In the hallowed halls of Imperial College London, a quiet yet profound shift in aerospace engineering was taking place. On a crisp evening, Professor Zahra Sharif Khodaei, a distinguished figure in the Department of Aeronautics, took the podium to deliver her lecture on the topic of advancing next-generation aerospace vehicles through Structural Health Monitoring (SHM). The audience—comprising academics, industry experts, and eager students—listened intently as she mapped out a vision that could redefine the future of flight. For decades, the aerospace industry has grappled with a constellation of challenges: environmental sustainability, safety imperatives, maintenance challenges, and the integration of cutting-edge technologies. With Europe’s ambitious goal of decarbonizing aviation by 2050, the stakes have never been higher. The sector faces a pivotal moment that demands not just incremental improvements but transformative changes across the entire lifecycle of aircraft. "We all know about the environmental impact," Professor Khodaei began, her voice measured yet resolute. "It's a real issue, and we need to address it to try to slow it down." She underscored that achieving true sustainability extends beyond alternative fuels. It necessitates a holistic approach encompassing design, manufacturing, maintenance, operation, and even the decommissioning of aircraft.
At the heart of her proposal is the development of smart aerospace vehicles—a concept that involves embedding advanced digital technologies throughout an aircraft's life cycle. This means integrating sensors from the manufacturing stage through operation, creating a fully integrated health management system. "If we are able to have sensors distributed over the structure at all stages—from manufacturing to operation—we can optimize all these stages by using the data that comes from these sensors," she explained. Traditional maintenance methods, such as the "tap test," where technicians manually inspect aircraft by tapping surfaces and listening for anomalies, are no longer sufficient. These methods are labor-intensive, time-consuming, and rely heavily on human expertise. More critically, they require grounding the aircraft, leading to increased downtime and operational costs. To illustrate the limitations of conventional techniques, Professor Khodaei conducted a simple demonstration. Holding up two identical cups—one intact and one with a hidden crack—she tapped each one, allowing the audience to hear the subtle difference. "Obviously, the first one is cracked because it has a different sound," she noted. "But what are the problems with this method? You need access to each part, you need to ground the plane during maintenance, and you have to rely on the qualification of that technician."
This is where Structural Health Monitoring comes into play. SHM utilizes sensors embedded within the aircraft's structure to automatically detect damage by monitoring stress waves or strain signals generated by impacts or structural changes. This approach offers several advantages:
Real-Time Monitoring: Continuous data acquisition allows for immediate detection of damage without grounding the aircraft.
Reduced Reliance on Human Inspection: Automated systems diminish the potential for human error and reduce labor costs.
Enhanced Safety: Early detection of damage prevents catastrophic failures and extends the aircraft's operational life.
However, implementing SHM is not without its challenges. Aircraft are inherently weight-sensitive; adding a network of sensors and wiring risks increasing weight, potentially affecting performance and fuel efficiency. To address this, Professor Khodaei and her team developed innovative solutions.
"We've developed a flexible layer where you can integrate your sensors on it," she revealed, displaying images of the technology. "You can print the wires onto it using an inkjet printer. This way, you can reduce the weight of the wires. Additionally, you have an adhesive film that can be bonded with heat to the surface of your structure and later removed in the same way, providing repairability." These flexible sensor layers can be bonded to the aircraft's surface and easily removed or repaired, minimizing added weight and maintenance complexity. The team also tackled the issue of sensor reliability under extreme operational conditions, such as temperature fluctuations from -40°C to +85°C. Extensive testing ensured that the sensors, bonding materials, and connectors could withstand these harsh environments.
The data generated by SHM systems is immense, and making sense of it requires advanced analytical methods. Here, machine learning and artificial intelligence play pivotal roles. By processing the sensor data, algorithms can identify patterns indicative of damage. In one experiment, the team simulated an impact on a composite wing panel—a material increasingly used in modern aircraft for its lightweight and high-strength properties. Sensors recorded stress waves generated by the impact. "If I have a network of sensors distributed over the structure, I can record all these sensor signals," she explained. "I can use the information recorded by these sensors to determine the location and magnitude of the impact." Machine learning models, such as artificial neural networks, are trained to analyze these signals and determine the location and severity of impacts. This capability is crucial because composite materials can sustain internal damage that is not visible externally—a phenomenon known as barely visible impact damage (BVID). Traditional inspection methods might miss such damage, posing safety risks.
The implications of Professor Khodaei's work extend beyond conventional aircraft. With the anticipated rise of urban air mobility—think air taxis and delivery drones—safety over populated areas becomes even more critical. SHM systems could provide the necessary real-time monitoring to ensure these vehicles operate safely. In space exploration, SHM is vital for detecting damage from hypervelocity impacts caused by space debris. "Currently, we have more than 23,000 pieces of space debris that are flying around," she noted. "We want to equip structures with sensors that can provide this information."
Her team has been working on integrating sensors within space structures, such as shields and main bodies of spacecraft, to detect and characterize damage without the need for direct inspection. This capability is particularly important for reusable launch vehicles, where assessing the integrity of the structure after each mission is essential for safety and cost-effectiveness.
Looking ahead, Professor Khodaei emphasized the development of digital twins—virtual replicas of physical structures that use real-time sensor data to simulate and predict performance and degradation. "Our future research direction can be summarized in one concept: digital twinning," she stated. "We are developing hardware, we are gathering data, and we're also looking into modeling." Digital twins enable predictive maintenance by allowing engineers to anticipate failures before they occur, optimize performance continuously, and make informed decisions about extending an aircraft's operational life based on accurate, real-time data.
Beyond the technical aspects, Professor Khodaei's lecture was imbued with personal reflections on her journey. Originally from Iran, she pursued civil engineering before transitioning to aerospace—an unconventional career path. "I never dreamed of being a professor at Imperial College," she admitted. "I never dared to dream that. I thought it would never even be on the cards for me."
She acknowledged the challenges faced by women in engineering, particularly those balancing professional ambitions with motherhood. "I would say I like to celebrate the first female professor who's a mother and gets to that achievement," she remarked, highlighting the need for greater support and recognition. Her dedication extends to inspiring the next generation. "I want everyone to dare to dream because it's possible even when you think it's not possible," she said passionately.
As the lecture concluded, it was evident that Professor Khodaei is not only pushing the boundaries of aerospace technology but also challenging conventional thinking within the industry. Her vision for integrating SHM into next-generation aerospace vehicles offers a pathway to harmonize safety, efficiency, and sustainability—an alignment that could revolutionize the sector. In an era where environmental concerns are escalating and the demand for safer, more efficient air travel is intensifying, her work provides tangible solutions. By embracing advanced sensor technologies, machine learning, and digital twins, the aerospace industry can move toward smarter, more resilient vehicles. As the audience dispersed, the impact of her words lingered—a testament to the power of innovative thinking and the promise of a future where technology and sustainability coalesce to redefine what is possible in flight.
