Abstract
Out-of-plane fiber waviness, also referred to as wrinkling, is considered one of the most significant effects that occur in composite materials. It significantly affects mechanical properties, such as stiffness, strength and fatigue and; therefore, dramatically reduces the load-carrying capacity of the material. Fiber waviness is inherent to various manufacturing processes of fiber-reinforced composite parts. They cannot be completely avoided and thus have to be tolerated and considered as an integral part of the structure. Because of this influenceable but in many cases unavoidable nature of fiber waviness, it might be more appropriate to consider fiber waviness as effects or features rather than defects. Hence, it is important to understand the impact of different process parameters on the formation of fiber waviness in order to reduce or, in the best case, completely avoid them as early as possible in the product and process development phases. Mostly depending on the chosen geometry of the part and the specific manufacturing process used, different types of fiber waviness result. In this study, various types of waviness are investigated and a classification scheme is developed for categorization purposes. Numerous mechanisms of wrinkling were analyzed, leading to several recommendations to prevent wrinkle formation, not only during composite processing, but also at an earlier design stage, where generally several influence factors are defined.
Highlights
Fiber-reinforced composite materials allow for a significant mass reduction due to the comparably low density (c.f. four to five times less than steel) and, in addition, fibers can be aligned in accordance with the load paths
The placement of the fibers or semi-finished textile products is still often carried out by hand-lay-up, especially in the aviation industry. This allows a diverse draping of the unidirectional (UD) layers, woven textiles, or non-crimped fabrics (NCF) onto the production tool
Tam and Gutowski [27] demonstrated that wrinkling will occur when the shear required to accommodate the material to a specific geometry is too high
Summary
Fiber-reinforced composite materials allow for a significant mass reduction due to the comparably low density (c.f. four to five times less than steel) and, in addition, fibers can be aligned in accordance with the load paths. For parts with significant double curvature and requiring the use of a large area draped reinforcement layer, the selection of a woven fabric with a narrow rather than a wide tow reduces the level of fiber waviness [22] By including these influencing factors in the design decisions, this effect. By including these influencing factors in the design decisions, this effect can be reduced
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