The Non-Destructive Testing/ Evaluation (NDT/ NDE) one of the important areas, where the reliability of the materials/product is evaluated without destructing it. The large-scale adoption of this technique is important to ensure that the products that are supplied to the end-customer will serve its purpose and deliver the indented performance.

Composite materials which itself heterogeneous in nature and variations bound to happen either at the raw materials stage or during manufacturing process or under service conditions. Some of the common problems and defects in the Fibre Reinforced Polymer composites are air bubbles, pin holes, debonding, delamination, under cure, temperature build up, blisters, improper wetting, shrinkages, warpage, foreign matter contamination including oil, crease, particulates, etc and these defects affects the performance of the composites based on the size and scale of the defects and its service and environmental conditions.

It is important that the user gets the right product that is looking good not only in its external appearance but also internally, as a defect free product as specified by the customer or as applicable for the service conditions.

Following is the discussion with Prof Krishnan Balasubramanian, Institute Professor in the Department of Mechanical Engineering and Head of the Center for Nondestructive Evaluation at IIT Madras

What are the latest and most versatile techniques in NDT that can be adopted by the composites Industry especially in the medium and small- scale enterprises?

Traditionally, the NDT industry has been driven by the metals industry with a significant emphasis on weld inspection, particularly during fabrication. Also, metals corrode over time, and for in-service inspection, detection of corrosion has also been a strong driver. The techniques that are traditionally prevalent in the industry include visual inspection (aided by magnetic particles or liquid penetrants), radiography (x-rays, gamma rays, etc.) and ultrasound.

However, with the emergence of composites as an alternative material system to metals, the old paradigms in NDT are not valid. Composites, from an NDT perspective, may be classified into (a) Aerospace type, and (b) Structural type. The former typically uses carbon fiber-based composites while the latter is more glass based.  The type of defects and its criticality will be a necessary input in order to select the NDT technology. Over the past 40 years, ultrasonics has been a workhorse for inspection of the aerospace composites, particularly since these structures are often thin and delamination defects are more of concern. Additionally, recent advancements in Infra-Red Thermal Imaging technique and optical methods such as Shearography has led to improved and faster inspection of composite structures. For thick fiber-glass based structures, these NDT methods have been found to be not very effective. Hence, for thicker structures, the use of microwave and terahertz bands in the electromagnetic domains are emerging. Additionally, low frequency ultrasonic guided waves are also being effectively deployed.

Another important approach of deploying NDT technology is through permanently attached/embedded sensors in a Structural Health Monitoring (SHM) mode. Here, guided ultrasonics waves, optical fibers, and other sensors have found success. The SHM approach provides continuous data over the period of service of the structure, and hence has the potential to provide additional capabilities to provide prognosis of the state of the composite materials.

What are the hinderances in the large- scale adoption of NDT by the Industry? And what are the direct benefits that an industry can realize both in short term as well as in long term?

Costs and availability of skilled operators are key deterrents to widescale adaptation of NDT methods in the industry. Often, for a manufacturer, NDT is added cost and effort. Hence, the first choice will be to avoid this cost. Hence, the industry must be convinced of the RoI (Return on Investment). Another key contributor to this is the end customer or the regulatory bodies that insist on inspection prior to accepting the as-manufactured component.

The direct benefits to the manufacturer is the improvement of quality, reduction of waste, and early detection of any sub-optimal materials related issues, all of which will lead to cost savings. The direct benefits to the end-user is the improved performance, longer life, and safer deployment of the components.

The long-term benefits of NDT is the change in the culture of the manufacturing industry to a quality first culture that drives the improvement and increase of efficiency of the process and in the long run will drive down costs and improve quality.

The NDT is particularly important for structural profiles and critical components in Aerospace and defence products, how NDT can give confidence to the end user about the product?

NDT assures quality and reliability, thereby reducing costs for the end user as well as improving safety and availability of the products. It is well documented that for many critical systems the life-cycle costs of a product is 3 times the actual as-manufactured cost. Hence, a relatively small increase in manufacturing costs for NDT will significantly reduce maintenance costs and improve confidence.

There are Composites Structures that are being used for bridges / walkways and how NDT based sensors and Internet of Things (IOTs) can be integrated for structural health monitoring and real-time data acquisition and updates that can be shared to the stakeholders?

Yes, the use of composites for infrastructure including bridges, pipes, pressure vessels, ships, etc. have expanded the scope of the composites. This is mostly driven by the fact that metals corrode while composites do not. However, it must be noted that composites are often made of polymers that do degrade due to environmental and other factors over a period of time. Also, like welds in metals, the composites use either mechanical or adhesives for joints, that are vulnerable to failure and must be inspected with care.

Using NDT techniques tremendous amount of data can be generated, what is the status of Artificial Intelligence/ Machine Learning (AI/ML) in this domain, how these tools can be effective for the accuracy of the prediction in the failure analysis and prediction/ preventive care of composites products under various service conditions?

The SHM using NDT sensors are a vital addition to the strategy to make composite structures more reliable and cost effective. The mode of deployment is via Internet Of Things (IOT) and the continuous data provide information that can be used not only to detect the beginning of a damage, but also track the  growth of the damage that enables corrective intervention at the appropriate time. It will benefit the end use by maximizing the useful life of the component while optimizing the safety. The use of AI driven data analytics as an integral part of these system cannot be emphasized enough here. These AI engines have the potential to re-define the SHM approach through continuous learnings from the data. They will also have the information that can lead to improved design of composites that have longer life or endure harsher conditions.

