3D analysis of functionally graded material plates with complex shapes and various holes
Orario di ricevimento
Geim, The Electronic Properties of Graphene, , Shen, Y. Hu, C. Li, C. Qin, M.
Orario di ricevimento
State of the art Although graphene is considered the material of the future, its research and applications have not yet reached the construction industry. This paper focuses on the potential of developing graphene-embedded composites to enhance the electrical and thermal performance of traditional and widespread construction materials such as concrete and clay.
A number of performing prototypes were fabricated at different stages of the study using different approaches for embedding graphene nanoplatelets into clay and mortar. Our experimentation with these composites has led to the conclusion that there is significant potential in enhancing the thermal and electrical properties of traditional materials.
These first tests demonstrate both the achievable performance as well as the feasibility of producing such composites without access to a professional grade laboratory. In every phase of the research a prototype was produced as a proof of concept which was later gone through different tests. These tests were focusing on measuring the electrical conductivity of each composite or geometry, the thermal conductivity and heat distribution and the potential use of the prototype in an active or passive heating system.
All the experiments were carried out in a non professional grade lab, where different fabrication technics and testing methods where employed in each phase to achieve conclusions that would lead to the next experiment.
Recent European Journal of Mechanics - A/Solids Articles
These research phases and the conclusions drawn from them are described bellow. The goal of this phase of experimentation was to test the two different composites in terms of their material properties, but also make a geometrical investigation in order to understand how different patterns would affect the result of the experiment. Four patterns where produced, each one with a different density. The overall size of each prototype was 70 mm x mm.
Testing: Voltage of 9. A thermal camera was recording the increasing temperature of the surface and the distribution of heat in the prototype. Conclusions: The polyester - graphene composites had inadequate results in terms of conductivity, with the densest pattern having a resistance of 0. Also the presence of the polyester in the composite, was compromising significantly the performance of the prototype in terms of heat resistance.
The changes in viscosity where related to the presence of benzilic alcohol in the composites.
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The different mixes where later placed on elastic surfaces PCV sheet, LATEX sheet, silicone sheet in order to measure changes in resistance in relation with elastic expansion of the prototype in the direction of the current. Testing: The different mixes where placed in glass cases and then tested by applying voltage with electrodes. Then they where placed on the elastic surfaces and the same measurements where made in different positions of expansion.
Conclusions: These tests showed very inadequate results of electrical properties, as the presence of benzilic alcohol was severely compromising the conductivity of the composite. The same setup with the elastic surfaces was repeated to try the resistance of graphene in different expansion positions.
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Testing: Having the electrical properties present again, measurements with application of voltage were possible on the prototypes. The measurements in different expansion phases were repeated. Conclusions: The conductivity of the mixes was adequate to create a basic electrical circuit. This phase of experiments was the first of the investigation of brittle materials and graphene composites.
In this case two different types of prototypes where produced. The first type is a volume of homogenous mix of the brittle material clay and graphene. PCL is added to the mix as a binder between the hydrophobic graphene nanoplates and the wet clay. The wet mixes were forced into an acrylic casts and let to dry.
The second type included two cast clay layers with a graphene nanoplates — pvp mix circuit between them. Testing: The prototypes were tested with electrodes, connected to the pieces with silver paste. Measurements of resistance along the prototypes length were made in both types and recordings were made with a thermal camera.
Conclusions: The homogenous composite showed satisfying results in terms of coherence and conductivity, as it was conductive enough to create electrical circuits and presented similar mechanical properties to normal clay. The same type of acrylic casts was employed to create the first prototypes, that included both types of homogenous mix volumes and pieces with an integrated graphene — pvp circuit. After the first phase of experimentation, a series of more complicated prototypes were created, made by two cement slabs, shifted in two directions to interlock in a repetitive building system as bricks.
The circuit was exposed in the shifted areas of the brick, allowing to connect with the cross circuit of the next one.
