Material could be used to mitigate impacts in the aerospace area
When carbon nanotubes – which have diameters around a hundred thousand times smaller than a strand of hair – are lined up side by side like in a eucalyptus forest, they give rise to a type of sponge capable of protecting objects from mechanical impacts. Researchers from American and Swiss universities demonstrated this ability by analyzing the impact effects caused on eggs protected, in the impact area, by sponges made of polymeric materials and carbon nanotubes.
To understand the mechanical responses of these types of “forests”, different physical models have been proposed. These models take into account several characteristics of these nanoscopic materials and try to predict their properties, in addition to optimizing their effects. Later, materials with nanoscopic carbon springs were developed to replace straight nanotubes. It was then found that the sponges thus created had a 50% greater capacity to absorb impacts. However, for these “forests” formed by nanosprings, there were still no physical models that could computationally simulate their characteristics, behaviors and mechanical properties and that could even contribute to the discovery of new properties.
Given this, physicist Vitor Rafael Coluci, professor at the Faculty of Technology (FT) at Unicamp, based in Limeira, proposed to his master's student Vanessa C. Scheffer, graduated in mathematics and computing, the development of a model that considered the structure helical structure of the nanosprings and had the ability to reproduce the main deformation mechanisms of these arrangements. The model developed, which also considered the entanglement between neighboring springs, made it possible to describe with great approximation the deformations and reactions to impacts observed in the laboratory by researchers from other countries. In addition to other uses, these materials could be used in the aerospace area.
Vanessa presented part of the work, while it was being developed, at the XV Brazsil MRS Meeting, organized by a team of professors from Unicamp, held in Campinas in 2016, receiving the Bernhard Gross Award and an award from the American Chemical Society. Brazil MRS-Meeting is organized by SBPMat - Brazilian Society for Materials Research - and is the Brazilian version of the Materials Research Society's major event on materials held annually in the USA. The Bernhard Gross Award, established by SBPMat, which honors one of the pioneers in materials research in Brazil, aims to promote and recognize the participation of young people in the study and technology of materials, selecting the best works by undergraduate and postgraduate students. degree presented at the society's annual meetings. Once completed, the work gave rise to an article published in January 2018, in collaboration with professor Ramathasan Thevamaran, from the University of Wisconsin-Madison, in the journal Applied Physics Letters, the most cited last year in the area of applied physics.
The walk
The professor recalls that he became involved in these studies around ten years ago, during his postdoctoral studies, when he worked only with mathematical models, without considering simulations. With the arrival of his student, he decided to resume his work and expand it using exclusively the equipment and computational resources available in his unit and which had been assembled and developed by him over the years.
Initially, Vanessa adopted the so-called atomistic models to study compression behavior, which considers, like reality, springs formed by chains of atoms. However, as this modeling proved to be very expensive and would require a lot of time, the researchers decided to no longer model individual atoms, but a set of atoms that represented a piece of the nanosprings.
This model made it possible to simulate, on a larger scale (mesoscale), the mechanical behavior of the material, allowing the compression response force to be extracted from it. The professor explains: “We intended to arrive at a model that incorporated the main characteristics of these helical 'forests' and that would allow us to determine how much this shape influenced the response to the impact. One of these characteristics was how close neighboring springs were, which had not yet been studied systematically, given the complexity of entanglement.”
The idea was to arrive at a computational model prior to the experiment, which is much faster and cheaper, and then study the conditions that make it possible to obtain the materials.
Professor Coluci considers that the next stage of these studies, at doctoral level and using the finite element method, will be the development of a model capable of also simulating the growth of these structures to better understand the behavior of these “forests” of nanosprings.
