M.D. Fariñas, E. Cuevas*, M. García Merino*, T. Gómez Álvarez-Arenas

US-BIOMAT, ITEFI, CSIC, Serrano 144, 28006, Madrid, Spain

*TECNATOM, S.A. Avda. de Montes de Oca 1 28703, San Sebastián de los Reyes, Madrid, Spain

A non-contact ultrasonic technique is proposed for the inspection of carbon fiber reinforced polymer (CFRP) prepreg laminates during lay-up fabrication. A through transmission technique is

proposed using air-coupled transducers to transmit ultrasonic signals through the prepreg laminate and the mold where it is fabricated using normal incidence. The results show the ability of

this technique to determine the degree of compaction of the laminate and the presence of delaminations.

NON-CONTACT ULTRASONIC INSPECTION OF CFRP PREPREGS FOR

AERONAUTICAL APPLICATIONS DURING LAY-UP FABRICATION

Ultrasonic Inspection System. Design Parameters for the

Air-coupled Ultrasounds Technique.

3

-80

-70

-60

-50

-40

Ma

gn

itude

(d

B)

cured

uncured

0.30 0.45 0.60 0.75 0.90

5

10

15

20

25

30

Phase

(ra

d)

Frequency (MHz)

cured

uncured

Transmission coefficient spectra

MATERIAL DENSITY (KG/M3)

RESONANT FREQUENCY (FRES) (KHZ)

ULTRASOUND

VELOCITY (M/S)

ULTRASOUND

ATTENUATION @ FRES (NP/M)

UNCURED CFRP

1580 ± 120 650 ± 80 1370 ± 175 540 ± 80

CURED CFRP

1850 ± 120 685 ± 6 2840 ± 40 20 ± 2

Transmission coefficient spectra of CFRP

Transmission coefficient spectra of CFRP laminated and the Aluminium Mold

thickness = 2 mm thickness = 6 mm

thickness = 13 mm thickness = 13 mm

@ 250 kHz

Compaction Attenuation

(dB/layer)

@ 0.25 MHz

Long 0.3-0.75

Short 2.5-3.0

None 7-10

Pulser/Receiver

• DASEL USB-Ultrascope

Tone burst [1-5] cycles

Up to 400 V

Gain up to 60 dB

• Panametrics P/R 5058 Spike

Up to 900 V

Gain up to 60 dB

Preamplifier = 30 dB

Transducers

• Air-Coupled

• Center frequency =

250 kHz

• Bandwidth = 500 kHz

B

Mechanics

• U-shaped holder

• Automatic and portable

scanning system

D

Mold

• Aluminium

• Thickness = 13 mm

Material

• Several samples

• 300 x 300 mm

• Up to 30 layers

• 3 different compaction: o None

o Short (15-30 min)

o Large (4-8 hours)

• Some with Teflón 10x10

mm insertions at

depths: o 2 layers

o 15 layers

o 28 layers

A

E

-2

-1

0

1

2

No sample

-0.2

-0.1

0.0

0.1

0.2

Am

plit

ude

(V

) 8 layers, long compaction

50 100 150 200 250 300 350

-0.2

-0.1

0.0

0.1

0.2 30 layers, long compaction

Time (s)

md.farinas@csic.es

t.gomez@csic.es

CHALLENGES/REQUIREMENTS

Contact with the material is prohibited to prevent any material contamination.

Non contact technique.

Very large Insertion loss: Very large attenuation in the CFRP.

CFRP must be inspected along with the fabrication mold.

BENEFITS o Cost reduction: Repairing or

discarding unsound material

before the autoclave stage

o Possibility to perform 2D scans

C

Experimental Results. Influence of

compaction. Detection of Teflon insertions.

4

0 20 40 60 80 100 120 140 160 180-14

-12

-10

-8

-6

-4

-2

0

Norm

aliz

ed R

eceiv

ed A

mplit

ude (

dB

)

Scan distance (mm)

• A non-contact method for the inspection of CFRP prepreg material during lay-up fabrication has been proposed.

• A detailed experimental study of the properties in uncured laminated prepregs was performed in order to determine velocity and attenuation of ultrasonic

waves in this material.

• A model of ultrasonic propagation through the whole system (laminates and mold) are used to design optimum inspection configuration. The design

variables of this set-up include: transducers center frequency and bandwidth, material to fabricate the mold and thickness of the mold and pulser / receiver

used.

• Finally, the method has been applied for the inspection of several 300 x 300 mm samples with up to 30 layers. Three different compactions and 10 x 10 mm

Teflon insertions at several depths have been used in order to test the technique.

Ultrasonic Properties of CFRP

Laminates. Cured versus Uncured material.

Description of the problem. Objectives and

Requirements.

1 2

Scan