Abstract:Technical textiles have the ability to deform under load by shearing, which distinguishes them from thin sheet materials such as paper. This particular property helps them to deform and take the shape of the complex part that they were intended to create. Draping, flexibility and handling of technical textiles are greatly affected by their shearing behaviour. In this paper, the influence that factors such as stitch (i.e., presence or absence of it), testing speed and the pre-tension force applied have on the s… Show more
“…A continued work on the deformability characterization [85][86][87][88][89][90][91][92] creates a comprehensive database to be used in the forming simulations. This work also includes specific problems as fabric-tool friction characterization [93], localization of transverse tension [86], superposition of transverse tension and shear [94], difficulties in assessing the strain fields via DIC, caused by the fabric surface distortion [95], compaction characterization [96], forming of NCF composites with continuous NCFs [97].…”
Section: Specific Deformability Of Stitched Ncfmentioning
The increase in the number of structural applications of composite materials, especially in the aerospace and automotive industries, has led to a demand for robust models to simulate composite forming processes. The mechanical behaviour of composite materials during forming is relatively complex due to their fibre-matrix composition. Many research studies have been conducted in the past 25-plus years into experimental methods for the characterization of the mechanical behaviours that are exhibited by textile-reinforced composite material systems during forming and into the development of material models to be used in computer codes for forming simulations. These studies have been presented and discussed in the ESA-FORM conferences since 1997 and especially in the 'Composite Forming Processes' mini-symposium launched in 2001. This article presents a survey of the research carried out in this context. Mechanical characterization tests specific to composite forming are presented as well as recent analysis techniques such as digital image correlation and X-ray tomography. Threedimensional mechanical behaviour laws, in particular hypo-and hyperelastic, have been developed and extended to second gradient models. Specific shell approaches have been presented and their application to wrinkling analysis. Resin flow and permeability analysis is another area of research in composite forming processes which are discussed in this article. Research on certain processes is also presented, in particular thermoforming of thermoplastic composites, wet compression moulding, pultrusion, automated fibre placement and three-dimensional printing. This comprehensive review of the works of multiple research groups is a recognition of the breadth and depth of efforts that have been invested into the understanding of the manufacturability of textile-reinforced composite materials.
“…A continued work on the deformability characterization [85][86][87][88][89][90][91][92] creates a comprehensive database to be used in the forming simulations. This work also includes specific problems as fabric-tool friction characterization [93], localization of transverse tension [86], superposition of transverse tension and shear [94], difficulties in assessing the strain fields via DIC, caused by the fabric surface distortion [95], compaction characterization [96], forming of NCF composites with continuous NCFs [97].…”
Section: Specific Deformability Of Stitched Ncfmentioning
The increase in the number of structural applications of composite materials, especially in the aerospace and automotive industries, has led to a demand for robust models to simulate composite forming processes. The mechanical behaviour of composite materials during forming is relatively complex due to their fibre-matrix composition. Many research studies have been conducted in the past 25-plus years into experimental methods for the characterization of the mechanical behaviours that are exhibited by textile-reinforced composite material systems during forming and into the development of material models to be used in computer codes for forming simulations. These studies have been presented and discussed in the ESA-FORM conferences since 1997 and especially in the 'Composite Forming Processes' mini-symposium launched in 2001. This article presents a survey of the research carried out in this context. Mechanical characterization tests specific to composite forming are presented as well as recent analysis techniques such as digital image correlation and X-ray tomography. Threedimensional mechanical behaviour laws, in particular hypo-and hyperelastic, have been developed and extended to second gradient models. Specific shell approaches have been presented and their application to wrinkling analysis. Resin flow and permeability analysis is another area of research in composite forming processes which are discussed in this article. Research on certain processes is also presented, in particular thermoforming of thermoplastic composites, wet compression moulding, pultrusion, automated fibre placement and three-dimensional printing. This comprehensive review of the works of multiple research groups is a recognition of the breadth and depth of efforts that have been invested into the understanding of the manufacturability of textile-reinforced composite materials.
“…For the wet compaction characterisations and the infusion experiments, the resin EPIKOTE RIMR 135 and the curing agent EPIKURE RIMH 137 from Hexion were used because of its long processing time at room temperature. The resin has a density of 1.13 g/cm 3 and the viscosity ranges between 0.3 − 0.5 Pa⋅s at 25° C within the first hour.Figure 1.(A) Top view, (B) back view and (C) a schematic diagram of the used NCF (adapted from 33 ).…”
The compaction behaviour of technical textiles such as non-crimp fabrics (NCF) is of much interest to build high quality parts in liquid composite moulding processes (LCM). In this paper, the compaction response of a glass fibre NCF was investigated in two different ways: (1) characterisation tests via a universal testing machine and (2) height measurements via a line laser measurement unit during the infusion process. Results from both measurement systems are compared and it is found that the results of characterisation tests via testing machine can be used only to a certain extent. The pressure-thickness correlation during the infusion process cannot be described by the results of the testing machine, while the compaction results before and after the infusion process are in good agreement for both the methods. With the data of the line laser measurement, a model for the pressure-thickness correlation is derived, which can be used in future simulations. The infusion process was carried out using different scenarios at the vent, on the one hand a semi-permeable membrane and on the other hand an omega profile at the venting port. The results obtained using these two different venting scenarios were compared and it was found that using a semi-permeable membrane as an outlet can lead to thicker parts (up to 10 %).
The forming behaviour of a unidirectional non-crimp fabric (UD-NCF) consisting of polyamide stitches with a tricot-chain stitching pattern is explored. Notably, there are no stabilising tows orientated transverse to the main tow direction in this fabric, a common feature in many ‘quasi’ UD-NCFs, this allows extension of the stitch in the transverse direction under certain loading conditions. The lack of stabilising tows introduces a possible low-energy deformation mode to the UD-NCF, which is absent in biaxial fabrics and to a large extent in ‘quasi’ UD-NCFs. The in-plane shear behaviour is initially investigated using both standard ‘tightly-clamped’ picture frame tests and uniaxial bias extension tests. Preliminary results show a dramatic difference in results produced by the two test methods. During the picture frame test, fibres can be subjected to unintended tension due to sample misalignment in the picture frame rig. To mitigate error arising from this effect, the picture frame test procedure is modified in two different ways: by using an intentional pre-displacement of the picture frame rig, and by changing the clamping condition of test specimen. Results show that the modified picture frame test data contain less error than the standard ‘tightly-clamped’ test but also that the shear stiffness of the UD-NCF is notably lower when measured in the bias extension test compared to the picture frame test, mainly due to the difference in loading conditions imposed during the two tests.
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