Download complete journal in PDF form - Academy Publish

PARAMETRIC STUDY OF SANDWICH PANEL BUCKLING IN COMPOSITE WIND TURBINE BLADES
Shicong Miao, Steven Donaldson, and Elias Toubia
excluding sandwich plates or shells. Therefore, it is useful to perform a
parametric study of both flat and curved section strips representing
different characteristic regions of sandwich laminates in blades.
A parametric study of the buckling performance of core materials on
the basis of transverse shear modulus and thickness, within a given
design domain (a fixed set of laminate designs and critical buckling
loads) is presented. This will provide insight into optimal core
solutions. This study considers both flat and curved-section rectangular
sandwich strip models with long aspect ratios, which provide close
approximations to the buckling loads and mode shapes (wavelengths)
expected in the sandwich panel regions of the blades. Considering the
design process and the characteristic strains in axial compression
conditions, the buckling trends are on the basis of both critical buckling
load and strain.
A complete parametric study using practical design properties does not
appear to exist in the literature, and was therefore the goal of this study.
The results of the present work in practical design optimization studies
would then involve assessing the cost and weight of various core
products as an indication of optimal thickness values, then comparing
the cost and weight of the various solutions.
ANALYSIS AND DESCRIPTION
Finite Element Analysis
In setting up the model, two panel models (flat and curved -section)
were considered to represent different regions of the blade shell. It was
assumed that all layers of the panel were perfectly bonded together and
thus the displacements were continuous throughout the thickness.
The model of the panel strips were built in ABAQUS 6.10 with
elements of S4R (ABAQUS User’s Manuals, Version 6.10). For the
flat-section model, there were a total of 1111 nodes and 1000 elements
used. The curved section model used 1313 nodes and 1200 elements.
This mesh density was established in a prior convengence study by
Toubia (Toubia, 2008).
The general boundary condidtions of the sandwich panel models are
shown in Figure 1. In the flat-section model, on the loaded edge, U 2 =
U 3 = 0. The long edges have U 2 = U 3 = 0, and the far end has U 1 = U 2 =
U 3 = 0. In the curved-section model, on the loaded edge, U t = U r = 0.
In this initial study, the load profile was assumed to be uniform across
the ends (later studies to examine non-uniform loading are appropriate).
The long edges have U t = U r = 0, and the far end has U t = U r = U z = 0.
The analyzed material data and panel model information can be found
in Table 1 and Table 2. The facing material used in this study is E_TLX
5500 ( E_TLX5500, 15 December 2011.) which is [0/45/-45] E-glass
material commonly used as composite reinforcement in wind turbine
blade shell regions. Four representative core materials (M1 to M4) are
selected to cover the prevalent material shear modulus range. The
critical buckling eigenvalues were found by buckling analysis using
ABAQUS, and then applied in the linear analysis approach to obtain
the critical buckling strains. Sample dominant buckling mode shapes
are shown in Figure 2 and Figure 3.
Figure 1. General bounduary conditions of the infinitely long strip of the panel (1, 2, 3) and shell (r, t, z)
AcademyPublish.org – Journal of Engineering and Technology Vol.2, No.2 4