Alvine Njionhou

Abstract

Contribution to the study of variability of infused laminates properties made by liquid resin infusion

Alvine Njionhou - 8 April 2011

The aeronautical sector is now very interested by the development of out-of-autoclave processes and low cost structures. The question is to find the possible links between the parameters of these new processes and mechanical properties of composite parts obtained. In this study, experimental plan method by Taguchi tables is used to establish the possible relationships between the process parameters of liquid resin infusion and the ultimate tensile strengths, ultimate compressive strengths and interlaminar shear strengths, and also the properties in impact and compression after impact of infused laminates. Laminates are infused using the quadriaxial Non-Crimp-Fabrics (NCF) stitched and unstitched with epoxy resin RTM 6. The possible links with the process parameters and morphological properties of these laminates such as fiber volume fraction, void contents, glass transition temperature and thickness of the structure have also been investigated. Eight process parameters (number of NCF layers, stitching, number of High Porous Media (HPM) layers, plate side during the infusion, vacuum level, injection temperature, mould temperature, curing temperature) and an interaction between the number of NCF layers and HPM layers have been identified by literature review. Statistical analysis using multilinear regression method was performed on the properties of infused laminates stitched and unstitched to find influence of parameters on each property. Stitching has a good effect on ultimate compressive strength and compression after impact strength. It contributes also to increase interlaminar shear strength and to reduce damage propagation inside material. Microscopic observations were done to complete and improve the comprehension of statistical analysis results. They allowed detecting presences, sizes, localisations, and number of residual voids inside laminates. Different damages modes caused by impact were also observed. Voids content obtained in infused laminates made is generally lower (less than 1%) with higher fiber volume fraction (greater than 60%). These results allow using this process for aircraft parts. The presence of macro voids goes to the reduction of ultimate strengths of infused laminates. These defects cause increase of residual indentation. The link established by experimental plan method seems to ensure the explication about the creation of the blocking debris of this indentation.

Keywords: Liquid Resin Infusion, experimental plan, Non-Crimp-Fabric, mechanical properties, Impact, Compression after impact, voids content

Last modified: 04/21/2011 07:14 PM