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Engineering Task on Multifunctional Composite Materials/Structures

Abstract
This project report has prepared with the aims of reviewing, analyzing and presenting the information on multifunctional composite materials or structures. By using multifunctional composite materials/ structures, the requirement of excessive components has eliminated by the combination of one or few more functional wise capabilities of subsystem structures so thatthe volume and mass of the entire system can be reduced and hence can improve the overall efficiency of the system. Al last this report is briefly describing the structural capacitor materials made from carbon fiber epoxy composites as the selected multifunctional composite material and its characteristics as well.

  1.  Introduction

A multifunctional composite material can be defined as a material that has unique, multiple set of useful characteristics specially beyond strength and stiffness that are usually expected from a normal traditional composite material. Laminate is one particular term refer with these composite materials which is made of laminae and it is reason for these materials to have enhanced properties. Once these multifunctional composite materials are manufactured, it would satisfy multiple objectives.
Multifunctional materials (MFS), Multifunctional composites (MFC) and Multifunctional structures (MFS) are the sub branches of Multifunctional material systems (MFMS).
The requirement of excessive components has eliminated by the combination of one or few more functional wise capabilities of subsystem structures so that the volume and mass of the entire system can be reduced and hence can improve the overall efficiency of the system. Both multiple structural and nonstructural functions of these multi-functional materials have been the reason for them to have high demand over the par years. Few functional capabilities of multifunctional composite materials are listed below. [1]

Figure 1. Structural and non-structural functions of MFCMS

2.  Literature Review

The design process of MFCMS has identified as a challenging task due to the complexity of the structures results in the areas of the selection of materials for fabrication and the process steps of fabrication in order to get required functional capabilities. The design of these materials can be implemented by the integration of functional devices which exhibits the additional functions within the structural materials.
Due to its advantages, there has been number of researches and findings with relate to the multifunctional composite materials and the way that use of those materials have been effective. Few of them are discussed further in this report.
Some researchers have expressed the concept of piezoelectric embedded aircraft wing box which can use to harvest the energy for the structures with large scale. The design of MFCM has been implement in jet aircraft wing box which has piezo electric layer stacked in the laminated composite. However the additional weight added to the wing was a difficulty and it was successfully addressed by the optimization techniques. But the result was, improved electrical power of 25.24 KW is generated for 14.5 m wing span which is compared to the early literature results of similar designs. As another, some channels that used to store and transport fluid to the desired location have been made using laminated composite structures and then those have been altered introducing multifunctional sandwich panel design with eventually showed good fracture resistance than previous. [2]

Figure 2. Multifunctional sandwich panel, fluid passage and load support design [2]

Another research suggests that by embedding lithium ion battery materials in composite  reinforced
polymers results in maximizing the utilization of particular material when comparing with the standard lithium ion cells. Also #D printing techniques for these MFCMs has improved the printability as well as functional capabilities such as mechanical strength, electrical conductivity and electromechanical sensitivity. [1]

 

Moreover, Techniques has developed using these MFCMs to enhance the electronic adhesion by means of creating a large potential difference in electrodes and generating attractive force enabling fine attachment and exhibits good structural functions in the polymer composite structures. Also another research has described embedded microvascular networks as multifunctional structure which exhibits additional functions such as self-healing and thermal management. Moreover introducing multifunctional laminated composite structures in aircraft morphing wings and automobiles has result in reducing additional components of the total structure. [3]

3. Areas of Engineering Applications

Use of multifunctional composite materials in Nano composites
Graphene Nano ribbons usually introduced into polyurethane sponges which used in super capacitor applications.
Ceramic matrix composites
These are useful in hot engine structures, electronic devices and exhibits multifunctional ties such as crack healing, electromagnetic shielding, self-lubrication and energy absorption.
elastomeric fibers
These are electrically conductive, usually used in intelligent textiles as a strain sensing component of the structure
Robotic birds or flapping wing aerial vehicles
The wings deforms while flapping and generate necessary aerodynamic forces which are required to flight. The solar cells used to increase the payload capacity by harvesting the electrical energy.
Core shell coaxial structures
Useful in healing, anti-bacterial drugs and bio compatible applications

