EFFECT OF MOISTURE ON CFRP ADHESIVE BONDED JOINTS

Dr.A.JOSEPH STANLEY,PROFESSOR & DEAN,

DEPT. OF AEROSPACE ENGG.,MADRAS INSTITUTE OF TECHNOLOGY.

Under the guidance of

By,A.T.Chandrasekar (20053006),R.Kannan (20053012),S.Prabhu (20053023),N.Senthil Kumar (20064901).

Introduction This Project is about moisture effect on CFRP

Laminate Adhesive joint.

Degradation of Lap shear strength of the joint due to moisture will be found.

Acoustic Emission is used to monitor the propagation of defect.

Ultrasonic(A-Scan) is used to identify the defects caused due to moisture absorption.

DESCRIPTION

25 specimens were made.(Araldite-Bond)

5 specimens were tested in FIE UTM machine.

20 specimens were scanned using Ultrasonic(A-Scan) and then 10 specimens are immersed in water,10 are kept in climatic chamber.

After 20 days (which is immersed in water), 5 specimens were scanned using Ultrasonic(A-Scan) and then tested in UTM.

Specimen

ASTM D 5868 – 01 Standard

Specimen Conditioning

• Specimens are immersed in water for different periods.

» 20 days» 30 days 5 specimens each.

• Specimens are conditioned for accelerated environment in climatic chamber. (ASTM-D5229)

o 70% humidityo 50°c.

20 days30 days 5 specimens each.

Acoustic Emission SAMOS E3.10 data acquisition system of Physical

Acoustics Corporation (PAC) Threshold : 45 dB. AE measurements were achieved by using two

resonant Nano PAC sensors Frequency range :1 kHz–200 KHz at -3dB The amplitude distribution range :0–100 dB Peak definition time=30 micro s; Hit definition time=300 ms; Hit lock time=600 ms

Sensor Placement

All dimensions are in mm.

Acoustic emission observation

Purpose of pencil-break study• It ensures that the transducers are in good acoustic contact

with the part being monitored. • It checks the accuracy of the source location setup.

Acoustic emission observation

Wave velocity study

wave velocity V = (D2-D1) (t2-t1)• D1 distance between sensor1 and source• D2 distance between sensor2 and source• t1 time interval at which signal is detected in sensor1• t2 time interval at which signal is detected in sensor2

Acoustic emission monitoring Tensile testing of specimens

Acoustic emission sensors were coupled with specimens and were tensile loaded on a100 kN FIE servo hydraulic universal testing machine. The load rate was set at 0.25 kN/min.

Time for each 0.25kN interval of the loading is noted.

Test is continued till the specimen fails and the failure load of specimen is noted.

FAILURE LOADS OF SPECIMENS

SP-21 4.95

SP-24 5.65

SP-25 4.89

SPECIMEN FAILURE LOAD (KN)

SP-3 4.425

SP-4 4.65

SPECIMEN IMMERSED IN WATER FOR 20 DAYS

Acoustic emission GraphsSpecimen-3Immersed in water for 20 daysFailure load – 4.425 kN

ULTRASONIC INSPECTION• Widely used NDT technique• Detection of most manufacturing flaws and in-service flaws• Ultrasonic transducers for NDT consist of

– a single active element that both generates and receives high frequency sound waves,

– or two paired elements, one for transmitting and one for receiving.

ULTRASONICS (A-Scan)

• Simple RF waveform presentation showing the time and amplitude of an ultrasonic signal.

• An A-scan waveform represents the reflections from different layers in the test piece.

• Ultrasonic wave propagation is influenced by the microstructure of the material.

• The velocity of the ultrasonic waves is influenced by the material properties and the defects in the material.

Bonded region

Un-bonded region

ULTRASONICS - Attenuation• Attenuation in ultrasonics is the reduction in amplitude

of the ultrasound beam as a function of distance through the specimen.

• It is the combined effect of scattering and absorption.

A = A0 * e / L

Where, A – Amplitude at any locationA0 – Amplitude at reference locatione – Attenuation co-efficientL – Distance from reference point

X-axis – Echo distanceY-axis – Amplitude

Normal specimen

Specimen after 20 days in water

Comparison of specimens–Unconditioned & conditioned specimen

Unconditioned specimen

Specimen immersed in water for 20 days

Bonded region

Bonded region

THANK YOU