Mitigating forming defects by local modification of dry preforms

Composite preforming defects: a review and a classification

“…This causes a drop in the local fiber density, so low that it is considered a "gap". This defect has been also called in the literature by "laddering" [8] and "weave pattern heterogeneity" [45]. In some cases, these pattern disturbances can be highly irregular and look seemingly random due to the coupling of different in-plane deformations like the defects mentioned above that are concentrated in the same area.…”

“…They have found that when the geometry holds a highly curved shape or small radii, it creates additional stress in that specific local area that forces the fabric to adapt to the distinctive form of the geometry. There is a limit to this adaptability [48], it can end up with wrinkles [8,45] or in rare cases with bridging [49][50][51]: it is when the fabric is not able to copy the radii of a corner of the geometry with it will maintain a bigger radius, thus a void between the shape and the fabric in this local area occur. It is also found that the wrinkling can be delayed by using the punch and die vacuum bag, which creates normal compressing making the energy needed to deform out-of-plane more important, thus resisting and maintaining its plane form for longer.…”

“…Thereby, these defects are most likely to occur with the unidirectional or NCF [48] or the unbalanced fabric [39][62] where the friction and cohesion are not equally distributed in all directions or asymmetrical. This defect has been called both " sliding "or "slippage" or both and also called "fabric shifting" [8]. For this particular defect the direction of the yarn or filament movement can be transversal or longitudinal, but what is in common is that this "sliding" affects the latter in a homogeneous way all along with the fabric.…”

“…Wrinkles [6-8, 22, 37-39, 41, 43-48, 95] ; Bucking [33,34,36,52,104,105] Wrinkles When the fabric deforms in an outof-plane curved form, identical to the "wrinkles" mechanism described, the two sides of the curves will fall, one on the other, multiplying the thickness of the fabric locally. Sliding [39,62] ; Slippage/ Fabric shifting [8] Buckling/ In-plane Buckling [2] Sliding:…”

“…The effort has been put to understand these defects and the cause of their appearance [2][3][4][5][6][7] along with suggesting solutions to avoid them [8][9][10][11]. It was either manipulate one of these factors or add a new one to oppose the effect of the first.…”