Physical camouflage works as an act of disappearance for structural defects

Whether it is to design a window on an airliner or a cable duct for an engine, the manufacturers devote a lot of efforts to strengthen the openings for structural integrity. But reinforcement is rarely perfect and often creates structural weaknesses elsewhere.

Now, Princeton and Georgia Institute of Technology engineers have developed a technique that can maintain structural integrity by essentially hiding the opening of the surrounding forces. Rather than strengthening the opening to protect itself from some selected forces, the new approach reorganizes almost all forces sets that could affect the surrounding material to avoid opening.

In an article, entitled “Impartial Crape-Mechanics” in the Proceedings of the National Academy of SciencesThe researchers said that they surrounded microstructure openings designed to protect themselves from many charges – from external forces that cause stress, movement or deformation. The shape and orientation of the microstructures are calibrated to operate with the most difficult loads in the face of the structure, allowing designers to counter several constraints at the same time.

“Think of a plate with a hole in it. If you put it under constraint, if you pull there, you will obtain a concentration of stress where the plate fails earlier than without the hole,” said Emily D. Sanders, assistant professor of mechanical genius at Georgia Tech and one of the authors. “We want to conceive of something around this hole or this defect, so it seems that the hole does not exist.”

Glaucicio Paulino, main author and engineering professor Margareta Engman Augustine in Princeton, said that designers generally strengthen the structure in openings like Windows or Tunnels. But he said that by increasing the structural force in one direction, the reinforcement can introduce other problems by creating a new stress in a different direction.

The objective of the camouflage technique is to protect the structure by redirecting force without creating new or unwanted stress levels.

The researchers were inspired by nodes in trees, where it seems that microstructures in the nodes of direct force around the intrusions site such as branches or roots and maintain the structural force. The researchers wanted to know if they could design structures to do the same in the materials made.

Paulino said the technique is based on two optimization problems, which are designed to select the best solutions from a range of choices. The first problem discovers the charges that will produce the greatest challenge to the structure of the object. It is more difficult than it seems because the loads on a structure or a machine can change with the circumstances.

“Any structure can potentially have an infinite number of loads.

The researchers found that the calculation of six to 10 of the Les worst loads for a structure gives the most effective results. With this information, they execute a second optimization problem to find the most effective way to create and deploy microstructures surrounding the window or the duct.

“The optimization technique introduced by the authors represents a revolutionary methodology to achieve the invisibility of a defect, whatever the direction of any force applied outside,” said Davide Bigoni, professor of solid and structural mechanics at Universita ‘Di Trento in Italy.

“The result is an omnidirectional coat, a property with wide applications. These include the guarantee of the neutrality of mechanical stress in the replacement of organic tissues, the modification of the structural elements to facilitate the passage of installations in the machines or the civil infrastructure and improve the restoration of the art.”

The idea is similar to masking techniques that have been developed to hide objects on the electromagnetic spectrum, such as stealth aircraft. Paulino explained that solid material equations can be more difficult than those of electromagnetism. But he said the goal was the same.

“Any elastic disturbance is hidden by the cape,” he said. “It is as if it does not exist.”