No abstract

The work presented in this paper addresses various techniques for automated preforming of profiles for structural components made from fiber-reinforced polymer composites. After reviewing the existing preforming techniques, a quantitative comparison with respect to two different application scenarios is presented. The technology comparison is conducted individually for the two application scenarios by means of a weighted decision matrix approach incorporating a list of technical and economic criteria. The preforming costs are derived by means of a bottom-up cost estimation model and are incorporated in the technology comparison.

Biaxial braided sleevings are commonly used for producing hollow complex-shaped composite parts through bladder inflation moulding. To enable feasibility analyses, part design and the prediction of mechanical properties of the resulting fibre-reinforced component, various geometrical and weight-related parameters of the braided fabric in its draped state must be known, such as fibre orientation, fibre volume fraction and areal weight. In the present work, a comprehensive analytical model describing fabric formation, preform architecture and weight as well as the change of relevant textile parameters of a biaxial braided sleeving during draping is established. The principal modelling approach is based on sporadic investigations found in literature and was substantially expanded to compile an extensive collection of relationships for the utilisation in a sleeving-on preforming process. Furthermore, a critical overview about the state of the art in the area of geometrical modelling of tubular 2D braided structures and a comparison of the identified procedures in regard to the desired application is given.

A common approach for the manufacturing of hollow composite parts based on textile reinforcement materials is the utilization of bladder-assisted resin transfer molding (BARTM). Here, the process-induced compaction of the preform is a decisive factor in the injection stage as it significantly influences filling times and part qualities. However, the use of expandable elastomeric bladders impedes the determination of local compaction pressures and thicknesses of compliant preforms during BARTM. This paper therefore presents an efficient methodology for evaluating the compaction state of tubular fabrics during preform compaction and subsequent resin injection by considering the membrane stiffness of an elastomeric bladder as well as the compressibility of the textile preform. First, different process models are developed to describe preform compaction based on single-point and full preform compaction data. The acquisition of exemplary model data for bladder expansion and preform compaction is accomplished through experimental methods. A specifically developed test rig comprising optical measurement techniques is used to directly characterize the radial expansion behavior of tubular silicone rubber bladders. The compaction behavior of single-and multi-layered braided preforms is evaluated by means of dry compression experiments. The resulting measurement data is used to create an integral model-based process window for combined bladder expansion and preform compaction. Lastly, a prediction of relevant local compaction pressures and preform thicknesses is conducted for an exemplary BARTM process.

The work presented in this paper addresses the development of an efficient approach to investigate the unsaturated in‐plane impregnation behavior of tubular braided reinforcement materials in a bladder‐assisted resin transfer molding process. The basic idea is to record the macroscopic flow front advancement during a pressure‐driven injection of a test fluid by using a transparent monolithic mold and optical measurement methods. The experimental setup further comprises sophisticated process control to accomplish a fully automated and highly repeatable test procedure. As the filling behavior of the braided fabrics predominantly shows unidirectional characteristics, the so‐called unsaturated apparent permeability of these textile reinforcements can be determined, which can be used as an input parameter in one‐dimensional flow simulations. A verification of the test setup is accomplished by means of saturation measurements on different braided preforms, which are compared with predicted flow front profiles. POLYM. COMPOS., 39:4666–4677, 2018. © 2017 Society of Plastics Engineers