A.C. Long

Design and manufacture of textile composites

Manufacturing and internal geometry of textiles Mechanical analysis of textiles Rheological behaviour of pre-impregnated textile composites Forming textile composites Manufacturing with thermosets Composites manufacturing - thermoplastics Modeling, optimization and control of resin flow during manufacturing of textile composites with liquid molding Mechanical properties of textile composites Flammability and fire resistance of composites Cost analysis Aerospace applications Application of textile composites in the construction industry Textile reinforced composites in medicine Textile composites in sports products.

A Simulation of Reinforcement Deformation during the Production of Preforms for Liquid Moulding Processes

Composite materials offer an attractive alternative to metals in the automotive and aerospace industries. Of the many possible production methods, liquid moulding processes such as resin transfer moulding (RTM) and structural reaction injection moulding (SRIM) demonstrate potential for high-volume manufacture. It is common to use preformed reinforcements, although this can cause certain problems. Fibre movement during forming can cause adverse effects such as wrinkling and thinning. The high levels of waste generated by subsequent trimming operations are proving unacceptable for medium to high volumes. An accurate modelling capability would allow defects to be predicted at the design stage, and would also allow prediction of the net-shape reinforcement required to form the component with no waste. This paper presents models for both random and directional reinforcement deformation. Random reinforcements are simulated using a modified plasticity theory, while directional reinforcements are modelled using the pin-jointed deformation model.

Experimental characterisation of the consolidation of a commingled glass/polypropylene composite

Commingled fabrics offer a cost-effective solution to the manufacture of thermoplastic composites with aligned reinforcements. Consolidation and subsequent void reduction would appear to be the rate-determining stage during processing. Models for consolidation have concentrated on transverse flow of matrix into the reinforcement tows. Experimental studies for other materials have suggested alternative mechanisms, in particular dissolution of entrapped air into the polymer matrix under continued application of pressure. In this study a series of experiments were used to determine the effects of rate, temperature and holding pressure on the consolidation of a glass/polyproplyene commingled fabric. Results are presented in terms of consolidation pressure, void content and micrographs to illustrate the evolution of the microstructure. Increasing rate resulted in increased consolidation pressure as expected, although significant shear thinning occurred even at modest mould closure speeds. Increased rate also led to an increase in void content at the end of the consolidation phase (prior to dissolution into the matrix). The application of pressure during cooling resulted in a dramatic decrease in void content, with levels of less than 1% observed for 3 MPa (regardless of the rate of consolidation). Experiments where the material was heated to 200°C and then cooled to the required temperature prior to consolidation indicated a significant effect of supercooling. This resulted in almost no change in the required consolidation pressure with increasing material temperature above 150°C. Observations of the microstructure at various stages during consolidation suggested that pre-heating of the material resulted in pools of coalesced matrix both within and between the tows. At the end of consolidation the remaining voids were predominantly in the matrix rich regions between tows.

The effect of shear deformation on the processing and mechanical properties of aligned reinforcements

Abstract The growth of liquid moulding processes for the production of structural and semi-structural components has been eased by the development of computer-aided engineering tools for structural analysis and process modelling. However, the accuracy of these tools is dependent on the available material property data. These are usually obtained from experimental or theoretical analysis of flat plaques. These methods do not take into account reinforcement deformation during the preforming process. Deformation, caused by forming two-dimensional reinforcements over threedimensional surfaces, can result in local fibre reorientations and volume fraction changes within the preform. In this study the major deformation mode, simple shear, is isolated. The effects of simple shear deformation on permeability and elastic properties of engineered and woven glass fabrics are investigated. Predictions of elastic properties are made by using established methods and compared with experimental data for a range of fabric architectures. A semiempirical method is applied to characterise the effects of shear on reinforcement permeability.

Composites forming technologies

Composite forming mechanisms and materials characterisation Constitutive modelling for composite-forming Finite element analysis of composite-forming Virtual testing for material formability Optimisation of composites forming Simulation of compression moulding to form composites Understanding composite distortion during processing Forming technology for composite/metal hybrids Forming of self-reinforced polymer materials Forming technology for thermoset composites Forming technology for thermoplastic composites The use of draping simulation in composite design Benchmarking of composite forming modelling techniques.

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

Finite element modelling of fabric compression

The mechanical behaviour of woven fabric under compression is investigated using 3D finite element analysis in conjunction with a nonlinear mechanical model for the yarn. The FE model captures the main fabric compression response, including geometric and material nonlinearities, yarn interactions and hysteresis. It is found that the behaviour of fabric in compression is governed by the stiffness of the yarn cross-section and the transverse–longitudinal shear modulus. The stiffness along the yarn direction has no noticeable effect. The model is sufficient to simulate the known responses of a fabric as well as to predict the behaviour of novel fabrics based on the properties of the component yarns and yarn interactions.

Characterizing the processing and performance of aligned reinforcements during preform manufacture

Abstract Liquid moulding processes are now finding a wide range of applications for both structural and semistructural components. This has been facilitated in part by the development of computer-aided engineering tools for structural analysis and process modelling. However, the accuracy of these tools is dependent on the available material property data, which are usually determined using two-dimensional flat plaque experiments. This approach may not be satisfactory for complex component geometries, as preform manufacture often results in large variations in both fibre orientation and volume fraction. In recent years, several authors have developed reinforcement deformation of ‘drape’ models that may be used to predict the fibre architecture at the design stage. These models are usually based on the assumption that reinforcement deformation is facilitated by inter-fibre shear, whereas in reality a number of mechanisms are available. In this study, reinforcement deformation is characterized using an automatic strain analysis system. This is applied to a number of generic components with increasing depth of draw, enabling the validity of the interfibre shear model to be established. The effects of deformation on reinforcement permeability and component structural properties are then established using experiments based on sheared reinforcements.

Finite element modelling of fabric shear

In this study, a finite element model to predict shear force versus shear angle for woven fabrics is developed. The model is based on the TexGen geometric modelling schema, developed at the University of Nottingham and orthotropic constitutive models for yarn behaviour, coupled with a unified displacement-difference periodic boundary condition. A major distinction from prior modelling of fabric shear is that the details of picture frame kinematics are included in the model, which allows the mechanisms of fabric shear to be represented more accurately. Meso- and micro-mechanisms of deformation are modelled to determine their contributions to energy dissipation during shear. The model is evaluated using results obtained for a glass fibre plain woven fabric, and the importance of boundary conditions in the analysis of deformation mechanisms is highlighted. The simulation results show that the simple rotation boundary condition is adequate for predicting shear force at large deformations, with most of the energy being dissipated at higher shear angles due to yarn compaction. For small deformations, a detailed kinematic analysis is needed, enabling the yarn shear and rotation deformation mechanisms to be modelled accurately.

Normalization of Shear Test Data for Rate-independent Compressible Fabrics

This article describes a method of using both picture frame (PF) and bias extension (BE) tests together to characterize accurately the trellis shearing resistance of engineering fabrics under low in-plane tension conditions. Automated image analysis software has been developed to reduce the amount of laborious manual analysis required to interpret BE data accurately. Normalization methods for both PF and BE tests on rate-independent compressible fabrics are presented. Normalization of PF test results is relatively straightforward while normalization of BE test results for direct comparison with PF data is more complicated. The normalization method uses a number of simple assumptions to account for the nonuniform shear strain field induced across BE samples during testing. Normalized results from BE tests on samples of different aspect ratios are compared and provide validation of the theory.