Application of Carbon Nanotube-Based Mechanical Sensors for Defect Identification of Engineering Components

Professor Vaidehi Ganesan, Senior Scientist at the Centre for Nanoscience and Nanotechnology, Sathyabama University, talks to AZoSensors about the application of carbon nanotube-based mechanical sensors for defect and strain measurements of engineering components.

The future use of non-destructive testing is becoming a key subject area for the engineering industry. Can you summarise what non-destructive testing involves?

This is a carbon nanotubes (CNT)-based nanocomposite material used as a mechanical sensor for defect and strain measurements on engineering components. The nanomaterial film can be pasted by non-conductive adhesive on the locations of interest on engineering components. We can identify any defect initiation or strain at isolated locations using two probe electronic circuit and calibration curves generated in the laboratory (defect size vs Resistance using standard calibration curves and strain vs voltage using a Universal Testing Machine [UTM]). This novel NDE technique can be used for online monitoring and in-service inspection of components in any plant.

What are the main non-destructive techniques available?

The main NDE techniques are: ultrasonics, acoustics, eddy current, thermal imaging, radiography, XRD residual stress analysis, phased array, In-situ metallography, ferritoscope, Liquid penetrant testing, Magnetic particle testing, etc.

Why have you used carbon nanotube-based nanosensors as a new non-destructive evaluation technique for defect identification?

Carbon nanotube is a nanomaterial and sensors made using this novel material will have superior qualities compared to other existing sensors with the following qualities:

• Better Sensitivity
• Quick response time
• Better conductivity.

The sensitivity and resolution is improved by using CNT based nanosensors.

How do CNT-based nanosensors work for defect identification and structural strain measurements of engineering components?

The nanomaterial synthesised should be pasted on the defective location by non-conductive adhesive. The resistance across the film can be measured using a two probe electronic circuit. The density of electron scattering increases with defect size and hence the resistance measured is also increased. This property is used for defect identification. The CNTs embedded in polyvinylidene difluoride (PVDF) film (nanosensor material) has very good piezo-electric properties. The network of CNTs improve the conductivity. These properties are used in determining the strain. We should generate calibration curves, i.e. defect size vs resistance using standard calibration blocks and strain vs voltage using UTM, and use the same for online monitoring of defect identification and structural strain monitoring.

Nanosensor arrangement displaying strain vs voltage in UTM laboratory experiments. Changes in the voltage as a function of strain. Image Credits: Professor Vaidehi Ganesan, IGCAR, Kalpakkam.

What makes this work novel when comparing it to existing NDTs?

• High sensitivity of the developed sensor
• Quick response time
• High Gauge factor
• Ability to withstand high stress.

This technique is using CNTs-PVDF nanomaterial. The sensitivity and resolution is much better, easy to use and a simple technique. Interpretation of the results and analysis is also very simple. The details are provided in the technical report.

What are the technical features and benefits of CNT-based nanosensors?

The nanosensors are made up of polymers and CNTs which have superior qualities such as:

• High mechanical strength
• High sensitivity
• High conductivity.

What type of defects can this new technique measure?

This technique can measure surface defects on any engineering components (for example, Turbine blades) and metal plates. Defects in the oil & pipeline industries can also be identified.

At present this technique can be used for identifying the Surface defects only. It is difficult to pick up the signals from volumetric defects.

How can you apply this new technique in industry?

We can do in-service inspection and online monitoring of engineering components in Industries. We can paste the nanofilm at the location of interest and measure.

How do you plan on advancing your CNT-based nanosensors for defect identification and diversifying such areas of application?

Advancements to this technology includes the following:

• Varying the polymer used
• Attaching different functional groups to CNT
• Nano films based sensors synthesized can also be used in other applications like  EMI shielding
• Nanosensor attached robots for carrying out specific tasks.
• Geaphene instead of CNTs.

We have to generate calibration curves with different defect size and shape. We have to calibrate systematically with different strain range (elastic and plastic). We should have more quantitative details. We should explore the possibility of imaging the defects using the nanosensor-based NDE technique. Graphene can also be used instead of CNTs. Graphene may improve the sensitivity, response and resolution much better than CNTs.

References

• Vaidehi Ganesan and A. Deepak. “ Synthesis, Characterization and Applications of some Nanomaterials”, Invited lecture, Proceedings of International Conference on Advanced Nanomaterials and Emerging Engineering Technologies [ ICANMEET-2013], july 24-26, 2013, Sathyabama University in association with DRDO, New Delhi, ISBN: 978-1-4799-1377-0, www.icanmeet2013.com, India, IEEE.
• Deepak, V.Karthik, Vaidehi Ganesan, P.Shankar. “Defect Detection And Strain Analysis On The Surface Using Carbon Nanotube Based Electro Mechanical Systems” in Sixth International Symposium On Macro And Supramolecular Architectures And Materials, 2012, pp 35-40, ISBN: 978-93-82563-34-1.
• Ganesan V, Deepak A. Synthesis, Characterization and Application of Some Nanomaterials. Proceedings of the “International Conference on Advanced Nanomaterials and Emerging Engineering Technologies” (ICANMEET-2013) organized by Sathyabama University, Chennai, India in association with DRDO, New Delhi, India, 24^th-26^th July 2013.

About Professor Vaidehi Ganesan

Vaidehi was formerly the Senior Scientist from Metallurgy & Materials Group, at the Indira Gandhi Centre for Atomic Research (IGCAR), Dept of Atomic Energy, Kalpakkam. Vaidehi has served for 37 years at IGCAR (April 1976- Dec 2012). Vaidehi has complete many research and development projects at IGCAR, DAE, during her 37 years of service. After joining DAE, Vaidehi worked and contributed in various research and development projects related to Metallurgy & Material Science and Engineering.

Vaidehi also received the Madam Marie Curie award during the 4^th National Women Science Congress at Bangalore, Bharat Jyothi award from Delhi, Thambidurai Award from Indian Society for Non-destructive Testing, Best paper presentation awards from professional societies. Vaidehi is now the Senior Scientist at the Centre for Nano Science and Nano Technology, Sathyabama University.