements and Determination of Elastic Constants of Composite Materials, The Ohio State University, Columbus, Ohio, American Journal Acoustics Society, 91, June 6, 1992.

6 Ultrasound Terms and Experimental Setup Example Receiver moves during scan θ 2 r 2 Composite Laminate r 1 θ 1 Pulser remains stationary during scan

7 Snell s Law Calculations Snell s Law is given as: sin sin V 1 = wave velocity in 1 st acoustic medium V 2 = wave velocity in 2 nd acoustic medium Using Snell s Law in combination with the longitudinal and shear wave velocities through the part, we can determine the angle at which the longitudinal and shear waves travel through the part θ L θ s θ 1 Suppose: θ 1 = 10 and considering the 4 ply laminate: V 1,water = in/μs V 2, cf long. = in/μs V 2, cf shear = in/μs θ L = = angle of the longitudinal wave travel θ s = = angle of the shear wave travel

8 Varying Receiver Orientation Longitudinal Wave Scatter Longitudinal Wave Scatter Longitudinal Shear Shear Quasi- Shear As the angle of the receiver is changed, we observe the longitudinal and shear waves differently in a given scan The 4 case is almost exclusively a longitudinal wave, which is to be expected since the pulser is at 5 Same colorbar axis, representing signal amplitude, is used on each plot (blue = 0%, red = 100%) Same vertical and horizontal axes used for each plot

9 Test Matrix As discussed in the previous slide, we determined the parameters necessary to obtain both a shear wave and a longitudinal wave within the same scan of a carbon fiber reinforced laminate Using these parameters, we have collected data for 2, 4, 8, 12 and 16 ply 8HS carbon fiber laminates Two different configurations were used Pulser oriented at 5 and the receiver oriented at 14 relative to the part surface normal Pulser oriented at 10 and the receiver oriented at 18 relative to the part surface normal Laminate Rotation Horizontal = weft Horizontal = warp warp Pulser = 5 Receiver = 14 2, 4, 4*, 8, 8*, 12*, 16 2, 4, 4*, 8, 8*, 12*, 16 Pulser = 10 Receiver = 18 2, 4, 4*, 8, 8*, 12*, 16 2, 4, 4*, 8, 8*, 12*, 16 weft * Refers to square shaped laminates instead of rectangular

10 Experimental Setup During the through transmission scan, the pulser and receiver were oriented at 5 and 14 relative to the part surface normal, respectively. Receiver Part Pulser Pulse echo scans were also performed on the parts where the laminate was bonded to the aluminum. The purpose of the pulse echo scans was to get a better idea of the bond between these materials while removing the complexity of the oblique incident angle of the wave. Receiver Part Pulser

11 Through Transmission Scans (1 of 3) 8 ply, 8HS weave Pulser = 5 deg, Receiver = 14 deg Pulser and receiver = 5 MHz (x,y) = (0.611,0.179) Shear Wave

12 Through Transmission Scans (2 of 3) 8 ply, 8HS weave Pulser = 5 deg, Receiver = 14 deg Pulser and receiver = 5 MHz (x,y) = (0.611,0.624) Longitudinal Wave

13 Through Transmission Scans (3 of 3) 8 ply, 8HS weave Pulser = 5 deg, Receiver = 14 deg Pulser and receiver = 5 MHz (x,y) = (0.611,0.831) Likely scatter, but further testing will be used to confirm

14 Laminate Bonded to Aluminum Scans were performed on a part where the laminate was co cured to an aluminum step wedge Experiments have also been performed on a part where the carbon fiber laminate was bonded to the aluminum using various types of viscoelastic couplants, such as a shear wave ultrasound gel and petroleum jelly 4 ply 8 ply 12 ply Notice the step wedge

15 Through Transmission Scans (1 of 4) 8 ply co cured with aluminum, 8HS weave Pulser = 5 deg, Receiver = 12 deg Pulser and receiver = 5 MHz Scanned from carbon fiber side (x,y) = (0.489,0.318)

