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microstructural defects in complex shape laminates also include ply wrinkling, corner thickening or thinning for parts manufactured on concave or convex tools, respectively, and, in extreme cases, delamination [11]. Moreover, resin cure shrinkage and anisotropic thermal expansion can induce residual stresses in angle laminates during autoclave processing, leading to dimensional changes such as spring-in at corners and warpage in flat sections [12, 13]. Resin flow and fiber bed compaction are critical governing factors for defect formation in complex shape laminates. Percolation flow, during which the resin transport occurs relative to a compacting fiber bed, and shear flow, during which the fiber bed and resin are considered an inextensible viscous fluid, are the two major mechanisms of flow behavior during cure [14]. The compaction of angle laminates involves the interaction of both mechanisms [11, 15]. In addition to resin flow and fiber bed compaction, studies also show that during autoclave processing, the lay-up method has a significant effect on the thickness uniformity of cured laminates, while the corner curvature radius, flange length and laminate thickness have less effect on the thickness uniformity of the cured quasi-isotropic laminates than on the [90o]n laminates [16]. Within this context, the low compaction pressure available during VBO cure and the distinctive flow and compaction characteristics of VBO prepregs are likely to further complicate the fabrication of complex parts. Studies on the OoA/VBO manufacturing of laminates with corners or other sharp curvatures have been reported. Laminates manufactured over concave (female) tools exhibited resin accumulation and corner thickening, whereas corner thinning was observed for convex (male) tooling, in agreement with their autoclave counterparts [17]. Lightfoot et al. [18] suggested a mechanism of wrinkling formation in L-shape laminates governed by the shear force generated by mismatches of coefficient of thermal expansion between tool and laminate, as well as ply slippage during compaction, and experiments based on this mechanism were able to minimize wrinkles and DOI: 10.1002/pc.23773 4PDF Image | Vacuum Bag-Only Prepregs
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