If you haven't heard of nacre or mother of pearl before, it might sound like a stretch when I say this natural material may solve one of our biggest hurdles of implementing ceramics in aerospace. As you may know, ceramics are naturally brittle materials which results in mechanical failure at low strains. Under impact tests, these materials generate and propagate cracks at extremely fast rates which leads to the catastrophic failure of the impacted structure. There is little resistance to the propagation of cracks due to the structural properties of the material. What if we could design a system that disrupts such crack propagations? And is there an industrially scalable way to architecture ceramic materials such that they mimic the properties of naturally found materials like nacre?
The solution that I developed was manufacturing a composite that consisted of hexagonal ceramic tiles bonded together by a polymer adhesive layer. The idea was as such: the fracture toughness of ceramics can be improved by using an elastic material to aid in the energy absorption of impacts. In addition, the combination of hard and soft segments creates an overall system with superior strenght and toughness compared to their base materials. By using a high energy pico-second laser, I was able to cut various designs into ceramic tiles that would be bonded in a composite structure as shown below:
From the impact tests, there was a clear improvement on the maximum strain in the sample before failure. For information about the specific differences compared to a plain ceramic sample, please refer to our publishing: https://www.sciencedirect.com/science/article/pii/S2352431620301425
The micro-structure of nacre is not a perfect honeycomb lattice, but instead a series of random hexagonal shapes. As a result, we attempted an implementation of pseudo-ordered structures. The primary aim of this study was to elucidate the differences in mechanical properties between an ordered and disordered structure. I was able to simulate the differences in fracture mechanics and energy absorption of the two designs by using the Explicit Dynamics solver in ANSYS. The video below demonstrates the ability to model the fracture of the pseudo-random hexagonal structure by driving an impactor through the sample.
I was grateful to have the opportunity to work with Behnam Ashrafi, who was my supervisor during my year at the National Research Council of Canada (NRC).
Commenti