To cite this version:A. Shanwan, Samir Allaoui. Different experimental ways to minimize the preforming defects of multi-layered interlock dry fabric. International Journal of Material Forming, Springer Verlag, 2018Verlag, , 10.1007Verlag, /s12289-018-1407 Different experimental ways to minimize the preforming defects of multilayered interlock dry fabric. Abstract:This study presents a strategy to improve the quality of a dry fabric's preforms. Preforming tests were realized with one and two-layers of interlock carbone fabric at different configurations.Initial results led to preforms with several defects. For one-layer preforming, a new blank holder geometry and an increase of the pressure applied on the fabric allowed to improve the quality of the preforms. On the other hand, for two-layer preforming, the insertion of a mat fabric in the interface of the two preformed layers allowed to decrease the friction and to improve the preforms quality, significantly.

This paper deals with the influence of buckles that are a mesoscopic out of plane defects on the fatigue behavior of a GFRP. Three cases were investigated: Healthy samples with no defect and specimens with buckles defects that are first generated in the longitudinal direction and then on the transverse direction.. First, static tests were used to measure the differences of the mechanical properties of both defect orientations and, thanks to digital image correlation, to see where were localized the areas of maximal local strain on the samples. Secondly, fatigue tests were performed in the three configurations. The results revealed that both defect orientations have a significant effect on the fatigue life and on the strain field. The configuration with defects in the transverse direction is the most crippling condition as expected from the static tests but the longitudinal direction configuration was also very affected by the presence of the mesoscopic defects. Those observations lead to conclude that this mesoscopic out of plane defect has a major negative influence on the fatigue life of such a composite.

Composite materials can be produced by several technologies, such as Liquid Composite Manufacturing (LCM). In this technology, a fabric can be formed by highly double curved punch geometries. During its forming, the fabric is submitted to several deformations and mechanical stresses, like biaxial tensile stress, shear, bending, compaction and friction. The cumulative effect of these stresses leads to the appearance of different types of defects such as wrinkles, buckles, sliding, etc. These defects may have a significant influence on the mechanical properties of the final composite materials. In order to understand the forming mechanisms of these defects, as well as their effect on the behavior of composite materials, an experimental machine was designed and built. The aim of this machine is to generate different types of defects with controlled and adjusted amplitudes (calibrated defects), in samples of a fabric. These samples are then used to manufacture composite samples with calibrated defects, by an LCM process. The defected composite samples are then tested and compared with composite samples without defects. The obtained results have identified the experimental parameters corresponding to the appearance of different types of defects.

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