RTM Processes Research Articles

Prediction of shape distortions. Part II. Experimental validation and analysis of boundary conditions

Abstract During cure of thermoset composite structures residual stresses and/or shape distortions are always present. Residual stresses can cause apparent strength reduction or failure, even prior demoulding, respectively, shape distortions can deform a component so that the component becomes useless. For this reason a lot of effort has been spent to develop simulation tools to be able to foresee problems related to residual stresses and/or shape distortions and make the first part right. In a companion paper a process model for shape distortion predictions was developed and implemented into ABAQUS. In the present paper the model is validated for a material and cure schedule typical for RTM and autoclave processes. Comparisons between predicted and experimental shape distortion shows that the model and simulation approach used capture both effects from different cure schedules as well as the mechanical interaction between composite and tooling during in-mould cure. The results show that changing the mechanical boundary conditions significantly affects the shape distortion prediction. Therefore accurate modelling of the composite–tooling interaction is an important part of a shape distortion analysis.

Study on void formation in multi-layer woven fabrics

Abstract The presence of voids has a deleterious effect on composites mechanical properties. In this paper, two simplified unit cells for in-plane impregnation in multi-layer woven fabrics (MWFs) have been suggested. A mathematical model has been developed to describe the mechanism of void formation during RTM processes. The flow fronts and void formation in these two cells were also numerically simulated using control-volume method. The simulated results agree well with the result predicted by the mathematical model. The results show that, for a given fiber preform the ratio of weft axial permeability Kba and warp transverse permeability Kbt is responsible for the size of void.

Use of genetic algorithms to optimize gate and vent locations for the resin transfer molding process

AbstractResin infusion processes are finding increasing applications in the manufacture of composite parts that have geometric and material complexities. In such cases, the placement of gates and vents is non‐intuitive and may require expensive repetitive experimentation. Finite element based resin flow simulation codes have been successfully used for modeling and analysis of the mold filling process. Such filling simulations, when coupled with a search algorithm, can also prove useful for optimal design of the filling process. Genetic algorithms (GAs) mimic natural selection and can efficiently “evolve” near‐global optimal solutions from a large number of alternative solutions. In this paper, GAs are used to optimize gate and vent locations for the resin transfer molding process in order to minimize fill times and dry spot formation. A process performance index or cost function is defined that incorporates the fill time and dry spot formation as primary variables. A part having material and geometric complexities was chosen for a case study. A genetic algorithm and mold filling simulations were used interactively to search for optimal gate and vent locations to locate near optimal solutions. The GA was able to find good solutions using less than 1% of simulations of the possible permutations of gates and vents. The case study was also repeated in the presence of recetracking channels. Again, the optimal locations were found by the GA using less than 1% of all possible combinations. Thus, GAs can be efficiently used for minimization of fill time and dry spot formation through optimal location of gates and vents in RTM processes. However, the optimal location will be a function of the cost function, the choice of which depends on the trade‐offs between different factors and the quality of the part desired.

Design, Processing and Performance of Structural Preforms

Abstract Present and future requirements for preforms in the automotive and aerospace industries are identified with respect to quality, processing, mechanical properties and economic manufacture for RTM and SRIM processes. The status of current preform technology is reviewed including textile, non-woven, continuous and chopped fiber based methods. Automotive applications are considered with an emphasis on structural parts. Key areas for development are identified and progress towards these presented as an integrated design method comprising of surface modeling, deformation analysis, flow considerations and high speed fiber placement.