X-Stiffener

X-STIFFENER™

THE X-STIFFENER™ PREVENTS TWISTING OF THE MAIN AND REAR BOX OF THE BLADES.

Longitudinal cracks on the leading edge are very often found after only a few years of operation. Experimental and theoretical modelling has proven that the installation of X-Stiffeners™ significantly reduces twisting and peeling stresses to a non-critical level. The twisting and peeling stresses increase with the length of the blades in particular blades with large flat-backs can benefit from X-Stiffener™ installation. The installation of X-Stiffeners™ extends the lifetime of your blades.

The X-Stiffener™ connects the two sides of the blades like a cross in a bookshelf, thereby avoiding deformation of the shear webs.  

When rotating, the total load on the blade is comprised of the edgewise loading and aerodynamic forces caused by the wind, a so called combined loading scenario. The combined loading implies an alternating twisting, Cross Sectional Shear Distortion (CSSD) - of the blade which in turn cause critical peeling stresses in the bond lines.

X-Stiffener™ development
The X-Stiffener™ was matured during the LEX project and are presently being tested in a large scale test at DTU. The X-Stiffeners™ are installed in either the main- or rear box. Depending on the individual blade the number of crosses installed may differ.

The X-Stiffeners™ are glued into the blade, a noninvasive installation. The anchoring points are glued into the corners of either the main- or the rear box and a string is used to support the blade. The string is installed with pretension, a mechanism inbuilt into the anchoring part.