Wind turbine blades are highly complex structures with complex 3 dimensional forms governed by their aerodynamics that allow a maximum of power output and efficiency. On the structural side there is always an immense interest in keeping the blades as light and as rigid as possible. No structure being perfectly rigid, the wind turbine blades are specifically designed to keep their deformation in check. Deflection twist couplings are also designed into the blades to have favorable aerodynamic properties even in the deformed state. A combination of experimental and numerical work has been used to address the most critical failure mechanisms and to get an understanding of the complex structural behavior of wind turbine blades. Different failure mechanisms observed during the tests performed for reduced scale tests (smaller test specimens) and the corresponding FE-analysis are presented.