Comparison Of The Mechanical Properties Of Conformal Load-bearing Antenna’s Substrate And Glass Fiber Reinforced 3D Orthogonal Composites

Smart materials that are rapidly developed since 1990s are such composite structures which can sense and detect external(or internal) stimuli like electricity,light and heat;can respond with active control in real or near-real time in accordance with the designed mode.Smart materials are widely used in aerospace field,such as shape-changing airplane,smart skin technology,etc.The most effective way to realize smart structures is to embed the active element into the structures like the wings and airframes,to enhance the structure efficiency.Nowadays in the world the most popular smart skin technology CLAS-conformal load-bearing antenna structures,is a combination of microstrip antennas and sandwich core composites or laminated composites.Microstrip antennas are embedded into the structures to be conformal with the airframe,which overcome the shortcomings of traditional antennas from the structure point of view,with improved anti-damage capabilities and aerodynamic properties.E-glass fibers are selected in this study as the reinforced dielectric substrates.Two co-planar fed microstrip antennas are designed and the possibility for designing extensive antenna patch arrays has been explored.In the fabrication process,the upper and the bottom layer of the 3D woven composite preform were replaced with copper wires,to fabricate the microstrip line,the patch and the ground according to the yarn density of the composites,using a special method.The three parts of the radiation element were composed of high performance fibers,which were bond by Z-yarns.Hence there would not be any problem with delamination subject to load or damage.Two antenna patches have been designed in this experiment,orthogonal patch and interlaced patch.In the former one warp and weft yarns were aligned orthogonally,bond by Z-yarns while in the later one warp and weft yarns were interlace with each other.Mechanical properties of the microstrip antennas based on 3D woven composites in this experiment have been tested,including the following four aspects:tensile,bending,compression and impact.The results of tensile,bending and compression show that the microstrip antennas based on 3D woven composites can achieve the mechanical properties of the normal 3D woven composites:tensile strength of 3DIMA is 334 MPa(compared with the baseline-normal 3D woven composites without copper ground 343 MPa),Young’s modulus 20.6 GPa(baseline 16.5 GPa),bending strenghth 238 MPa(baseline 347 MPa), bending modulus 14.9 GPa(baseline 16.9 GPa),compression strength 164 MPa(baseline 165 MPa),compression modulus 10.4 GPa(baseline 12.5 GPa).As for impact testing,data do not show the brittle nature of the damage process of the materials.The impact strength is only 6.29 kJ/m2,however the data diffraction is as high as 67%.This is because the existence of the conductive ground interferes the failure mechanism of the composites,that when impacted under relatively high velocity (compared with the quasi-static damage in bending test),the bottom layer copper wires which are stretched cannot afford the high load as the high performance fibers do,thus greatly undermines the impact strength and energy absorption of the composites.We conclude that the 3DIMA developed in this study can almost achieve the same level of the traditional copper film antennas and at the same time,the mechanical properties of 3DIMA can present the strength of normal 3D orthogonal woven composites,which are superior to dielectric substrates for traditional microstrip antennas-laminated composites.