A continuum damage model to predict the influence of ply waviness on stiffness and strength in ultra-thick unidirectional Fiber-reinforced Plastics

Abstract

Ply waviness is a commonly observed manufacturing defect of ultra-thick composite materials essentially affecting stiffness, strength, and fatigue behavior of the composite. A specimen's geometry is designed to represent the failure mechanisms in thick wavy laminates, typically observed in spar caps of today's wind turbine blades. A material model is developed to simulate the phenomenological processes in wavy laminates to obtain a strength knock-down. Particular attention is taken on the nonlinear shear behavior and kink band formation. The presented model correlates well with results achieved by experiments. This paper shows a significantly higher influence of compressive compared with tensile loading on the mechanical material behavior of wavy laminates.

Process Induced Defects in Liquid Molding Processes of Composites

“…However, fiber misalignment in LCM is reported to originate mainly from improper placement of the preform in the mold cavity prior to resin injection, which often leads to a substantial scatter from the fibers' intended direction, and leads to fiber misalignment (Altmann at al., 2016;Gereke et al, 2013;Khan et al, 2016;Li et al, 2016). For instance, Gan et al (2012) For personal use only.…”

“…For example, forcing a slightly oversized preform into a mold cavity has been reported to induce both fiber waviness and wrinkling (Altmann et al, 2016;Bloom et al, 2013). These wrinkles tend to be localized such as those occasionally observed on composite wind turbine blade skins (Bloom et al, 2013).…”

“…Furthermore, fiber undulation is inevitably induced in composite parts with curvatures (Altmann et al, 2016;Lightfoot et al, 2013;Mizukami et al, 2016). When a normally straight and continuous preform is forced to conform to a curvature, the fibers on the inside of the curvature are loaded in compression.…”

“…For instance, wrinkling is commonly reported and most critical in the thick, load carrying sections of wind turbine blades, such as the spar caps (Altmann et al, 2015;Bloom et al, 2013). Wrinkling has been also reported to be more pronounced in other thick LCM parts with complex shapes, extensively used in large wind turbine blades, submersibles, and aerospace platforms (Altmann et al, 2016;Khan et al, 2016). In addition, wrinkling is observed to occur in RTM composites when the fiber preform is compressed during mold closure inducing tension forces around curvatures and bends, particularly in massive, geometrically-complex parts (Dong, 2014).…”

“…Following the success of such applications, there has been increased interest in using advanced composites for higher production rate and cost sensitive fields such as automotive, marine and wind energy applications, among others (Altmann et al, 2016;Gourichon et al, 2006;Kedari et al, 2011;Wang et al, 2013). In this context, significant attention has been placed on developing lower-cost, higher performance Liquid Composite Molding (LCM) processes that can produce medium to large composites structures.…”