F. Robitaille

Use of Resin Transfer Molding Simulation to Predict Flow, Saturation, and Compaction in the VARTM Process

Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) are among the most significant and widely used Liquid Composite manufacturing processes. In RTM preformed-reinforcement materials are placed in a mold cavity, which is subsequently closed and infused with resin. RTM numerical simulations have been developed and used for a number of years for gate assessment and optimization purposes. Available simulation packages are capable of describing/predicting flow patterns and fill times in geometrically complex parts manufactured by the resin transfer molding process. Unlike RTM, the VARTM process uses only one sided molds (tool surfaces) where performs are placed and enclosed by a sealed vacuum bag. To improve the delivery of the resin, a distribution media is sometimes used to cover the preform during the injection process. Attempts to extend the usability of the existing RTM algorithms and software packages to the VARTM domain have been made but there are some fundamental differences between the two processes. Most significant of these are 1) the thickness variations in VARTM due to changes in compaction force during resin flow 2) fiber tow saturation, which may be significant in the VARTM process. This paper presents examples on how existing RTM filling simulation codes can be adapted and used to predict flow, thickness of the preform during the filling stage and permeability changes during the VARTM filling process. The results are compared with results obtained from an analytic model as well as with limited experimental results. The similarities and differences between the modeling of RTM and VARTM process are highlighted.Copyright

Effect of resin properties and processing parameters on crash energy absorbing composite structures made by RTM

The effects of resin properties and resin processing parameters on the crush behaviour of thermoset composite tubes manufactured using resin transfer moulding are considered. The aims were to quantify the performance of tubes produced over a broad spectrum of conditions and to correlate this performance to the properties of the material. The effects of the mould temperature, post-cure time and resin composition were investigated for random and engineered reinforcement fabrics. Relationships between Youngs moduli and ultimate stresses of the material in tension and compression were established from plaques moulded under similar conditions. Random reinforcement fabrics gave higher specific energy absorption (SEA) levels than engineered fabrics, but were more sensitive to processing conditions. Epoxy absorbed more energy than vinyl ester. Vinyl ester absorbed more than polyester, and additions of vinyl ester resin to unsaturated polyester gave a linear increase in SEA. The ultimate compressive strength of the composite proved the best indicator of performance for the selected materials and processing conditions.

Automatically generated geometric descriptions of textile and composite unit cells

This paper presents an algorithm that generates geometric descriptions of unit cells of textiles and composite materials. The purpose of these geometric descriptions is to act as domains for calculations preformed at the scale of the unit cell, where the heterogeneity of the material must be considered. The algorithm defines both the volumes of the tows and the empty volumes that extend between the tows within the calculation domain, for general textiles. Resulting geometric descriptions are provided as assemblies of topologically simple volumes that encompass either part of a tow or part of an empty volume. Typical applications of the geometric definitions include the calculation of local permeability values for textile preforms and the investigation of local stress distributions in textile composites.

Effects of fibre architecture on reinforcement fabric deformation

Abstract In this paper, the shear properties of a number of woven and non-crimp (multiaxial warp knit) fabrics are analysed. These are shown to be related to the fibre architecture and, for non-crimp fabrics, the pattern and orientation of the stitching thread. A detailed geometric model has been developed for the deformation of woven fabrics during in plane shear, and this is used as a basis for a mechanical analysis to predict shear compliance. This model incorporates intertow friction, tow compaction, and in plane (membrane) tension. Finally an iterative model for fabric forming is described, based on fabric shear energy obtained either from the mechanical model or from experimental measurements. This is validated for a hemisphere and an automotive transmission tunnel and is shown to offer greater accuracy than the traditional geometric mapping, while associated computation times are at least an order of magnitude lower than those associated with non-linear finite element analysis.

Geometric modelling of industrial preforms: Woven and braided textiles:

Abstract Predictive calculations of the physical properties of fibrous preforms and composite parts require an appropriate description of the preform geometry. Most internal dimensions of a preform are set during its manufacturing through mechanical interactions occurring between the tows and threads. However, the global shape and the interlacing patterns of the constituent textiles are determined independently. In this paper, a formal procedure for the description of the interlacing patterns is proposed. This procedure, which is based on the individual textile manufacturing processes, is general in the textiles considered and in the possible applications. The interlacing patterns are expressed by a series of vectors that follow a universal set of criteria and are generated from the values taken by the processing parameters. Defining examples are given for three-dimensional woven textiles and three-dimensional tubular braided textiles, and geometrical applications are also presented. Further examples for warp-knitted textiles and multiple-layer stacks will be given in a subsequent paper, together with examples of physical applications.

