Introduction and aims
A greater focus on conservation efforts across numerous industries has led to an uptick in demand for sustainable materials. In recent years, wildfires have also become more common, with over 1.5 million acres of land scorched in the United States alone, leaving behind charred wood that harms surrounding ecosystems. To repurpose this organic waste material, biochar, or pyrolyzed biomass, can be created. The benefits of this organic material include inputs easily found in nature (i.e. pine wood), high biodegradability, and high relative strength due to a carbon-heavy makeup. Additionally, the pyrolysis process of wood and other factors is readily available, and the kiln and other machines can in fact be powered by biofuel, a byproduct of pyrolysis, creating a net-zero carbon emission process. When biochar was combined with epoxy resin, it was hypothesized that this composite would create a stronger, more environmentally-favourable material. In this session, participants will be exposed to the simulation techniques and biomechanics behind this material, along with the expansion of the impacts of this research as they pertain to the UN Sustainable Development Goal #11 of creating sustainable communities and cities.
Abstract
In this study, the finite element analysis software (ABAQUS) was used with the standard explicit model setting.
In this method’s preprocessing, for each of the configurations, a 3-dimensional, deformable, solid extrusion part was created in the parts tab of ABAQUS, with a side length of 40 units throughout. For the cube with spherical corners, the embedded region constraint was used, and half of a semi-circle dome was inserted into the cube, with a radius of 20 units. For the cube with the triangular prism corners, a cell partition was created by connecting the three auto-created vertices from the centre of each edge. Finally, for the cube with a spherical mass inside, the embedded region constraint was used, and a sphere of radius 20 units was placed inside the cube.
Whilst the structure's construction is different for each type of biochar configuration, the assigning of biochar and epoxy resin is similar. These sections could be assigned two characters, the biochar or epoxy resin. These materials were created in the materials library to simulate the specific mechanical properties of pyrolyzed biochar and epoxy resin through the Young's Modulus, and the Poisson's Ratio values found through extensive literature review.
To assign the different characters to the sections, the total amount of biochar-epoxy resin ratio was considered. For the cube configurations with differing corners (spherical and cube), there were four standard settings. In the first there were two alternate corners of biochar; in the second there were double alternate corners of biochar (four total), and finally, in the third, there were all eight corners of biochar, to observe the effect of maximum biochar character. As a control, a setting with epoxy resin for all corners was considered.
For each RVE, the boundary constant stayed the same and was applied to every edge and partition edge. The boundary condition was applied in all directions to prevent the RVE from moving out of the frame of reference as load was applied. Whilst applying load, there were six types applied, differing in amount and applied axis. For both categories, 16, 32 and 64 pressure units were applied in total to determine if strain results directly from applied pressure. To determine the effects of the type of stress applied, stress was applied uniaxially, and then hydrostatically to investigate the effects of stress upon multiple axes.
Finally, in order to analyze certain sections, the model was meshed. As there were irregular attributes due to the partitions, meshing the part required first seeding the part instance and then selecting the "tet" feature with the hexagonal setting, in order to mesh every irregular part of the RVE.
To gather data from the applied stress to individual nodes, a job for each variation in pressure, configuration, and biochar percentage was created. From here, these ranges were compared against other RVEs with similar properties, to observe the impact of a single variable on the likelihood of the material to reach a permanent plastic deformation state.
Expected outcomes
First, the relationship between increased load amount and the reaction to the pressure is proportional, meaning biochar-epoxy resin composites behave in a predictable fashion under higher stresses. Secondly, as measured through lower von Mises percentages, the configuration of 4 assignable biochar sections lends itself well to lower maximum von Mises percentages, while the configuration of 8 assignable biochar sections lends itself well to lower minimum von Mises percentages, as evidenced by the pinewood RVE results for 16 MPa of applied pressure. Additionally, the location of biochar closer to boundary conditions creates higher von Mises concentrations, however, this can be avoided through the application of hydrostatic (instead of uniaxial) stress, as this spreads the pressure along numerous axes leading to a better dispersion of force, allowing less elastic deformation. Furthermore, as seen by the smallest von Mises percentage of 1.375 and the highest von Mises percentage of 6.049 for 16 and 64 MPa of pressure respectively, the ranges of the probability of yield and fracture seem to be more varied for the softwood blend RVEs, due to the blend’s heterogeneous makeup, that incorporates an increasing number of uneven surfaces even within the RVE that contribute to more diverse percentages ranging from lower to higher values. This contrasts with the reaction of the pure epoxy resin nodes, which act in opposite force pairs to the original biochar. Most importantly, these composites withstand the industry standard of 5000 psi and thus confirm the earlier hypothesis of a stronger and more sustainable material.
