PSI - Issue 47

Aghiles Khris et al. / Procedia Structural Integrity 47 (2023) 888–891 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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to be obtained by processes such as RTM (Resin Transfer Moulding). Due to the role that the defects that are created in the preforms play on the quality of composite parts, several studies have focused on the development of methods for the characterization of the defects in fabric materials, Fu and X. Yao (2022). Indeed, the formation of folds in preforms can generate cracks in the composites, the misalignment and buckling of the roving causes drop in strength of the composite, Cruanes et al. (2018). In this work, we are interested in the study of the effect of the orientation of the fabric on the creation of defects during the forming of a Taffeta 500. Two orientations were used 22.5°, and 45°. The punch is a rectangular shaped tool at an angle of 60° on one side. The experimental tests were carried out on a specific device. Three blank-holder pressure of 4.7, 7.2 and 9.7mbar were used, with two different spring configurations (4R and 8R). 2. Experiment The forming tests were carried out on a specific test bench designed and produced in our laboratory (Fig. 1). This bench consists of a polycarbonate matrix, an electric cylinder with a punch holder and a steel table carrying eight guide rods of the springs. The blank-holder on which exerts the pressure generated by the springs is also fabricated with polycarbonate. The test consists of placing the fabric on a die, then placing a blank holder and applying uniform pressure on it thanks to springs placed on the blank holder as shown in (fig 4). The shaping of the fabric is carried out by the vertical displacement of the tool by the electric actuator.

Fig. 1. Schematization of the fabric-forming device.

To perform forming trials, we designed a punch specifically for this study (Fig 2. ). The punch is a modified parallelepiped rectangle with a face inclined at 60°. The footprint of the punch is 90x70x70mm 3 . This geometry is used to promote the appearance of defects. The reinforcement used is a Roving 500 taffeta fabric, therefore with a density of 500 gr/m².For each test, a sample of dimensions 300 x 300 mm² is cut from a roll 50 m in length. In order to measure the geometric defects after shaping, we produced a grid composed of marked points on the yarns. To study the correlation between fabric orientation, defect formation and shear in taffeta rowing 500 preforms, four test configurations were considered by varying two parameters: pressure and spring configurations. Three pressures on the blank holder were applied: 4.7 mbar,7,2mbar and 9.7 mbar and two configurations To obtain these pressures, four springs with a stiffness of 0.5 N/mm were used and compressed with the appropriate displacement.

Fig. 2. (a) 4 springs with orientation 22.5° ; (b) 8 springs with orientation 45°. a b.