Abstract
Morphing blades have been promising in lifting restrictions on rated capacity of wind turbines and improving lift-to-drag ratio for aircraft wings at higher operational angles of attack. The present study focuses on one aspect of the response of morphing blades viz. dynamic delamination. A numerical study of delamination in morphing composite blades is conducted. Both components i.e. the composite part and the stiffener are studied. The eXtended Finite Element Method (XFEM) and nonlocal continuum mechanics (peridynamics) have both been used to study fracture in the isotropic stiffener used in conjunction with the blade. As for the composite morphing blade, cohesive elements are used to represent the interlaminar weak zone and delamination has been studied under dynamic pulse loads. Intraply damage is studied using the nonlocal model as the peridynamic model is capable of addressing the problem adequately for the necessary level of sophistication. The differences and similarities between delamination patterns for impulsive, dynamic, and quasi-static loadings are appreciated and in each case detailed analyses of delamination patterns are presented. The dependence of delamination pattern on loading regime is established, however; further parametric studies are not included as they lie beyond the scope of the study. Through the use of fracture energy alone the nonlocal model is capable of capturing intra- and interlaminar fractures. The proposed modelling scheme can thus have a major impact in design applications where dynamic pulse and impact loads of all natures (accidental, extreme, service, etc.) are to be considered and may therefore be utilised in design of lightweight morphing blades and wings where delamination failure mode is an issue.
Highlights
As the level of functional requirements for an aircraft or turbine blade elevates so does the level of sophistication in design
Several regimes of loading are considered, intra-ply damage has not been included as (1) the focus has been on delamination and it is believed that this mode of damage precedes fibre failure, which is the detrimental mode of damage to a composite lamina and (2) enrichment functions are not implemented for anisotropic media and the use of continuum damage mechanics requires implementation of a mesh-objective damagemechanics based constitutive model which lies outside the scope of the present study
Since fracture introduces a discontinuity into the displacement field and stress/strain field singularities at the crack tip, the analysis of fracture requires special techniques such as continuum damage mechanics (CDM), or extended finite element method (XFEM)
Summary
As the level of functional requirements for an aircraft or turbine blade elevates so does the level of sophistication in design. Plate action which follows could lead to mode II and mixed-mode interlaminar fracture [23,24] similar to dynamic debonding of soffit plates in a strengthened beam [20] Detailed analyses of such cases using numerical methods, such as the finite element method, and analytical models, as first- and higher-order shear deformation laminated plate theories [25,26], are possible and the theories can be used to study such cases. Several regimes of loading are considered, intra-ply damage has not been included as (1) the focus has been on delamination and it is believed that this mode of damage precedes fibre failure, which is the detrimental mode of damage to a composite lamina and (2) enrichment functions (asymptotic crack tip functions) are not implemented for anisotropic media and the use of continuum damage mechanics requires implementation of a mesh-objective damagemechanics based constitutive model which lies outside the scope of the present study.
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