final year seminar

NDT of fiber-reinforced composites with a new laser-ultrasound system

Guided By:Prof Arun JMechanical Eng Department

Presented By:Aaron K JohnMechanical Engineering

Introduction

• Non contact method• Currently no non-contact NDT method approaches the

sensitivity of contact NDT method• Methods:

non-contact NDT: Michelson Interferometernew non contact NDT: LU Interferometercontact NDT: Piezoelectric Transducer

About seminar

In this new approach we utilize recent

progress in fiber laser systems andtelecommunication optics to improve thesensitivity of non-contact method

Current non contact methodMichelson Interferometer

• Combine laser beams to obtain interference pattern, to measure surface defects etc.

• Very sensitive to environmental noise

Experiment Samples

• 3.6 mm thick andcontained 19 individuallayers.

• Artificial defects ofabout 20um thick

- brass foil- tape- polymer

New laser-ultrasound method

Experiment components

1. Pulsed laser source2. Super luminescent diode (SLD)3. Polarization controller4. Receive Head5. Polarizing Beam splitters (PBS)6. Photo Detector (PD)

Interferometer

1. laser radiation initially polarized

2.Divided into two arms with a polarization beam splitter PBS1

3.PBS2 combines the delayed beams into one fiber

4.focuses the probe radiation onto the sample surface5.Radiation back to the fiber contains 2 delayed waves, similar to incident beams

6.beams are split again to reduce noise

EXPERIMENT ARRANGMENT AND PROCEDURE

• When no pulsed laser present, interferometerrecords nothing• But when pulsed laser present, acoustic pulsegenerated, interferometer records the pressuredifference

Experiment with PVDF Transducer

• Polyvinylidene Fluoride (PVDF)• A type of piezoelectric transducer

Results

Signals recorded with LU (grey line) and with contactPVDF (dark line)

Result 1.

image obtained with Interferometer

Result 2.

Image obtained with contact PVDF detector

Inference

1. From Result 1 we infer that the sensitivity ofthe non contact LU detector is comparable tothat of a contact piezoelectric transducer.

2. From Result 2 PVDF transducer is about oneorder of magnitude more sensitive than theSagnac detector. Hence we infer LU detectorin comparable to a piezoelectric transducer

Conclusions

The new laser ultrasound

- is a non contact method

- does not need adjustment and stabilization

- can be mounted on any surface

- less expensive

Reference

1. National Center for BiotechnologyInformation (USA)

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3971821/

2. NDT of fiber reinforced composites with anew fiber optic pump probe laser ultrasoundsystem. (Science Direct)

THANK YOU