16 Through Transmission Scans (2 of 4) 8 ply co cured with aluminum, 8HS weave Pulser = 5 deg, Receiver = 12 deg Pulser and receiver = 5 MHz Scanned from carbon fiber side (x,y) = (0.535,0.712)

17 Through Transmission Scans (3 of 4) 8 ply co cured with aluminum, 8HS weave Pulser = 5 deg, Receiver = 12 deg Pulser and receiver = 5 MHz Scanned from carbon fiber side (x,y) = (0.567,1.004)

18 Through Transmission Scans (4 of 4) 8 ply co cured with aluminum, 8HS weave Pulser = 5 deg, Receiver = 12 deg Pulser and receiver = 5 MHz Please note the vertical axes are different Scanned from carbon fiber side Scanned from aluminum side

19 Pulse Echo Scan (1 of 2) 8 ply co cured with aluminum, 8HS weave Transducer = 0 deg Transducer frequency = 5 MHz Scanned from carbon fiber side Sample grips Both images have the same axes and colorbar Scanned from aluminum side

20 Pulse Echo Scan (2 of 2) Bonded Region Disbonded Region Bonded Region Disbonded Region

21 Future Work (1 of 3) Markham (1970) proposed a method for determining the elastic constants of a unidirectional laminate by measuring three velocities through the laminate: a quasi longitudinal and two quasi shear velocities He related the velocities to the elastic constants via the following equation: where 2 C direction cosine of the wave normal to axis density of the part wave velocity Markham, M.F., Measurement of the Elastic Constants of Fibre Composites by Ultrasonics, Division of Molecular Science, National Physical Laboratory, Teddington, Middlesex, England, Composites, March, 1970.

22 Future Work (2 of 3) Rokhlin and Wang (1992) developed a double through transmission technique to measure the longitudinal and shear velocities traveling through a unidirectional composite part for a given incident angle They coupled their phase velocity measurements with the Christoffel equation to solve for the part s elastic constants The Christoffel equation can be written as: where 0 1,,, 1, 2, 3 = 0, 1, 2, 3 the elastic constant tensor the unit vector normal KroneckerDelta Phase velocity Rokhlin, S.I. and W. Wang, Double Through-Transmission Bulk Wave Method for Ultrasonic Phase Velocity Measurements and Determination of Elastic Constants of Composite Materials, The Ohio State University, Columbus, Ohio, American Journal Acoustics Society, 91, June 6, 1992.

23 Future Work (3 of 3) Both Markham (1970) and Rokhlin and Wang s (1992) research focused on determining the elastic constants associated with laminates manufactured with a unidirectional carbon fiber material The complexity of the problem increases as we look at woven fabrics, such as an 8HS weave A reasonable starting point is to apply the two methods previously described to the results obtained from our measurements and compare the calculated elastic constants with measured values More than likely, the change in material will need to be considered in the mathematical equations, and this is one of my focus points for this upcoming academic year

24 Anisotropic Material Properties There are various degrees of anisotropy We are treating the laminates as orthotropic Orthotropic systems consist of 9 independent variables as seen in the 6x6 contracted form of the stiffness tensor at right Unidirectional laminates are treated as transversely isotropic with 5 independent variables 1 1 Generalized Form of Hooke s Law 6x6 Contracted Form of Stiffness Tensor

25 Summary Developed a through transmission setup for capturing a longitudinal and shear through a carbon fiber reinforced laminate in a single scan Appropriate scan parameters were determined for the pulser having an orientation of 5⁰ and an orientation of 10⁰ Scan data was collected for 2, 4, 8, 12, and 16 ply 8HS carbon fiber laminates using the through transmission setup Ultrasound data was also collected for 4, 8, and 12 ply carbon fiber laminates bonded to aluminum using through transmission as well as pulse echo Future work includes identification of elastic constants for the bulk laminate using the measured velocity of the longitudinal and shear waves through the laminate

26 Acknowledgements Ciji Nelson Andrew Lentfer NSF Graduate Research Fellowship Grant No. DGE Questions?