Composite Box-Beam Failure Modes and Strength: 3D Modeling and Analysis and Comparison with Experimental Results

Abstract

This paper presents a study to develop detailed understanding of the structural strength and failure modes observed in the testing of adhesively bonded composite box-beam specimens. The box-beam specimens were scaled structures which were designed and fabricated to emulate the characteristics of the main load-bearing component of a large composite wind turbine rotor blade (i.e., the box beam formed with the turbine blade spar caps and shear webs). Several composite box-beam specimens were assembled, using thick adhesive layers between spar caps and shear webs. The spar caps and shear webs were fabricated with glass fabric composites using a vacuum assisted resin infusion molding (VARIM) process. The structural integrity of the box-beam specimens was evaluated in both 3- and 4-point bending experiments. To obtain proper understanding of the observed bending test results, detailed deformation and strength behavior of the tested box beams were modeled and analyzed using the finite element methods. A series of linear eigenvalue analyses were conducted to determine the buckling modes and loads of the tested box beams. Incremental loading analyses were conducted to investigate the progressive development of local nonlinear deformation, instability and stress distributions in the box beam spar caps, shear webs and adhesive layers during the bending tests. The numerical results were correlated and compared with the observed bending test results to develop detailed understanding of damage and failure progression in the tested box beams. The factors that influenced the ability of the box-beam specimens to carry additional loads beyond the first buckling load were assessed. The good agreement between bending test and numerical analysis results suggests that the analysis procedures taken in the study could be used to analyze and predict ultimate strength and failure modes of the composite box-beam specimens under different bending loads.