4. Structural capacitor materials made from carbon fiber epoxy composites

The use of lightweight materials in structural applications is ever increasing. Today, lightweight engineering materials are needed to realize greener, safer and more competitive products in all transportation modes.
Structural capacitors were made from carbon fibre epoxy composites to facilitate high performance mechanical electrodes. The electrode layers (laminae) were made from 0.125 mm thick pre-preg weaves. The resulting composite have a fibre volume fraction of 52%. A dielectric layer in a composite laminate separated the electrode layers.

During manufacturing pre-preg layers stacked in a release agent coated mould. In order to achieve homogeneous surface properties on both two sides of the laminate the structural capacitor laminates are manufacturing using peel plies on both top and bottom surfaces.
A Vacuum is applying and debulking without heat is the next step of manufacturing. The mould then place in an oven and heated according normally to the recommendations of material suppliers (120ºC for 30 minutes) in order to achieve cured laminates (fully). Voids needs be to be kept in minimum number. Since Air has a much lower dielectric constant then the tested dielectrics. Presence of voids will therefore locally reduce the isolative properties of the dielectric, also mechanical properties are lowered.

4.1 Experimental characterisation

To experiment the characteristics of the multifunctional composite material/ structure, several test specimen have been used and they have tested in following ways for their characteristics.

4.1.1  Capacitance

Capacitor is charged into an increasing voltage (V) until the moment that structural capacitor is short-circuited. For each voltage the structural capacitor is discharge and the charge (Q), in Coulombs, giving the capacitance is calculated using coulomb law. For further characterizations the measurements of dynamic capacitance and losses also can calculate.
C=Q/V

4.1.2  Dielectric breakdown voltage

Dielectric breakdown voltage (dielectric strength), of the specimen capacitors are measuring using the ASTM standard for direct current measurement of dielectric breakdown. Voltage is applied until the failure is evident by large drop of voltage.

4.4.3  Interlaminar shear strength

The mechanical strength was measured using this intetrlaminar shear strength parameter and it is performed to identify negative or positive effects of the dielectric, at mid-thickness, on the mechanical performance of the composite. Short beam three point bending test can be used to evaluate the mentioned parameter for the composite according to ASTM D2344 standard. [4]

4.1.4  Energy density

This parameter enables the comparison between the different capacitor devices. Energy density can be measured using following equation.
Γ_(sc )= ( 1/2 CV^2)/m_sc
Multifunctional performance of the composite
Multifunctional performance of the composite is usually evaluate by assessing energy density vs. specific interlinear shear strength and calculated specific in plane stiffness. Although capacitance and dielectric strength are important properties for the performance of a capacitor, use of these properties individually to assess multifunctional performance of a structural capacitor will produce contradicting results.

5.  Discussions

The structural capacitor materials were made from carbon fibre epoxy pre-preg woven lamina as electrodes separated by a dielectric material. Multifunctional efficiency of the developed structural capacitors was evaluated on the basis of achieved energy density and interlaminar shear strength as well as in plane stiffness. All capacitors employing a polymer film dielectric separator investigated indicate potential for high multifunctional efficiency. Depending on film thickness and surface plasma treatment significantly improved multifunctional designs with overall weight savings can be achieved. Further research is needed to identify best choice of polymer film and film thickness as well as best practice for surface treatment.

6.  References

[1] Jagath Narayana , Ramesh Gupta Burela, A review of recent research on multifunctional composite materials, vol. 5, p. 5580–5590, 2017.
[2] T. Carlson, Multifunctional Composite Materials – Design, Manufacture and Experimental Characterisation, 2013.
[3] Faxiang Qin a, Hua-Xin Peng, “Ferromagnetic microwires enabled multifunctional,” vol. 58 , p. 183–259, 2013.
[4] L. E. Asp, “Multifunctional composite materials for Energy Storage,” vol. 42, no. 133-160, 2013.