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To prevent damage caused by earthquakes and violent winds, architects use earthquake-resistant systems. Indispensable when it comes to elevated structures, these techniques help strengthen structural elements and foundations. Cylinders, springs, ball bearings, etc., reduce the effect of destructive forces on buildings by making them flexible. A new solution created by civil engineering researchers will increase building resistance by applying the principle of flexibility to the structural elements.
Many of nature’s creatures that inspire biomimetic scientific research, have mechanical properties that enable them to combat external forces similar to those to which buildings are subjected. A team from Purdue University has created a cement-based material by mimicking arthropod exoskeletons. These can resist external forces by propagating them through their constituent layers, increasing their resilience.
The material, which is made using a 3D printing technique, will help increase construction strength when integrated into the manufacture of structural elements more resistant to mechanical constraints, like beams and poles.
Bouligand Internal Assembly
The team mimicked the arthropod cuticle, or outer wall that protects the entire body surface. This layer is characterized by a particular overlapping arc structure. It is also called a Bouligand structure, taking the name of the biologist and surveyor who discovered its geometric and morphogenetic characteristics. The French scientist discovered that the molecular assemblies of the shells and walls of several natural organisms are structured according to well-defined geometric principles, which also give them the observed mechanical resistance. The geometry of the overlapping arc structure is in the form of superimposed planes. Each plane consists of parallel fibrils. The layers are superimposed so that the fibrils are oriented in different directions. This way a crisscrossed and resistant structure is obtained, even in fragile materials. The layering principle corresponds to the morphogenic process of exoskeletons and shells studied by Bouligand.
Until recently, engineers faced many challenges in obtaining this type of 3D-printed cement-based structure. The researchers at Purdue University were the first to meet this challenge. In addition to the overlapping arc structures, they created patterns inspired by the shell of the Stomatopoda squill, or squilla mantis, and the rhombohedral structure of a wax cake. As shown in this video, 3D printing of the material evokes the growth principle of the natural structures that it mimics. From the material, it is possible to obtain resistant and flexible honeycomb shapes.
Mechanical Behaviour Observations
The team used X-ray microtomography (micro-CT) to observe the mechanical behaviour of the printed structures on a microscopic scale. Using this visualization technique, high-resolution images can be obtained from very small samples without altering their structures, as explained in this video.
The images make it possible to visualize the material’s characteristics and make it more resistant to mechanical stresses. The following video shows a longitudinal XZ section of a Bouligand architecture.
The study entitled “Additive Manufacturing and Performance of Architectured Cement-Based Materials” was published in Advanced Materials on August 29, 2018. It was co-authored by Mohamadreza Moini, Jan Olek, Jeffrey P. Youngblood, Bryan Magee and Pablo D. Zavattieri. The research was also presented at the first RILEM International Conference on Concrete and Digital Fabrication, held in Zurich on September 9, 2018.