Recent European Journal of Mechanics - A/Solids Articles - Elsevier
The circuit was also reaching the sides of the brick with five cylindrical connections of the same composite. These connections were important for conductivity measurements in different parts of the prototypes. The fabrication method of this brick was based on a laser — cut plywood cast. The faces of the cast were covered with Vaseline to avoid breaks while un-casting.
The casting included three phases. Firstly, one of the slabs is casted and the four metal reinforcements are placed with half of their height exposed to be later embedded in the next slab. Before the mortar dries completely, the graphene — pvp cross circuits is applied on the mortar surface and when it begins to solidify the next slab is cast on top. Finally, when the piece is un-casted, the parts of the cast that create the cylindrical holes are removed and the holes are filled with graphene — pvp composite to create the ten side connections.
Figure Isometric drawing of a modular surface composed by the cement mortar brick. The connected cross shaped patterns of the bricks are visible forming a grid, embedded in the concrete slab. Voltage of A thermal camera recorded the distribution of heat in the mortar mass. Left to right: 1. Parametric model of a non uniform section conduction representing the graphene composite circuit, 2. Graph of Restistance per section along the lengh of the conductor, 3. Graph of heat production along the lenght for the given values of voltage applied and amperage, 4.
Visual representation of the heat production along the length. The first phase prototypes with mortar presented worst results than the ones with clay, as they had lower conductivity values and the ones with a distinct graphene circuit in the middle were cracking. The heat produced from the brick after applying power was enough to render it comparable in terms of power consumption to existing heating systems.
3D Analysis Of Functionally Graded Material Plates With Complex Shapes And Various Holes
The goal of this experiment was to expose the one side of each brick to a heat source and measure the temperature change of the other side after a given period of time to observe differences in heat conduction, related to the presence of graphene. Testing: Two plywood boxes were constructed and painted white. The inside of the box surrounding the brick was filled with heat insulation of expanded polyurethane to avoid heat leaks.
Both boxes were left exposed to the sun and temperature measurements of both the inside and the outside part were taken by a laser thermometer in equal amounts of time. Conclusions: Although the differences in temperature where not extreme between the two pieces, the measurements gave promising results for a passive heating system, showing that the presence of graphene made the cement mortar conduct heat faster that the brick that was made solely by mortar.
Cement mortar was once again replaced with clay, which had presented better properties in previous experiments when homogeneously mixed with the graphene — pvp composite. A series of bricks were manufactured again, aiming to find the optimized formula for the mix, using the least graphene nanoplates possible to achieve the best performance in terms of conductivity and heat production.
The fabrication process of this phase was still manual, but the properties of the composite were already trying to match the demands of a mixture that could be potentially 3d printed or extruded. Using the composite of clay — graphene and pvp, a catalogue of brick shapes was created and taxonomized depending on geometry factors. The functional criteria for the creation of these geometries were based on heat generation and radiation and potentially air circulation in a structure composed of these units. The vertical direction of the current, is defined by the extruded shape of the structure, rendering it a geometry with a uniform section in the vertical axis and therefor a predictable performance when electricity is applied.
Testing: The bricks were tested once more with electrodes connected to the piece with silver paste. When a satisfying mix was achieved, an acrylic apparatus was constructed to create pieces of the material with precise dimensions. These pieces were then tested with a direct current, equally distributed across their section to measure their resistance and then knowing their precise dimensions, the resistivity of the material was extracted to characterize it.
After achieving a mix in which the concentration of graphene could be controlled, the research focused on an investigation of functionally graded materials FGM. The previous focus on creating a wall system that would replace the heating and electrical installations of a building, is now replaced by an interpretation of form through the prism of the properties of gradient materials.
Hand drawing of a wall being the core of a structure, containing information, producing heat and transfering data. Functionally graded material of graphene and clay The research focuses at this point on functionally graded materials, which constitute a very important part of contemporary material science for reasons connected with their advantages in terms of property and material optimization.
Functionally graded materials FGM are those in which composition and structure change over the volume, resulting in corresponding changes in the properties of the material, trying to optimize the properties of both components, depending on the specific use demanded for the result. At this point the mixture that has been developed is a functionally graded material of graphene and clay.