Tech Briefs

Engineers use the B-Spline Analysis Method to assess component damage tolerance.

AFRL researchers developed a unique design and structural analysis tool for composite materials, and they subsequently transitioned their product to manufacturers of helicopters and other rotorcraft. The new tool, the B-Spline Analysis Method (BSAM), makes it quicker and less expensive to characterize and predict the behavior of flaws or damage in the structures used to build these aircraft. AFRL developed the technology in coordination with the University of Dayton Research Institute (UDRI) and the United Technologies Research Center (UTRC) and then transitioned it to Sikorsky Aircraft Corporation.

Graphical depiction of cracked composite part under tensile loading
Air Force initiatives to make composite aerospace structures more affordable have concentrated on the design and manufacture of highly unitized structures, a focus that eliminates joints and fasteners and thereby lowers manufacturing costs.1 The use of adhesively bonded joints in primary aircraft structures and critical load paths is constrained both by the lack of an established nondestructive evaluation technique for quantifying the integrity of the adhesive bond and by the inability to predict the long-term performance and damage tolerance of the adhesively bonded joint under environmental or mechanical service loading. These complex composite materials pose major challenges to current modeling techniques, particularly in assessing the damage tolerance of composite structures. Traditional damage assessments rely on risk reduction testing and detailed finite element models (FEM). AFRL scientists developed BSAM as a tool that engineers can apply early in the design process to rapidly assess component damage tolerance, a capability that shortens design timelines and decreases risk reduction activities.

BSAM employs a revolutionary numerical approach in modeling solidmechanics problems. It analyzes the three-dimensional stress behavior within a layered composite material, operating at the composite's ply level and maintaining the continuity of strains and stresses throughout a homogeneous ply while allowing strain discontinuity at ply interfaces. A general-purpose solidmechanics analysis method, BSAM employs an innovative method of assembling B-spline approximations of deformation in a numerical format, which enables the code to efficiently solve complex mechanics problems. Comparative analysis of composite materials with fastener holes indicates that BSAM demonstrates excellent agreement with experimental results and is more efficient than state-of-the-art FEM methods.