How Industry can collaborate with NDT experts in academic domain, how academia and Industry partnership building can take place and how to bridge the gap in the composites sector?

Academia provides avenues for industry to solve problems that they do not have the time or expertise to resolve. However, there are significant gaps between the two communities. For example, academia is very competent in the Technology Readiness Level (TRL)-TRL 0-2 stages, while the industry wants technologies in the TRL 8-9 stage. Hence, the gap is huge.

One of the approaches that should reduce this gap will be intermediaries such as industry supported Centers of focused research and development, that are closely associated with academia on one side and industry on the other. This mode is often consortia based and sector or problem specific. There are several such examples, particularly in Europe and US, where Centers like the Center for Composite Materials in University of Delaware, or the Fraunhofer Institutes in Germany, among others, who have filled this gap admirably well.

In India, the consortia based pre-competitive research is still not recognized by industries. The industry must realize that such consortia-based research as pre-competitive stages will leverage research monies and allow them to optimize their R&D budgets. Additionally, matching funding from Government or Quasi-Governmental source can further enhance the outcomes.

The skilled technician in the composites domain with NDT expertise is very limited. How Augmented Reality /Virtual Reality (AR/VR) can be effectively utilized in combination with online training and physical mode of training process?

There are several ways to improve the availability of trained NDT personnel. However, there is always a supply-demand issue that must be addressed by the industry in a pro-active manner. First, a commitment to quality must not only be acknowledged, but also evangelized within the industry in order to build necessary confidence in the potential individuals who are willing to come into this field, as well as the trainers and educational institutions who can invest into NDT training and certification for composites. The role played by Indian Institute of Welding (IIW) and American Welding Society (AWS) in collaboration with American Society for Nondestructive Testing (ASNT) is an excellent model to emulate, where the welding societies are working closely with the NDT society to address this issue.

Technology is already playing a key role in education and training or personnel in many fields. This is already available in the training and evaluation of ultrasonic weld inspection. Hence, similar modules can be developed for composite inspection, but must be pro-actively supported and driven by end-user industry.

From academic side what is your expectation from the Industry and the support needed from the Government Policy makers?

Commitment towards R&D, towards Training & Certification, towards consortia-based problem-solving approach.

If industry comes-together and creates a fund for solving pre-competitive challenges, academia in India such as the Center for NDE at IIT Madras, will respond very positively.

This will automatically lead to Government support.

Some of the NDT equipment’s and sensors are very expensive, what are the ways to reduce the cost so that it can be made affordable for the medium and small-scale enterprises?

Any technology must show RoI for it to be acceptable to the industry. However, the industry must also be conscious of quality and the tangible and intangible benefits of NDT driven quality enhancements.

Today, cost of NDT systems is high primarily due to many of them being imported. Furthermore, the middlemen, custom duties, transportation costs, and breakdown costs are all adding to this.

The solution is to support and promote “make-in-India” by the Indian industries. Indian built products will not only reduce costs but also will improve availability of the equipment.

How the start-up companies progress in this domain and what are the global opportunities and also the challenges faced by them especially by the young entrepreneurs?

There are several Indian manufacturers and systems-integrators who are building world-class products in NDT today. The start-up eco-system in India has made this very strong.

For instance, in the NDE2024 Conference and Exhibition held in Chennai, the number of Indian products and startups comprised of close to 40% of the exhibition.

Unfortunately, the appetite for the Indian Industry for imported equipment is still very strong and are detrimental to the viability of Indian technologies and Indigenous companies.

Some of the companies have found more customers and success from clients outside India. This has change and we must have pride in our Country and its future as major technology provider, both for India and for World.

About Prof. Krishnan Balasubramanian

Prof. Krishnan Balasubramanian is a distinguished Institute Professor in the Department of Mechanical Engineering at IIT Madras, and currently leading the Centre for Non-destructive Evaluation since its founding in 2001. He is currently the President of the Indian Society for NDT (ISNT).  He also is the faculty-in-charge of Gopalakrishnan Deshpande Center for Innovation and Entrepreneurship, Accenture Center for Product X and the Center for Advanced Automotive Research. He also served as the Dean, Industrial Consulting and Sponsored Research at IIT Madras between 2012-18.

With over 40 years of experience in Non-destructive evaluation, his work spans maintenance, quality assurance, manufacturing, and design. He is a FELLOW of the Indian National Academia of Engineers (INAE), National Academia of Sciences India (NASI), Indian Academia of Sciences (IASc) and Academia International NDT (Italy). Having guided numerous Ph.D. and M.S. students, he has received notable awards such as the Roy Sharpe Prize (UK), ISTEM Entrepreneurial Faculty Member Award (USA), National NDT Award, DRDO Academy Excellence Award, Abdul Kalam National Technology Innovation Fellowship, Distinguished Alumni Award from NIT Tiruchirappalli and a Lifetime Achievement Award from IIT Madras. He has over 300+ SCI Journal Publications and over 60 Patent filings in India and abroad. Actively engaged in innovation, he is instrumental in incubating 12 startups that employ more than 1250 professionals and operate across 12 countries.

Published in January 2005 issue of Advanced Materials magazine