Comparative study on submillimeter flaws in stitched T-joint carbon fiber reinforced polymer by infrared thermography, microcomputed tomography, ultrasonic c-scan and microscopic inspection

Abstract. Stitching is used to reduce dry-core (incomplete infusion of T-joint core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography, and laser spot thermography are used to investigate the internal flaws in a stitched T-joint carbon fiber-reinforced polymer (CFRP) matrix composites. Then, a new microlaser line thermography is proposed. Microcomputed tomography (microCT) is used to validate the infrared results. A comparison between microlaser line thermography and microCT is performed. It was concluded that microlaser line thermography can detect the internal submillimeter defects. However, the depth and size of the defects can affect the detection results. The microporosities with a diameter of less than 54  μm are not detected in the microlaser line thermography results. Microlaser line thermography can detect the microporosity (a diameter of 0.162 mm) from a depth of 90  μm. However, it cannot detect the internal microporosity (a diameter of 0.216 mm) from a depth of 0.18 mm. The potential causes are given. Finally, a comparative study is conducted.

Pulsed micro-laser line thermography on submillimeter porosity in carbon fiber reinforced polymer composites: Experimental and numerical analyses for the capability of detection

In this article, pulsed micro-laser line thermography (pulsed micro-LLT) was used to detect the submillimeter porosities in a 3D preformed carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to verify the thermographic results. Then, finite element analysis was performed on the corresponding models on the basis of the experimental results. The same infrared image processing techniques were used for the experimental and simulation results for comparative purposes. Finally, a comparison of experimental and simulation postprocessing results was conducted. In addition, an analysis of probability of detection was performed to evaluate the detection capability of pulsed micro-LLT on submillimeter porosity.

Geometric modelling of industrial preforms: Warp-knitted textiles

Abstract The processing properties of fibrous preforms and the final properties of liquid moulded composite parts are strongly related to the internal architecture of the preforms. The architecture of a preform is determined by the individual textile layers from which it is made. In order to calculate the processing and final properties in the same way over all the volume of a preform or part made from different types of textile, some sets of equations that generate similar definitions of the textiles from their manufacturing parameters are required. The similarity of these definitions is assessed through a series of criteria stated in a previous paper by the present authors; definition modules for woven and braided textiles were also presented in that paper. This paper presents a definition module, or a set of equations, that generates similar definitions for non-crimp reinforcements assembled by warp knitting; the equations also apply for the stitched threads used to assemble multiple-layer preforms. The definitions obtained from this module obey the criteria mentioned previously. The sets of equations presented in both papers cover most technical textiles; similar sets of equations can be created for speciality reinforcements and applied to the calculation of diverse physical properties of the preforms and parts. As an example, this paper discusses the mapping of the voids which are defined between the tows and threads of non-crimp stitched reinforcements.

Comparative study of microlaser excitation thermography and microultrasonic excitation thermography on submillimeter porosity in carbon fiber reinforced polymer composites

Abstract. Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Thermographic approaches including microvibrothermography, microlaser line thermography, and microlaser spot thermography on the basis of pulsed and lock-in techniques were proposed. These techniques are used to detect the submillimeter porosities in a stitched T-joint carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to validate the thermographic results. Finally an experimental comparison of microlaser excitation thermography and microultrasonic excitation thermography was conducted.

Infrared thermography, ultrasound C-scan and microscope for non-destructive and destructive evaluation of 3D carbon fiber materials: a comparative study

3D Carbon fiber polymer matrix composites (3D CF PMCs) are increasingly used for aircraft construction due to their exceptional stiffness and strength-to-mass ratios. However, defects are common in the 3D combining areas and are challenging to inspect. In this paper, Stitching is used to decrease these defects, but causes some new types of defects. Infrared NDT (non-destructive testing) and ultrasound NDT are used. In particular, a micro-laser line thermography technique (micro-LLT) and a micro-laser spot thermography (micro-LST) with locked-in technique are used to detect the micro-defects. In addition, a comparative study is conducted by using pulsed thermography (PT), vibrothermography (VT). In order to confirm the types of the defects, microscopic inspection is carried out before NDT work, after sectioning and polishing a small part of the sample..