Experimental and Numerical Investigations on Minimization of Spring-back Deformation in CFRP Parabolic Antenna Reflector Used for Space Applications

Abstract

The last few decades have witnessed a considerable increase in the use of carbon fiber reinforced polymer (CFRP) mainly for aerospace structures, automobiles, marine components, sporting goods and space applications. The selection of carbon fiber composite materials is based on the characterization and evaluation of thermo-mechanical properties. The characterization of epoxy-based composites is performed to obtain high-quality parts with greater consistency and to minimize the experimental work required to establish a cure cycle for new components. The use of prepregs for composites manufacturing offers the advantage of high fiber volume fractions and adaptability for manufacturing complex parts. Autoclave curing is widely practiced because of its robustness and has attracted the attention of industries and researchers. As autoclave curing is preferred for complicated parts requiring good dimension stability, warpage, spring-back deformation, and process induced deformations must be minimal. Understanding the cure behavior as well as resulted in thermo-mechanical properties of a thermosetting system are essential in the development and optimization of composites manufacturing processes. The development of residual stresses in the part and the mould is inevitable during the manufacturing of composite laminates as, the parts cure at high temperatures. The antenna reflector is a standalone device used for redirecting radio frequency energy or reflects electromagnetic waves in satellite communications. These high precision parabolic shape antenna reflectors used in the space communication satellites are made from CFRP material using an autoclave manufacturing process with backup structure. High dimensional fidelity is the primary challenge for the large size CFRP antenna reflectors used in space applications. The dimensional control of CFRP components mainly governed by the section of crucial process parameters. It is very much essential that the profile of the CFRP reflector should confirm that of mould and a small deviation will result in an improper functionality of the reflector. The scope of the present study is to investigate the effect of various process parameters viz. mould material, part thickness, lay-up sequence and curing cycle on spring-back deformation of the parabolic antenna reflectors during an autoclave curing. The selection of composite materials is based on a comparison of thermo-mechanical properties for prepreg tape along with different epoxy resin systems. In the present work, HCU200/A45 carbon fiber prepreg along with HinpoxyC, HinpoxyVB, ARL135, and ARL136 epoxy resin systems with suitable hardeners are used for the selection of carbon fiber composites and their characterization. The DMA, isothermal and dynamic modes of DSC, Kissinger equation and the universal tensile test are used to determine various thermo-mechanical properties of composites namely glass transition temperature, the heat of reaction, degree of cure, activation energy, pre-exponential factor, and tensile strength. The simple additive weighting method is applied to compare different epoxy resin systems and it is found that the overall thermo-mechanical properties for the ARL136 resin system are within 5% variation of the same properties measured for the prepreg system. In the current work, the influence of the mould material, curing cycle, lay-up sequence and laminate thickness on spring-back deformation during autoclave curing have been investigated by fabricating a large number of parabolic reflectors using the unidirectional prepreg system. The proper mould materials and consolidation materials have been selected as per requirement in experimental work. The spring-back deformation has been measured for each fabricated reflector using a non-contact type accurate 3D scanning technique. The full factorial orthogonal array as per the Taguchi approach has been applied to perform experimental work. The design of experiment has been performed to determine optimum combination for curing process parameters resulting in minimum spring-back deformation. The effect of individual process parameters as well as interaction effects of process parameters on spring-back deformation has been discussed. The results reveal that the spring-back deformation of parabolic reflectors is significantly affected by the mould material and laminate thickness, whereas the lay-up sequence and curing cycle do not have a significant effect. The finite element simulation has been performed using COMPRO plug-in with ABAQUS software of the autoclave curing process for the determination of spring-back deformation. The finite element based composites process modelling code called COMPRO determines component internal temperature, resin degree of cure, resin flow and the development of residual stress and deformation. The thermo-chemical, flow-compaction and stress-deformation analysis has been performed using COMPRO along with finite element solver to predict temperature profile, degree of cure, fiber volume fraction, thickness variation, residual stress, and deformation. The effect of each process parameters on spring-back deformation based on simulation results has been discussed. The spring-back deformation of antenna reflectors obtained by the simulation approach has been compared with results achieved from the experimental approach. The results obtained for spring-back deformation by simulation are quite agreed and almost 15 % higher compared to the experimental approach. In summary, this work has thus provided an optimum combination of process parameters which gives minimum spring-back deformation in autoclave processing for a CFRP parabolic antenna reflector used in space applications based on experimental and numerical investigations. Also, the methodology for the evaluation of thermo-mechanical properties for carbon fiber composites has been described.