Researchers from Texas A&M and Sandia National Labs develop 3D-printed joints that adapt to stress, temperature, and movement for stronger structures.

In a move that could reshape industries from aerospace to biomedical engineering, researchers from Texas A&M University and Sandia National Laboratories have developed 3D-printed nickel-titanium alloys with shape memory capabilities, paving the way for stronger, more adaptable structures without the need for traditional nuts and bolts.

For centuries, nuts and bolts have been the backbone of nearly everything mechanical, holding together the joints and trusses from towering skyscrapers to everyday electronics. These humble fasteners, though simple in design, play a crucial role in maintaining the structural integrity of countless systems, ensuring that assemblies remain secure under stress.

From automobiles and aircraft to bridges and household appliances, nearly every industry relies on nuts and bolts. However, as engineering advances, the limitations of traditional fasteners – such as wear, the need for manual assembly, and their inability to adapt to changing conditions – are becoming more apparent.

As the demand for stronger, more adaptable structures grows, researchers have turned their focus to innovative alternatives that go beyond the traditional fastener.

One such advancement is the development of interlocking metasurfaces (ILMs), a breakthrough by Texas A&M and Sandia National Laboratories in joining technology that promises to overcome the limitations of nuts and bolts by offering flexibility, strength, and reusability, all while maintaining structural integrity.

ILMs work by using specially designed surfaces that interlock, much like Velcro or Lego blocks, to connect two materials. However, the key difference lies in the use of shape memory alloys (SMAs) – specifically, nickel-titanium.

These alloys have the remarkable ability to return to their original shape after deformation by responding to changes in temperature. This property allows the ILMs to engage, disengage, and re-engage on demand, offering flexibility without sacrificing strength or stability.

"ILMs are poised to redefine joining technologies across a range of applications, much like Velcro did decades ago," said Ibrahim Karaman, professor and head of the Department of Materials Science and Engineering Department at Texas A&M.

In traditional joining methods, nuts and bolts require manual effort for assembly and can loosen over time. Meanwhile, adhesives lie on the opposite end of the spectrum, offering permanent bonds that lack the flexibility for reconfiguration.

ILMs with SMAs, on the other hand, provide a dynamic solution: joints that can be actively controlled and reconfigured through temperature changes, making them ideal for industries that require precise assembly and disassembly, such as aerospace and robotics.

"In collaboration with Sandia National Laboratories, the original developers of ILMs, we have engineered and fabricated ILMs from shape memory alloys," added Karaman. "Our research demonstrates that these ILMs can be selectively disengaged and re-engaged on demand while maintaining consistent joint strength and structural integrity."

Texas A&M University; Ibrahim Karaman

An illustration of interlocking metasurfaces (ILMs) designed using shape memory alloys, offering a flexible and reconfigurable alternative to traditional fasteners. Pictured: An individual cell of the proposed versions of ILMs in their different engagement states.

This breakthrough was made possible through advanced 3D printing techniques that allowed the precise design and fabrication of the complex structures involved.

Utilizing nickel-titanium, an SMA known for its ability to revert to its original form after deformation, and integrating it into the ILMs, the teams were able to design joints that react dynamically to temperature changes, enabling selective engagement and disengagement of the interlocking surfaces.

Additionally, the use of 3D printing provided the flexibility to experiment with different configurations of ILMs, tailoring the geometry of the surfaces for maximum strength and adaptability.

This approach, combined with the unique properties of nickel-titanium, opened the door to creating reconfigurable joints that retain structural integrity even after repeated cycles of use.

"Active ILMs have the potential to revolutionize mechanical joint design in industries requiring precise, repeatable assembly and disassembly," said Abdelrahman Elsayed, graduate research assistant in the materials science and engineering department at Texas A&M.

The practical applications of this breakthrough extend across several industries. In aerospace engineering, where parts often need to be assembled and disassembled multiple times, Active ILMs could offer a reconfigurable solution that maintains strength while allowing for flexibility in assembly, reducing reliance on traditional fasteners and providing greater durability under stress.

In robotics, these ILMs have the potential to create flexible, adaptable joints that enhance functionality and movement. The ability to adjust and reconfigure components on demand could significantly improve the precision and efficiency of robotic systems, particularly in environments requiring repeatable, high-performance assembly.

Even the biomedical field stands to benefit from this innovation. Active ILMs could be applied to prosthetics and implants, allowing them to adjust to body movements and temperatures, providing patients better comfort and functionality – adaptable joints could even enhance how medical devices integrate with the body over time.

The current findings primarily rely on the shape memory effect of SMAs, which enables the ILMs to recover their shape through temperature changes. However, the researchers aim to push this further by utilizing the superelasticity effect of SMAs, which would allow ILMs to withstand larger deformations and recover instantaneously under high stress levels.

"We anticipate that incorporating SMAs into ILMs will unlock numerous future applications, though several challenges remain," said Karaman. "Achieving superelasticity in complex 3D-printed ILMs will enable localized control of structural stiffness and facilitate reattachment with high locking forces. Additionally, we expect this technology to address longstanding challenges associated with joining techniques in extreme environments. We are highly enthusiastic about the transformative potential of ILM technology."