Abstract
Wind turbine industry utilizes composite materials in turbine blade structural designs because of their high strength/stiffness to weight ratio. T-joint is one of the design configurations of composite wind turbine blades. T-joints consist of a skin panel and a stiffener co-bonded or co-cured together with a filler material between them. T-joints are prone to delaminations between skin/stiffener plies and debonds between skin-stiffener-filler interfaces. In this study, delamination/debond behavior of a co-bonded composite T-joint is investigated under 0° pull load condition by 2D finite element method. Using Abaqus® commercial FE software, zero-thickness cohesive elements are used to simulate delamination/debond in ply interfaces and bonding lines. Pulling load at 0° is applied and load-displacement behavior and failure scenario are observed. The failure sequence consists of debonding of filler/stringer interface during one load drop followed by a second drop in which the 2nd filler/stringer debonds, filler/skin debonding and skin delamination leading to total loss of load carrying capacity. This type of failure initiation has been observed widely in the literature. When the debond strength is increased 30%, failure pattern is found to change in addition to increasing the load capacity by 200% before total loss of loading carrying capacity occurs. Failure initiation and propagation behavior, initial and max failure loads and stress fields are affected by the property change. In all cases mixed-mode crack tip loading is observed in the failure initiation and propagation stages. In this paper, the detailed delamination/debonding history in T-joints is predicted with cohesive elements for the first time.
Highlights
Wind turbine blades, composed of skin panels and stiffeners, are manufactured by using laminated composite materials
Numerical Results Numerical investigations of the T-joint for 0° pull load are conducted in three sections:
In the second section, the load-displacement curve, stress fields and delamination/debond behavior of the T-joint with cohesive layers are investigated in detail
Summary
Wind turbine blades, composed of skin panels and stiffeners, are manufactured by using laminated composite materials They are mainly used for their high strength/stiffness to weight ratio. In T-joints, because of the stiffness difference between the skin and the stiffeners, a complex 3D stress state is generated in the structure This makes the T-joint a critical delamination/debond region. Cracks can initiate in cohesive layers anywhere in the structure which allows multiple crack initiations and propagations as an outcome of the model Because of these advantageous characteristics, CZM is being increasingly used in delamination/debond modeling in laminated composites. GiC, or the critical displacement, δiC, is achieved, cohesive element does not carry further load and crack growth initiates
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